Annual variation in laying date and breeding success of Brown Noddies on Aride Island, Seychelles

Abstract

We examined annual variation in timing of breeding, productivity, growth-rates of chicks and adult body condition of Brown Noddies (Anous stolidus) on Aride Island, Seychelles, from 1995 to 2002 (8 years), and assessed whether poor breeding success was related to El Niño events. Our results were compared with similar studies on tern species that feed more in inshore waters and with faster chick growth, the Lesser Noddy (A. tenuirostris) and the Roseate Tern (Sterna dougallii), to evaluate the extent of variation in laying date and breeding performance of tropical terns in the western equatorial Indian Ocean. Most of the Brown Noddy population laid eggs between late May and late June in most years. Breeding success varied substantially between years. Productivity of < 0.15 chicks per breeding pair occurred in three out of the eight study years. The years with poorest breeding success were El Niño (1997 and 2002) and La Niña (1999) years. Chick mass at hatching was significantly correlated with an egg-volume index, but there were no correlations between size of eggs and either hatching date or linear growth-rate. Both adult mass and body condition were significantly lower in an El Niño year (1997), when birds laid later and were less successful, than in non-El Niño years (1995 and 1996). Overall, our data suggest strong variations in food availability among years. The productivity of Brown Noddies was significantly correlated with that of Lesser Noddies, but not with that of Roseate Terns, which suggests that similar ecological forces may influence the breeding of the two noddy species.