UCB Moorea Class: Biology and Geomorphology of Tropical Islands

Land breeding sites are important conservation priorities for the preservation of seabirds that cannot breed over the ocean. An example of a seabird that must breed on land is the white-tailed tropicbird (Phaethon lepturus). This bird is frequently seen on the island of Mo’orea in French Polynesia, but little is known about whether this species spends time there for the purpose of breeding. I hypothesized that these birds are breeding on Mo’orea and therefore conducted a study that included (1) observations of group interactions; (2) time budget construction; and (3) number surveys. My group interaction observations revealed courtship behavior previously described by the literature but I observed no definite evidence of cliff‐face nesting. The time budget results showed that the tropicbirds spend a significant portion of their time flying over the land by themselves (73%), and at low elevation near vegetation (61%). The number survey revealed that the birds preferred to be on land at mid‐day and favored one valley, ‘Opunohu, over the 2 others I surveyed. Because of the amount of time the birds spend by themselves and the absence of definite nest site data, I am unable to conclude that white‐tailed tropicbirds are breeding on Mo’orea at this time of year. However, their courtship behavior and extensive interaction with vegetation that may indicate potential nest sites in tree hollows lead me to conclude that Mo’orea could be a land breeding site for this species at other times of year.