Are Nest Exclosures an Effective Tool in Plover Conservation?

Abstract

High levels of egg predation by numerous vertebrates has been implicated as a limiting factor in many avian populations. In response, ornithologists often attempt to control potential egg predators through lethal methods or large scale fencing of breeding habitat. More recently, individual nest exclosures have been employed to deter egg predators. During 1999 and 2000, we experimentally tested nest exclosure effectiveness at enhancing Killdeer (Charadrius vociferus) nest success in the Great Basin, USA. We demonstrated that nests with exclosures had significantly lower daily mortality rates compared to nests without exclosures. Although nest exclosures increased Killdeer nest success in this study, it is necessary to identify predators impacting nest success prior to the exclosure design. Nest exclosures are unlikely to be equally successful among sites, and variation in exclosure design may be required across both the range of a species and/or breeding seasons at a single site. The exclosure design we used did not deter small mammals and birds, or reptiles; and we observed small mustelids killing incubating birds. However, these exclosures were effective at increasing hatching success by deterring larger predators (ravens, gulls, canids). Any benefit derived from the nest exclosure used may potentially be offset by increased predation on incubating adults. Nest exclosures are not a means of preserving biological diversity over geologic time, but rather a potential temporary site-specific tool that increases nest success while long-term conservation plans are developed.