Sub-colony variation in foraging behaviour and at-sea distribution of a breeding tropical seabird and consequences for marine spatial planning

Abstract

Many species of seabirds are threatened and understanding their at-sea distributions during breeding is a priority for their conservation. Recent developments in tracking technology, data analytical frameworks and tools are proving invaluable in the identification of at-sea areas of high use and hence conservation importance, which can be used to inform marine spatial planning. However, the outputs from these frameworks and tools are contingent on the underlying tracking data, which are shaped by the myriad of decisions made when designing and implementing a tracking program. These decisions include breeding colony choice and identification of areas (sub-colonies) within the colony in which to deploy tracking devices. However, our understanding of the consequences of this on the resulting tracking data and hence identification of at-sea priority areas is limited and rarely considered. In April 2022 we tracked 196 foraging trips of 54 breeding red-footed boobies (Sula sula) at two sub-colonies (1.5 km apart) on South Island, Farquhar Atoll in south-west Seychelles. We found that foraging trip distance and duration did not differ between the two sub-colonies, but trip orientation did: resulting in sub-colony segregation at sea predominantly to the north and south of the atoll with consequences for the identification of at-sea areas of high use. Our findings indicate that sub-colony variation in at-sea distribution of breeding seabirds may be more commonplace than current research suggests and if our tracking program had involved only one sub-colony then key outputs which could serve towards marine spatial planning efforts may be biased.