No evidence of optimal foraging in chick-raising black-legged kittiwakes (Rissa tridactyla) in the Southern Barents Sea

Abstract

The black-legged kittiwake (Rissa Tridactyla) situation is getting more serious as the population numbers have declined over the last decades, and this well-known species is now considered endangered (EN) in the Norwegian redlist 2010. This study investigates the differences between adult and chick diet considering prey selection to be an important point. Earlier chick diet has been considered a proxy for adult diet, but the optimal-foraging theory suggests that this may not be accurate. Knowing the composition of both adult and chick diet is important for further preservation of the species. Studies of differences between self-feeding and chick provisioning have been carried out on several occasions, and the theory has been confirmed in several species such as the common guillemot (Uria aalge) and cape petrel (Daption capense), but never in kittiwakes. The water offloading method was used to sample stomach samples that were compared to regurgitated samples that indicate chick diet. Differences in diet were based on frequency of occurrence, and differences in total fish length of prey animals. Knowing the true diet of adult kittiwakes has important implications on how to manage the Norwegian populations. This study showed no signs of optimal foraging for kittiwakes during the 2012 breeding season. The main prey for both adults and chicks was capelin.