It’s in the bag: Corticosterone levels and behavioral responses of Eastern Bluebirds (Sialia sialis) vary with type of holding bag

Publication Type:
Journal Article
Year of Publication:
Renee E. Carleton, Rachel M. Caldwell
Wilson Journal of Ornithology
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Birds react to capture, restraint, and handling by both innate physiological and behavioral means, which function to promote survival. Following capture, small birds are typically placed into holding bags for transport and restraint before data collection and/or banding. We examined physical characteristics of holding bags constructed from opaque cotton cloth or polyester mesh and measured behavioral responses of adult breeding Eastern Bluebirds (Sialia sialis) during a 20 min holding period in each bag type, and corticosterone levels at the end of restraint. Bags differed in thread count, percent internal temperature change, and light transmittance, but not in cloth thickness or CO2 permeation. Birds held in mesh bags struggled and vocalized more over the 20 min holding period and had higher corticostemne levels at the end of the holding period than those held in opaque cloth bags. All birds, regardless of type of bag used to restrain them, returned to feeding their young within 30 min of release and none abandoned their brood. Research involving vertebrate animals ethically and legally requires the refinement of methods to reduce pain or distress. The results of this study suggest bag characteristics influence acute responses associated with capture and thus should be considered when designing capture and holding protocols and interpreting capture-induced corticosterone levels and behavioral responses.


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