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

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.

Annual Mortality Limit for Four Gull Species in the Atlantic Flyway

We estimated the allowable annual take of great black-backed gulls Larus marinus, herring gulls L. argentatus, ring-billed gulls L. delawarensis, and laughing gulls Leucophaeus atricilla in the U.S. portion of the Atlantic Flyway to help meet human safety and resource management goals. Gulls can pose a serious threat to aviation, negatively impact other colonial-nesting migratory bird species, and conflict with other human activities. We estimated an annual take limit using a model that incorporated intrinsic population growth rate, minimum population size, and a recovery factor for each species. We estimated intrinsic population growth by combining allometric with life table approaches. We used the recovery factor to restrict the take level of the great black-backed gull beyond that of the other species because of poor data quality and concern about its population status. The herring gull was the only species with comprehensive demographic data. Population sizes used in estimating potential take limit varied greatly among the four species, but estimates of intrinsic population growth rate were similar (range 0.118 to 0.197). The annual potential take limits for the four gull species were 7,963 for herring gulls, 2,081 for great black-backed gulls, 15,039 for laughing gulls, and 14,826 for ring-billed gulls. Comparing average annual take from 2012–2019 to our modeled potential take limit, overharvest has not occurred for great black-backed and laughing gulls, occurred once every 8 y for ring-billed gulls, and occurred over half the time for herring gulls.

Nest sanitation behavior does not increase the likelihood of parasitic egg rejection in herring gulls

Birds’ behavioral response to brood parasitism can be influenced not only by evolution but also by context and individual experience. This could include nest sanitation, in which birds remove debris from their nests. Ultimately, nest sanitation behavior might be an evolutionary precursor to the rejection of parasitic eggs. Proximately, the context or experience of performing nest sanitation behavior might increase the detection or prime the removal of parasitic eggs, but evidence to date is limited. We tested incubation-stage nests of herring gulls Larus argentatus to ask whether nest sanitation increased parasitic egg rejection. In an initial set of 160 single-object experiments, small, red, blocky objects were usually rejected (18 of 20 nests), whereas life-sized, 3 D-printed herring gull eggs were not rejected whether red (0 of 20) or the olive-tan base color of herring gull eggs (0 of 20). Next, we simultaneously presented a red, 3 D-printed gull egg and a small, red block. These nests exhibited frequent nest sanitation (small, red block removed at 40 of 48 nests), but egg rejection remained uncommon (5 of those 40) and not significantly different from control nests (5 of 49) which received the parasitic egg but not the priming object. Thus, performance of nest sanitation did not shape individuals’ responses to parasitism. Interestingly, parents were more likely to reject the parasitic egg when they were present as we approached the nest to add the experimental objects. Depending on the underlying mechanism, this could also be a case of experience creating variation in responses to parasitism.

Inter-individual variation in the migratory behaviour of a generalist seabird, the herring gull (Larus smithsoniansus), from the Canadian Arctic

The Arctic is warming three times faster than the rest of the globe, causing rapid transformational changes in Arctic ecosystems. As these changes increase, understanding seabird movements will be important for predicting how they respond to climate change, and thus how we plan for conservation. Moreover, as most Arctic-breeding seabirds only spend the breeding season in the Arctic, climate change may also affect them through habitat changes in their non-breeding range. We used Global Location Sensors (GLS) to provide new insights on the movement of Arctic-breeding herring gulls (Larus smithsoniansus) in North America. We tracked gulls that wintered in the Gulf of Mexico (n = 7) or the Great Lakes (n = 1), and found that migratory routes and stopover sites varied between individuals, and between southbound and northbound migration. This inter-individual variation suggests that herring gulls, as a generalist species, can make use of an array of regions during migration, but may be more susceptible to climate change impacts in their overwintering locations than during migration. However, due to our limited sample size, future, multi-year studies are recommended to better understand the impacts of climate change on this Arctic-breeding seabird.

Quantifying the impacts of urban human-wildlife conflicts – how can we solve the urban gull problem in St Andrews?

Interactions between urban wildlife and people are increasing globally. Some of these interactions can be negative and lead to human-wildlife conflicts. In St Andrews, Scotland, residents and business owners have come into conflict with herring gulls (Larus argentatus) and lesser black-backed gulls (Larus fuscus) that nest and forage in the town. This study quantified the number, species and distribution of nesting gulls; the vulnerability of different sources of rubbish to attack; and the likelihood of negative human-gull interactions related to food. Surveys were conducted in St Andrews during the 2016 breeding season (May-July). Nesting gull density and distribution were estimated during weekly street surveys of buildings; vantage surveys were conducted for some buildings and a correction factor estimating a minimum number of nesting gulls was produced. 110 nesting gull pairs were estimated and these occupied ~10% of buildings. The vulnerability of waste sources to attack was monitored during transects recording whether or not rubbish sources were attacked. Black bin bags had the highest probability of being attacked, but placing these in secured hessian bags prevented this. The frequency of negative human-gull interactions involving food at street-level was determined during 10-minute timed watches at various locations. Incidences of gulls taking food were rare; only eight were seen in 30 hours of watches. Altering human behaviour (for example, disposing of waste securely) will mitigate potential issues with urban wildlife. Findings from this study will enable effective management of human-gull conflicts in St Andrews and have potential applications in other urban communities.