Central place foraging and feather regrowth rate in bridled terns (Onychoprion anaethetus): an insight from stable isotopes

Abstract

In this study, the stable isotope ratios of δ13C and δ15N of bridled terns’ (Onychoprion anaethetus) tail feathers were used to investigate changes in the food sources assimilated by the birds on Penguin Island, Western Australia, during different phases of the breeding season. Samples were taken immediately after they arrived on the island returning from migration (BM), before egg-laying (BEL), after egg-laying (AEL), after hatching (AH) and from fledglings (F). A one-way MANOVA (excluding the BM phase) and two one-way ANOVAs (including all phases), showed that the δ13C and δ15N values differed significantly between the stages of the breeding season, with the greatest differences between the BM and BEL stages. The mean δ13C values were higher and those for δ15N were lower for BM birds than all other stages, indicating that the food source assimilated by the birds, and their foraging locations, changed during the breeding season. These results support the hypothesis of the Central Place Foraging Theory, i.e. that adult breeding birds adjust their foraging strategies when they are bound to a central place to care for their young. Induced feathers were regenerated over ~70 days and their regrowth rates were similar before and after egg-laying.