Stable isotopes reveal strategic allocation of resources during juvenile development in a cryptic and threatened seabird, the Marbled Murrelet (Brachyramphus marmoratus)

Abstract

Identifying factors that influence growth throughout development is important for understanding the consequences of variation in resource quality on recruitment. Marbled Murrelets ( Brachyramphus marmoratus (J.F. Gmelin, 1789)) are threatened seabirds that are extremely cryptic in their nesting behaviour, which makes it challenging to understand how juveniles allocate resources during development. From a single capture at sea, we analyzed stable carbon isotopes in feathers and blood of juvenile murrelets to infer diet composition during both the pre- and the post-fledging periods. Consistent with the challenges juveniles face during their first year of life, we found that wing and bill growth were prioritized in the nest, whereas development of energy stores was delayed until after nest departure. We also found that diet quality after nest departure influenced bill size and body condition, two body components that continue to grow after independence. Our results provide evidence that murrelets strategically allocate resources according to their stage of development and that the availability of high-quality prey is likely to be important to juvenile development. These results identify a potential mechanism through which feeding conditions may influence reproduction of murrelets and demonstrate the utility of stable isotopes to examine the influence of diet quality on growth over multiple stages of development.