Comparative nest attendance and chick provisioning strategies in coastal and desert nesting Grey Gulls (Leucophaeus modestus) in northern Chile

Grey Gulls (Leucophaeus modestus) are unique among gulls in that they forage in the coast but breed up to 115 km inland in the barren Atacama Desert of northern Chile. By nesting in the desert, adults are limited to a single daily foraging trip to feed their chicks and relieve their incubating/brooding mates. Birds perform long-distance and energetically expensive trips between foraging and breeding grounds. We describe how Grey Gulls modify nest attendance and chick provisioning strategies from an unusual coastal colony established at Playa Brava, northern Chile, during the 2017–2018 season. Contrary to what it is usually observed in desert colonies, incubating, and brooding Grey Gulls at Playa Brava relieved mates at the nest regularly and fed chicks several times throughout the day. Some adults even left their chicks unattended at the nest to forage on the nearby shoreline (<0.15 km) for a variable amount of time (up to 57 min) before returning to resume brooding. These behaviours are likely to ease parental duties by allowing multiple pair changeovers, reduce energy expenditure by avoiding extensive trips between the desert and the coast, increase chick growth rates by allowing multiple meals during the day, among other advantages. Our observations show that, when moving their colonies from the desert to the coast, Grey Gulls accordingly adjust their breeding behaviour to cope with this new habitat.