Differences in foraging range between white-tailed tropicbirds breeding on inner and outer Seychelles Islands

The foraging ecology and distribution of Phaethontiformes, an order of tropical seabirds, remains generally poorly understood, despite being essential to inform their conservation. Here, we tracked, for the first time, the foraging movements of breeding white-tailed tropicbirds Phaethon lepturus, a common but poorly studied seabird, in the Indian Ocean. We compared the foraging movements and habitat preferences of 2 populations, one from Aride Island in the inner Seychelles and the other from Aldabra Atoll in the outer Seychelles, ca. 1200 km to the southwest. We found considerable differences in foraging trip metrics between populations, with birds from Aride having an average foraging range 2 times greater (231 km on Aride vs. 105 km on Aldabra), and both populations feeding far beyond the protected areas around their respective colony. We also found differences in foraging range between incubation and chick-rearing stages and sexes. Using habitat models, we highlight the birds’ preference for deep waters, which may explain the greater foraging range of Aride birds, although human activities may also play a role. Our study provides unprecedented insight into the foraging ecology of white-tailed tropicbirds in the Western Indian Ocean.

Methods
The data collection methods are described in the paper and its electronic supplementary materials.