Diet and nestling growth of red-legged and black-legged kittiwakes: an interspecies cross-fostering experiment

Abstract

I conducted an interspecific cross-fostering experiment to investigate how diet composition and feeding rates affected nestling survival, growth, and gastrointestinal development of Red-legged and Black-legged kittiwakes on St. George Island, Alaska. Red-legged Kittiwakes (Rissa brevirostris) fed nestlings primarily lanternfish (Myctophidae), a high-lipid diet, whereas Black-legged Kittiwakes (R. tridactyla) fed nestlings mostly walleye pollock (Theragra chalcogramma), a low-lipid diet. Nestling meal size was similar for the two species, but Red-legged Kittiwakes fed nestlings at about half the rate of Black-legged Kittiwakes. Interspecific differences in nestling growth were explained by differences in adult body mass. Survival rates and lean body mass did not differ between fostered nestlings and conspecific controls. Nestlings raised by Red-legged Kittiwakes had 50% larger fat reserves than those raised by Black-legged Kittiwakes. Thus growth rates of lean tissue were genetically constrained, while rates of fat deposition were determined by diet Interspecific differences in gastrointestinal anatomy were partly genetic and partly dietary in origin.