The effectiveness and cost efficiency of different predator exclosure designs to increase piping plover (Charadrius melodus) nest success and fledging rate in Alberta, Canada

Abstract

An estimated 30% of the North American piping plover (Charadrius melodus) breeding population occurs in Canada, where it is Endangered. Predator exclosures are a common management tool across the species' range to increase nest success. Using data from 1998 to 2010 on 820 nests, collected as part of an ongoing management program in Alberta, we compare daily nest survival (DNS), numbers of chicks hatched and fledglings produced, and cost/chick among three treatments (large, medium, small exclosures) and natural nests. During the early period (1998)(1999)(2000)(2001), when all three types of exclosures were applied, there were no significant differences in DNS between exclosed nests and natural nests. During the late period (2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010), when only small exclosures were applied, nests with small exclosures had a significantly higher DNS rate (x = 0.994, n = 594) compared with natural nests (x = 0.984, n = 88). Nests with small exclosures also hatched more chicks (x = 3.21, n = 598) and produced more fledglings (x = 1.17, n = 337) than natural nests (x = 1.73 chicks, n = 31; x = 0.59 fledglings, n = 21) during the late period. However, considering only successful nests, the differences were not significant for either period, indicating no added benefit of exclosures beyond protecting the nest. The cost/chick rate was lowest using small exclosures (cylindrical, 40 by 60 cm), and this portable design is well-suited for widespread application in the field. We demonstrate increased DNS for nests with small exclosures and a mean fledging rate close to the goal of 1.25 chicks/nest/year, although this did not increase Alberta's piping plover population beyond the timeframe of systematic exclosure application. Long-term, cost-efficient management tools that increase nest success and fledging rates should continue.