Opportunistic feeding of Kelp gulls associated to urban centres: a case study in inland environment of Argentine Patagonia

ROSCIANO, N.; OJEDA, V.; YORIO, P.

Conferencia; BOUasm21 - Birds and People conference; 2021

Gulls are an opportunistic species that take advantage of anthropogenic food subsidies worldwide, often resulting in conflicts with human populations. In Argentina, Kelp gulls (Larus dominicanus) breed along the Atlantic marine coasts and in a few freshwater habitats. Dietary analyses to asses feeding habits and trophic relationships of this gull breeding in inland ecosystems are crucial to understand potential gull-human conflicts. We used complementary dietary approaches (pellet, stomach content and stable isotope analyses) to assess Kelp gull diet requirements during the incubation and chick stages of 2019 at two colonies in the Nahuel Huapi Lake (261 and 314 nests), in Andean Patagonia. These two colonies are located close (<10 km) to the city of Bariloche (>120,000 inhabitants). Preliminary results showed that a high percentage of incubating adult pellets presented mouse bones and hair (89%), followed by plastic (22%) and paper (14%). Adult stomach content samples from the same period presented chicken skin and bones (50%) and remains of terrestrial arthropods (33%). Chick (~3 weeks old) stomach content samples presented a variety of prey items, including terrestrial arthropods (33%), mouse (25%), chicken parts (17%) and fish flesh (17%). Results show that Kelp gulls fed mainly in terrestrial environments, including garbage dumps. Kelp gull consumption of mouse coincided with an episodic blooming event of woody bamboo (Chusquea sp.) that resulted in a rodent outbreak, which shows its opportunistic feeding habits. This outbreak was characterized by thousands of dead mice accumulated at lake shores during late 2019. As expected, results also showed that breeding Kelp gulls depend on garbage dumps for self-feeding and chick provisioning. The use of anthropogenic food subsidies may influence Kelp gull population trends and have negative effects on public health, since Kelp gulls were previously identified as pathogen and parasite hosts in the same inland area.