Evaluation of a reproductive index for estimating songbird productivity: Case study of the golden-cheeked warbler

Abstract

It is critically important to determine and understand relationships between endangered species populations and landscape and habitat features to effectively manage and conserve populations and the habitats they rely on. Several recent studies focused on the golden-cheeked warbler (Setophaga chrysoparia), an endangered songbird that breeds exclusively in central Texas, USA, have used a reproductive index to link pairing and breeding success to various factors of interest. However, no field test has evaluated the performance of a reproductive index at estimating productivity of golden-cheeked warblers or similar forest songbirds. We computed reproductive index ranks for 5 observers from multiple plots during 2013 and 2014 and compared these ranks with actual reproductive success determined from territory mapping and nest monitoring of color-banded adults. At the territory level, we found no significant correlation between 84 matched territories delineated by the reproductive index and territories delineated by intensive monitoring. At the plot level, index monitoring underestimated the total number of territorial males, but density from index monitoring was weakly correlated with actual density. We found no significant relationship for pairing success estimated from the reproductive index and actual pairing success, or with breeding success from the reproductive index with nest survival or actual breeding success, when controlling for observer. The reproductive index did not produce reliable estimates of reproductive performance at either the territory or plot level and we recommend intensive monitoring of color-banded individuals when absolute estimates of reproductive success rates or other demographic measures are required, such as in species viability or threat assessments. © 2015 The Wildlife Society.