Sex - specific food choices in Whiskered Terns

individual decisions concerning the trade-off between somatic and reproductive investment (Dänhardt et al. 2011). Birds feeding chicks should deliver the most nutritious and optimally sized prey items to chicks in order to maximise chick growth (Baird 1991). How ever, whether a parent delivers prey to chicks or eats it itself, depends not only on prey value but also on the time and energy cost of transporting each prey item (Schoener 1979). For example, Caspian Gulls Larus cachinnans capture larger fish in ponds located further from the colony than in ponds near the colony (Skórka et al. 2009). Similarly, Snowy Owls Nyctea sandiaca prefer to deliver heavier rodents to the nest, whilst taking smaller rodents for themselves (Potapov & Sale 2012). To maximise energetic investment in reproduction, colony-breeding single loaders, such as terns, mostly bring energy-rich prey items to their chicks (Dänhardt et al. 2011). Furthermore, parents should bring energyrich prey to chicks when hunting at large distances from the nest (Schoener 1979). However, in species with sexual size dimorphism, males and females may differ in the selection of prey to feed chicks, depending on the distance from the nest. The larger sex is more predisposed to catch and transport large prey (González-Solis et al. 2000, Gwiazda & Ledwoń 2015). Sexual differences in foraging and provisioning behaviour have been observed in several size-dimorphic seabird species (Lewis et al. 2002). The aim of this study was to determine whether there are differences between males and females in the proportion of different prey species and prey sizes that they consume themselves or carry to their chicks, in relation to the distance from the nest. Therefore, we studied Whiskered Terns Chlidonias hybrida, which are socially monogamous marsh terns (both partners incubate, brood and feed chicks), with no sexual plumage dimorphism (Cramp & Simmons 1985). In this species, males are significantly larger than females, with head Short notes