Data from: Marked differences in foraging area use and susceptibility to predation between two closely-related tropical seabirds

Ecological theory predicts that closely-related species must occupy
different niches to coexist. How marine top predators achieve this during
breeding, when they often gather in large multi-species colonies and are
constrained to central-place foraging, has been mostly studied in
productive temperate and polar oceans with abundant resources, but less so
in poorer, tropical waters. Here, we track the foraging movements of two
closely-related sympatric seabirds—the white-tailed and red-tailed
tropicbirds Phaethon lepturus and P. rubricauda—breeding on Aldabra Atoll,
Seychelles, to investigate potential mechanisms of niche segregation and
shed light on their contrasting population trends. Combining data from
GPS, immersion, depth and accelerometry loggers, we show that the two
species have similar behaviour at sea, but are completely segregated
spatially, with red-tailed tropicbirds flying further to feed and using
different feeding areas than white-tailed tropicbirds. Using nest-based
camera traps, we show that low breeding success of both species—which
likely drives observed population declines—is caused by high nest
predation. However, the two species are targeted by different predators,
with native avian predators mainly targeting red-tailed tropicbird nests,
and invasive rats raiding white-tailed tropicbird nests when they leave
their eggs unattended. Our findings provide new insight into the foraging
ecology of tropicbirds and have important conservation implications. The
extensive range and spatial segregation highlight the importance of
considering large-scale protection of waters around tropical seabird
colonies, while the high level of nest predation provides evidence in
support of rat eradication and investigating potential nest protection
from native avian predators.