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The Journal of Veterinary Medical Science logoLink to The Journal of Veterinary Medical Science
. 2018 Dec 27;81(2):298–313. doi: 10.1292/jvms.17-0717

A review: poisoning by anticoagulant rodenticides in non-target animals globally

Shouta MM NAKAYAMA 1,#, Ayuko MORITA 1,#, Yoshinori IKENAKA 1,2, Hazuki MIZUKAWA 3, Mayumi ISHIZUKA 1,*
PMCID: PMC6395208  PMID: 30587672

Abstract

Worldwide use of anticoagulant rodenticides (ARs) for rodents control has frequently led to secondary poisoning of non-target animals, especially raptors. In spite of the occurrence of many incidents of primary or secondary AR-exposure and poisoning of non-target animals, these incidents have been reported only for individual countries, and there has been no comprehensive worldwide study or review. Furthermore, the AR exposure pathway in raptors has not yet been clearly identified. The aim of this review is therefore to comprehensively analyze the global incidence of primary and secondary AR-exposure in non-target animals, and to explore the exposure pathways. We reviewed the published literature, which reported AR residues in the non-target animals between 1998 and 2015, indicated that various raptor species had over 60% AR- detection rate and have a risk of AR poisoning. According to several papers studied on diets of raptor species, although rodents are the most common diets of raptors, some raptor species prey mainly on non-rodents. Therefore, preying on targeted rodents does not necessarily explain all causes of secondary AR-exposure of raptors. Since AR residue-detection was also reported in non-target mammals, birds, reptiles and invertebrates, which are the dominant prey of some raptors, AR residues in these animals, as well as in target rodents, could be the exposure source of ARs to raptors.

Keywords: anticoagulant rodenticide, comprehensive review, non-target animal, raptor, residue

Worldwide use of anticoagulant rodenticides (ARs) for vertebrate pest control has frequently led to the unintentional exposures of non-target animals, especially raptors, to these poisons. Recently, more than 420 birds, including 46 bald eagles (Haliaeetus leucocephalus), died because of a rat-eradication program on an Alaskan island [2]. Reporting that more than 130 dead raptors found in and around Vancouver, Canada, and virtually 100% of the owls and the hawks in this group, had AR residues in their livers, the Nature News article “killing rats is killing birds” had a strong impact on the world [29]. The occurrence of AR poisoning in raptors is related to many factors, such as the exposure pathway, the degree of ARs inhibiting the target molecule (vitamin K 2,3-epoxide reductase, VKOR), and AR metabolism by cytochrome P450 (CYP).

Although it is thought that raptors are sensitive to ARs, the mechanism for this sensitivity has not yet been revealed. Several toxicokinetic of avian species have been studied. Compared to mammals, eastern screech-owls (Megascops asio) have a long elimination half-life of diphacinone in the liver [39]. Furthermore, owls have very low CYP-dependent warfarin metabolic activity compared to rats and other avian species [62]. These facts imply that owls have a limited ability to detoxify ARs. However, toxicokinetics of the other raptor species has been rarely studied.

In spite of frequent incidents of primary or secondary AR-exposure and poisoning in non-target animals, including predatory mammals and birds (especially raptors), these incidents have been reported only in individual countries and there has been no comprehensive worldwide study or review. Therefore, we comprehensively reviewed and analyzed the published literature on AR-exposure occurrence based on the kind of ARs, the country type, and the animal groups. In addition, this review discussed diets of raptors. Some possible exposure pathways in addition to the target rodents were also discussed.

The chemical structures of nine typical anticoagulant rodenticides (ARs) are shown in Fig. 1. ARs are classified into two classes: 4-hydroxycoumarin derivatives (coumarin: warfarin, coumatetralyl, brodifacoum, bromadiolone, difenacoum, difethialone, and flocoumafen), and 1,3-indanedione derivatives (indanedione: chlorophacinone and diphacinone are the most commonly used examples).

Fig. 1.

Fig. 1.

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Chemical structure of nine typical ARs (A to I) and vitamin K (J). First-generation anticoagulant rodenticides (FGARs) are represented by the coumarin (warfarin, A, and coumatetralyl, B) and indanedione (diphacinone, C, and chlorophacinone, D) rodenticides. Examples of second-generation anticoagulant rodenticides (SGARs) are brodifacoum (E), bromadiolone (F), difenacoum (G), difethialone (H) and flocoumafen (I). The main chain structures of ARs are similar to that of vitamin K (J).

By the early 1950s, warfarin was being used as a pesticide to control rats and mice [41]. Warfarin and other early ARs, such as coumatetralyl, chlorophacinone, and diphacinone, are called first-generation ARs (FGARs). Multiple ingestions of these compounds are required to cause death in rodents. Since then, FGAR-resistant rats and mice have appeared, so the more potent second-generation ARs (SGARs), such as brodifacoum, bromadiolone, difenacoum, difethialone, and flocoumafen, were developed [41]. SGARs require only a single ingestion to cause death in the targeted rodents. For mice, SGARs have a longer T1/2 than FGARs (Table 1): in the plasma, T1/2 for SGARs is 20.4–91.7 days, while that for FGARs is 0.52–14.9 days; and in the liver, T1/2 for SGARs is 28.1–307.4 days, whereas that for FGARs is 15.8–66.8 days. In addition to longer T1/2, SGARs have a lower LD50 than FGARs (Table 2): LD50 for SGARs and FGARs are 0.4–1.75 and 20.5–1,000 mg/kg in mice; 0.35–0.84 and 11–323 mg/kg in rats; 0.25–8.1 and 0.88–50 mg/kg in dogs; 3.15 and 942 mg/kg in chickens; 0.26–138 and 258–2,150 mg/kg in northern bobwhites; 10 and >100 mg/kg in ring-necked pheasants; and 4.6 and 620–3,158 mg/kg in mallards. In Australian harriers, LD50 for brodifacoum (SGARs) is 10 mg/kg; and in American kestrels, LD50 for diphacinone (FGARs) is 97 mg/kg. These longer T1/2 and lower LD50 for SGARs imply that SGARs are more toxic than FGARs.

Table 1. Eliminated half-life, T1/2 (days) for FGARs (warfarin, coumatetralyl, chlorophacinone and diphacinone) and SGARs (brodifacoum, bromadiolone, difenacoum, difethialone and flocoumafen) in animals. Modified from [12, 18, 20, 39, 40, 57].

FGARs SGARs
Warfarin Couma-tetralyl Dipha-cinone Chloro-phacinone Brodi-facoum Broma-diolone Difen-acoum Difeti-alone Flocou-mafen
T1/2 in the plasma
Mousea) 14.9 0.52 - 11.7 91.7 33.3 20.4 38.9 26.6
T1/2 in the liver
Mousea) 66.8 15.8 - 35.4 307.4 28.1 61.8 28.5 93.8
Rat - - 3 - - - - - -
Pig - - 5.43 - - - - - -
Screech owl - - 11.7 - - - - - -
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a) dose=half of LD50.

Table 2. Median lethal dose, LD50 (mg/kg) for FGARs (warfarin, coumatetralyl, chlorophacinone and diphacinone) and SGARs (brodifacoum, bromadiolone, difenacoum, difethialone and flocoumafen) in animals. Modified from [12, 18, 20, 39, 40, 57].

FGARs SGARs
Warfarin Couma-tetralyl Dipha-cinone Chloro-phacinone Brodi-facoum Broma-diolone Difen-acoum Difeti-alone Flocou-mafen
Mouse 374 <1,000 141–340 20.5 0.4 1.75 0.8 1.29 0.8
Rat 14–323 - 30 11 0.35–0.5 0.56–0.84 - 0.55 -
Dog 20–50 - 0.88–15 - 0.25–1.0 8.1 - - -
Cat 2.5–20 - 5–15 - <25 >25 - - -
Chicken 942 - - - 3.15 - - - -
Northern bobwhite >2,150 - 2,014 258 - 138 - 0.26 -
Ring-necked pheasant - - - >100 10 - - - -
Mallard 620 - 3,158 - 4.6 - - - -
American kestrel - - 97 - - - - - -
Australasian harrier - - - - 10 - - - -
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AR EXPOSURE GLOBALLY

From 1998 to 2015, altogether 30 papers were published reporting primary or secondary exposure and poisoning by ARs in non-target animals. Of these, 19 papers report poisoning of raptors. There are six publications from the U.S.A. [9, 42, 45, 48,49,50], three from Canada [1, 18, 55], nine from the U.K. [7, 19, 31, 46, 47, 58,59,60,61], two from France [13, 25], three from Spain [28, 43, 44], two from Denmark [5, 11], one from Norway [26], and four from New Zealand (NZ) [6, 8, 14, 35]. These reports and the proposed exposure pathways are summarized below.

Presence of ARs in non-target animals

According to the literatures published between 1998 and 2015, totally 2,694 out of 4,891 (55%) individual non-target animals have been found to have a residual accumulation of ARs in their livers (Table 3A). Because the kinds of analyzed rodenticides were different depending on the papers, the number of analysis was different for each compound. Brodifacoum was detected in 31% (n=1,465 out of 4,790) of non-target animals, bromadiolone in 30% (n=1,346 out of 4,513), and difenacoum in 26% (n=1,048 out of 4,001). The other compounds were detected in less than 10% of the animals: flocoumafen in 5.7% (n=175 out of 3,077), difethialone in 5.0% (n=101 out of 2,035), chlorofacinone in 5.6% (n=113 out of 2,013), diphacinone in 5.0% (n=99 out of 1,972), coumatetralyl in 4.5%, (n=108 out of 2,391), and warfarin in 1.0% (n=27 out of 2,639). Some animals had more than two types of ARs in their liver.

Table 3. Detection rates and the numbers of non-target animals in which ARs have been detected in their liver, classified based on (A) type of AR, (B) country and (C) animal groups. Altogether, there were 2,694 out of 4,891 individuals (55%) of non-target animals have been reported to have AR residues in their livers between 1981 and 2013 [1, 5,6,7,8,9, 11, 13, 14, 18, 19, 25, 26, 28, 31, 35, 42,43,44,45,46,47,48,49,50, 55, 58,59,60,61].

(A) FGARs SGARs
Warfarin Couma-tetralyl Dipha-cinone Chloro-phacinone Brodi-facoum Broma-diolone Difen-acoum Difeti-alone Flocou-mafen
Detection rate (%) 1.0 4.5 5.0 5.6 31.0 30.0 26.0 5.0 5.7
The number of detection 27 108 99 113 1,465 1,346 1,048 101 175
The number of analysis 2,639 2,391 1,972 2,013 4,790 4,513 4,001 2,035 3,077
(B) Denmark Canada NZ U.S.A. Norway Spain U.K. France
Detection rate (%) 93 67 59 58 53 51 44 23
The number of detection 523 241 171 474 16 437 790 42
The number of analysis 560 362 288 812 30 849 1,809 181
(C) Carnivora Raptors Mammals excluding Carnivora Birds excluding raptors Reptiles
Detection rate (%) 56.8 56.6 52.1 52.1 50.0
The number of detection 382 1,892 212 207 1
The number of analysis 672 3,345 407 397 2
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High detection-rates of brodifacoum, bromadiolone and difenacoum reflect the relative frequency of use of these SGARs and differences in tissue T1/2 values between compounds. Because brodifacoum has longer T1/2 compared with the other ARs (Table 1), it would be expected that brodifacoum is detected for a long time and is over-reported relative to the amount of use compared with the other compounds. Because of the high toxicity of SGARs, as indicated by their longer T1/2 values in the liver and lower LD50 values relative to FGARs (Tables 1 and 2), the potential adverse effects of SGARs on non-target animals are a particular cause for concern.

AR exposure of non-target animals in each country

In terms of occurrence in each country (Table 3B), residues of rodenticides were detected in 523 out of 560 animals (93%) in Denmark, 241 out of 362 animals (67%) in Canada, 171 out of 288 animals (59%) in NZ, 474 of 812 animals (58%) in the U.S.A., 16 out of 30 animals (53%) in Norway, 437 out of 849 animals (52%) in Spain, 790 out of 1809 animals (44%) in the U.K., and 42 out of 181 animals (23%) in France. Although these rates seem to imply the degree of AR exposure in each country, it is difficult to compare the percentage with each country, because these percentages probably reflect residue detection limits as well as the relative frequency of use. The minimum detectable amounts of individual ARs described in the study of Denmark and Canada were lower than those of France (e.g. 2–5 to 70–80 µg/kg for brodifacoum respectively) [1, 5, 11, 13, 18, 25, 55]. On the other hand, the detection limits for brodifacoum were 10–50, 2–20, 5, 1–6, and 1.4–50 µg/kg of NZ [8, 14, 35], the U.S.A. [9, 42, 45, 48,49,50], Norway [26], Spain [28, 43, 44], and the U.K. [7, 19, 31, 46, 47, 58,59,60], respectively. Therefore, high (or low) sensitivity of detection seemingly not always cause over (or under)-estimation, but in some cases might affect accounting of AR exposure. We would like to note that, although AR detection rates were various in eight countries (from 23 to 93%), AR exposure of non-target animals might certainly occur in all eight countries.

The largest number of species in which AR residues have been found in one country (Table 4) was 39 (Spain), followed by 31 (the U.S.A.), 21 (NZ), 13 (Denmark), 11 (the U.K.), ten (France), five (Canada), and two (Norway). In all of these countries except NZ, raptors constituted the majority of exposed species: 18 in Spain, 13 in the U.S.A., 11 in Denmark, seven in the U.K., four in France and Canada, and two in Norway. In NZ, the majority of exposed species were in the group “birds excluding raptors” (16 species). Various species (totally 94 species), especially raptors (34 species), were exposed to ARs.

Table 4. The number of non-target animal species in which ARs have been detected in the liver. References are given in Table 5.

U.S.A. Canada U.K. France Spain Denmark Norway NZ Totala)
Raptors 13 4 7 4 18 11 2 2 34
Other birds 9 1 - 2 9 - - 16 34
Carnivora 5 - 3 4 8 2 - - 15
Cetartiodactyla 1 - - - - - - 2 3
Erinaceomorpha - - 1 - 2 - - - 2
Rodentia 2 - - - - - - - 2
Lagomorpha - - - - 1 - - - 1
Chiroptera - - - - - - - 1 1
Marsupialia 1 - - - - - - - 1
Reptiles - - - - 1 - - - 1
Total 31 5 11 10 39 13 2 21 94
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a) This is not necessarily the sum of the values for each country, because some species were reported in several countries.

AR residues in non-target animals have only been reported in these eight countries. This is probably because this research is implemented only in North America, Europe and NZ. However, ARs have been frequently used worldwide [21]. Global AR market data is difficult to obtain because of confidential business information, but estimates are described as hundreds of millions dollars annually in the U.S.A. and European countries [41]. Primary and secondary AR exposure of non-target animals may indeed occur all over the world, so increased surveys are needed worldwide to determine the extent of the problem.

Classification of animal species exposed to ARs

Table 3C shows that the accumulation of AR residues was detected in 382 out of 672 individuals of Carnivora (56.8%), 1,892 out of 3,345 raptors (56.6%), 212 out of 407 mammals excluding Carnivora (52.1%), 207 out of 397 birds excluding raptors (52.1%), and 1 out of 2 reptiles (50%). Percentages of Carnivora, raptors and reptiles are presumed to be secondary exposure degree, and those of mammals excluding Carnivora and birds excluding raptors seem to be primary exposure degree.

Although secondary exposure seems to occur in Carnivora and raptors at a comparable frequency, secondary poisoning should be considered to occur in raptors frequently relative to Carnivora. Critical liver SGAR concentrations associated with hemorrhaging and mortality have not been defined for most raptor species. However, the potentially lethal range for SGARs in raptors has been described as >100–200 µg/kg [5, 55, 60]. On the other hand, the lethal concentration of SGARs in Carnivora livers have been reported that brodifacoum of 700 µg/kg was detected in stoat and weasel, bromadiolone of 230 µg/kg accumulated in stoat, and difenacoum of 1,400 µg/kg was measured in polecats [31, 46]. Because most of the cited references in the current review did not mention AR concentrations of individual animals, we could not calculate AR-poisoning rate of individual species. However, raptors are presumed to be poisoned by ARs frequently rather than Carnivora, because of the low lethal range for SGAR residues in raptors. Moreover, screech owls have longer T1/2 for diphacinone compared with rats and pigs (Table 1), and owls have very low warfarin metabolic activity relative to rats and other avian species [62]. The adverse effect of AR exposure on raptors is of interest.

The high AR-exposed rate was reported in various raptor species rather than Carnivora species. The number of species ARs detected in more than 60% of individuals was 11 in raptors, and it comprised 48% of 23 raptor species that the number of analysis was more than nine individuals (Note: We did not include the species whose analyzed individual sample size was less than 8. This was to avoid the over-estimation e.g. 100% of detection rate such a case that the one individual detected from the one individual analyzed.). In contrast, 3 species, which had over 60% AR-detection rate, composed 27% of 11 Carnivora species that AR residue was examined in more than nine individuals. AR exposure to extensive raptor species implies that various kinds of raptors have a risk of AR poisoning.

SECONDARY EXPOSURE TO AR IN RAPTORS

Frequently reported raptor species

Of the 39 raptor species analyzed, 34 species were reported to have AR accumulation in their liver, and 17 species had more than 60% detection rate of ARs (Table 5): two out of two turkey vultures (Cathartes aura; 100%), one out of one short toed snake-eagle (Circaetus gallicus; 100%), three out of three marsh harriers (Circus aeruginosus; 100%), five out of five moreporks (Ninox novaeseelandiae; 100%), 15 out of 17 little owls (Athene noctua; 88%), 33 out of 39 Eurasian eagle owls (Bubo bubo; 85%), 20 out of 24 bald eagles (Haliaeetus leucocephalus; 83%), five out of six short-eared owls (Asio flammeus; 83%), 26 out of 32 rough-legged buzzards (Buteo lagopus; 81%), 116 out of 145 sparrowhawks (Accipiter nisus; 80%), 108 out of 138 red kites (Milvus milvus; 78%), 62 out of 80 long-eared owls (Asio otus; 78%), 154 out of 206 kestrels (Falco tinnunculus; 75%), 26 out of 38 barred owls (Strix varia; 68%), 14 out of 22 golden eagles (Aquila chrysaetos; 64%), and 192 out of 308 great horned owls (Bubo virginianus; 62%).

Table 5. Presence of ARs in animal species reported in various countries. AR concentrations (µg/kg) given are in the form minimum–maximum, or mean ± S.D. (values marled with an asterisk are medians, with a sharp are standard error, S. E. and † means prevalence of any ARs); N gives the number of analysis; n+ gives the number of individuals with detectable residues; % means detection rate; and n is the total number of individuals in which each AR has been detected.

Species Year Country N n+ % Warfa-
rin		 Couma-
tetralyl		 Dipha-
cinone		 Chloro-
phacinone		 Brodi-
facoum		 Broma-
diolone		 Difen-
acoum		 Difeti-
alone		 Flocou-
mafen		 References
Raptors (39 species analyzed)
Turkey vulture
Cathartes aura 		1998–2001 U.S.A. 2 2 100 n=0 n=0 n=1 n=0 n=1 n=1 n=0 n=0 - [50]
Short toed snake-eagle
Circaetus gallicus 		2005–2010 Spain 1 1 100 n=0 n=0 n=0 n=0 n=1 n=1 n=1 [44]
9 10 n=0 n=0 2
Marsh harrier
Circus aeruginosus 		2000–2009 Denmark 3 3 100 - n=† - - n=† n=† n=† - n=† [5]
Morepork Ninox novaeseelandiae 1994–1999 NZ 5 5 100 - - - - n=5 - - - - [8, 35]
610–3,440
Little owl
Athene noctua 		17 15 88 n=5 n=1 n=2 n=1
2005–2013 Spain 8 6 75 n=0 - - - 62–574 79.5 2, 56 n=0 33 [28, 44]
2000–2009 Denmark 9 9 100 - n=† - - n=† n=† n=† - n=† [5]
Eagle owl
Bubo bubo 		39 33 85 n=20 n=13 n=11 n=3 n=7
2005–2013 Spain 21 18 86 n=0 n=0 n=0 n=0 10–2,008 2–208 1–281 35–200 3–90 [28, 44]
2000–2009 Denmark 10 10 100 - n=† - - n=† n=† n=† - n=† [5]
2009–2011 Norway 8 5 63 - - - - 74–158 n=0 39, 181 - 13 [26]
Bald eagle
Haliaeetus leucocephalus 		1995–2009 U.S.A. 24 20 83 n=1 n=0 n=0 n=0 n=18 n=0 n=1 n=0 - [9, 49, 50]
1,400 429–2,599
Short-eared owl
Asio flammeus 		6 5 83
1998–2001 U.S.A. 1 0 0 n=0 n=0 n=0 n=0 n=0 n=0 n=0 n=0 - [50]
2000–2009 Denmark 5 5 100 - n=† - - n=† n=† n=† - n=† [5]
Rough-legged buzzard
Buteo lagopus 		32 26 81 n=3 n=19 n=5 n=23
1998–2001 U.S.A. 1 0 0 n=0 n=0 n=0 n=0 n=0 n=0 n=0 n=0 - [50]
2000–2009 Denmark 31 26 84 - 1–3 - - 3*–34 0–130 14*–105 - n=0 [5]
Sparrowhawk
Accipiter nisus 		145 116 80 n=3 n=53 n=62 n=90 n=1
2000–2013 U.K. 131 104 79 n=0 n=0 n=0 n=0 n=48 n=57 n=85 3.3 n=0 [19, 59]
2009–2012 Spain 14 12 86 n=0 n=0 - 0.34 ± 0.57 13.2 ± 8.1 31.9 ± 22.6 3.6 ± 2.0 n=0 - [43]
Red kite
Milvus milvus 		138 108 78 n=40 n=74 n=78 n=1 n=5
1994–2011 U.K. 127 98 77 n=0 n=0 n=0 n=0 71–222 56–94 40–67 n=1 15 [19, 58, 60]
2005–2010 Spain 8 7 88 n=0 n=0 n=0 n=0 129, 210 5–490 1 n=0 53, 400 [44]
2000–2009 Denmark 3 3 100 - n=† - - n=† n=† n=† - n=† [5]
Long-eared owl
Asio otus 		80 62 78 n=4 n=1 n=1 n=39 n=22 n=36 n=3
1998–2001 U.S.A. 7 2 29 n=0 n=0 n=1 n=0 n=1 n=1 n=0 n=0 - [50]
2009–2013 Spain 35 24 69 n=0 n=0 - 0.5 ± 0.4 12–42 77.2 ± 29.6 1–53 n=0 n=0 [28, 43]
2000–2009 Denmark 38 36 95 - 0*–29 - - 3*–40 0*–33 7*–52 - 0*–2 [5]
Kestrel
Falco tinnunculus 		206 154 75 n=12 n=3 n=71 n=94 n=106 n=1 n=18
2000–2011 U.K. 115 78 68 - - - - n=21 n=52 n=58 n=1 n=0 [19, 58, 60]
2003 France 4 3 75 n=0 n=0 - - 80–250 80–250 n=0 - - [25]
2009–2012 Spain 21 14 67 n=0 n=0 - 0.6 ± 1.8 57.4 ± 34.6 79.8 ± 34.4 8.2 ± 6.9 n=0 - [43]
2000–2009 Denmark 66 59 89 - 0*–64 - - 2*–298 0*–679 6.5*–450 - 0*–20 [5]
Barred owl
Strix varia 		38 26 68 n=1 n=2 n=4 n=18 n=20 n=1
1998–2001 U.S.A. 13 3 23 n=0 n=0 n=1 n=0 n=1 n=1 n=0 n=0 - [50]
1988–2003 Canada 25 23 92 2.6 - 10 2.5–15 1–927 2–1,012 - 3 - [1]
Golden eagle
Aquila chrysaetos 		22 14 64 n=1 n=9 n=7 n=3
1996–2001 U.S.A. 2 2 100 n=0 n=0 n=1 n=0 30 n=0 n=0 n=0 - [49, 50]
2005–2010 Spain 4 1 25 n=0 n=0 n=0 n=0 n=0 n=0 n=0 n=0 6 [44]
2009–2011 Norway 16 11 69 - - - - 11–110 13–154 n=0 - 15, 117 [26]
Great horned owl
Bubo virginianus 		308 192 62 n=4 n=4 n=3 n=157 n=111 n=1 n=7
1994–2012 U.S.A. 136 74 54 730 n=0 n=0 n=0 7–970 28–1,080 22 n=0 - [48, 49, 50]
1988–2003 Canada 172 118 69 2.5–720 - 8–12 2.5–14 1–610 1–570 - 3–30 - [1, 55]
Black kite
Milvus migrans 		2005–2010 Spain 5 3 60 n=0 n=0 n=0 n=0 n=1 n=0 n=0 n=0 n=2 [44]
25 55, 84
Common buzzard
Buteo buteo 		639 380 60 n=4 n=31 n=2 n=130 n=238 n=236 n=3 n=35
2000–2010 U.K. 407 195 48 n=0 n=0 n=0 n=0 n=24 n=122 n=110 - - [19]
2003 France 11 10 91 350–2,000 n=0 - - 80–250 80–290 80–250 - - [25]
2005–2013 Spain 80 43 54 n=0 n=0 n=0 0.3, 120 4.9–1,356 1–586 2.9–1,921 85–539 1–175 [28, 43, 44]
2000–2009 Denmark 141 132 94 - 0*–435 - - 2*–613 7.5*–282 10*–170 - 0*–115 [5]
Australasian harrier
Circus approximans 		1994–1999 NZ 4 2 50 - - - - n=2 - - - - [8, 35]
610, 660
Screech owl
Otus asio 		1997–2001 U.S.A. 24 12 50 n=0 n=0 n=0 n=0 n=10 n=3 n=0 n=0 - [49, 50]
7–800 50–500
Red-tailed hawk
Buteo jamaicensis 		362 176 49 n=1 n=1 n=155 n=59
1994–2010 U.S.A. 297 137 46 n=0 n=0 340 180 6–1,600 31–543 n=0 n=0 - [48, 49, 50]
2011 Canada 65 39 60 - - - - 1–170 1–64 - n=0 - [55]
Scops owl
Otus scops 		2011–2013 Spain 33 16 49 n=0 n=0 n=0 n=0 n=9 n=5 n=8 n=0 n=2 [28]
3–158.4 2–44 1–10 3, 10
Barn owl
Tyto alba 		769 370 48 n=1 n=13 n=3 n=3 n=149 n=235 n=203 n=22 n=25
1988–2003 Canada 78 48 62 2.5 - 10–20 n=0 10–470 5–720 - 2.5–720 - [1]
2000–2011 U.K. 535 193 36 - - - - n=33 n=111 n=115 n=4 n=9 [19, 58, 60]
2003 France 10 7 70 n=0 640 - - n=0 80–260 80–260 - - [25]
2005–2013 Spain 66 47 71 n=0 n=0 - 1.2 ± 1.0 2–839 7.1–180 1–198 45–4,463 14–299 [28, 43, 44]
2000–2009 Denmark 80 75 94 - 0*–18 - - 4*–957 16*–252 11*–223 - 0*–34 [5]
Tawny owl
Strix aluco 		276 109 40 n=6 n=53 n=65 n=51 n=4 n=12
1990–2010 U.K. 200 45 28 - - - - n=12 n=26 n=13 - n=0 [19, 60]
2003 France 5 2 40 n=0 n=0 - - n=0 80, 250 n=0 - - [25]
2011–2013 Spain 27 21 78 n=0 - - - 2–1582 2–77 1–84 93–430 0–118 [28]
2000–2009 Denmark 44 41 93 0*–39 - - 3*–220 8*–496 7*–90 - 0*–42 [5]
Cooper’s hawk
Accipiter cooperii 		1998–2001 U.S.A. 50 18 36 n=1 n=0 n=1 n=0 n=12 n=5 n=0 n=0 - [50]
100 100 8–220 40–600
Peregrine falcon
Falco peregrinus 		30 10 33 n=1 n=1 n=3 n=8
1986–2009 U.S.A. 4 3 75 1,480 n=0 n=1 n=0 n=2 n=1 n=0 n=0 - [9, 49, 50]
2000–2010 U.K. 24 7 29 n=0 n=0 n=0 n=0 n=1 n=7 n=0 - n=0 [19]
2009–2011 Norway 2 0 0 - - - - n=0 n=0 n=0 - n=0 [43]
Northern goshawk
Accipiter gentilis 		3 1 33 n=1
1998–2001 U.S.A. 1 0 0 n=0 n=0 n=0 n=0 n=0 n=0 n=0 n=0 - [50]
2005–2010 Spain 2 1 50 n=0 n=0 n=0 n=0 38 n=0 n=0 n=0 n=0 [44]
Saw-whet owl
Aegolius acadicus 		1998–2001 U.S.A. 3 1 33 n=0 n=0 n=1 n=0 n=1 n=1 n=0 n=0 - [50]
Bearded vulture
Gypaetus barbatus 		2005–2010 Spain 3 1 33 n=0 n=0 n=0 n=0 n=0 n=1 n=0 n=0 n=0 [44]
1
Snowy owl
Nyctea scandiaca 		1993, 1998–2001 U.S.A. 3 1 33 n=0 n=0 n=1 n=0 n=0 n=0 n=0 n=0 - [49, 50]
260
Barbary falcon
Falco peregrinoides 		2009–2012 Spain 16 5 31 n=0 n=0 - n=1 n=1 n=3 n=1 n=0 - [43]
0.1 0.8 26.2 ± 18.6 1.4
Eurasian griffon
Gyps fulvus 		2005–2010 Spain 23 3 13 n=0 n=0 n=0 n=1 n=0 n=1 n=1 n=0 n=0 [44]
4 208 1
Spanish imperial eagle
Aquila adalberti 		2005–2010 Spain 8 1 13 n=0 n=0 n=0 n=0 n=0 n=0 n=1 n=0 n=0 [44]
8
Sharp-shinned hawk
Accipiter striatus 		1998–2001 U.S.A. 11 1 9 n=0 n=0 n=1 n=0 n=1 n=1 n=0 n=0 - [50]
Broad-winged hawk
Buteo platypterus 		1998–2001 U.S.A. 11 0 0 n=0 n=0 n=0 n=0 n=0 n=0 n=0 n=0 - [50]
Black vulture
Coragyps atratus 		1998–2001 U.S.A. 1 0 0 n=0 n=0 n=0 n=0 n=0 n=0 n=0 n=0 - [50]
Merlin
Falco columbarius 		1998–2001 U.S.A. 1 0 0 n=0 n=0 n=0 n=0 n=0 n=0 n=0 n=0 - [50]
Gyrfalcon
Falco rusticolus 		2009–2011 Norway 1 0 0 - - - - n=0 n=0 n=0 - n=0 [43]
Osprey
Pandion haliaetus 		2009–2011 Norway 3 0 0 - - - - n=0 n=0 n=0 - n=0 [43]
Birds excluding raptors (40 species analyzed)
Common myna
Acridotheres tristis 		1994–1999 NZ 3 3 100 - - - - n=3 - - - - [8]
540–1,270
Gray duck
Anas superciliosa 		1994–1999 NZ 1 1 100 - - - - n=1 - - - - [8]
910
Gray heron
Ardea cinerea 		2005–2010 Spain 1 1 100 n=0 n=0 n=0 n=0 n=1 n=0 n=0 n=0 [44]
n=0 10
Lapland longspur
Calcarius lapponicus 		2009 U.S.A. 2 2 100 n=0 n=0 n=0 n=0 n=2 n=0 n=0 n=0 - [9]
560, 2,989
Rock sandpiper
Calidris ptilocnemis 		2009 U.S.A. 1 1 100 n=0 n=0 n=0 n=0 n=1 n=0 n=0 n=0 - [9]
43
Emperor goose
Chen canagica 		2009 U.S.A. 1 1 100 n=0 n=0 n=0 n=0 n=1 n=0 n=0 n=0 - [9]
27
Great spotted cuckoo
Clamator glandarius 		2005–2010 Spain 1 1 100 n=0 n=0 n=0 n=1 n=0 n=0 n=0 n=0 n=0 [44]
6
Common crow
Corvus brachyrhynchos 		1997 U.S.A. 1 1 100 n=0 n=0 n=0 n=0 n=1 n=0 n=0 - - [49]
1,340
Raven
Corvus corax 		14 14 100 n=14
1996 U.S.A. 1 1 100 n=0 n=0 n=0 n=0 1,040 n=0 n=0 - - [49]
1995 Canada 13 13 100 - - - - 980–2,520 - - - - [18]
Chaffinch
Fringilla coelebs 		1994–1999 NZ 3 3 100 - - - - n=3 - - - - [8]
120–2,310
Southern black-backed gull
Larus dominicanus 		1994–1999 NZ 1 1 100 - - - - n=1 - - - - [8]
580
Gray-crowned rosy finch
Leucosticte tephrocotis 		2009 U.S.A. 1 1 100 n=0 n=0 n=0 n=0 n=1 n=0 n=0 n=0 - [9]
1,219
Kaka
Nestor meridionalis 		1994–1999 NZ 3 3 100 - - - - n=3 - - - - [8]
1,200–4,100
Pukeko
Porphyrio porphyrio 		1994–1999 NZ 8 8 100 - - - - n=8 - - - - [8]
520–1,350
Spotless crake
Porzana tabuensis 		1994–1999 NZ 1 1 100 - - - - n=1 - - - - [8]
40
Paradise shelduck
Tadorna variegata 		1994–1999 NZ 4 4 100 - - - - n=4 - - - - [8]
240–800
Black bird
Turdus merula 		1994–1999 NZ 13 13 100 - - - - n=13 - - - - [8]
10–1,100
Northern fulmar
Fulmarus glacialis 		2009 U.S.A. 1 1 100 n=0 n=0 n=0 n=0 n=1 n=0 n=0 n=0 - [9]
57
Pelagic cormorant
Phalacrocorax pelagicus 		2009 U.S.A. 1 1 100 n=0 n=0 n=0 n=0 n=1 n=0 n=0 n=0 - [9]
44
Glaucous-winged gull
Larus glaucescens 		2009 U.S.A. 10 9 90 n=0 n=0 n=0 n=0 n=9 n=1 n=2 n=0 - [9]
709–4,189 n=1 n=2
Rock dove
Columba livia 		2005–2010 Spain 97 64 66 n=0 n=0 n=0 n=64 n=0 n=0 n=0 n=0 n=0 [44]
550–55,100
Weka
Gallirallus australis 		1994–1999 NZ 55 31 56 - - - - n=31 - - - - [8]
10–2,300
Kakariki
Cyanoramphus sp. 		1994–1999 NZ 2 1 50 - - - - n=1 - - - - [8]
30
Saddleback
Philesturnus carunculatus 		1994–1999 NZ 4 2 50 - - - - n=2 - - - - [8]
50, 600
Brown kiwi
Apteryx australis 		1994–1999 NZ 29 14 48 - - - - n=14 - - - - [8]
10–690
Lesser black-backed gull
Larus fuscus 		2005–2010 Spain 8 3 38 n=0 n=0 n=0 n=0 n=0 n=3 n=0 n=0 n=0 [44]
2–5
Common starling
Sturnus vulgaris 		2005–2010 Spain 3 1 33 n=0 n=0 n=0 n=0 n=0 n=1 n=0 n=0 n=0 [44]
15
Calandra lark
Melanocorypha calandra 		2005–2010 Spain 7 2 29 n=0 n=0 n=0 n=2 n=0 n=0 n=0 n=0 n=0 [44]
1,040, 2,090
Mallard
Anas platyrhynchos 		23 6 26 n=3 n=2 n=1
2003 France 15 1 7 n=0 n=0 - - - 80–250 - - - [25]
2005–2010 Spain 6 3 50 n=0 n=0 n=0 710–2,170 - n=0 n=0 n=0 n=0 [44]
1994–1999 NZ 2 2 100 - - - 900, 1,230 - - - - [8]
Black coot
Fulica atra 		2003 France 13 3 23 n=1 n=0 - - n=1 n=1 n=0 - - [25]
23,520 80–250 80–250
Magpie
Gymnorhina tibicen 		1994–1999 NZ 30 6 20 - - - - n=6 - - - - [8, 35]
80–990
Robin
Petroica australis 		1994–1999 NZ 10 2 20 - - - - n=2 - - - - [8, 35]
350, 580
Red-legged partridge
Alectoris rufa 		2005–2010 Spain 7 1 14 n=0 n=0 n=0 n=0 n=0 n=0 n=0 n=0 n=1 [44]
143
Eurasian collared-dove
Streptopelia decaocto 		2005–2010 Spain 8 1 13 n=0 n=0 n=0 n=0 n=0 n=1 n=0 n=0 n=0 [44]
127
Bellbird
Anthornis melanura 		1994–1999 NZ 2 0 0 - - - - n=0 - - - - [8, 35]
Northwestern crow
Corvus caurinus 		1995 Canada 9 0 0 - - - - n=0 - - - - [18]
Common moorhen
Gallinula chloropus 		2003 France 1 0 0 n=0 n=0 - - n=0 n=0 n=0 - - [25]
Whitehead
Mohoua albicilla 		1994–1999 NZ 12 0 0 - - - - n=0 - - - - [8, 35]
Tomtit
Petroica macrocephala 		1994–1999 NZ 5 0 0 - - - - n=0 - - - - [35]
Fantail
Rhipidura fuliginosa 		1994–1999 NZ 2 0 0 - - - - n=0 - - - - [8, 35]
Carnivola (15 species analyzed)
Skunk
Mephitis mephitis 		1996 U.S.A. 3 3 100 n=0 n=0 n=0 n=0 n=0 n=3 n=0 - - [49]
20–280
Mountain lion
Puma concolor 		1997–2006 U.S.A. 4 4 100 n=0 - n=1 n=0 n=4 n=4 - n=1
<250 310–570 370–1,270 <250
Bobcat
Lynx rufus 		1988–2012 U.S.A. 169 148 88 n=11 - n=67 n=10 n=135 n=133 - n=50 - [42, 45]
n=11 30 ± 120 n=10 140 ± 200 380 ± 550 40 ± 310
Weasel
Mustela nivalis 		80 69 86 n=15 n=39 n=17 n=60 n=20
1996–1997 U.K. 10 3 30 n=0 8.5–60 - - n=0 250 n=0 - n=0 [31]
2005–2010 Spain 1 1 100 n=0 n=0 n=0 n=0 2,930 n=0 n=0 n=0 n=0 [44]
1984–2008 Denmark 69 65 94 - 4–45 - - 4–159 7–1,610 5–292 - 3–49 [11]
Feral cat
Felis catus 		2005–2010 Spain 4 3 75 n=0 n=0 n=0 n=0 n=2 n=1 n=1 - n=1 [44]
34, 350 52 70 72
Stoat
Mustela erminea 		101 68 67 n=22 n=31 n=34 n=49 n=25
1996–1997 U.K. 40 9 23 n=0 4.6–9.7 - - 120 40–380 n=0 - n=0 [31]
1993–2007 Denmark 61 59 97 - 2–61 - - 2–317 3–1,290 2–280 - 1–86 [11]
Stone marten
Martes foina 		2005–2010 Spain 19 11 58 n=0 n=0 n=0 n=0 n=5 n=6 n=3 n=1 n=5 [44]
19–390 7–17,900 7–520 926 8–230
Raccoon
Procyon lotor 		16 8 50 n=6 n=2
1992–1997 U.S.A. 6 6 100 n=0 n=0 n=0 n=0 320–5,300 n=0 n=0 - - [49]
2005–2010 Spain 10 2 20 n=0 n=0 n=0 n=0 n=0 1,090, 6,800 n=0 n=0 n=0 [44]
Red fox
Vulpes vulpes 		33 14 42 n=7 n=8 n=1
1996 U.S.A. 2 2 100 n=0 n=0 n=0 n=0 1,320, 4,010 n=0 n=0 - - [46]
2005–2010 Spain 31 12 39 n=0 n=0 n=0 n=0 5–4,500 5–12,300 78 n=0 n=0 [44]
Domestic dog
Canis familiaris 		2005–2010 Spain 11 4 36 n=0 n=0 n=0 n=0 n=0 n=3 n=1 n=0 n=0 [44]
6–308 4
Common genet
Genetta genetta 		2005–2010 Spain 7 2 29 n=0 n=0 n=0 n=0 n=2 n=2 n=1 n=0 n=1 [44]
16, 2,020 1, 350 12 60
European otter
Lutra lutra 		14 4 29 n=1 n=2 n=1
1990–2002 France 11 3 27 n=0 n=0 - 5,000 n=0 6,00, 7,100 n=0 n=0 - [13]
2005–2010 Spain 3 1 33 n=0 n=0 n=0 n=0 n=0 n=0 n=0 n=0 353 [44]
Polecat
Mustela putorius 		133 36 27 n=3 n=17 n=22
1992–1999 U.K. 100 31 31 - - - - 8–70 16–217 5–917 - n=0 [49, 50]
1990–2002 France 33 5 15 n=0 n=0 - n=0 n=0 600–9,000 n=0 n=0 - [13]
American mink
Mustela vison 		1990–2002 France 47 7 15 n=0 n=0 - n=4 n=0 n=3 n=0 n=0 - [13]
3,400–8,500 1,900–4,200
European mink
Mustela lutreola 		1990–2002 France 31 1 3 n=0 n=0 - n=0 n=0 n=1 n=0 n=0 - [13]
5,000
Cetartiodactyla (3 species analyzed)
White-tailed deer
Odocoileus virginianus 		1994–1997 U.S.A. 7 7 100 n=0 n=1 n=2 n=0 n=5 n=0 n=0 - - [49]
500 200, 930 120–410
Red deer
Cervus elaphus 		1994–1999 NZ 37 33 89 - - - - n=33 - - - - [8, 35]
<30
Domestic pig
Sus scrofa 		1994–1999 NZ 40 26 65 - - - - n=26 - - - - [8, 35]
7–1,780
Erinaceomorpha (2 species analyzed)
Algerian hedgehog
Atelerix algirus 		2011–2013 Spain 106 61 58 n=1 - - - n=18 n=35 n=29 n=4 n=0 [28]
611.8 5–1,533 6–2,548 1–659 71–256
European hedgehog
Erinaceus europaeus 		170 57 34 n=29 n=28 n=28 n=2 n=6
2004–2006 U.K. 120 27 23 - - - - 50 ± 10# 590 ± 240# 100 ± 30# - n=0 [7]
2005–2013 Spain 50 30 60 n=0 - - - 3–1,390 2–1,110 0–672 4, 142 1–29 [28, 44]
Rodentia (2 species analyzed)
Gray squirrel
Sciurus carolinensi 		1981–1997 U.S.A. 7 7 100 n=1 n=0 n=1 n=1 n=5 n=0 n=0 - - [50]
228 2,000 620 530–4,100
Eastern chipmunk
Tamias striatus 		1992 U.S.A. 1 1 100 n=0 n=0 n=0 n=0 n=1 n=0 n=0 - - [50]
3,800
Lagomorpha (1 species analyzed)
Iberian hare
Lepus granatensis 		2005–2010 Spain 25 8 32 n=0 n=0 n=0 n=7 n=2 n=0 n=1 n=0 n=0 [44]
580–9,520 130, 270 15
Chiroptera (1 species analyzed)
NZ lesser short-tailed bats
Mystacina tuberculata 		2009 NZ 12 10 83 - - n=10 - - - - - - [6]
190–680
Marsupialia (1 species analyzed)
Opossum
Didelphis virginiana 		1996, 1997 U.S.A. 2 2 100 n=0 n=0 n=0 n=0 n=1 n=1 n=0 - - [49]
180 800
Reptile (1 species analyzed)
Horseshoe whip snake
Hemorrhois hippocrepis 		2005–2010 Spain 1 1 100 n=0 n=0 n=0 n=0 n=0 n=0 n=0 n=0 n=1 [44]
540
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Of these 17 species, ten species included some individuals, which had liver SGAR concentrations more than 100 µg/kg (Table 5). The potentially lethal level for brodifacoum residues were reported in some individuals of all ten species: at least five moreporks (610–3,440 µg/kg), one little owl (574 µg/kg), four Eurasian eagle owls (133–2,008 µg/kg), 18 bald eagles (429–2,599 µg/kg), one sparrowhawk (112 µg/kg), three red kites (129–222 µg/kg), two kestrels (240 and 298 µg/kg), one barred owl (927 µg/kg), one golden eagle (110 µg/kg), and 15 great horned owls (100–970 µg/kg). High bromadiolone concentrations were reported in six species: at least one Eurasian eagle owl (208 µg/kg), one red kite (490 µg/kg), one kestrel (679 µg/kg), one barred owl (1,012 µg/kg), one golden eagle (154 µg/kg), and four great horned owls (226–1,080 µg/kg). High difenacoum accumulations were reported in two Eurasian eagle owls (181 and 281 µg/kg) and one kestrel (450 µg/kg), at least. High flocoumafen accumulations were reported in one red kite (400 µg/kg) and one golden eagle (117 µg/kg). High difethialone accumulations were reported in one Eurasian eagle owl (200 µg/kg). Four sparrowhawks were reported to have sum SGAR concentrations of 100–157 µg/kg. Because of the high AR exposure rates and including some individuals that have high liver SGAR concentrations, these ten species are seemingly affected by ARs more severely than other raptor species.

Threatened raptors

A wide variety of raptor species was found to have been exposed to ARs. Furthermore, these reported raptors include species with special conservation status, such as red kites (Near Threatened, IUCN Red List [54]) and the Spanish imperial eagle (Aquila adalberti, Vulnerable, IUCN Red List [51]).

Although there are no reports of AR residues in the livers of raptors from Russia or Mongolia, it has been reported that the numbers of breeding pairs of Eastern imperial eagles (Aquila heliaca, Vulnerable, IUCN Red List [52]) and Saker falcons (Falco cherrug milvipes, Endangered, IUCN Red List [53]) decreased following bromadiolone application [15, 36]. In Japan, diphacinone was used on Ogasawara Island and it was reported that at least three Eastern buzzards (Buteo japonicus toyoshimai), classified as locally Endangered (Ministry of the Environment, Government of Japan [33]), might have been poisoned as a result [4, 16]. These incidents imply that poisoning by ARs could have occurred worldwide, despite the lack of studies on the existence of AR residues in the livers of raptors from these areas.

EXPOSURE PATHWAYS

Diets of raptors

Although it is widely thought that preying on the target rodents is the dominant pathway by which raptors are exposed to ARs, there have been a few studies on the relationship between the diets of raptors and the incidence of AR-exposure. This study is the first to discuss the exposure pathways for ARs based on both a comprehensive analysis of primary and secondary AR-exposure worldwide and the diets of raptors.

The most affected raptor species have commonly been thought to prey predominantly on mammals, especially the targeted rodent species. Figure 2 shows the diet composition of raptors whose AR-exposure are frequently reported. Because mammals constitute 60–80% of the diets of great horned owls [3], barred owls [27], kestrels [24], Eurasian eagle owls [37], and red kites [34], targeted rodents can be the source of ARs in some cases. Moreover, ARs were detected in barn owls (Tyto alba) pellets that contained rat fur [10]. However, the Eurasian eagle owls occasionally prey on larger mammals (e.g., hares, foxes, and deer) [37], and red kites sometimes feed on hares, rabbits, and as carrion, foxes, stoats, polecats and deer [34]. Therefore, a wide range of mammals can be the source of ARs as well as target rodents. On the other hand, raptors also prey on other animals, such as birds, reptiles, amphibians, fish, and invertebrates. Birds constitute even 99 and 73% of the diets in sparrowhawks [63] and golden eagles [22], respectively; and 26, 21 and 14% in bald eagles [32], red kites [34] and great horned owls [3] following, respectively. In addition, the Eurasian eagle owls occasionally prey on other raptors (e.g., buzzards, falcons, tawny owls, and long-eared owls), and the diets of Eurasian eagle owls also consist of amphibians (28%) [37]. Diets of bald eagles consist of fish (70%) [32]. Invertebrates compose 99, 72 and 25% of prey of moreporks [17], little owls [56] and kestrels [24], respectively. Therefore, preying on targeted rodents does not necessarily explain all causes of secondary AR-exposure in raptors.

Fig. 2.

Fig. 2.

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Diet composition of ten raptor species, which frequently reported AR-exposure. Predominant prey of raptors is mammal in great horned owls (80%), barred owls (72%), kestrels (65%), Eurasian eagle owls (64%), and red kites (61%), whereas it is bird in sparrowhawks (99%) and golden eagles (73%), fish in bald eagles (70%), and invertebrate in moreporks (99%) and little owls (72%) [3, 17, 22, 24, 27, 32, 34, 37, 56, 63].

AR residues in the prey of raptors

Relatively high concentrations of AR residues have been detected in the livers of mallards (chlorophacinone, 710–2,170 µg/kg, and brodifacoum, 1,230 µg/kg), rock doves (chlorophacinone, 550–55,100 µg/kg), chaffinches (brodifacoum, 120–2,310 µg/kg), Algerian hedgehogs (brodifacoum, 5–1,533 µg/kg and bromadiolone, 6–2,548 µg/kg), European hedgehogs (brodifacoum, 3–1,390 µg/kg and bromadiolone, 2–1,110 µg/kg), Iberian hares (chlorophacinone, 580–9,520 µg/kg), and a horseshoe whip snake (flocoumafen, 540 µg/kg) (Table 5). Because all of these animals are the prey of raptors, non-target animals (i.e., non-target rodents, birds, hedgehogs, hares and snakes) could also be a source of exposure to ARs.

Some studies have also reported AR residues in other reptiles (geckos) and invertebrates such as ants, cockroaches, beetles, slugs, and snails [10, 23, 38]. In addition, recent studies have shown that ARs can be detected not only in shorebirds and seabirds, but also in marine biota, including fish, crabs, sea urchins, and shellfish [30, 38]. These papers suggest exposure pathways for ARs from marine biota to shorebirds and/or seabirds, and from shorebirds and seabirds to raptors. In the case of Rat Island in Alaska, when gulls died after eating bait containing brodifacoum, their carcasses attracted bald eagles [9]. During the study period, 46 bald eagle carcasses were collected, and the brodifacoum residues were detected in the livers of all the carcasses tested (18 bald eagles).

In conclusion, primary AR exposure has occurred in non-target mammals, reptiles, invertebrates, marine biota, and birds, including land birds, shorebirds and seabirds. It is possible that AR residues in these animals constitute exposure pathways for raptors, resulting in the secondary exposure (Fig. 3). In some cases, these exposure pathways are presumed to cause secondary poisoning in raptors. More studies focusing on the dose-response relations between hepatic AR concentration and both hemorrhage and mortality of various raptor species are necessary to understand incidents of secondary AR poisoning in raptors accurately. Furthermore, toxicokinetics studies of raptors (e.g. AR metabolism, and degree of ARs inhibiting the target molecule) are also necessary to reveal the risk of raptors poisoned by ARs.

Fig. 3.

Fig. 3.

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Proposed pathways by which raptors are exposed to ARs. Primary poisoning occurs in target rodents, non-target mammals, reptiles, invertebrates, marine biota, and birds, including land birds, shorebirds and seabirds. It is possible that AR residues in these animals are transferred to raptors, causing secondary poisoning.

CONFLICTS OF INTEREST

The authors declare no conflict of interest.

Acknowledgments

This study was supported by Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology of Japan awarded to M. Ishizuka (No. 16H0177906) and Y. Ikenaka (No. 26304043, 15H0282505, 15K1221305), and S.M.M. Nakayama (No. 16K16197, 17KK0009), and the foundation of JSPS Core to Core Program (AA Science Platforms) and Bilateral Joint Research Project (PG36150002 and PG36150003), as well as Ministry of Environment, Japan awarded to S.M.M. Nakayama (4RF-1802). We also acknowledge financial support from The Soroptimist Japan Foundation, The Nakajima Foundation, The Sumitomo foundation, The Nihon Seimei Foundation and The Japan Prize Foundation. This research was supported by JST/JICA, SATREPS (Science and Technology Research Partnership for Sustainable Development). The data analyses were partially supported by Mr. Takahiro Ichise, Ms. Mio Yagihashi and Ms. Nagisa Hirano.

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