Nestling diet and breeding success of Little Bitterns Ixobrychus minutus at two artificial fishpond complexes in south-western Slovakia

摘要

Artificial fishponds are assumed to be suitable alternative habitat for many waterbirds including fish-eating predators such as herons. However, fish farming may lead to contrasting consequences for birds breeding in these biotopes and act as an ecological trap. I examined nestling diet and reproductive success of the least studied heron species in Europe, the endangered Little Bittern Ixobrychus minutus, at two fishpond complexes in south-western Slovakia. A total of 95 breeding attempts by this species were recorded during 2015-2019 in the study area, 84% of which produced at least one nestling. Despite relatively high nest success at both sites, the number of fledged nestlings differed significantly between the two fishpond complexes. The observed differences were mainly caused by higher nest predation at one of the fishponds. The diet of nestlings also differed between study sites. While the food taken at fishponds that are used for intensive farming of Common Carp Cyprinus carpio contained significant proportions of insects (41%) and amphibians (14%), at fishponds used mainly for individual sport fishing, parents fed their nestlings exclusively fish. However, the total amount of food delivered to nestlings was similar at both fishpond complexes. This suggests that Little Bittems are able to adapt to fishponds with various intensities of management. Nevertheless, considering differences in nest predation risk between studied fishponds, other factors such as abundance and structure of littoral vegetation and predator abundance, can influence the breeding success of this species in artificial fishpond habitats. Identifying such factors may be important for the conservation and management of this species.