Area utilization of gulls in a coastal farmland landscape: habitat mosaic supports niche segregation of opportunistic species

Abstract

The intensively farmed coastal lowland landscape of Germany, adjacent to the North Sea, provides important foraging opportunities for Blackheaded, Common, Herring and Lesser Black-backed gull (Larus ridibundus, L. canus, L. argentatus and L. fuscus). We expected that spatial and temporal utilization of the landscape mosaic as well as behavioural traits and utilization of food resources would differ between these closely related species, facilitating niche segregation. We recorded habitat types and their utilization by the four species over a whole year. Furthermore, we related species abundance to several abiotic parameters. Black-headed and Common gulls were the most numerous species in the study area throughout the year. In general, the former species preferred bare fields with recently prepared soils and was often associated with tractors in the fields, whereas the latter species was most often found on pastures. Black-headed gulls seem to have a higher ability to exploit ephemeral, food sources associated with human activities whereas common gulls prefer habitats with low human activity and with naturally distributed prey. The most prominent abiotic parameter influencing gull abundance was presence of tractors. Black-headed gulls have most likely benefited from recent changes in agricultural practice, particularly the increase in cropped land, while Common gulls may have suffered from a decline in pastures. At present, utilization of the farmland habitat mosaic leads to niche segregation and supports coexistence, as two of the four gull species mainly forage in the marine environment, while there is significant habitat partitioning between the other two temporally, spatially and behaviourally.

Plant establishment and invasions: an increase in a seed disperser combined with land abandonment causes an invasion of the non-native walnut in Europe

“…Short or absent vegetation also guarantee good visibility and early detection of predators or competitors [42]. Rooks are not an exception; many birds, including shrikes (Lanidae), birds of prey and gulls (Laridae) prefer to forage among short vegetation on ploughed fields and grasslands [43,44]. The habitat where rooks cached walnut seeds in our study area corresponds to results of earlier studies indicating that corvids preferred ploughed fields in agricultural landscapes [20,22].…”

Corridors, local food resources, and climatic conditions affect the utilization of the urban environment by the Black‐headed Gull Larus ridibundus in winter

“…An effective way to prevent the dispersion of BHGs in the urban environment would be the creation of habitat patches in the vicinity of ecological corridors at the city's borders, which would be a natural source of food for the studied species. These could include various kinds of green areas such as lawns (Schwemmer et al 2008). …”

Indexing winter gull numbers in Great Britain using data from the 1953 to 2004 Winter Gull Roost Surveys

“…Reductions in the food available at landfills due to improved management (and the trend towards other means of waste disposal, such as incineration) may have contributed to the recent declines seen in Black-headed Gull numbers in six regions. Intensification of agriculture, with which Black-headed Gulls are particularly associated (Vernon 1970, 1972, Schwemmer et al 2008, has led to a largescale reduction in farmland bird abundance in recent decades (Chamberlain et al 2000) and may have also been a factor in these declines.…”