Associate Editor: M. J. Peterson.
Do digestive contents confound body mass as a measure of relative condition in nestling songbirds?
Article first published online: 12 FEB 2014
© The Wildlife Society, 2014
Wildlife Society Bulletin
Volume 38, Issue 2, pages 305–310, June 2014
How to Cite
Streby, H. M., Peterson, S. M., Lehman, J. A., Kramer, G. R., Vernasco, B. J. and Andersen, D. E. (2014), Do digestive contents confound body mass as a measure of relative condition in nestling songbirds?. Wildlife Society Bulletin, 38: 305–310. doi: 10.1002/wsb.406
- Issue published online: 10 JUN 2014
- Article first published online: 12 FEB 2014
- Manuscript Accepted: 30 SEP 2013
- Manuscript Received: 14 FEB 2013
- U.S. Fish and Wildlife Service
- U.S. Geological Survey
- Minnesota Department of Natural Resources through Research Work Order no. 87 at the Minnesota Cooperative Fish and Wildlife Research Unit.
- digestive contents;
- fledgling survival;
- golden-winged warbler;
- nestling mass;
- stomach contents;
- Vermivora chrysoptera
Relative nestling condition, typically measured as nestling mass or as an index including nestling mass, is commonly purported to correlate with fledgling songbird survival. However, most studies directly investigating fledgling survival have found no such relationship. We weighed feces and stomach contents of nestling golden-winged warblers (Vermivora chrysoptera) to investigate the potential contribution of variation in digestive contents to differences in nestling mass. We estimated that the mass of a seventh-day (near fledging) nestling golden-winged warbler varies by 0.65 g (approx. 9% of mean nestling mass) depending on the contents of the nestling's digestive system at the time of weighing, and that digestive contents are dissimilar among nestlings at any moment the brood is removed from the nest for weighing. Our conservative estimate of within-individual variation in digestive contents equals 72% and 24% of the mean within-brood and population-wide range in nestling mass, respectively. Based on our results, a substantive but typically unknown amount of the variation in body mass among nestlings is confounded by differences in digestive contents. We conclude that short-term variation in digestive contents likely precludes the use of body mass, and therefore any mass-dependent index, as a measure of relative nestling condition or as a predictor of survival in golden-winged warblers and likely in many other songbirds of similar size. © 2014 The Wildlife Society.