Mercury concentrations provide an indicator of marine foraging in coastal birds

Thorne, Lesley H.; Fuirst, Matthew; Veit, Richard R.; Baumann, Zofia

doi:10.1016/j.ecolind.2020.106922

Cited by 17 publications

(8 citation statements)

References 67 publications

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“…Gulls often make short movements around the colony assumably to rest and drink, thus only foraging trips that were at least 20 min in duration and 0.5 km away from the colony were considered in our analysis. Additionally, we only analyzed birds that took at least 6 foraging trips during tag deployment to ensure that tracks accurately represented individual gull foraging behavior and habitat use 58 . Area restricted search (ARS) behavior was identified using the first passage time (FPT) analysis, which is based on the time it takes an animal to travel through a spatial circle with a given radius 59 .…”

Section: Methodsmentioning

confidence: 99%

Closely related gull species show contrasting foraging strategies in an urban environment

Lato

Madigan

Veit

et al. 2021

Sci Rep

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The expansion of urban landscapes has both negative and positive effects on wildlife. Understanding how different species respond to urbanization is key to assessing how urban landscapes influence regional wildlife behavior and ecosystem structure. Gulls are often described as strong urban adapters, but few studies have explored species-specific differences in habitat use. Here, we use GPS tracking in conjunction with stable isotope analysis (SIA) to quantify the habitat use and trophic ecology of great black-backed gulls (Larus marinus) and herring gulls (L. argentatus) in an urbanized area. Non-Metric Multidimensional Scaling (NMDS) of foraging locations revealed significant differences in the habitat use between species. Great black-backed gulls foraged primarily in marine habitats and herring gulls foraged primarily in specific urban habitats (e.g., landfills, dumpsters) and showed higher site fidelity in terms of the proportion of foraging sites revisited. Further, great black-backed gulls had significantly higher δ15N and δ13C than herring gulls, reflecting the use of marine, rather than urban, food sources. This study highlights the variability in urban habitat utilization among closely related species, assesses stable isotope signatures of urban diets in wild birds, and discusses ecological implications of the relative contribution of urban and marine foraging.

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Section: Methodsmentioning

confidence: 99%

Closely related gull species show contrasting foraging strategies in an urban environment

Lato

Madigan

Veit

et al. 2021

Sci Rep

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“…62 In these studies, variation in δ 13 C values reflected differences in foraging habitat, with species that foraged in warmer subtropical waters having higher THg concentrations than those foraging in colder waters. 57,61,62 In telemetry studies of other gull species, blood THg concentrations were higher in western gulls (L. occidentalis) from the Northeast Pacific and herring gulls (L. argentatus) in the Northeastern U.S. that foraged in ocean habitats relative to gulls feeding inland in terrestrial, freshwater habitats from urban colonies, 30,55 suggesting that Hg is a strong indicator of marine foraging. 30 Considering there has been a long-term decline in δ 13 C, δ 15 N, and δ 34 S values in gulls but not in cormorants, our results suggest that the gradual shift from marine to greater terrestrial foraging may explain stable THg concentrations in glaucouswinged gulls over time.…”

Section: Mercury-based Preservatives and Thg Trendsmentioning

confidence: 99%

“…57,61,62 In telemetry studies of other gull species, blood THg concentrations were higher in western gulls (L. occidentalis) from the Northeast Pacific and herring gulls (L. argentatus) in the Northeastern U.S. that foraged in ocean habitats relative to gulls feeding inland in terrestrial, freshwater habitats from urban colonies, 30,55 suggesting that Hg is a strong indicator of marine foraging. 30 Considering there has been a long-term decline in δ 13 C, δ 15 N, and δ 34 S values in gulls but not in cormorants, our results suggest that the gradual shift from marine to greater terrestrial foraging may explain stable THg concentrations in glaucouswinged gulls over time. As a result of this shift in diet, THg concentrations in glaucous-winged gulls may not accurately reflect regional trends of Hg exposure in the North Pacific.…”

Section: Mercury-based Preservatives and Thg Trendsmentioning

confidence: 99%

“…25−29 We predicted that, because gulls have shifted to lower trophic and/or terrestrial/freshwater prey over time, THg trends in gull feathers would have increased at a slower rate than trends in North Pacific Ocean food webs. Mercury is also a strong indicator of marine foraging in seabirds; 30 ■ MATERIALS AND METHODS Sample Collection. We sampled head (n = 171), flank (n = 65), and primary (n = 22) feathers for total mercury (THg) and methylmercury (MeHg) from glaucous-winged gull museum skins collected from 1887 to 1996 at 28 nesting colonies (48.42−49.68°N, 122.82−124.93°W) in the Salish Sea ecosystem in British Columbia, Canada, and Washington.…”

Section: ■ Introductionmentioning

confidence: 99%

“…We examined Hg in head, flank, and primary feathers from museum collections, as feathers reflect the Hg body burden during growth. − We predicted that, because gulls have shifted to lower trophic and/or terrestrial/freshwater prey over time, THg trends in gull feathers would have increased at a slower rate than trends in North Pacific Ocean food webs. Mercury is also a strong indicator of marine foraging in seabirds; therefore, stable Hg trends in gulls may provide further evidence of a shift to freshwater and/or terrestrial prey. Our objectives were to: (1) analyze long-term trends in THg and MeHg concentrations in gull feathers from 1887 to 1996; (2) model potential drivers of MeHg and THg exposure to gulls, such as year, biological factors (sex, age), and colony; and (3) compare THg trends in gulls to those in other seabirds [double-crested cormorants (Nannopterum auritum) and pelagic cormorants (Urile pelagicus)] in the Salish Sea ecosystem.…”

Section: Introductionmentioning

confidence: 99%

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Stable Mercury Trends Support a Long-Term Diet Shift Away from Marine Foraging in Salish Sea Glaucous-Winged Gulls over the Last Century

Choy

Blight

Elliott

et al. 2022

Environ. Sci. Technol.

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Marine predators are monitored as indicators of pollution, but such trends can be complicated by variation in diet. Glaucous-winged gulls (Larus glaucescens) have experienced a dietary shift over the past century, from mainly marine to including more terrestrial/freshwater inputs, with unknown impacts on mercury (Hg) trends. We examined 109-year trends in total mercury (THg) and methylmercury (MeHg) concentrations in glaucous-winged gull feathers (1887− 1996) from the Salish Sea. Adult flank feathers had higher MeHg concentrations than immature feathers, and males head feathers had higher THg concentrations than females. Overall, we found no evidence of a trend in feather MeHg or THg concentrations over time from 1887 to 1996. In the same individuals, δ 15 N, δ 13 C, and δ 34 S declined over time in gull feathers. In comparison, egg THg concentrations declined from 1970 to 2019 in two species of cormorants, likely reflecting decreases in local Hg sources. We conclude that diet shifts through time may have countered increased Hg deposition from long-range transport in glaucous-winged gulls. The lack of Hg trends over time in glaucous-winged gull feathers provides additional support that these gulls have decreased the amount of marine forage fish in their diet.

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Peri‐urban systems alter trophic niche size and overlap in sympatric coastal bird species

et al. 2023

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Urban habitats can create empty trophic niche space by providing abundant alternative dietary resources, allowing some generalist species to either shift or expand their trophic niches. Resulting changes to trophic niche size may consequently affect interspecific interactions and competition, although trophic impacts are less clear in peri‐urban systems, where both natural and urban resources are readily accessible to highly mobile species. We combined stable isotope (δ13C, δ15N, δ34S) data with GPS tracking of two sympatric coastal bird species (Larus argentatus, L. marinus) across four study sites on the east coast of the United States, ranging from a study site in New York City (the most populous city in the United States) to less‐urban sites off Massachusetts. We quantified the trophic niche size and trophic niche overlap in three‐dimensional isotopic space and assessed spatial overlap in foraging habitat between species at both peri‐urban and less‐urban study sites. We found that for both species, birds at peri‐urban study sites had significantly larger trophic niches than birds from the less‐urban sites. Furthermore, for study sites where both species occurred, we found that overlap in trophic niche space and foraging habitats between species was lower at the peri‐urban study site than at the less‐urban site. These results suggest that peri‐urban environments may facilitate trophic niche expansion and decrease niche overlap in mobile generalist species, contrasting with previous studies showing increased trophic niche overlap in more isolated urban populations. Following further analysis, we found that trophic niche expansion was facilitated by both within‐ and between‐individual differences in foraging strategies. We posit that peri‐urban environments, particularly along coastal areas, can reduce interspecific competition between sympatric species by providing access to a variety of natural and anthropogenic diet items, especially for highly mobile generalist consumers that can access both natural and urban foraging areas. Research assessing how and at what scale peri‐urban systems influence wildlife is key to understanding how further global urbanization will shape ecosystem structures.

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Mercury concentrations provide an indicator of marine foraging in coastal birds

Cited by 17 publications

References 67 publications

Closely related gull species show contrasting foraging strategies in an urban environment

Closely related gull species show contrasting foraging strategies in an urban environment

Stable Mercury Trends Support a Long-Term Diet Shift Away from Marine Foraging in Salish Sea Glaucous-Winged Gulls over the Last Century

Peri‐urban systems alter trophic niche size and overlap in sympatric coastal bird species

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