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.

Density and nest survival of golden‐cheeked warblers: Spatial scale matters

“…Temporal trends of nest survival were consistent with previous studies on the BCP and Fort Hood (Peak , Reidy et al , Peak and Thompson ), with nest survival declining throughout the breeding season and varying by year. Our results re‐enforce the importance of monitoring populations over time and not inferring nest success or reproductive output based on limited sampling or reproductive indices (Reidy et al ). These temporal patterns may result from changes in predator activity patterns or abundance.…”

A before–after control–impact assessment to understand the potential impacts of highway construction noise and activity on an endangered songbird

“…We calculated fledging success as the number of paired territorial males that successfully fledged one or more host young relative to the total number of paired territorial males. Direct measures of nest success would provide more detailed analyses of reproductive output (Reidy, O'Donnell, & Thompson, 2015).…”

“…Direct measures of nest success would provide more detailed analyses of reproductive output (Reidy, O'Donnell, & Thompson, 2015). However, reproductive indices, such as the Vickery method, allow observers to avoid potential biases associated with nonrandomly collected nest data (Martin & Geupel, 1993), sample a larger spatial extent (Villard & Pärt, 2004), and predict territory outcomes when females or nests are difficult to locate and monitor (Craft, 1998).…”

Determining When Bobolink Finish Breeding to Time Agricultural Activity in Nesting Refuges

“…A modified Vickery index (Vickery et al 1992) enabled reasonably accurate identification of bobolink breeding status in a field using transect surveys and point counts, compared to spot map methods. Previous studies have documented weaknesses of the Vickery index to correctly identify breeding success compared to nest monitoring for other bird species: dickcissel ( Spiza americana ; Rivers et al 2003), golden‐cheeked warbler ( Setophaga chrysoparia ; Reidy et al 2015), and Savannah sparrow (Morgan et al 2010). In contrast, Christoferson and Morrison (2001) reported that the Vickery index accurately identified the breeding status of painted redstart ( Myioborus pictus ), plumbeous vireo ( Vireo plumbeus ), and western wood‐pewee ( Contopus sordidulus ) on each visit to a territory compared to nest monitoring.…”