Assessing Accuracy of Sampling Schemes to Estimate Western Snowy Plover Reproductive Success

Abstract

AbstractLike many wildlife species of management concern, the western snowy plover Charadrius nivosus nivosus is the subject of intensive population monitoring. However, intensive monitoring of reproductive success for this shorebird is time-consuming, financially costly, and potentially disruptive to the birds of interest. These constraints mean that intensive monitoring is not feasible throughout the range of the federally threatened Pacific Coast population. In this study, we used data collected from one intensively monitored subpopulation to assess how reductions in monitoring effort (number of chicks individually marked) would affect the accuracy of estimates of fledging success for western snowy plover chicks. We used monitoring data collected on chicks hatching at 1,845 nests from 2003 to 2012 as a theoretical subpopulation from which to draw random samples for this assessment. As expected, we found that accuracy (as measured by the inverse of percentage difference between sampled and actual fledge rates) increased with increasing percentage of the subpopulation monitored each year. We also found that the day of the week that chicks hatched and were banded had no effect on fledging success. Thus, reducing monitoring effort by banding chicks on specific days of the week is one suitable method for subpopulation sampling that has no embedded biases in the subsequent estimate of fledging success. The results of our analyses provide estimates of the accuracy of different sampling schemes, which should help managers of this threatened shorebird assess appropriate monitoring methods. We recommend use of our methods for others interested in assessing accuracy of sampling schemes for reproductive success of western snowy plover or other birds with similar life-history traits.