August 11, 2025Open Access

Foraging Ecology of Red-billed Tropicbird Phaethon aethereus in the Caribbean during Early Chick Rearing Revealed by GPS Tracking

HMHannah MaddenPortland State University YSYvan G. SatgéOregon Department of Fish and Wildlife BWBradley WilkinsonAssociation of Fish and Wildlife Agencies

Key Points

The red-billed tropicbird primarily forages in deeper waters with higher chlorophyll concentrations.
Diet samples from St. Eustatius were mainly dominated by exocoetidae species, accounting for 59.5%.
GPS tracking showed maximum travel distances of 953.7 km, with average trips of 176.8 km.
Conservation may need transboundary collaboration due to the tropicbird's extensive travel across marine protected areas.

Abstract

Investigating the foraging patterns of tropical seabirds can provide important information about their ocean habitat affinities as well as prey choice. Foraging studies of Red-billed Tropicbird Phaethon aethereus populations in the Caribbean are lacking. We sought to rectify this by opportunistically sampling regurgitates at nest sites on the island of St. Eustatius, Lesser Antilles, and by linking the GPS tracks of foraging adults to remotely sensed environmental variables. Diet samples were dominated by Exocoetidae (59.5%) and Belonidae (14.9%), although we were unable to identify 25.5% of samples due to digestion. Tropicbirds nesting on St. Eustatius exhibited diurnal foraging patterns, foraged in deeper waters with higher chlorophyll concentration, and consumed fewer Exocoetidae species compared to travelling behaviour. The maximum distance travelled from the colony was 953.7 km, with an average trip length of 176.8 (± 249.8) km. The biologged birds crossed multiple exclusive economic zones and marine protected areas, and on that basis, we suggest that efforts to protect and conserve this species may require transboundary collaboration throughout the wider Caribbean.

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