Site- and species-related variation in population development of three gull species: The importance of resource availability.
Supervisor: Morten Frediksen (Aarhus University)
Most coastal ecosystems where seabirds forage have been drastically altered by anthropogenic activities throughout the last century. In particular, several large gull species are threatened now in many countries across Europe, showing declining population trends and raising many conservation concerns. Hence, understanding the factors that drive patterns of distribution and abundance of large gulls is fundamental for environmental management and conservation. However, spatial variation in population dynamics is generally poorly understood. Here, the spatio-temporal developments of Great Black-backed Gull (Larusmarinus), Lesser Black-backed Gull (L. fuscus) and Herring Gull (L. argentatus) populations in Denmark are described for the last half century. First, deeper insight has been gained by investigating the population trends on colony, regional and national scale. Between 1970 and 2018, the three species showed different developments, but all of them increased on the national scale. Nevertheless, on a regional and colony scale, the population trends of Lesser Black-backed and Herring Gulls differed considerably between eastern and western Denmark, showing spatially clustered variation in changes of colony size. In addition, colony growth rates were compared among 279 colonies of Great Black-backed Gull, 145 colonies of Lesser Black-backed Gull and 431 colonies of Herring Gulls across the country, in order to relate them to the local resource availability around each colony during the breeding season. The spatial regression models fitted here indicate that the variation in colony growth rate of Great Black-backed Gulls is best explained by the distribution of built-up areas, fishery activities and mink farms in the coastal environment; the variation for Lesser Black-backed Gulls is related to the extent of built-up areas within the foraging range of the colonies; and the variation for Herring Gulls has been partly driven by the distribution of mink farms and variation in the extension of subtidal zone around the colonies. Therefore, the large dataset investigated here provides strong support for the hypothesis that food availability, and particularly that derived from anthropogenic activities, is an important regulator of large gull populations. Furthermore, these results emphasize the need for area-specific management of large gull species breeding in Denmark.
Privacy & Cookies Policy
Necessary cookies are absolutely essential for the website to function properly. This category only includes cookies that ensures basic functionalities and security features of the website. These cookies do not store any personal information.
Any cookies that may not be particularly necessary for the website to function and is used specifically to collect user personal data via analytics, ads, other embedded contents are termed as non-necessary cookies. It is mandatory to procure user consent prior to running these cookies on your website.