Zoological Studies

Vol. 53, 2014

Resource partitioning between incubating and chick-rearing brown boobies and red-tailed tropicbirds on Christmas Island

Joan Navarro1*, Rocio Moreno2,3, Lena Braun4, Carola Sanpera3 and Janos C Hennicke4,5

1Institut de Cičncies del Mar (ICM-CSIC), P. Marítim de la Barceloneta 37-49, Barcelona 08003, Spain
2British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 0ET, UK
3Departament de Biologia Animal (Vertebrats), Facultat de Biologia, Universitat de Barcelona, Av. Diagonal 645, Barcelona 08028, Spain
4Department of Ecology and conservation, Biocentre Grindel, University of Hamburg, Martin-Luther-King-Platz 37, Hamburg 20146, Germany
5Centre d’Études Biologiques de Chizé, UPR 1934 du CNRS, Villiers-en-Bois 79360, France

Background: In oligotrophic tropical marine environments, the main mechanism explaining the coexistence of sympatric seabirds is segregation by habitat or segregation by prey within the same habitat. Both types of segregation can play a role during the breeding season due to different constraints associated with different phases of the breeding cycle. By using stable isotope analyses, we investigated intra- and interspecific foraging segregation in two tropical seabird species, the red-tailed tropicbird Phaeton rubricauda and the brown booby Sula leucogaster, breeding sympatrically on Christmas Island, Indian Ocean. We compared isotopic values of δ13C and δ15N in blood
from incubating and chick-rearing adults of both species.

The results showed small but significantly interspecific and intraspecific differences in δ13C and δ15N values. Differences in δ13C values suggest spatial segregation in the main foraging grounds between the two species during the breeding season as well as between incubating and chick-rearing brown boobies. In contrast, red-tailed tropicbirds probably exploited similar foraging habitats during both breeding stages. δ15N values did not indicate diet-related differences, neither within nor between species, suggesting a highly opportunistic feeding behavior to cope with the limited prey available in the oligotrophic marine environment.
Conclusions: Competition for prey in breeding red-tailed tropicbirds and brown boobies seems to be reduced by spatial segregation enabling both species to successfully reproduce in sympatry in an oligotrophic tropical marine environment.

Key words: Feeding segregation; Stable isotope analysis; Tropical ecosystems; Seabirds.

*Correspondence: E-mail: joan@icm.csic.es