Spatio-temporal responses of black-tailed gulls to natural and anthropogenic food resources

Urbanization affects animal movements. However, how urban omnivores respond to natural and human-related food sources with different spatio-temporal structures remains poorly understood. Here, we used animal-borne GPS, video data loggers and high-resolution mapping to examine the foraging behaviour of black-tailed gulls Larus crassirostris during their incubation and hatching period. As expected, the gulls fed not only on natural food at sea (e. g. anchovy and cuttlefish), but also on human-related food sources in 3 kinds of feeding grounds on land, i.e. fishery- or meat-processing plants or markets, private houses and paddy fields. Furthermore, the gulls responded to the different temporal and spatial dynamics of the feeding grounds. The gulls were distributed among these feeding grounds in response to the availability and ephemerality of each food source. Natural-food foraging trips (i.e. ocean) and anthropogenic- food trips (i.e. inland) have different spatial properties, showing a Levy search of mu = 2 with larger foraging range and patterns closer to ballistic movement with smaller foraging range, respectively. Thus, the gulls responded flexibly to the contrasting food resources of natural and human-related food sources with different temporal and spatial heterogeneities.