Interspecies conflict, precarious reasoning, and the gull problem in the Gulf of Maine

Abstract

Contemporary conservation science requires mediating conflicts among nonhuman species, but the grounds for favoring one species over another can be unclear. We examined the premises through which wildlife managers picked sides in an interspecies conflict: seabird conservation in the Gulf of Maine (GOM). Managers in the GOM follow a simple narrative dubbed the gull problem. This narrative assumes Larus gulls are overpopulated and unnatural in the region. In turn, these assumptions make gulls an easy target for culling and lethal control when the birds come into conflict with other seabirds, particularly Sterna terns. Surveying historical, natural historical, and ecological evidence, we found no scientific support for the claim that Larus gulls are overpopulated in the GOM. Claims of overpopulation originated from a historical context in which rising gull populations became a nuisance to humans. Further, we found only limited evidence that anthropogenic subsidies make gulls unnatural in the region, especially when compared with anthropogenic subsidies provided for other seabirds. The risks and consequences of leveraging precarious assumptions include cascading plans to cull additional gull populations, obfuscation of more fundamental environmental threats to seabirds, and the looming paradox of gull conservation—even if one is still inclined to protect terns in the GOM. Our close look at the regional history of a conservation practice thus revealed the importance of not only conservation decisions, but also conservation decision‐making.

INTRODUCTION

Conservation science traditionally involves managing impacts of humans on nonhuman species, including overharvesting, habitat destruction, introduction of novel species, and climate change (Diamond, 1989; Román‐Palacios & Wiens, 2020). Frequently, such anthropogenic effects are overlaid by conflicts among nonhuman species. Managers must then make decisions about how to respond to these conflicts. Some of these decisions follow relatively explicit guidelines. For example, a non‐native species is culled, whereas a native species is subsidized (IUCN, 2018; e.g., Wiles et al., 2003), or one species is granted legal protections, whereas its competitor is not (e.g., Yackulic et al., 2019). However, conservation science is a crisis discipline (Soulé, 1985) that demands rapid, actionable decisions even when data are deficient and time is short. Managers may thus make decisions about how to protect, or control, different species based on incomplete methods, frameworks, or arguments (cf. Sells et al., 2018; Yanco et al., 2019). Such conservation decisions can persist with a precarious foundation; whether the decisions prove right or wrong, they may never have been completely justified.

We considered a case study of precarious conservation decisions in an interspecies conflict among seabirds in the Gulf of Maine (GOM) (United States). The many islands between Cape Cod and the Bay of Fundy provide nesting habitat to a diverse group of seabirds (Allen et al., 2012) supported by what was previously one of the richest fisheries in the world (Jensen, 1967; Pershing et al., 2015). In addition to its regional importance for seabird populations, the GOM has played a leading role in the development and application of seabird conservation around the world (Jones & Kress, 2012; Spatz et al., 2023).

The seabirds currently breeding in the GOM include several species of gulls (Laridae: Larinae), terns (Laridae: Sterninae), and auks (Alcidae), as well as double‐crested cormorants (Nannopterum auritum) and a small population of Leach's storm‐petrels (Hydrobates leucorhous) (Table 1). Two of these groups, gulls and terns, have come into direct conflict. Large Larus gulls can disturb tern nesting behaviors, depredate nests, and even eat adult birds (Drury, 1973; Scopel & Diamond, 2017; USFWS, 2017). Conservation managers in the GOM have chosen a side in this conflict. For several decades, gulls have been deterred or culled, whereas terns and other species have been encouraged and protected (e.g., Anderson & Devlin, 1999; Kress, 1983; Scopel & Diamond, 2018). Managers have come to focus on the “gull problem” (sensu Tinbergen, 1953), arguing that colony pressure and predation by gulls are primary conservation threats to terns (e.g., Howard, 1968; Kress, 1997; Scopel & Diamond, 2017, 2018).

TABLE 1.

Conservation status summary for breeding seabirds in the Gulf of Maine (GOM) (USA).

			Government protection status
Taxon a	GOM strategy	IUCN status	MA	NH	ME	NB	NS	United States b	Canada c
Herring gull (Larus argentatus subsp. smithsonianus)	Culled	LC, decreasing	–	–	–	–	–	–	–
Great black‐backed gull (Larus marinus)	Culled	LC, unknown	–	–	–	–	–	–	–
Laughing gull (Leucophaeus atricilla)	Culled	LC, increasing	–	–	SC	–	–	–	–
Common tern (Sterna hirundo)	Conserved	LC, unknown	SC	T	–	–	–	–	–
Roseate tern (Sterna dougallii)	Conserved	LC, unknown	E	E	E	E	E	E (1987)	E (2003)
Arctic tern (Sterna paradisaea)	Conserved	LC, decreasing	SC	SC	T	–	–	–	–
Least tern (Sternula antillarum)	Conserved	LC, decreasing	SC	E	E	–	–	–	–
Atlantic puffin (Fratercula arctica)	Conserved	VU, decreasing	–	–	T	–	–	–	–
Razorbill (Alca torda)	Conserved	LC, increasing	–	–	T	–	–	–	–
Common murre (Uria aalge)	Conserved	LC, increasing	–	–	SC	–	–	–	–
Black guillemot (Cepphus grylle)	Conserved	LC, unknown	–	–	–	–	–	–	–
Double‐crested cormorant (Nannopterum auritum)	Culled	LC, increasing	–	–	–	–	–	–	–
Leach's storm‐petrel (Hydrobates leucorhous)	Conserved	VU, decreasing	E	–	SC	–	–	–	–

^a Excludes sea ducks, shorebirds, and nonbreeding seabirds. Taxonomy follows Clements et al. (2023).

^b Year species was listed under the United States Endangered Species Act (16 U.S.C. § 1531 et seq.).

^c Year species was scheduled under the Canadian Species at Risk Act (S.C. 2002, c. 29). All taxa shown are protected under the Migratory Bird Treaty Act (16 U.S.C. §§ 703–712) covering the United States and Canada.

We assessed the logic of the gull problem in the GOM. We considered the consequences of leveraging a poor justification for gull control, even if one still aims to protect terns. In a world of complicated ecologies, we argue for transparent, coherent conservation arguments, especially when the foundation of those arguments might involve subjective preferences or political realities.

THE GULL PROBLEM NARRATIVE

The modern era of seabird conservation in the GOM began in the 1970s. Wildlife managers were operating in the context of new federal policies (e.g., US Endangered Species Act of 1973; 16 U.S.C. § 1531 et seq.), restructured agencies with revised management philosophies (Meine et al., 2006), and emerging popular concerns about declining tern and puffin populations (e.g., Howard, 1968). As such, the US Fish and Wildlife Service (USFWS) prioritized tern population restoration in the management of its local National Wildlife Refuge properties. The groundwork was laid by the National Audubon Society's Project Puffin, a flagship effort to restore Atlantic puffins to historic nesting islands in the GOM. Project Puffin began operations on Eastern Egg Rock in 1973 and expanded to Seal Island, part of the USFWS's refuge complex, in 1984 (Hall & Kress, 2004). The region's first tern restoration program started at Eastern Egg Rock in 1978 and eventually expanded to 5 more islands (Hall & Kress, 2004; USFWS, 2017). As of 2023, all 4 tern species breeding in the GOM, along with Atlantic puffins, remain under state or federal protection (https://www.fws.gov/refuge/maine‐coastal‐islands‐complex/what‐we‐do/projects‐research; USFWS, 2017) (Table 1).

One obstacle to conserving these seabirds involves breeding disruption and predation by Larus gulls (Table 1). Larus gulls can pose a direct threat to other seabirds in 3 ways. First, these gulls are larger than many other seabirds and establish their nesting territories relatively early in the year (Drury, 1973; Nisbet, 1973). A heavy representation of gulls can thus prevent smaller, late‐nesting seabirds, such as terns, from securing refuge on GOM islands (Kress, 1983, 1997; USFWS, 1998). Second, gulls are often predators of seabird eggs, chicks, and adults (Donehower et al., 2007; Kress, 1997; Scopel & Diamond, 2017; USFWS, 2017). Third, gulls partake in other aggressive encounters such as kleptoparasitism or breeding behavior disruptions (Crowell & Crowell, 1946; Hatch, 1970; Scopel & Diamond, 2017). Drawing from these facts, managers settled on the idea that Larus gulls are the main cause of tern colony collapse in the GOM (Drury & Melvin, 1989; Kress, 1997; Scopel & Diamond, 2018). For example, Kress (1997) concludes, “while there may be other reasons that seabirds have abandoned former breeding areas (i.e. loss of nesting habitat to rank vegetation, disturbance from humans, mammal predators, food supplies, etc.)…expanded colonies of Herring and Great Black‐backed Gulls are the principal reason why terns have abandoned many of their historic colonies in New England and the Canadian Maritimes.” It is clear some managers perceive a conflict between gulls and terns in the GOM.

Having perceived this conflict in the interests of gulls and terns, managers must arrive at a separate, normative decision about how to respond (Yanco et al., 2019). The current decision involves controlling gulls in an effort to protect terns and puffins (Drury & Melvin, 1989; USFWS, 2017). Lethal and nonlethal gull control has become standard practice at seabird restoration sites in the GOM (Anderson & Devlin, 1999; Kress, 1997; Scopel & Diamond, 2017; USFWS, 2017) and around the world (Spatz et al., 2023).

Through what reasoning did this decision emerge? Our review of published reports yielded few arguments based on standardized metrics, such as relative International Union for Conservation of Nature (IUCN) status, global population sizes, or straightforward comparisons of regional population sizes. Instead, the justification for gull control apparently relies on specific assumptions: gulls are overpopulated and unnatural in the GOM. Demonstrating the assumption of overpopulation, Scopel and Diamond (2017) argue, “localized control [of gulls] must continue at seabird colonies while the large gull population stabilizes.” Howard (1968) puts it more simply: “The problem today: too many gulls” (see also Anderson & Devlin, 1999; Donehower et al., 2007; Hatch, 1970; Kress, 1983). The related assumption of unnaturalness extends from the fact that gulls eat human refuse (Drury, 1965; Howard, 1968). Driven by the awareness that landfills provide food for gulls, Larus populations around the world have been cast as “anthropogenic” (Kress, 1997), “inflated” (Scopel & Diamond, 2017), “subsidized” (Ackerman et al., 2018; Sanz‐Aguilar et al., 2009), or “enhanced” and “artificially increased” (Spatz et al., 2023). Such characterizations fit gulls into the threat category of “problematic native species…originally found within the ecosystem(s) in question, but [which] have become ‘out of balance’ or ‘released’ directly or indirectly due to human activities” (Salafsky et al., 2008). These assumptions make it seem like an easy decision to control gulls for the sake of other seabirds, such as terns. However, we now argue these assumptions are precarious: there is insufficient evidence to characterize gulls as uniquely overpopulated or unnatural in the region.

PRECARIOUS ASSUMPTIONS

Overpopulation

Demographic histories of gulls and terns in the GOM are summarized in Figure 1. Regional demographic surveys have been limited and mainly focused on terns in recent decades. However, it is clear gull and tern populations rose then declined over the last century, with gull populations reaching greater heights than tern populations. In recent years, Larus gulls continued to decline, and Arctic terns have faced recent drops in population size (Anderson et al., 2016; Scopel & Diamond, 2017). These demographic patterns cannot indicate which population sizes are correct. Different patterns of population growth and decline across multiple species also mean one cannot readily identify an environmental baseline—even a degrading one—to work toward (Pauly, 1995). Where can one turn to understand whether gulls are, or were, overpopulated in the GOM?

FIGURE 1.

Demographic histories of gull and tern species breeding in the Gulf of Maine (order of magnitude differences among y‐axes; filled points, values reported for Maine or Gulf of Maine; open points, values summed across multiple Gulf of Maine localities reported separately from the same source; vertical bars, lower and upper estimates available; time line, eras relevant to seabird conservation [see “Precarious Assumptions: Overpopulation”]; HGCP, Herring Gull and Cormorant Project; gray regression line, locally estimated scatterplot smoothing). Sources differ widely in geographic scope, survey methods, and reporting standards across years and species. Full reference information and additional reports from neighboring regions are in Appendix S1.

Archaeological records are one source of data on long‐term biodiversity patterns. Seabird colonies are often rich sources of food where available (e.g., Falk & Durinck, 1992), and indigenous GOM residents traveled substantial distances over open water (Sanger, 1988), meaning midden remains in the area could demonstrate which birds were readily available for human consumption. At one Maine island, shell middens dated from 4500 BP to 500 BP indicate seabirds constituted just 0.1% of the diet of Native American inhabitants (Spiess et al., 2006). These midden remains include ducks (Anatidae), cormorants (Phalacrocoracidae), and alcids, including razorbills, murres (Uria), and the extinct great auk (Pinguinus impennis), suggesting residents at least occasionally foraged for seabirds in the area. However, there is no clear evidence for the GOM's most well‐known contemporary residents: gulls, terns, and puffins. At most, then, midden remains imply the biodiversity of the GOM was once quite different (see also Lotze & Milewski, 2004).

Data from the historical era are similarly limited. Either there were few seabirds in the GOM, or the number is uncertain. Unpublished reports from excavations at Appledore Island, Maine, suggest gulls were present in the 17th century but reduced in number around 1700 (Weseloh et al., 2020 [citing N. D. Hamilton, personal communication]). Two key 19th‐century sources on the region's avifauna are J. J. Audubon and T. Nuttall. Audubon made multiple trips from Boston to Canada but says little about birds in the GOM. He begins his major accounts of seabirds only upon nearing the Bay of Fundy around Eastport, Maine, and Grand Manan, New Brunswick (Audubon, 1835, 1901). Nuttall (1832) writes of terns nesting in Cape Cod, south of the GOM, and relies on Audubon's account to say gulls are breeding in the Canadian Maritimes north of the GOM. At most, lack of comment by these prolific observers implies a dearth of seabirds in the GOM during the 19th century.

One possibility is that GOM islands were kept largely devoid of birds by humans, dogs, and predatory sea mink (Neogale macrodon) (Manville, 1966). The sea mink—which existed either primarily or exclusively in the GOM—completely disappeared between 1860 and 1880 (Manville, 1966). Meanwhile, extensive clearcutting and grazing reduced vegetation height on many islands (Forbush, 1925; McLane, 1982). Such changes would have made islands more suitable for ground‐nesting seabirds. Accordingly, clearer records of breeding seabirds in the GOM appear around 1880 and continue into the early 20th century (Drury & Melvin, 1989; Knight, 1908; Norton & Allen, 1931; Palmer, 1949; Vickery, 2020). It is possible that contemporary GOM seabird diversity and breeding habitats are less than 2 centuries old. The historical record offers no guidance for a proper, stable, or long‐term population size for gulls, terns, or any other seabird in the GOM.

However, the historical record does shed light on the origins of an overpopulation narrative for the region's gulls. In the early 20th century, gulls were considered valuable and worthy of protection. Waterbird populations had dwindled from the millinery trade and other human activity in the 1870s and 1880s (Dutcher, 1901; Kress, 1997; Kushlan, 2012) (Figure 1). This persecution inspired advocacy in the United States and the United Kingdom (Doughty, 1974; Ralfe, 1905). In 1900, newly reestablished Audubon societies collaborated with the American Ornithological Union to create the Thayer Fund, which paid lighthouse keepers along the east coast of North America to specifically protect gulls and terns (Drury, 1973; Dutcher, 1901). State legislatures were pressured to pass the model laws to protect nongame birds throughout the northeastern United States (Drury, 1973). In 1918, the international Migratory Bird Treaty Act (16 U.S.C. 703–712) codified a version of these local protections.

Conservation efforts seemed to work. Regional tern populations increased from 9,200 pairs in 1902 to 12,600 pairs by 1931 (McCullogh & Tudor, 2006). Likewise, herring gull populations in Maine surged from roughly 10,000 pairs in 1900 to 26,000 pairs in 1921 (Drury, 1973; Nisbet et al., 2013). In 1922, Maine ornithologist A. O. Gross celebrated this “splendid” success, describing gulls as “attractive graceful birds” with great aesthetic and ecological value (Gross, 1922). This perception shifted in the 1940s as gull populations continued to increase (Figure 1). Gross spearheaded the Herring Gull and Cormorant Project, a government‐funded initiative aimed at curbing these populations in the GOM (Gross, 1941–1954). The project destroyed nearly 1,000,000 herring gull eggs (Gross, 1941–1954).

The shift from celebrating gulls to culling them had little to do with ecology. A final report about the Herring Gull and Cormorant Project explicitly notes, “there is also no definitive evidence indicating that these populations should be controlled; or, if control is needed, to what extent it is desirable” (Dow, 1953). Instead, rising populations were initially viewed as a problem because gulls had become a nuisance to humans. Fishers and tourists complained about “filth” on the wharves and on the “fine boats and yachts of summer resorts,” and farmers were displeased by the birds damaging blueberry crops (Gross, 1922, 1941–1954). Gross wrote there was “no desire on the part of the Service, and the Maine State Fisheries Department which is cooperating in the project, to exterminate the Herring Gull. The objective is to merely reduce the numbers until they are no longer a serious menace to man's interests” (Gross, 1941–1954).

The Herring Gull and Cormorant project ended in 1954 without noticeably reducing gull populations in the GOM (Gross, 1941–1954). The perception of gulls as nuisance species persisted. The Canadian Wildlife Service issued national management plans for ring‐billed gulls (Larus delawarensis) under a “nuisance” classification, stirring much debate (Southern, 1987). Likewise, the USFWS issues most annual gull control permits to airports, landfills, and other public facilities, citing the protection of property and public safety (Seamans & Dwyer, 2021).

Larus gull populations in the GOM grew rapidly in the 20th century. The idea that such increases made Larus gulls overpopulated is not rooted in demographic or ecological metrics. The archaeological record offers no suggestion about long‐term population sizes for gulls in the region. In the early 20th century, gull populations were viewed as too small and worthy of intense conservation. A few decades later, these populations were seen as too large. This shift revolved around gulls becoming a “menace to man's interests” (Gross, 1941–1954), as opposed to science or natural history.

Unnaturalness

Toward the turn of the 21st century, Larus gull populations in the GOM began to decline (Figure 1). Estimates from Maine breeding populations suggest a 36% decline in herring gulls and a 50% decline in great black‐backed gulls from 1995 to 2013 (Langlois Lopez et al., 2023; Mittelhauser et al., 2016; Nisbet et al., 2013). In this context, some managers have deemphasized numerical arguments about overpopulation. For example, Scopel and Diamond (2017) write, “declining numbers of large gulls in the region offer no relief to the need for lethal control; gull behavior, not population size, determines their predatory impact.” Why should predatory impact, regardless of predator population status, be seen as a justification for lethal control? The answer to this question is because predatory populations of gulls are seen as fundamentally anthropogenic (Kress, 1997).

The root of this idea is that gull populations are bolstered by human refuse. At a population level, Larus gulls are adaptable, generalist omnivores that can forage effectively in both terrestrial and marine habitats (Isaksson et al., 2016; Weseloh et al., 2020). Individuals will often specialize their foraging strategies, whether through intertidal foraging, hunting smaller seabirds, or scavenging human food waste (Pierotti & Annett, 1991). Both natural and anthropogenic food sources, including landfills, fisheries sites, and urban locations, comprise important parts of contemporary gull diets in the GOM (Gutowsky et al., 2023; Shlepr et al., 2021). This contrasts with terns and puffins, which almost exclusively forage for small aquatic prey in open waters (Arnold et al., 2020; Lowther et al., 2020).

However, we were unable to find studies on how anthropogenic food availability affects gull population dynamics in the GOM. Whether anthropogenic food supports gull population growth—or even individual productivity—varies by time and location (Belant et al., 1993; Coulson, 2015; Kilpi & Öst, 1998; Pierotti & Annett, 1987). Popular references for causal links between food subsidies and gull populations in the GOM merely assert: gulls eat human refuse; gull populations were growing in the first half of the 20th century (e.g., Drury, 1965, 1973); and gull populations have declined during the more recent period of landfill closure (e.g., Mittelhauser et al., 2016). As Mittelhauser et al. (2016) point out, fishery discard practices, the marine food web, and avian and mammalian predator populations have also undergone major shifts during this period. Remarkably, there are no firm conclusions regarding the root cause of either rapid population growth or rapid decline in the region's Larus gulls (Anderson et al., 2016; Mittelhauser et al., 2016).

Beyond empirical gaps, it is striking that anthropogenic food subsidies for gulls were characterized as unnatural just as intensive conservation efforts were reshaping the region for other seabirds. For example, Howard (1968) despairs of how “growing discharge of garbage and sewage from cities created an ecological niche” for herring gulls but is eager to see creation of “optimal tern nesting habitat through manipulation of the vegetation.” Kress (1983) documents the restoration of “tern habitat” on an island where gulls, but not terns, had been nesting since at least 1920 (Drury & Melvin, 1989). Intensive predator control, extensive habitat manipulation, and the use of decoys to manipulate recruitment patterns have become standard practices for seabird conservation in the GOM and worldwide (Jones & Kress, 2012; Kress, 1997; Spatz et al., 2023). Even further, tern management strategies aim for large, stable colonies at a select few sites (Scopel & Diamond, 2017; USFWS, 1998). In contrast, older research describes colonies that frequently shifted location due to predation, weather, and other breeding disturbances (Austin, 1940; Crowell & Crowell, 1946; Drury, 1965). Like Larus gull populations, Sterna tern populations may appear subsidized, enhanced, and artificial.

Humans provide accidental, indirect food subsidies to gulls, and purposeful, direct habitat subsidies to terns. Both subsidies occur in a radically altered, and rapidly changing, environment. It is even a modern invention to think that foraging for human refuse is “bad behavior” (cf. Trotter, 2019). Where Drury (1965) grumbles that young gulls can “freeload,” others once celebrated the birds for screaming and eating trash (Dutcher, 1901; Thayer et al., 1900). It is difficult to say what is natural.

RISKS AND CONSEQUENCES

For decades, wildlife experts around the GOM have worked passionately to protect seabirds (see especially Kress, 1983; Scopel & Diamond, 2017). This inspirational work has reshaped global marine conservation efforts (Jones & Kress, 2012; Spatz et al., 2023). However, we suggest that flaws in initial assumptions complicate this conservation story. One cannot justify current gull control strategies based on the premise that gulls are overpopulated and unnatural.

Yet terns are still under threat. Despite 55 years of active restoration efforts by USFWS and its partners, some tern populations still face precipitous declines. Arctic tern populations have declined 56% from 2004 to 2017 (Scopel & Diamond, 2017), and roseate terns remain endangered after 36 years. New threats are accumulating, including offshore wind development and habitat loss due to climate change (Dias et al., 2019; USFWS, 2017). Why poke holes in the gull problem? Because committing to an unsubstantiated premise in the present has consequences for future conservation decisions. We present 3 examples.

First, managers in the GOM are now moving to suppress laughing gull populations (Allen et al., 2012; Scopel & Diamond, 2017; USFWS, 2017). Laughing gulls were abundant nesters off Massachusetts as of the 19th century and had stable footholds in Maine as of the 20th century (Gross, 1945; Nisbet, 1971) (Figure 1). There were only a few hundred breeding pairs in the GOM for most of the 20th century, but this number increased to thousands of pairs in the 21st century (Allen et al., 2012; Nisbet, 1971). When populations were smaller, laughing gulls were lumped with terns as a sensitive seabird needing protection from larger, Larus gulls (Drury, 1965; Gross, 1945; Howard, 1968; Nisbet, 1971; Palmer, 1938). Indeed, the Maine Department of Inland Fisheries and Wildlife recognizes laughing gulls as a “species of special concern.” Yet, the species gained notoriety as a nuisance to humans at landfills and airports (Seamans & Dwyer, 2021) and was recast with Larus gulls as a threat to terns (Scopel & Diamond, 2017; USFWS, 2017). Laughing gulls can kleptoparasite terns or eat small numbers of tern eggs and chicks (Donehower et al., 2007; Hatch, 1970), but direct impacts on tern populations are poorly understood (Scopel & Diamond, 2017). It is an easy decision to control laughing gulls if one believes gulls are overpopulated and unnatural in the GOM and a more difficult decision otherwise.

Second, the focus on gulls as unnatural predators obscures other dangers to seabirds in the GOM. For example, Kress (1997) and Scopel and Diamond (2018) raise several alternative threats to terns—humans, weather, and food—but largely dismiss them in favor of the gull problem. Such a frame reduces a complex history and ongoing conservation dilemma into a simple problem with, to use the terminology of Dias et al. (2019), a proven solution. It is hard to confront the habitat loss and human disturbance caused by coastal development (Coverdale et al., 2013; O'Donnell, 2017), the fisheries policy that dictates seabird food availability (Read & Brownstein, 2003), the climate change accelerating ecosystem collapse in the GOM (Pershing et al., 2015; Siedlecki et al., 2021), and the global disease outbreaks that could cause mass mortality at dense island breeding colonies (Rijks et al., 2022). Instead, it is easy to kill gulls.

Third, the assumption that gulls are fundamentally overpopulated precludes the idea they also need protection. The causes of gull population decline in the GOM remain unclear, and comprehensive monitoring is desperately needed to understand current and future population dynamics (Andreson et al., 2016). Worldwide, the once‐common European herring gull (Larus argentatus argenteus) is on the United Kingdom Birds of Conservation Concern Red List (Stanbury et al., 2021), and the great black‐backed gull meets criteria to transition from least concern to vulnerable under the global IUCN Red List of Threatened Species (Langlois Lopez et al., 2023). Ties between gulls and population dynamics in other seabirds are clear from other regions. For example, a study of yellow‐legged gulls (Larus michahellis) and 10 sympatric species in the Mediterranean showed correlated population growth rates and similar local colony extinction rates (Oro & Martínez‐Abraín, 2007). What ecological threats are shared—rather than opposed—such that gulls are also at risk?

CONCLUSION

Even if gulls are not overpopulated and unnatural in the GOM, there are other ways to conclude that one should still control gulls. If one favors rarer species, gulls today have numerically larger populations than terns in the GOM (Figure 1). If one wants to maximize economic benefit, terns and puffins provide an ecotourism benefit that gulls may not be able to match (Drury & Melvin, 1989; https://seabirdinstitute.audubon.org/Puffin%20Cruises). If one operates on aesthetic preferences, biologists and the public often love terns and puffins, whereas gulls can be more of an acquired taste (Dee, 2019; Tinbergen, 1953; L.T., personal observation). How have these factors played a role in conservation decision‐making, and how should they?

Western conservationists have long attempted to provide a “land ethic” (Leopold, 1949) or “normative postulates” for conservation science (Soulé, 1985). Both Soulé and Leopold were deeply invested in the scientific enterprise, but both realized the ethical structure of conservation would come from practitioners rather than simple scientific formulations. As Yanco et al. (2019) discuss, sound decisions thus require being clear and transparent about one's reasoning, including norms and values along with data. Successful conservation depends not only on reassessing evidence (re adaptive management; Allen et al., 2011), but also on reassessing the assumptions that shape one's view.

Supporting information

Dataset for Precarious reasoning and the Gull Problem in the Gulf of Maine

Taylor, L. U. , Hodge, W. , Shlepr, K. R. , & Anderson, J. (2024). Interspecies conflict, precarious reasoning, and the gull problem in the Gulf of Maine. Conservation Biology, 38, e14299. 10.1111/cobi.14299