Parental duties and foraging strategies of a tropical pelagic seabird (Phaethon aethereus, Aves: Phaethontidae) during the breeding season

Breeding seabirds must balance the energetic demands of feeding themselves and their offspring while coping with the constraints imposed by central-place foraging. As such, foraging strategies and parental care patterns are usually linked. Here, the foraging behavior of the Red-billed Tropicbird (Phaethon aethereus; n = 161) of Pena Blanca Islet, Mexico (19(degrees)06MODIFIER LETTER PRIME 11" N, 104(degrees) 29MODIFIER LETTER PRIME 12" W) during the incubation and chick-rearing (<= 4 weeks of age) stages was characterized with the aid of GPS loggers. Blood samples from adults and chicks were collected to determine delta N-15 and delta C-13, and parental presence at the nest, meal size, and parent-chick feeding events were recorded. During incubation, parents made long trips offshore to areas far from the colony; however, immediately after their chicks hatched, the parents switched to a bimodal foraging strategy by undertaking both short and long foraging trips. The delta N-15 values indicated that trophic differences were present between parents and their offspring, with chicks being fed prey enriched in N-15. Parental presence at the nest was greater during early chick-rearing, which was associated with a higher provisioning rate. Parents adopted a strategy in which the parent on nest duty only made short foraging trips to provide for its offspring without leaving it unattended for long periods, while its mate undertook long trips to feed itself. After the early chick-rearing period, the parents gradually reduced the time spent at the nest and increased the time spent foraging, compensating with larger meal sizes for their offspring.