Changing numbers of three gull species in the British Isles

Between-population variation of changes in numbers can provide insights into factors influencing variation in demography and how population size or density is regulated. Here, we describe spatio-temporal patterns of population change of Herring Gull (Larus argentatus), Lesser Black-backed Gull (L. fuscus) and Great Black-backed Gull (L. marinus) in the British Isles from national censuses and survey data. The aim of this study was to test for density-dependence and spatial variation in population trends as two possible, but not mutually exclusive, explanations of population changes with important implications for the understanding of these changes. Between 1969 and 2013 the three species showed different population trends with Herring Gulls showing a strong decline, Great Black-backed Gulls a less pronounced decline and Lesser Black-backed Gulls an increase until 2000 but then a decline since. Population changes also varied between different regions of the British Isles, with the Atlantic coast showing declines and the North Sea coast increases in all three species. Population changes were density-dependent in the Herring Gull, and Lesser Black-backed Gulls showed faster population increases at lower Herring Gull densities. Contrasting numbers of gulls nest in coastal habitats or on roofs (mainly in urban habitats). Herring Gulls seem to seek refuge in urban environments, whereas Lesser Black-backed Gulls expand their range into the urban environment. The large declines in hitherto abundant species create a dilemma for conservation bodies in prioritizing conservation policies. The spatial variation in population changes and the differences between species suggest that there is no single cause for the observed changes, thus requiring region-specific conservation management strategies

Intercolony Comparison of Diets of Western Gulls in Central California

As human populations expand, they force free-ranging animals to adapt to an increasingly urban environment, resulting in changes in diets, reproductive success, and mortality. The diets of two western gull (Larus occidentalis) breeding populations in central California were compared. One colony, Año Nuevo Island (ANI), is 1 km from shore and within 30 km of a municipal landfill. The other colony, Southeast Farallon Island (SEFI), is located 45 km off the shore of San Francisco, CA. Given the proximity of ANI to the shore and the landfill, I predicted that gulls from ANI would have more garbage in their diets. Indeed, gulls from ANI consumed over three times more garbage. Twenty-three percent of wet diets from gulls at ANI contained garbage, whereas garbage made up only 6% of wet diets from gulls at SEFI. Despite the appearance of garbage in gull diets, birds from both colonies consumed a range of marine prey, and Clupeiformes, Euphausiacea, and Gadiformes were important to both colonies. Isotopic values (15N and 13C) measured in gull feathers were similar between colonies, suggesting that gulls from both populations consume similar prey from the marine environment during the non-breeding phase. The reliance on stable, easily accessible food from landfills during the breeding season may be an important adaptation for western gulls to cope with urbanization and declines in prey species in the California Current during the energy-intensive chick-rearing perio

Validation of water flux and body composition in Glaucous gulls (Larus hyperboreus)

Water influx rates (WIR) measured with tritiated water dilution were compared with direct measures of water and energy intake in glaucous gulls (Larus hyperboreus). Total body water (TBW) measured isotopically was also compared with TBW determined by body composition analysis (BCA) of the same birds. Seventeen wild gulls were captured and studied in outdoor enclosures at Ny-Ålesund, Svalbard, in July 2002. Gulls were hand-fed known quantities of Arctic cod (Boreogadus saida) or given water on the basis of one of four experimental treatments: (A) fasting, (B) fish only, (C) water only, or (D) fish and water. Water and energy content of Arctic cod was also determined. WIR of gulls (after subtracting metabolic water production) in treatments A, B, C, and D were 0, 101 ± 5, 62 ± 19, and 122 ± 21 SD g d-1, respectively. Measured water intake in each group was 0, 111 ± 2, 64 ± 3, and 134 ± 15 SD g d-1, respectively. On average, WIR underestimated measured water intake in each group. Errors were lowest but most variable for gulls fed water only (-2.2% ± 32.8%) compared with gulls fed fish only (-9.0% ± 5.4%) or fish and water (-9.0% ± 7.0%). Compared with measured water intake, errors in WIR were relatively low overall (-6.9% ± 17.4%) and comparable to previous validation studies. The difference in TBW determined by BCA versus isotopic dilution ranged between -1.02% and +8.59% of mass. On average, TBW measured isotopically (632 ± 24 g kg-1) overestimated true body water by a factor of 1.033

Seabird and Plastic Ingestion Data Set

Plastic debris is a pervasive and critical environmental challenge that is being described as a world-wide crisis for marine life. Seabirds are sensitive to pollutants and are of critical conservation concern. Because seabirds are excellent bioindicators of marine ecosystem health, information about their plastic ingestion can serve as an indicator of plastic exposure across multiple marine trophic levels. Our study describes the prevalence of plastic ingestion for four seabird species: Great Black-backed Gulls (Larus marinus), Herring Gulls (L. argentatus), Common Terns (Sterna hirundo), and Roseate Terns (S. dougallii) nesting in the Gulf of Maine. Samples were collected opportunistically, including pellets, regurgitant, discarded fish, and deceased seabirds. Plastics were primarily found in pellet samples, and common types included fragments and sheets. Herring Gulls displayed significantly higher plastic exposure than the other three species across all metrics analyzed (p-valu

Increased use of intertidal resources benefits breeding success in a generalist gull species

Determining how resource use impacts on a species’ demography is important, especially in habitats which are being altered by anthropogenic land-use change. If changes result in species consuming resources of reduced quality their demographic traits may be adversely affected. Generalist species are useful when investigating changes in resource availability as they can switch to alternatives if their preferred food becomes unavailable. For species that can forage on marine and terrestrial resources, it is often not known whether a switch from marine to terrestrial resources will have negative consequences. The herring gull, Larus argentatus, is one widespread generalist that opportunistically forages within marine and terrestrial habitats that are increasingly altered by humans. We determined marine and terrestrial resource use of gulls from eight colonies over two years across south-west Scotland and Northern Ireland using pellets and stable isotope analysis of chick feathers, which gave comparable results. Herring gulls in the study region used very little marine offshore resources but birds from colonies located in areas with sheltered coastlines, which provide abundant and diverse marine food from the intertidal zone, foraged more on marine intertidal resources. In contrast, colonies closer to built-up areas used more terrestrial resources. Herring gulls raised larger broods in colonies where they consumed a higher proportion of marine resource. Therefore, where generalist species, such as gulls, switch to an alternative resources that is available to them within their foraging range this may come at a cost of lower breeding success

Patrones temporales en la abundancia y uso de residuos por Gaviotas cocineras (Larus dominicanus) en un basural urbano y pesquero de la costa norte de Patagonia, Argentina

We quantified the use by Kelp Gulls (Larus dominicanus) of urban and fishery waste sites at Puerto Madryn, Argentina, during 1996 and 1997. Kelp Gulls were present at all monthly counts made at both waste sites throughout the two years of the study. Total numbers of gulls in each month were high and variable, with a mean of 4724 and 4612 individuals in 1996 and 1997, respectively. The mean number of gulls at the fishery waste site was significantly larger than at the urban waste site (3767 vs 901). Adult Kelp Gulls were significantly more abundant than non-adult gulls at every count at both the urban and fishery waste sites (mean = 811 vs 91 and 3147 vs 628, respectively). Among the younger age classes, individuals in their third year were the least abundant. The proportion of adults with respect to total gulls present was high during all visits to both sites, although it showed a slight decrease in the fishery waste site during the breeding season. During the breeding season, the number of gulls varied significantly throughout the day at both sites while, during the non-breeding season, numbers varied significantly only in the urban waste site. The Puerto Madryn fishery waste site constitutes a more attractive food source than the urban waste site probably due to the higher quality and quantity of discarded food. The use of waste sites at Puerto Madryn may be enhancing gull breeding success and individual survival during the winter, particularly of young birds. Potential conflicts due to Kelp Gull use of waste sites and the effects on their populations could be minimized by adequate urban and fish waste managementCuantificamos el uso por la Gaviota cocinera (Larus dominicanus) de los basurales urbanos y pesqueros en Puerto Madryn, Argentina, durante 1996 y 1997. La Gaviota cocinera estuvo presente en todos los censos mensuales efectuados en ambos basurales durante los dos años. Los números totales de gaviotas en cada mes fueron altos y variables, con una media de 4724 y 4612 individuos en 1996 y 1997, respectivamente. El número medio de gaviotas en el basural pesquero fue significativamente mayor que en el basural urbano (3767 vs 901). En todos los conteos en los basurales pesquero y urbano, las gaviotas adultas fueron significativamente más abundantes que las no adultas (media = 811 vs 91 y 3147 vs 628, respectivamente). Entre las clases de edad más jóvenes, los individuos del tercer año fueron los menos abundantes. La proporción de adultos respecto al total de gaviotas presentes fue alta en todas las visitas a ambos basurales, aunque mostró una leve disminución en el basural pesquero durante la temporada reproductiva. Durante la temporada reproductiva, el número de gaviotas varió significativamente a lo largo del día en ambos basurales, mientras que en la temporada no reproductiva los números variaron significativamente solo en el basural urbano. El basural pesquero de Puerto Madryn constituye una fuente de alimento más atractiva que el basural urbano, probablemente debido a la mayor cantidad y calidad de los residuos depositados. El uso de los basurales en Puerto Madryn podría estar favoreciendo el éxito reproductivo de las gaviotas y la supervivencia individual durante el invierno, particularmente de aves jóvenes. Los conflictos potenciales resultantes del uso por la Gaviota cocinera de los basurales y los efectos sobre sus poblaciones podrían ser minimizados con un adecuado manejo de los residuos urbanos y pesquerosFil: Giaccardi, Micel. Secretaría de Turismo y Áreas Protegidas; ArgentinaFil: Yorio, Pablo Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; Argentina. Wildlife Conservation Society; Estados Unido

Breeding Lesser Black-backed Gulls Larus graellsii and Herring Gulls Larus argentatus: coexistence or competition?

While Lesser Black-backed Gull Larus graellsii numbers increase substantially at the German North Sea coast since the late 1980s, Herring Gull Larus argentatus numbers have been roughly stable since the mid-1980s. In order to investigate whether a different ecology might explain the current trends, we studied diet, colony attendance, reproductive output and aggressive behaviour in a mixed-colony on Amrum, southeastern North Sea, in 1994 and 1995. During incubation Lesser Black-backed Gulls fed mainly upon crustaceans and molluscs which were taken from the intertidal zone. During chick-rearing, they took mainly crustaceans and fish which were gathered mostly as trawler discards. The main food of Herring Gulls throughout the reproductive season were molluscs and crustaceans which were obtained from the intertidal zone. Numbers of Lesser Black-backed Gulls in the colony mainly varied with season and time of day, those of Herring Gulls with tide and season. Numbers of Herring Gulls commuting to the open sea roughly equalled those commuting to the Wadden Sea. Lesser Black-backed Gulls generally flew to the open sea but hardly towards the Wadden Sea. Nest attendance was significantly higher in Lesser Black-backed Gulls than in Herring Gulls during the chick-rearing period. Hatching success and fledging success tended to be higher in Lesser Black-backed Gulls. Lesser Black-backed Gulls won interspecific aggressive interactions significantly more often than Herring Gulls in the chick-rearing period. Our study indicates that Lesser Black-backed Gulls currently enjoy a few ecological advantages compared with Herring Gulls, particularly because they feed on food of apparently higher quality. We conclude that Lesser Black-backed Gulls have filled an empty niche rather than have out-competed Herring Gulls during the past decade

MIGRATION AND DISPERSAL OF LAUGHING GULLS IN THE UNITED STATES

The 3662 recovery records for Laughing Gulls (Larus atriczlla) banded in North America from 1924 to 1991 were analyzed to determine migration and dispersal patterns for Northeast (Maine to Virginia) and Gulf Coast (west coast of Florida to Texas) populations. Autumn migration for Northeast Laughing Gulls was initiated in October. Northeast Laughing Gulls migrated greater distances and were recovered farther south during winter than Gulf Coast gulls. Significantly more Gulf Coast Laughing Gulls wintered along the Gulf Coast than did Northeast Laughing Gulls. In contrast, significantly more Northeast Laughing Gulls wintered in Central and South America. Adult Laughing Gulls returned to breeding areas between March and May. Sixty-four percent of adult recoveries during subsequent breeding seasons were within 50 km of their natal banding locations. Significantly more Laughing Gulls were recovered north of their natal banding location than south during subsequent breeding seasons. Autumn dispersal of hatching-year Laughing Gulls was characterized by northward movements before migration. There was little interchange between Northeast and Gulf Coast populations

The urban Herring gull, foraging niche and interactions with humans

Gulls (Laridae) are of significant interest because of their use and breeding in urban environments, which has increased human-wildlife conflicts. However, there is a lack of information that summarises population trends in gulls, that is driving them towards conflicts with humans; the attitude towards gulls that the public has, especially in urban environments and the factors that determine those attitudes; and how gulls utilise the urban environment for reproductive success. In this thesis, I explore the literature around gull trends throughout the Western Hemisphere. Using a questionnaire, I attempt to collate information about the public’s attitude towards gulls, paired with spatial correlation to demonstrate geographic differences. I also use gull pellets and foraging effort to explore the niche of gulls, and test for differences between urban and rural birds. The findings show gull population changes are constant, and that public attitude is negative towards gulls, with age and knowledge about gulls effecting negative perceptions. I also demonstrate that rural and urban gulls have differing habitat use periodically through the breeding season but have commonality in foraging effort

Investigating the Nightime Departures of Glaucous-Winged Gulls (Larus Glaucescens) and the Role of Social Facilitation

Daytime behaviors and occupancy patterns of Glaucous-winged Gulls (Larus glaucescens) have been described and can be mathematically predicted based on environmental factors. However, little is known about the nighttime behaviors of Glaucous-winged Gulls. I used trail cameras to study the daytime and nighttime colony occupancy patterns of Glaucous-winged Gulls on a breeding colony on Protection Island, Washington, USA. Early in the breeding season gulls desert the colony en masse during nighttime even after some gulls have initiated clutches. Using acoustic recording units to identify an acoustic cue that signals the onset of the coordinated nightly departures from the colony, I found that five to ten minutes prior to the nighttime departures the gulls engage in a bout of synchronous extended long-calling. The departing gulls form two large rafts at night to the north and south of the island, both of which get closer to the colony as the season progresses. As more gulls initiate clutches, a switch occurs such that all gulls remain overnight on the colony even though a majority of them have yet to initiate clutches. The first gulls to initiate clutches influence the transition from leaving to remaining on the colony at night through social facilitation