Chronic Tidally-Induced Nest Failure in a Colony of White Ibises

Abstract

Over five seasons, I censused an estuarine colony of White Ibises (Eudocimus albus) in South Carolina using aerial counts before and after tidal washovers. I found 61% of all nesting starts were abandoned during these tides; since not all washovers were monitored, this figure is conservative. An analysis of tide gauge data indicates these destructive tides were frequent, and predictable across seasons. This colony is growing in size, and there is circumstantial evidence of breeding site fidelity despite the washovers. This is surprising, since White Ibises are known for frequent colony shifts. Although egg predation at this colony was comparatively low, and clutch size comparatively high, breeders still suffered far more total nest loss than at other coastal colonies. I suggest White Ibises do not use nesting failure, or predictability of failure as cues for abandonment, but rely on environmental cues such as local food availability and frequency of nest-site predation instead.