Is colony attendance by shearwaters influenced by bright moonlight or inclement weather?

Abstract

If nocturnal colony attendance is associated with avoidance of predators, fewer nests would be visited by parent shearwaters on moonlit nights, or nests would be visited later, than on dark nights. Additionally, if shearwaters foraged at night on certain prey species, feeds delivered to nestlings would be larger on dark nights. We found that feed size and the probability of a nest visit were both greater on moonlit nights, while food delivery after midnight was not. A minimal risk of predation concurs with the disregard for moonlight shown by Flesh-footed Shearwaters, Puffinus carneipes, but does not explain their apparent preference for it. While nocturnal foraging is unlikely, it is not clear why feeds were significantly larger on moonlit nights, or why colony attendance by this species is strictly nocturnal. Weather may impact the ability of seabirds to forage at sea, although this is difficult to confirm. It was likely that nest attendance by parent shearwaters would be lower if certain variables negatively influenced foraging, but such influences may not manifest themselves immediately. Nest visits were examined in relation to local weather conditions at time-lag intervals of up to seven days. While no significant cross correlations were determined between burrow entry and two wind-velocity variables, a significant positive correlation was determined when the study site experienced pronounced unseasonal rainfall events.