Breeding biology of White-tailed Tropicbirds Phaethon lepturus in the Maldives, Indian Ocean

Summary

Seabirds are among the most threatened bird groups globally and often depend on invasive-predator-free breeding islands. In the tropics, coral atoll islands constitute important seabird refugia, yet some major atoll archipelagos remain poorly documented. The Maldives, an archipelago comprising over 1,200 atoll islands, has received little attention as a potential seabird breeding region, limiting the evidence base for bird conservation action. Here, we present the first quantitative assessment of breeding phenology, breeding performance, and colony trends for any seabird in the Maldives, focusing on the White-tailed Tropicbird Phaethon lepturus , a widespread yet globally-declining species. We conducted weekly surveys of breeding activity and developmental stages on an island in the central Maldives over 2.6 years (August 2022–March 2025; 138 survey weeks). In the Maldives, White-tailed Tropicbirds bred year-round with an approximately eight-month cycle in peak breeding activity. Breeding success was 60.2% and the number of active nests increased nearly two-fold over the study period, resulting in a total estimated population of over 100 breeding pairs by the end of the survey. Nest survival analysis identified a c.10-day period of elevated nest failure risk after hatching, likely driven by predation of hatchlings by a suppressed but residual invasive ship rat Rattus rattus population on the island. These findings provide the first quantitative baseline for seabird breeding in the Maldives and reveal highly productive breeding in this under-studied archipelago. Notably, the colony occurred on a tourist resort island, suggesting that when effective invasive predator suppression and protection of breeding habitat occur, seabird breeding can be enabled on inhabited islands. Establishing and scaling comparable management and monitoring standards across tourist islands could facilitate small but viable breeding populations across the Maldivian archipelago. These populations could act as important sources for recolonising uninhabited Maldivian islands when restored to predator-free status.