Is Winter Feeder Visitation by Songbirds Risk-Dependent? An Experimental Study

Winter bird feeders provide high-energy food for birds when natural food resources are in short supply. We performed an experimental study including two treatments and a control to investigate the reactions of eight passerine species visiting a winter feeder to the presence of a predator or a food competitor, measured by the number of visits and foraging time. We included in analyses the age and sex of the most numerous species, the Great Tit (Parus major). Our results showed that the number of feeder visits per 30 min differed significantly among species, treatments (predator, competitor, or control), and time intervals of time elapsed from the start of the treatment. The presence of food competitors and predation risk significantly deterred the birds from feeding at the feeder. The number of visits to the feeder by Great Tits was significantly affected by age (more frequent visits by immatures), sex (more frequent visits by males), treatment (less frequent visits by immatures during predation risk and by adults during both experiments), and the time elapsed since the start of the experiment (more frequent visits by adult females during the first eight time intervals after the start of the experiment). Surprisingly, the duration of the foraging visits to the feeder was significantly influenced by species (lower for all tit species compared to the other visiting species) and the time elapsed since the start of the treatment (shorter foraging duration during the first nine time intervals for Hawfinch (Coccothraustes coccothraustes), European Greenfinch (Chloris chloris) and European Robin (Erithacus rubecula)), but not by the treatment itself. This suggests that the decision to use the feeder is risk-dependent, but when birds choose to forage, their foraging time is risk-independent.