Continental scale dietary patterns in a New World raptor using web-sourced photographs

Connor T Panter; Vincent N Naude; Facundo Barbar; Arjun Amar

doi:10.1371/journal.pone.0304740

. 2024 Jul 15;19(7):e0304740. doi: 10.1371/journal.pone.0304740

Continental scale dietary patterns in a New World raptor using web-sourced photographs

Connor T Panter ^1,^*, Vincent N Naude ², Facundo Barbar ³, Arjun Amar ⁴

Editor: Dárius Pukenis Tubelis⁵

PMCID: PMC11249219 PMID: 39008480

Abstract

Dietary studies are essential to better understand raptor ecology and resource requirements through time and space, informing species habitat use, interspecific interactions and demographic rates. Methods used to collect data on raptor diets can constrain how dietary analyses can be interpreted. Traditional approaches to study raptor diets, such as analysis of pellets or prey remains, often provide dietary data at the local population level and tend to be restricted to pairs during the breeding season. The increasing use of citizen science data has the potential to provide dietary inferences at larger spatial, demographic and temporal scales. Using web-sourced photography, we explore continental-scale demographic and latitudinal dietary patterns between adult and non-adult Crested Caracaras (Caracara plancus), throughout the species’ range across the Americas. We analysed 1,555 photographs of caracaras feeding and found no age effects on the probabilities of different food groups being included in photographs. The probability of reptiles being included in photographs of caracaras from the northern population was significantly higher than those from the southern population, with the opposite pattern for birds. There were significant latitudinal effects with the probabilities of fishes and invertebrates in the diet of northern caracaras increasing towards the equator. Contrastingly, the probability of mammals in the diet increased away from the equator for both populations. Assuming the focal species is well-sampled, web-sourced photography can improve our understanding of raptor diets at large-scales and complements more traditional approaches. This approach is more accessible to raptor researchers without access to the field or expertise in physical prey identification techniques.

Introduction

Dietary studies are essential to better understand a species’ ecology and resource requirements through time and space [1]. Food availability and abundance can affect population dynamics of raptors [2]. Understanding raptor diets provides a foundation to build upon knowledge about habitat use [3], inter- and intraspecific interactions [4], demographic rates [5], threats including direct consumption and bioaccumulation of contaminants [6, 7], and other aspects of raptor ecology [8]. For generalist raptor species that often scavenge on animal carcasses, dietary information may benefit humans in the form of monitoring ecosystem service provisioning [9]. Most importantly, the methods used to collect data on raptor diets, and the scales at which data are collected at, may lead to a misunderstanding of natural environments due to the introduction and constraints of methodological limitations.

Traditional methods to study raptor diets, such as analysis of prey remains [10, 11], pellets [12], observations from bird blinds [13] and use of nest cameras [10, 14], may be restricted spatially in their ability to provide dietary data at the broader population-level. Furthermore, such approaches tend to often provide dietary data at the local population-level and are limited to pairs during the breeding season. Therefore, these approaches tend not to capture the diets of floaters, sexually immature birds or those that fail to breed [15]. More recent methods to explore raptor diet include coupling accelerometers to telemetry devices [16], stable isotope analyses [17–19] and DNA metabarcoding [4, 20, 21]. However, when attempting to explore dietary patterns at the wider population-level across larger scales, these approaches tend to be time- and cost-inefficient.

The increasing popularity and use of open-source intelligence and citizen science data [22], in the form of web-sourced photographs, has the potential to provide dietary inferences at larger spatial scales [23], complementing more traditional approaches. For species that inhabitant large geographical areas, exploring how diet varies latitudinally may improve understanding of its ecology. For example, ecological and climatic conditions along latitudinal gradients influence the availability and presence of prey species within the wider environment [24], affecting the diversity and dietary composition for many species including birds [25]. Reviews of the raptor diet literature found distinct latitudinal patterns in the proportions of prey groups in some raptor diets, with increased probabilities of mammalian prey at higher latitudes [25, 26]. In addition to these studies, web-sourced photography has already been used to explore raptor diets across large geographic areas. For example, it has been used to examine spatial differences in the diet of adult and non-adult Martial Eagles (Polemaetus bellicosus) throughout sub-Saharan Africa [27]. Studies have also explored sex- and age-related diet differences in the Eurasian Sparrowhawk (Accipter nisus) and explored changes in this species’ diet, between the sexes, throughout the entire year [28, 29]. Previous research, using this approach, examined diet specialization of Tiny Hawks (A. superciliosus) in relation to their hummingbird (Trochilidae) prey across the Neotropics [30]. However, the role of more traditional approaches to study raptor diets must not be underestimated as they provide vital data on cryptic species and those that can be challenging to study in the field, e.g., tropical forest raptors [31]. Despite this, web-sourced photography is a useful tool to study well-sampled species that inhabitant large geographic areas including open landscapes and those associated with human activities [28, 29].

The Crested Caracara (Caracara plancus) (hereafter ‘caracara’) is distributed throughout the Americas. It is a non-migratory, resident species that tends to occupy distinct territories outside of the breeding season [32]. The species’ most northerly limit extends across breeding populations in Texas [33], southern Arizona [34] and Florida [35–37]. The caracara’s southernmost range extends to the Tierra del Fuego archipelago in South America [38]. Dietary research has been conducted at the local population-levels (i.e., Florida, USA [37, 39–42]; Texas, USA [43]; Argentina [44–47]; Brazil [48]), however, little is known about the species’ diet at the continental-scale and how this may vary along a latitudinal gradient. Furthermore, how diet differs between age groups remains unknown.

To address this information gap, we used web-sourced photographs accessed from Macaulay Library and iNaturalist of caracaras feeding and examined spatial and demographic differences in the diet throughout the species’ range across the Americas. We employed a single technique to compare diet across a broad range of the species’ global population and provide the first dietary assessment between age groups. Specifically, we explore 1) dietary differences between adult and non-adult birds, 2) differences in probabilities of food groups between northern and southern populations, and 3) examine how the probabilities of different food groups within the caracaras’ diet differ along a latitudinal gradient. In line with previous research on the effects of latitude on raptor diet, we expect a distinct latitudinal effect on the probability of mammals within the caracara diet—consistent with known trends in mammalian prey assemblages [26], i.e., an increased probability of mammalian prey across northern latitudes [49] and towards the poles [25]. In addition, due to global climatic and species diversity patterns varying along latitudinal gradients spanning temperate through tropical biomes [50–52], we expect the probability of ectothermic food groups, e.g., fishes, invertebrates and reptiles, to increase in the caracaras’ diet towards the equator.

Materials and methods

Study areas

Our study area encompasses the caracara’s entire geographic range, spanning a latitudinal gradient from approximately 45°N to -55°S, and a longitudinal gradient from approximately -35°E to -125°W. Photographic samples span multiple regions including the Nearctic of North America, Mexican Transition Zone through North/Central America and into the Neotropical zone in Central/South America [53]. According to the Bioregions 2023 Framework (https://www.oneearth.org/bioregions/), North American photographs represent samples from numerous biogeographic subrealms including the North Pacific Coast, American West, Mexican Drylands, Great Plains and the Southeast U.S. Savannas and Forests. Photographs of caracaras from Central America include the Central America and Caribbean biogeographic subrealms, with those from South America spanning the Andes and Pacific Coast, Upper South America, Amazonia, Brazilian Cerrado and Atlantic Coast and the South American Grassland subrealms.

Web-sourced photographs and data extraction

Macaulay Library and iNaturalist data

All photographs and available metadata of ‘Crested Caracaras (Caracara plancus)’ uploaded onto Macaulay Library (https://www.macaulaylibrary.org/) and iNaturalist (https://www.inaturalist.org./) were downloaded on 27 January 2023 and 2 February 2024, respectively, where the use of these images for non-commercial scientific research purposes fell under the CC BY 4.0 license as authors were acknowledged where relevant in compliance with the terms and conditions for the sources of these data (i.e., Macaulay Library—https://www.birds.cornell.edu/home/ebird-data-access-terms-of-use/ and iNaturalist—https://www.inaturalist.org/pages/terms). Photographs were visually examined and classified as ‘of interest’ if they appeared to include caracaras hunting or scavenging on food items. The ‘of interest’ photographs were filtered again by a second researcher who confirmed whether the photograph contained a caracara either hunting or scavenging. These photographs were then classified as ‘useable’. For them, we extracted the following data: 1) caracara age (adult vs. non-adult), 2) food item (identified to the lowest taxonomic level possible), 3) latitude/longitude, 4) location of photograph and 5) observation date. For photographs that contained more than one caracara of each age group, we only extracted data for the individual interacting with the prey item. We checked for duplicated photographs of the same feeding events by filtering by observation date, visual characteristics or landscape features within the photograph and Macaulay Library recordist name or iNaturalist user ID, i.e., a duplicated photograph was identified if the photograph was taken within the same area, within up to 10 days of the initial observation and if the same recordist uploaded the photo. However, this was not always the case as there were occasions where multiple recordists uploaded images of the same feeding event across different days. This was particularly the case if the food item was large in size and thus took longer to decompose. We were able to ascertain whether these were duplicates by making an assessment based on the spatial location of the feeding event, evidence of the food item included and features of the surrounding location in the photograph. If a duplicated photograph was identified, then we retained the highest resolution photograph that showed the feeding event most clearly and removed all others.

Prey identification and caracara age

We attempted to identify food items to the lowest taxonomic level possible. We use the term ‘food item’ here as we were unable to determine whether observations reflected feeding events where caracaras actively hunted/killed the item or were photographed scavenging on carcasses not killed by the bird. Where we were unable to identify food items to species-level, we assigned these to a broader food group, e.g., ‘birds’ or ‘mammals’. If we could not identify a food item to a broader ‘food group’, e.g., a photograph of a partially decomposed body part or unidentifiable bone, it was categorized as ‘unknown’. All photographs of species- and food group-level identifications were visually assessed by at least two of the authors (C.P., F.B. or V.N.).

Adult caracaras were identified by characteristic dark plumage, whitish-buff auricular feathers, throat and nape, and whitish-buff barred dark chest, neck, mantle, back, upper tail coverts, crissum and basal part of the tail [54]. Juvenile birds tend to resemble adults in pattern, but are paler brown with vertical streaking on the chest, neck and back, also displaying grey legs and lighter ceres [54]. We classified all individuals that did not display adult characteristics as ‘non-adults’.

Population classification

Until recently, two distinct subspecies of caracara were recognized, i.e., the Northern Crested Caracara (C. p. cheriway) and the Southern Crested Caracara (C. p. plancus) [55]. The northern subspecies’ geographic distribution extends from Texas, southern Arizona and Florida, down to northern Amazonian rainforest into Brazil and Peru [33]. The southern subspecies’ geographic distribution extended from north-east Brazil, Bolivia and Chile down to the Tierra del Fuego archipelago in South America [38]. This species tends to inhabit more open landscapes where it scavenges and hunts for food, and is often observed in human-modified habitats [56]. As such, a distinct overlap zone occurs across the Amazonian rainforest between approximately 0° through 7° latitude dividing the northern and southern subspecies [57]. However, contemporary taxonomic revisions based on molecular analyses no longer recognize these two distinct subspecies, due to low evidence of genetic differentiation, instead merging both of these into one single species, i.e., the ‘Crested Caracara’ (C. plancus) [57, 58]. Despite this, the species still persists in two distinct populations and it is likely that some individuals occasionally cross the overlap zone from either population. Largely, the species remains divided by the geographic overlap zone through the Amazonian rainforest, which may mediate differences in the ecology and diet of the two populations.

In an attempt to address differences in the diet of birds from both populations, we obtained the original subspecies-level range maps from the BirdLife International Datazone database (http://datazone.birdlife.org/home; previously updated in 2023) and plotted these using DIVA-GIS [59], where we assigned each photograph a population classification (either ‘northern’ or ‘southern’) based on geographic locations of our photographic data points. No updated range maps are available for the recent taxonomic revision of the species, therefore, we relied on the original subspecies range maps and interpreted these as proxies for the distinct distributions of the two continental populations. We plotted all useable photographs in QGIS version 3.14.16 [60] and conducted an overlap analysis between the geo-referenced photograph data points and each population range polygon (Fig 1a and 1b). Data points (N = 60) located within the approximate overlap zone between the northern and southern populations were excluded from the analyses as we could not accurately assign them a population.

Fig 1 — a) Latitudinal spatial distributions of 1,555 photographs of Crested Caracaras (*Caracara plancus*) feeding on identified food groups throughout North, Central and South America between 1987 through 2022. Photograph samples stacked by caracara age (Adult vs. Non-adult) and approximate location of the overlap zone occurring between approximately 0° through 7° latitude. b) Spatial distribution of photographs with an approximate depiction of the overlap zone occurring between 0° and 7° latitude between the two populations (Northern vs. Southern). Note—latitudinal categories presented in a) do not correspond to spatial data shown in b). Species ranges maps were provided by the BirdLife International Datazone [81].

Spatial clustering

To account for potential pseudoreplication and non-independence between data points, i.e., photographs that are spatially distributed closely together may represent the diet of the same bird, we created spatial clusters. First, we computed 5,000 randomly distributed geographic data points across the entire Americas with a minimum spacing between points of 200 km. Caracaras tend to be a territorial species that display high site fidelity and occupy distinct home ranges of approximately 20,000 km² (ca. 100 km in radius) [32], hence we spaced each random point by at least 200 km to prevent overlap. We then calculated 100 km² radii buffer circles around each random point, which we interpreted as proxies of caracara home ranges. Next, we performed an intersection analysis in QGIS overlaying the caracara photograph data points with the home range proxies and assigned clusters of intersecting photographs a unique cluster ID. This was performed under the assumption that each cluster ID likely represents photographic data points from the same bird.

Statistical analyses

Age and population effects on caracara diet

All statistical analyses were conducted in R version 4.2.2 [61]. Data for food groups with ≥ 30 observations were included, therefore, a total of 30 photographs were omitted due to small sample sizes (amphibians: N = 14; plants: N = 16). We ran a multinomial log-linear model using the R package “nnet” [62] to explore age and population-level associations on the probabilities of food groups in the photographic data set. We fitted ‘food group’ (birds, fishes, garbage, invertebrates, mammals or reptiles) as the response term and the interaction between ‘age’ (adult or non-adult) and ‘population’ (northern or southern) as the explanatory term (S1 Table).

Latitudinal effects on caracara diet

To explore latitudinal effects on the probabilities of different food groups within the caracara diet, we created multiple binary response variables for each food group. Each photograph was scored as either 1 or 0 depending on the presence or absence of a particular food group in the photograph. For example, photographs of a caracara feeding on a bird species were scored a ‘1’ in a new binary variable termed ‘birdbin’ and those that did not include a bird were scored ‘0’. This was repeated for all food groups and for both population (northern or southern) subset data sets. Next, we ran a series of generalized linear mixed models (GLMMs) using the “lme4” package [63], with the binary food group variable fitted as the response terms, ‘latitude’ fitted as the explanatory terms and “cluster ID” fitted as random terms to account for potential non-independence between data points (S1 Table). These models explored the effects of latitude on the probability of each unique food group in the species’ diet while accounting for potential pseudoreplication and non-independence between closely distributed data points. Models were run using binomial data distributions with ‘logit’ link functions (S1 Table). We created subset data sets for both northern and southern populations, and only ran the GLMM models for food groups with more than 30 observations. For the northern population, we ran models for the following food groups: ‘birds’, ‘fishes’, ‘garbage’ (defined as any non-natural human sourced food or waste), ‘mammals’ and ‘reptiles’. For the southern population, we ran models for the following food groups: ‘birds’, ‘fishes’, ‘invertebrates’, ‘mammals’ and ‘reptiles’. Due to a limited sample size for photographs of invertebrate food items from the northern population (N = 31), we were unable to assign individual cluster IDs for these photographs. Therefore, we ran a generalized linear model (GLM) to explore latitudinal effects on the probability of this food group within photographs of caracaras. Similarly to the GLMMs, the binary food group variable was fitted as the response term and ‘latitude’ fitted as the explanatory term. This single GLM was run with a binomial data distribution with a ‘logit’ link function (see S1 Table). We used the ’emmeans’ package [64] to calculate the probabilities (± 95% confidence intervals (CI)) of different food groups within the caracaras’ diet and to undertake additional post hoc contrasts (see S1 Table for an overview of the statistical modeling process).

Results

Overview of photographic samples

A total of 78,059 photographs of caracaras, taken across the Americas between 1987 through 2022, were downloaded from Macaulay Library (N = 42,488) and iNaturalist (N = 35,571) and were visually examined. Approximately 4.4% (N = 3,451) (Macaulay Library = 2,454; iNaturalist = 997) of the photographs appeared to include caracaras feeding and were subsequently marked as ‘of interest’. Of these photographs, 68.9% (N = 2,381; Macaulay Library = 1,456; iNaturalist = 925) were classified as ‘useable’ as it was confirmed that they contained a caracara feeding. Of all useable photographs, there were a far higher proportion of adults (N = 1,948; 81.8%) than non-adults (N = 433; 18.2%) and photographs were distributed across both population ranges (Table 1) with distributions of photographs for both populations peaking between approximately ≥ 20 ≤ 29.9° (northern population) and ≥ -40 ≤ -30.1° latitude (southern population) (Fig 1a and 1b). A total of 1,445 (60.7%) photographs were from the northern population and 936 (39.3%) from the southern population (Table 1). For the northern population 1,214 (84% northern population) photographs were of adults and 231 (16%) included non-adults (see Fig 2a–2f for examples). For the southern population, 734 (78.4% southern population) photographs were of adults and 202 (21.6%) included non-adults. There were 796 photographs that we were unable to assign to a broad food group, and together with the 30 photographs representing amphibian and plant food groups, these were excluded prior to the analyses. We were able to assign broad food groups to 1,555 (65.3% of useable photos) photographs which were used in the analyses (Table 1).

Table 1. Photographic sample sizes of Crested Caracaras (Caracara plancus) feeding throughout North, Central and South America by population and prey group sourced from Macaulay Library and iNaturalist between 1987 through 2022.

Food group	Population		Total
	Northern	Southern	Total
	N (%/pop.)	N (%/pop.)	N (%/Total)
Macaulay Library
unknown^*	295 (32.2)	156 (28.8)	451 (31)
mammals	241 (26.3)	140 (25.9)	381 (26.2)
birds	124 (13.6)	101 (18.7)	225 (15.5)
fishes	89 (9.7)	83 (15.3)	172 (11.8)
reptiles	79 (8.6)	19 (3.5)	98 (6.7)
invertebrates	30 (3.3)	24 (4.4)	54 (3.7)
garbage	38 (3.2)	12 (2.2)	50 (3.4)
amphibians^*	10 (1.1)	3 (0.6)	13 (0.9)
plants^*	9 (1)	3 (0.6)	12 (0.8)
Macaulay Library Total (%/ML Total)	915 (62.8)	541 (37.2)	1456 (61.2)
iNaturalist
unknown^*	208 (39.2)	137 (34.7)	345 (37.3)
mammals	140 (26.4)	91 (23)	231 (25)
birds	66 (12.5)	78 (19.7)	144 (15.6)
fishes	54 (10.2)	54 (13.7)	108 (11.7)
reptiles	37 (7)	13 (3.3)	50 (5.4)
invertebrates	8 (1.5)	6 (1.5)	14 (1.5)
garbage	14 (2.6)	14 (3.5)	28 (3)
amphibians^*	1 (0.2)	0 (0)	1 (0.1)
plants^*	2 (0.4)	2 (0.5)	4 (0.4)
iNaturalist Total (%/iNat. Total)	530 (57.3)	395 (42.7)	925 (38.8)
Total (%/Total)	1445 (60.7)	936 (39.3)	2381 (100)

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*Photographs from these food groups were omitted prior to statistical analyses due to small sample sizes or being unable to be assigned a broad food group.

Fig 2 — a) Adult caracara feeding on a mammal (photograph credit: lucianomassa CC BY NC-SA iNaturalist), b) adult feeding on bird remains (eduardopaiva CC BY-BC-SA iNaturalist), c) adult feeding on crocodilian remains (isisanimals CC BY-NA-SA iNaturalist), d) non-adult feeding on a mammalian carcass (ericgalas CC BY-NA-SA iNaturalist), e) non-adult feeding on an invertebrate (varvarenja CC BY-NA-SA iNaturalist) and f) non-adult feeding on a fish carcass (mariocastanedasanchez CC BY-NA-SA iNaturalist). Panels g) and h) show age and population differences in the probabilities of each food group within photographs of caracaras feeding. Significant differences indicated with asterisks: ‘*’ P < 0.05 and ‘**’ P < 0.01. Error bars represent 95% confidence intervals.

Dietary composition

Overall, caracaras were photographed feeding on most major taxonomic groups across the range of both populations (Table 1). Of the 1,555 photographs containing identified food groups, mammals were recorded in 612 (39.4%) photographs followed by birds (369; 23.7%), fishes (280; 18%), reptiles (148; 9.5%), garbage (78; 5%) and invertebrates (Table 1).

Age and population effects on caracara diet

There was no significant age effect (age: X²_1,5 = 8.071, P = 0.152) or a significant interaction effect (age × population: X²_1,5 = 0.172, P = 0.999) between caracara age and population on the probabilities of different food groups in the photographic data set (S2 Table). However, there was a significant population effect (population: X²_1,5 = 36.431, P < 0.0001) with increased probabilities of reptiles being included in photographs taken of adult caracaras from the northern population relative to adult birds from the southern population (t_1,20 = 4.334, P = 0.002) but the opposite pattern for birds (t_1,20 = -3.48, P = 0.012) (Fig 2g and 2h; S2 Table).

Latitudinal effects on caracara diet

For photographs taken of individuals from the northern population, there was a negative latitudinal effect with the probability of fishes (z_1,533 = -2.251, P = 0.024) and invertebrates (z_1,918 = -4.616, P = < 0.0001; S4 Table) within the diet increasing towards to the equator (Fig 3a and 3b; S3 Table). Contrastingly, the opposite pattern was observed for mammals with an increased probability away from the equator towards higher latitudes (z_1,533 = 3.974, P < 0.0001) (Fig 3c; S3 Table). There were no significant latitudinal effects on the probability of birds, garbage or reptiles in the diet of caracaras from the northern population (S3 Table).

Fig 3 — Significant predicted latitudinal effects, with 95% confidence intervals, on the probability of a) fishes, b) invertebrates and c) mammals within photographs of Crested Caracaras (*Caracara plancus*) from the northern population feeding between 1987 through 2022. For the southern population, significant latitudinal effects for d) fishes and e) mammals within photographs of caracaras also shown.

Similarly, for photographs taken of individuals from the southern population, the probability of fishes being included in photographs increased towards the equator (z_1,376 = 2.467, P = 0.014) (Fig 3d; S3 Table). Furthermore, there was an increased probability of mammals being included in photographs of individuals from the southern population with increasing distance away from the equator (z_1,376 = -4.432, P < 0.0001) (Fig 3e; S3 Table). There were no significant latitudinal effects on the probabilities of birds, invertebrates or reptiles in photographs of caracaras from the southern population feeding (S3 Table).

Discussion

Crested caracara diet varied along latitudinal gradients

Our study represents the first continental-scale quantitative diet assessment for caracaras, throughout the species’ range across the Americas. As expected, for both caracara populations the probability of mammals in photographs increased with increasing distance away from the equator. There was a significant increase in the probability of reptiles in the diet of caracaras from the northern population, and the opposite pattern in the probability of birds in the diet of the southern caracara population. Although we suspect this may be a confounding effect of both larger sample sizes per-unit-area when compared to the southern population and availability of suitable habitat for reptiles especially across Mexico [65]. Contrary to patterns relating to global climatic and species diversity patterns along latitudinal gradients [50–52], the probability of reptiles showed no significant increase towards the equator for either population. However, there were significant latitudinal effects in the probabilities of fishes and invertebrates in photographs of northern caracaras, increasing towards the equator. These patterns may be driven by increased species richness within these groups towards the equator, and thus a presumed increase in availability in tropical/subtropical environments relative to temperate zones [66]. However, more research is needed to decipher these patterns.

Comparisons between other diet studies

Compared with previous studies, our findings confirm that caracaras are a generalist species that feed on most major taxonomic groups [39–48, 67]. Analysis of 299 prey remains found that mammals (31.4%), reptiles (24.1%), fish (23.7%), birds (13.4%) and amphibians (7.4%) represented the most numerous groups within the species’ diet in south-central Florida [40], showing some consistency with our findings from across the species’ range. Unlike another study of caracara diets in Andean Patagonia which concluded that adults tended to take smaller prey (such as arthropods) while supplying juvenile birds with larger vertebrate prey, there were no dietary differences between age classes in our data set [38]. This may be explained by the lack of observations of adults feeding young or that our approach did not allow us to distinguish between adult birds feeding themselves as opposed to taking food items to the nest. Other studies report that insects [41, 42, 44] and plant material (such as Pecans (Carya illinoinensis) [43] and palm fruits [68]) also featured within the species’ diet, however, fewer than 3% and 1% of food items in our study were attributed to these food groups, respectively.

Web-sourced photography is a useful tool to study raptor diets across large spatial scales

Apart from a previous study on Martial Eagles [27], which also used web-sourced photography, relatively few studies have explored raptor diets at large geographic scales. Other studies have attempted to do so by compiling dietary data from multiple separate studies across a species’ range, providing useful comparisons especially for our data on latitudinal trends [49, 69]. For example, a global examination of Western Barn Owl (Tyto alba) and American Barn Owl (T. furcata) diets found a positive relationship in the proportion of mammal prey in colder environments [25]. Unlike previous studies which studied the diets of Eurasian Sparrowhawk and Martial Eagles [27, 29], we did not find any age effects in the diet of caracaras which may be explained by their generalist nature and tendency to feed on carrion [47, 67]. Eurasian Sparrowhawk are avian specialists [27, 28] and age-related differences in diet may be more pronounced. Similar to our findings, a continental assessment of Montagu’s Harrier (Circus pygargus) diet found that mammalian prey increased at higher latitudes due to the prevalence of agricultural land cover at more northern latitudes [49]. A separate study on Montagu’s Harriers [70] combined the use of web-sourced photography with pellet analyses to explore seasonal-, regional- and sex-differences in the species’ winter diet. The proportion of key food groups in the species’ diet was largely consistent using both methods [70], demonstrating that using web-sourced photography alongside more traditional methods can improve studies of raptor diet.

Study limitations

Our approach, like most methods to study raptor diets [8, 71], has been shown to be potentially biased towards larger and more identifiable food items, e.g., mammals and birds, which require longer processing times [28, 29]. Consequently, this food-size bias may partly explain why we detected low relative proportions of smaller prey groups, such as invertebrates (2.9%), plant material (0.7%) and amphibians (0.6%) within our photographs. Furthermore, our approach assumes that the food items included in the photographs were actually consumed by caracaras. Due the lack of ability to ascribe individual cluster IDs to photographs of northern caracaras feeding on invertebrates, we were unable to account for potential pseudoreplication with a potential risk of non-independence between invertebrate data points. Spatial coverage of our photographs spanned the geographic ranges of both caracara populations. However, it is likely that a confounding variable and a sampling bias towards more urbanized habitats, roadsides or areas with higher human activities may persist in our data set. These locations are where more people may tend to take photographs, and food type and availability may potentially be affected by the degree of urbanization. A key assumption when using web-sourced photography pertains to the species being well-sampled. This approach, unlike more traditional techniques, e.g., analysis of pellet remains, is unsuitable when studying cryptic species or those that are challenging to observe in the field. Therefore, strengths lie in its ability to be used in conjunction with other methods complementing future raptor research [70]. Potential opportunities for future research include studying differences in urban and non-urban raptor diets using our approach. As with most methods that study the diets of predatory species that also scavenge, it is challenging to distinguish between food items that were hunted by caracaras and those which were scavenged. Furthermore, due to incompatibilities with small and uneven sample sizes, we were unable to account for differences in food groups within photographs of caracaras from smaller subpopulations, such as on the Falkland Islands [72].

Utilizing citizen science data can be a time- and cost-effective method to study raptor diets

Unlike more traditional methods to study raptor diet, web-sourced photography provides novel perspectives when quantifying raptor diets across large spatial scales. Traditional methods are often constrained to a few breeding pairs during the breeding season and unlikely represent dietary patterns for the entire population which includes floaters, sexually immature birds and individuals that fail to breed. Such approaches do not allow for the exploration of diet outside of the breeding season, which has been shown to change in response to prey availability [73] and changes in behaviour of adult birds [28]. Our approach is a time- and cost-effective method to study raptor diets, requiring minimal skill from the observer other than knowledge of key food items and access to the internet [23]. As a result, the increasing prevalence of open-source intelligence data in daily life [74], provides an accessible approach for researchers without access to large funds, time commitments required or the expertise necessary for long-term monitoring of multiple populations. Assuming that the study species is well-sampled this approach can be applied to many other predatory species, including those that are inconspicuous or more challenging to study in the field, such as snakes [75], providing novel perspectives on our understanding of predator ecology.

Conclusions

The findings of our study represent the first assessment of caracara diet throughout the species’ geographic range across the Americas. We were able to explore dietary differences between caracara age classes and between populations, which has not been attempted before for this species. Across their range, caracaras fed from most major taxonomic groups, and we found significant latitudinal effects on the probabilities of fishes, invertebrates and mammals within photographs of caracaras feeding which likely reflect latitudinal variations in climate and land cover type. Web-sourced photography complements other methods to study raptor diets, such as DNA metabarcoding [4, 19, 20] or stable isotope analysis [16–18], maximizing sampling effort across taxonomic groups that may be difficult to identify from a single photograph, e.g., insects. The role of open-source intelligence and citizen science data has expanded in ornithology and continues to increase in popularity due to the relative ease of accessing data, large sample sizes and increasing quality of available metadata. Continued availability of open-source intelligence and citizen science data provides a wealth of information on predator diets [27–29, 70, 76], interspecific interactions [30], polymorphism [77, 78], conservation policy and planning [79], species range shifts [80], and has the potential to benefit ongoing and future raptor research across large spatial-, demographic- and temporal-scales.

Supporting information

S1 Table. An overview of the statistical modeling process undertaken to explore the effects of age, population and latitude on the diet of Crested Caracaras (Caracara plancus) throughout North, Central and South America between 1987 through 2022.

‘GLM’ = Generalized Linear Model, ‘GLMM’ = Generalized Linear Mixed Model.

(DOCX)

pone.0304740.s001.docx^{(17.2KB, docx)}

S2 Table. Contrasts from the multinomial log-linear model exploring the effects age, population and their interaction (age × population) on the probability of different food groups in photographs of Crested Caracaras (Caracara plancus) feeding throughout North, Central and South America between 1987 through 2022.

Significant contrasts (P < 0.05) highlighted in bold.

(DOCX)

pone.0304740.s002.docx^{(17.9KB, docx)}

S3 Table. Outputs from the generalized linear mixed models exploring the effect of latitude on the probabilities of different food groups within photographs of Crested Caracaras (Caracara plancus) feeding throughout North, Central and North America.

SE = standard error, df = degrees of freedom. Significant effects (P < 0.05) in bold.

(DOCX)

pone.0304740.s003.docx^{(15.8KB, docx)}

S4 Table. Outputs from the generalized linear model exploring the effect of latitude on the probability of invertebrates within photographs of Crested Caracaras (Caracara plancus), from the northern population only, feeding throughout North, Central and North America.

SE = standard error, df = degrees of freedom. Significant effect (P < 0.05) in bold.

(DOCX)

pone.0304740.s004.docx^{(14.5KB, docx)}

Acknowledgments

The authors are thankful to all photographers who facilitate research such as this by uploading photographs of caracaras onto open access databases such as Macaulay Library and iNaturalist. In addition, we would like to thank T. Katzner, J. Morrison, E. Miranda, D. Tubelis and the anonymous reviewers for their helpful comments on earlier drafts.

Data Availability

All relevant data for this study are publicly available from the Dryad repository (https://doi.org/10.5061/dryad.rjdfn2zkz).

Funding Statement

The author(s) received no specific funding for this work.

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PLoS One. doi: 10.1371/journal.pone.0304740.r001

Decision Letter 0

Dárius Pukenis Tubelis

19 Jan 2024

PONE-D-23-42552Using web-sourced photographs to explore continental-scale dietary patterns in a New World raptor, the Crested Caracara (Caracara plancus)PLOS ONE

Dear Dr. Connor Panter,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process. Thank you for submitting to PLOS ONE your study on dietary patterns of a raptor species, based on community science data. We received three reviews, and I also reviewed it as I had published a few papers by using a similar approach.

Reviewer 1 has suggested Minor Revision. Numerous suggestions have been provided to improve the quality of your manuscript. His/her main concerns are: 1) the restriction of your sample to the Macaulay Library database (as there are others for the Neotropical region); 2) the absence of examination of seasonal variation in the occurrence of food items in the diet of the raptor species.

Reviewer 2 has suggested Minor Revision and provided numerous compliments on your research, and a wide range of suggestions to improve the quality of the manuscript. Note that he/she is surprised with the fact that you overlooked the WikiAves and iNaturalist databases/platforms.

Reviewer 3 has suggested Rejection mainly based on the fact that you gave substantial emphasis on the methodology, what he/she considers that makes your (interesting) study more suitable for an ornithological journal, and not for PLOS ONE. There are some suggestions that you can consider. I think that a rejection is not necessary, but you will need to make some changes in the Introduction and Discussion (reduce the emphasis on the methodology and increase the number of examples/studies and comparisons that examined latitudinal variation in the diet of birds).

I suggest that you consider these four reviews (please find mine below) to verify with what you agree, and thus follow. There is a great potential for the publication of a high quality study in PLOS ONE.

Dárius P. Tubelis

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Additional review by Dárius Tubelis:

Your study is very interesting and highlights that citizen science data (photographs) can be used to investigate dietary aspects of birds at large spatial and temporal scales in the Neotropics. The approach is quite appropriate and the results are interesting.

I´m mainly concerned with the restriction of your sample to data from the Macaulay Library (that encompasses eBird). For example, the WikiAves platform (https://www.wikiaves.com.br) harbors a lot of data about Brazilian birds, including 27,100 records of Caracara plancus. On 08 January 2024, I clicked on “Registros” (Records), and then on “Busca Avançada” (Advanced search). Then, I typed the name of the species (“Espécie”, Species) and then, near the page bottom, clicked on the option “Alimentando-se/caçando” (Feeding/hunting). This search resulted in 3,429 photographs of C. plancus. Of these, about 50% might have evidence of feeding activities by this raptor in Brazil (I guess this percentage based on studies that I have done using this platform – e.g., Rupornis magnirostris). This available amount of records would represent a good sample of food items along a considerable latitudinal range, in your study. Another option with less numerous records for South America would be iNaturalist….these two additional searches could double your sample size, or do even more….please think about (R1 and R2 also pointed out this question). The current sample could lead to negative criticism by readers, despite the large number of records/photographs. On other hand, your results appear to be quite robust (convincing), and thus your Macaulay-based sample would be enough. Please try to del with this aspect in the Methods and Discussion sections.

Abstract.

Ok.

Introduction.

Very well structured with relevant publications. But note that you provided few sentences regarding latitudinal variation in the diet of birds, including raptors. For example, along lines 70-80 you can briefly present the major results of these investigations at large spatial scales. After the current examples, you could add 2-3 examples mainly focusing latitudinal variation. Also, try to reduce the amount of information on the methods relative to diet of birds. The reading is running well, just need to do these modifications for a better suitability to PLOS ONE.

Line 51. Is there a word better than “however” ?

Line 90. “it how diet” is correct ?

Objectives. Ok.

Material and Methods

A Study Area section would be welcome. Please try to explain main aspects of the Americas that are pertinent to your study, such as North, Central, and South Americas, maximum values of Lat in both Hemispheres, the line of Equator position. It would be useful for readers from other parts of the world.

Section “Web-sourced…”.

If you decide to keep only with the Macaulay Library data, you will have to explain why you did not included searches in the WikiAves, iNaturalist and other databases. Like tell that you sample is large, huge, when compared with those of previous studies. On the other hand, if you decide to include other databases, then add text to explain how you did the searches.

Line 116. You repeated…why not use “For them….” ?

Line 117. What did you consider (adult or non-adult) when you could see an adult with a prey near a nestling in the nest ? This type of photograph has your two types of caracaras….

Line 188. I did not understand item 4 (location)…can you briefly explain within brackets ?

Line 123. These brackets are too distant. Do you really need them ? Six lines within them…can you try to reduce this text (Lines 121-130)?

Section “Prey and age”.

Line 141, if at least two authors, than should be more than CP and FB…please check the writing.

Line 142. Better if you start a new paragraph with “Adult caracaras…”.

Next lines. It is not clear if you included nestlings or not. It appears that you included only juveniles outside nests, and adults. But some photographs might show 1-2 adults in nests with prey and nestlings, as I could note in WikiAves. Please clarify it.

Section “Population”.

Lines 152 and 154. Extended or extends?

You could divide this section in 2-3 paragraphs. It is too long.

Calling a figure with a map would be welcome here.

Section “statistical Analysis”

How did you control for potential influence of seasonality on these results ? For example, you might have more photographs in the rainy or dry season for a given caracara population… please note that Reviewer 1 has concern about this, or similar potential influence on data.

Line 238. You have to place Table 1 here.

Results.

Line 244. As you write “Of these…”, this percentage would be 1501/2454). No ?

Lines 250. You have to call “(Fig 1)”, abbreviated with no dot.

In the end of this paragraph (Line 258), you have to bring the captions of Fig 1 and Fig 2 (but not the figures, that should be kept in the end of the manuscript). Please check Instructions again.

Line 277. Bring Table 2 here.

Line 287. Bring here: Caption of figure 3…

Discussion

It would be easier to read if you use subtitles for sections of the Discussion.

Make sure that you discuss more extensively with previous study on the diet of the species, influence or not of age among raptors, influence of latitude on raptor diets. Your current discussion is a bit poor relative to these topics. Try to the emphasis on methodology.

Always consider an international readership by citing studies conducted in several ecoregions, countries, involving several species.

Both reviewers made some comments that might be useful for you here in the Discussion. For example, R2 commented that this study can be considered an example for the study less common, or more “difficult” species.

References.

The correct is to use like this “2. Smith TC….” Instead, you used “[2] Smith TC….”.

Page numbers. There is no space before them (after the volume and :).

Page number. You have to use a long dash between then, not an hifen (-).

DOIs. You have to provide it for all references that have it. Follow the format: (http://doi.org/10.....).

Ref 6. The initials in capitals should not occur, except for the first word and names….check for all.

Ref 26. It occurs with a duplicate. You will need to change all these numbers here and in the text.

Please also check Instructions for books, chapters, websites….

Tables.

They should be moved to the text, by the end of the paragraph that cite them.

Figures.

Their captions should be in the text, as above for tables. Keep figures here in the end with their “Fig x”.

Fig 1. Can you increase a bit the size of letters and numbers ? Maybe, titles of axes in bold. Is “divide” correct ? (along the dashed line).

Fig 2. You used a duck, but do caracaras prey on them ? What about a pigeon or other smaller bird ?

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

**********

2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

**********

3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

**********

4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

**********

5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: I thank the editor for inviting me to review this manuscript. The authors have presented the background, methods, results and discussion in a technically sound manner. I have a few suggestions for some of the sections which I believe will help add more clarity to the manuscript. The detailed comments are as follows:

Introduction

Line 44-45: The sentence can be rephrased – “Food availability and abundance can affect population dynamics of raptors”

Line 50: “provisioning” instead of “provision”

Line 57-59: It will be good to add some citation. Suggestion: https://link.springer.com/article/10.1007/s10344-010-0480-z

Line 77-79: This sentence can be deleted. Information repeating in the beginning of the para.

Line 90: “it” can be removed from the last sentence

Line 91: Will be good to add information on status of the species in the Americas, especially since it occupies open habitats which are under threat globally.

Methods

Line 111: Any justification as to why only Macaulay library was considered for collecting photographs? What about other social media databases such as Facebook, Flickr etc.?

Line 169: Which year is the latest update of this range map?

Line 184: Were these data points location data? It will be good to specify for clarity.

Results

Line 261-264: Can this information also be presented in Table 1 separately? The table currently has information on 1501 photographs. But food groups could be assigned to only 1029 right?

Line 274: This result has not been discussed in detail in the discussion section. What might be the reason for higher probability of reptiles in the northern population diet?

Discussion

Line 303-306: Will it be good to test for seasonality of occurrence of these food groups from photographs? Maybe occurrence of invertebrates in diet might be more during the warmer months in areas away from the equator. The availability of these food sources might be limited to warmer seasons in the temperate regions.

Lines 315-318: This reference is missing in the literature cited. I believe it’s this study: https://doi.org/10.1006/jare.2000.0745

Line 329: There are two citations with the same number [26]. This has to be rectified in the references section.

Figures

Figure 1: Along with the latitudinal degrees, it will also be good to show the direction on the x-axis (N/S).

Figure 2 a.: The lat longs can be shown in the form of a grid on the map along with the equator line. Since the major part of the study is about latitudinal variation and possible differences in diet in regions away from the equator.

Figure 2 b.: The “**” is not clearly visible on the graph. The font can be made larger.

Reviewer #2: The present study utilizes an online dataset as a tool to acquire knowledge about the caracara diet. The researchers employed robust statistics and large sample sizes to test various hypotheses regarding caracara foraging. They exhibited wit and precision in their test choices and interpretations. Based on their observations, the authors infer that the caracara diet remains consistent with existing descriptions; the species is a known generalist. However, the proof of concept they present allows for the application of the same methods to eagles or other predators for which dietary data might be both crucial and scarce—a point that warrants discussion. Additionally, other observed diet patterns strongly align with their associated data. This study, both simple and robust, epitomizes citizen-based science in my view. I believe PLOS ONE is a suitable publication venue for this manuscript and I wholeheartedly recommend it for publication. Congratulations.

L52: Please rephrase this section since it's not about a misinterpretation but rather a misunderstanding of the natural world.

L66-77: This trend extends to other predators like giant snakes and carnivores, among others.

L77-80: In essence, this provides an opportunity to study a species that have been extensively researched; which is no opportunity at all. Please note that the methods mentioned and criticized in the beginning of the previous paragraph aren't limited to easy species. It feels like cherry picking from your side in favour of your collection method; an effort to address this would enhance the text. Moreover, it makes the argument over the selection of your study species somewhat circular. None of this, in my opinion, is detrimental to the paper, but the text should be revised—especially concerning the choice of the study species.

L94: It surprises me that you chose to overlook larger databases such as WikiAves or iNaturalist. Could you provide some background on your choice?

L108-237: I'm impressed by the clarity, elegance, and robustness of the methods and sample design. The threshold sample sizes for dietary analysis were particularly impressive. However, the categorization of prey and other food sources feels somewhat artificial to me. I believe including functional groups—like domestic animals or aquatic species? L225-228—might make more sense. Nevertheless, congratulations on the excellent work.

L257: I'm absolutely impressed by the broad and extensive sample. I'd like the study to explore a rarer, threatened, or less-known species. However, this doesn't diminish the outstanding work you've done.

Reviewer #3: In the manuscript entitled: “Using web-sourced photographs to explore continental-scale dietary patterns in a New World raptor, the Crested Caracara (Caracara plancus)” the authors used web-sourced photography and explored continental-scale demographic and latitudinal dietary patterns between adult and non-adult Crested Caracaras throughout the species’ range across the Americas. The paper is well written, well structured and has valuable information given that on the one hand, there is little work of this type and even less in the southern hemisphere.

However, the manuscript, as it is written now, I consider it to be methodological in nature as the focus is on the advantages of web-sourced photographs, so it may not be of interest to a wider audience such as PlosOne.

In addition, I have some comments that may help to improve the manuscript:

Abstract-Introduction:

In the introduction, predictions are made as to what they expected to find in terms of age, latitude, mammal consumption and taxonomic groups, however this is not indicated in the abstract.

Line 75. Indicates that previous work examined the diet, using this approach?

Materials and Methods:

Línea 204-206. This information is redundant, this was already stated in the sentence above (with other words), I think it is better to remove it.

Results:

Line 276. Figure?

Discussion:

At the beginning of the introduction, they should have made reference to what they had indicated at the end of the introduction (line 98-line 101). They do so in line 300-3001.

In general, the discussion is focused on the methodology, therefore, although it is correct, I consider that it would not be of interest to a wide audience and an Ornithological journal would be more appropriate for this interesting work.

**********

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Reviewer #1: No

Reviewer #2: Yes: Everton Miranda

Reviewer #3: No

**********

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PLoS One. 2024 Jul 15;19(7):e0304740. doi: 10.1371/journal.pone.0304740.r002

Author response to Decision Letter 0

25 Apr 2024

Response to reviewers PONE-D-23-42552

Comments from editor:

>>> Thank you for taking the time to consider our manuscript, and for your positive and constructive review. During the revision process, we explored whether including additional photographs from WikiAves would be suitable for our study. We decided that due to the photographs being restricted geographically to Brazil, that this may introduce a spatial bias within our continental scale dietary assessment. Despite this, we did indeed increase our sample size by collating and processing photographs of caracaras from iNaturalist. Overall, we processed an additional 35,571 photographs from iNaturalist and together with our sample from Macaulay increased our initial sample size to 78,059. From the new photographs, after screening and removing duplicates, we added some 925 new photos to our analyses, resulting in a data set comprising 1,555 photographs used in the statistical analyses. Interestingly, our results remained largely the same when including the additional photographs. We increased our sample size for caracaras from the southern population substantially which enabled us to explore latitudinal effects in food groups that before had insufficient sample sizes. We hope that the editor agrees with us that our manuscript is much more robust compared to the initial submission.

Title – we have revised the title to shorten it and to focus on our ability to assess diet at the continental scale using our approach.

“Continental scale dietary patterns in a New World raptor using web-sourced photographs” (L1-2).

Abstract.

Ok.

>>> the abstract has been updated given the new results from the inclusion of iNaturalist data (L26; L30).

Introduction.

>>> Thank you for these suggestions, we have expanded on latitudinal variation within bird and raptor diets in the suggested section while trying to also introduce the use of web-sourced photography as a tool to study diet. Upon reflection, we felt that this was appropriate at this point in the manuscript and provides a link to the following paragraph:

“For species that inhabitant large geographical areas, exploring how diet varies latitudinally may improve understanding of its ecology. For example, ecological and climatic conditions along latitudinal gradients influence the availability and presence of prey species within the wider environment [24], affecting the diversity and dietary composition for many species including birds [25]. Reviews of the raptor diet literature found distinct latitudinal patterns in the proportions of prey groups in some raptor diets, with increased probabilities of mammalian prey at higher latitudes [26,25].” (L68-75).

Line 51. Is there a word better than “however” ?

>>> To better emphasise the point that dietary assessments are dependent on the method and scale used, we have replaced the word “however” with “Most importantly” (L50).

Line 90. “it how diet” is correct ?

>>> Thank you for spotting this, we have now removed “it” from the sentence.

Objectives. Ok.

>>> No action required.

Material and Methods

>>> We have now revised the Methods accordingly and included a “Study Areas” subsection outlining the geographic extent of our study areas, regions and biogeographic subrealms:

“Study Areas

Section “Web-sourced…”.

>>> We have now included additional data from iNaturalist, please see response to comment above relating to this.

Line 116. You repeated…why not use “For them….” ?

>>> ‘useable’ now replaced with ‘For them’ (L142-143).

Line 117. What did you consider (adult or non-adult) when you could see an adult with a prey near a nestling in the nest ? This type of photograph has your two types of caracaras….

>>> The editor raises a very good point here relating to photographs where more than one bird (and age group) were visible in the photograph. We believe this was only the case for a handful of photographs. When this occurred, we only extracted age data from the bird that was interacting with the food item. We have clarified this in-text to benefit the reader

“For photographs that contained more than one caracara of each age group, we only extracted data for the individual interacting with the prey item” (L145-147).

Line 188. I did not understand item 4 (location)…can you briefly explain within brackets ?

>>> We assume the editor refers to “location” on line 120 of the original submission and not line 188. By location we refer to the surrounding features of the environment within the wider photograph, e.g., type of fencing present, road signs, etc. We have revised the text to clarify this point:

“visual characteristics or landscape features within the photograph…” (L148-149).

Line 123. These brackets are too distant. Do you really need them ? Six lines within them…can you try to reduce this text (Lines 121-130)?

>>> We agree with the editor here that the use of brackets is not appropriate for the text. As such, we have removed the brackets and streamlined the text within the paragraph:

“However, this was not always the case as there were occasions where multiple recordists uploaded images of the same feeding event across different days. This was particularly the case if the food item was large in size and thus took longer to decompose. We were able to ascertain whether these were duplicates by making an assessment based on the spatial location of the feeding event, evidence of the food item included and features of the surrounding location in the photograph.” (L152-157).

Section “Prey and age”.

Line 141, if at least two authors, than should be more than CP and FB…please check the writing.

>>> Thank you for highlighting this. We have revised to:

“visually assessed by at least two of the authors (C.P., F.B. or V.N.).” (L170).

Line 142. Better if you start a new paragraph with “Adult caracaras…”.

>>> New paragraph created as suggested (L172).

>>>

Section “Population”.

Lines 152 and 154. Extended or extends?

>>> “extended” replaced with “extends” (L182).

You could divide this section in 2-3 paragraphs. It is too long.

>>> New paragraph created after “In an attempt…” (L199).

Calling a figure with a map would be welcome here.

>>> We have cited Figure 1 here, which show the geographic spread of the data set graphically and in a map format:

“We plotted all useable photographs in QGIS version 3.14.16 [59] and conducted an overlap analysis between the geo-referenced photograph data points and each population range polygon (Fig. 1a-b).” (LXX).

Section “statistical Analysis”

>>> The editor raises an interesting point here in relation to temporal differences in caracara diet. There are certainly challenges associated with studying temporal changes in raptor diets across both the northern and southern hemisphere, however, it is possible with some additional analyses. However, we believe that an additional temporal analysis would be beyond the scope of the current study given multiple aspects of the species’ diet presented here, e.g., 1) overall diet composition, 2) age effects on diet and 3) diet variation across a latitudinal gradient. However, this certainly warrants further investigation in the form of an additional study where we have the space and opportunity to conduct a more thorough assessment of the species’ diet throughout the year, without being restricted by other results presented here.

Line 238. You have to place Table 1 here.

>>> Table 1 has been moved to the position suggested by the editor (L271).

Results.

Line 244. As you write “Of these…”, this percentage would be 1501/2454). No ?

>>> Absolutely and thank you for picking this up. We have revised the percentage to “68.9%” based on 2381/3451*100. (L286-287).

Lines 250. You have to call “(Fig 1)”, abbreviated with no dot.

>>> Revised throughout manuscript.

In the end of this paragraph (Line 258), you have to bring the captions of Fig 1 and Fig 2 (but not the figures, that should be kept in the end of the manuscript). Please check Instructions again.

>>> Full figures positioned at the end of the manuscript, captions in-text (L303-322).

Line 277. Bring Table 2 here.

>>> There is no Table 2 within the main text of the manuscript.

Line 287. Bring here: Caption of figure 3…

>>> Caption for Fig 3 placed in text where suggested (L351-355).

Discussion

It would be easier to read if you use subtitles for sections of the Discussion.

>>> Thank you for this suggestion, we have now included the following subtitles to help guide the reader through the Discussion section:

1. Crested Caracara diet varied along latitudinal gradients (L367).

2. Comparisons between other diet studies (L386).

3. Web-sourced photography is a useful tool to study raptor diets across large spatial scales (L402-403).

4. Study Limitations (L424).

5. Utilizing citizen science data can be a time- and cost-effective method to study raptor diets (L452-453).

6. Conclusions (L471).

Always consider an international readership by citing studies conducted in several ecoregions, countries, involving several species.

>>> We have now discussed our results in line with similarly, previous research on other raptor species:

“For example, a global examination of Western Barn Owl (Tyto alba) and American Barn Owl (T. furcata) diets found a positive relationship in the proportion of mammal prey in colder environments [25]. Unlike previous studies which studied the diets of Eurasian Sparrowhawk and Martial Eagles [27,29], we did not find any age effects in the diet of caracaras which may be explained by their generalist nature and tendency to feed on carrion [47,66]. Eurasian Sparrowhawk are avian specialists [27,28] and age-related differences in diet may be more pronounced. Similar to our findings, a continental assessment of Montagu’s Harrier (Circus pygargus) diet found that mammalian prey increased at higher latitudes due to the prevalence of agricultural land cover at more northern latitudes [49].” (L408-417).

>>> This is an excellent point, which we agree with fully. As such, we have revised the text to reflect the comments from the editor and reviewer 2:

“Assuming that the study species is well-sampled, this approach can be applied to many raptor species, especially those that are less common or more challenging to study in the field,” (L466-468).

References.

The correct is to use like this “2. Smith TC….” Instead, you used “[2] Smith TC….”.

>>> All reference numbers have been revised following the comments from the editor.

Page numbers. There is no space before them (after the volume and :).

>>> Spaces between colon and page numbers have been removed for all relevant references.

Page number. You have to use a long dash between then, not an hifen (-).

>>> All hyphens between page numbers have now been replaced with em dashes.

DOIs. You have to provide it for all references that have it. Follow the format: (http://doi.org/10.....).

>>> Revised.

Ref 6. The initials in capitals should not occur, except for the first word and names….check for all.

>>> We have checked for this issue in all references and included lower cases where appropriate in references 6 and 7.

Ref 26. It occurs with a duplicate. You will need to change all these numbers here and in the text.

>>> Now revised.

Please also check Instructions for

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PLoS One. doi: 10.1371/journal.pone.0304740.r003

Decision Letter 1

Dárius Pukenis Tubelis

17 May 2024

Continental scale dietary patterns in a New World raptor using web-sourced photographs

PONE-D-23-42552R1

Dear Dr. Connor Panter,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

An invoice will be generated when your article is formally accepted. Please note, if your institution has a publishing partnership with PLOS and your article meets the relevant criteria, all or part of your publication costs will be covered. Please make sure your user information is up-to-date by logging into Editorial Manager at Editorial Manager® and clicking the ‘Update My Information' link at the top of the page. If you have any questions relating to publication charges, please contact our Author Billing department directly at authorbilling@plos.org.

If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they’ll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org.

Kind regards,

Dárius Pukenis Tubelis, Ph.D.

Academic Editor

PLOS ONE

Additional Editor Comments:

Dear Dr Connor Panter,

Thank you for submitting the revised version of your submission PONE-D-23-42552.

I noted that you followed most suggestions provided by the three external reviewers and me. On the few occasions that you disagred, you convinced me with your answers.

Thus, I appreciated all answers to the reviewers and all changes done to this new revised version. The new version was substantially improved in several aspects.

This manuscript provides interesting data, and you properly discussed aspects of the methods and variation in the diet of birds across large scale latitudinal gradients.

Thus, I consider that this study reaches the standard expected for publication in PLOS ONE.

I suggest Acceptance, and that this manuscript goes through the final steps for publication.

In my last reading, I found a few minor things to be fixed by you and co-authors prior to or during the proofs corrections. They are shown below.

I believe it will be a great contribution to PLOS ONE.

Thank you for considering PLOS ONE as home of your study.

Dr Dárius Tubelis

PLOS ONE Editor

Final things to fix:

Major section titles. You are using ABSTRACT, INTRODUCTION ....with all in capitals. Instead, you have to use only the first letter in capital (Introduction)....please check this throughout.

Line 48. when you have two references, you have to add a space after the comma. e.g. [6, 7]...please check this along the text.

Line 62. when you have three or more consecutive refs, you have to use a long dash (not hyphen) to separate the numbers. Please check all.

Line 75. Invert the numbers. Smaller numbers come prior to larger ones.

Line 103. You forgot to add the iNaturalist search...please add.

Lines 224 and 226. I think the wright is "km" and not "kms".

Lin2 277. Add a dot point after Table 1.

Line 395. Delete 40. Then use 39-48, as they are in sequence.

Line 416. Place Tyto alba in italics.

Line 435. Can you use "explain partly" ? Maybe these perfer large prey.... Small prey are not cost-effective, I think. This obeserved preference for larger prey be, mostly, a natural aspect.

References.

You are using a very, very, very long dash to separate page numbers in articles. I hope this is the correct one. PLOS ONE people with check this and maybe contact you.

All references appear to be well formatted.

Well done.

Congratulations on your study!

Dárius

PLoS One. doi: 10.1371/journal.pone.0304740.r004

Acceptance letter

Dárius Pukenis Tubelis

28 May 2024

PONE-D-23-42552R1

PLOS ONE

Dear Dr. Panter,

I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now being handed over to our production team.

At this stage, our production department will prepare your paper for publication. This includes ensuring the following:

* All references, tables, and figures are properly cited

* All relevant supporting information is included in the manuscript submission,

* There are no issues that prevent the paper from being properly typeset

If revisions are needed, the production department will contact you directly to resolve them. If no revisions are needed, you will receive an email when the publication date has been set. At this time, we do not offer pre-publication proofs to authors during production of the accepted work. Please keep in mind that we are working through a large volume of accepted articles, so please give us a few weeks to review your paper and let you know the next and final steps.

Lastly, if your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org.

If we can help with anything else, please email us at customercare@plos.org.

Thank you for submitting your work to PLOS ONE and supporting open access.

Kind regards,

PLOS ONE Editorial Office Staff

on behalf of

Dr. Dárius Pukenis Tubelis

Academic Editor

PLOS ONE

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

‘GLM’ = Generalized Linear Model, ‘GLMM’ = Generalized Linear Mixed Model.

(DOCX)

pone.0304740.s001.docx^{(17.2KB, docx)}

Significant contrasts (P < 0.05) highlighted in bold.

(DOCX)

pone.0304740.s002.docx^{(17.9KB, docx)}

SE = standard error, df = degrees of freedom. Significant effects (P < 0.05) in bold.

(DOCX)

pone.0304740.s003.docx^{(15.8KB, docx)}

SE = standard error, df = degrees of freedom. Significant effect (P < 0.05) in bold.

(DOCX)

pone.0304740.s004.docx^{(14.5KB, docx)}

Attachment

Submitted filename: Miranda_PONE-D-23-42552.docx

pone.0304740.s005.docx^{(12.9KB, docx)}

Attachment

Submitted filename: Response to reviewers PONE-D-23-42552-R1 (2).docx

pone.0304740.s006.docx^{(54.1KB, docx)}

Data Availability Statement

All relevant data for this study are publicly available from the Dryad repository (https://doi.org/10.5061/dryad.rjdfn2zkz).

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Continental scale dietary patterns in a New World raptor using web-sourced photographs

Connor T Panter

Vincent N Naude

Facundo Barbar

Arjun Amar

Roles

Abstract

Introduction

Materials and methods

Study areas

Web-sourced photographs and data extraction

Macaulay Library and iNaturalist data

Prey identification and caracara age

Population classification

Fig 1.

Spatial clustering

Statistical analyses

Age and population effects on caracara diet

Latitudinal effects on caracara diet

Results

Overview of photographic samples

Table 1. Photographic sample sizes of Crested Caracaras (Caracara plancus) feeding throughout North, Central and South America by population and prey group sourced from Macaulay Library and iNaturalist between 1987 through 2022.

Fig 2. Age differences present in 1,555 photographs of Crested Caracaras (Caracara plancus) feeding throughout North, Central and South America between 1987 through 2022.

Dietary composition

Age and population effects on caracara diet

Latitudinal effects on caracara diet

Fig 3.

Discussion

Crested caracara diet varied along latitudinal gradients

Comparisons between other diet studies

Web-sourced photography is a useful tool to study raptor diets across large spatial scales

Study limitations

Utilizing citizen science data can be a time- and cost-effective method to study raptor diets

Conclusions

Supporting information

Acknowledgments

Data Availability

Funding Statement

References

Decision Letter 0

Dárius Pukenis Tubelis

Roles

Author response to Decision Letter 0

Decision Letter 1

Dárius Pukenis Tubelis

Roles

Acceptance letter

Dárius Pukenis Tubelis

Roles

Associated Data

Supplementary Materials

Data Availability Statement

ACTIONS

PERMALINK

RESOURCES

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