Nest site selection and reproductive success in the Brown Noddy (Anous stolidus) on Frenchcap Cay, U.S. Virgin Islands
Orton-Palmer, Amelia E.
MetadataShow full item record
The influence of nest site features (microclimatic parameters, nest exposure, and nearest neighbor distance) on reproductive success of the Brown Noddy (Anous stolidus) on Frenchcap Cay, U.S. Virgin Islands during the 1989 breeding season was examined. Noddies nested in four different habitat types: cliffs, rock outcrop, Ficus branches, and ground below Ficus. Microclimatic parameters were not related to breeding success in any of these habitats. Noddies probably relied on efficient behavioral and physiological thermoregulation to avoid heat stress. A subjective rating of nest exposure to predators also did not correlate with breeding success, possibly due to inherent inconsistencies in the rating methodology. Nearest neighbor distance was the only variable that influenced breeding success. Successful nests had shorter mean nearest neighbor distances than failed nests in the cliff habitat, but not in the nests of Ficus ground or branch habitats. Nesting closer together enhanced detection and mobbing of avian predators by noddy adults in open habitats such as the cliffs. Nearest neighbor distance was not important in Ficus ground nests, because Ficus vegetation hindered the ability for noddy adults to detect and mob predators. Ficus ground nests suffered the highest predation rate. Ficus branch nests had low predation, and nesting distances were not important, probably because these nests were less accessible to Laughing Gull (Larus atricillal predators. The most successful habitat, the rock outcrop, with well-protected nests tucked into pockets, had no nest failures. This habitat was apparently the most conducive to noddy reproductive success, and appeared saturated with nests. Ficus branch nests suffered the next least mortality, and may be more adaptive than nesting in cliff sites where energy expenditure for anti-predator defense is reguired. Birds nesting in the least successful Ficus ground habitat may be inexperienced breeders or birds less capable of outcompeting conspecifics for superior nest sites.