Chick measurements and stable isotope signatures

We inferred chick diets in a breeding colony from the stable isotope profile of their feathers, and raised chicks in captivity on an either fully marine or terrestrial unrestricted diet to disentangle effects of food composition from food availability. While no effect of diet is found on the realized size, condition or growth rates of chicks in captivity, a stronger terrestrial signature corresponded with smaller realized sizes and lower condition in free-ranging chicks.