Effect of heat and singeing on stable hydrogen isotope ratios of bird feathers and implications for their use in determining geographic origin

Abstract

Rationale: Stable hydrogen isotope (δ2H) ratios of animal tissues are useful for assessing movement and geographic origin of mobile organisms. However, it is uncertain whether heat and singeing affects feather δ2H values and thus subsequent geographic assignments. This is relevant for birds of conservation interest that are burned and killed at concentrating solar-energy facilities that reflect sunlight to a receiving tower and generate a solar flux field. Methods: We used a controlled experiment to test the effect of known heat loads (exposure to 200, 250 or 300°C for 1 min) on the morphology and δ2H values of feathers from two songbird species. Subsequently, we examined the effects of singeing on δ2H values of feathers from three other songbird species that were found dead in the field at a concentrating solar-energy facility. Results: Relative to control samples, heating caused visual morphological changes to feathers, including shriveling at 250°C and charring at 300°C. The δ2H values significantly declined by a mean of 27.8‰ in experimental samples exposed to 300°C. There was no statistically detectable difference between δ2H values of the singed and unsinged portions of field-collected feathers from the same bird. Conclusions: Limited singeing that did not dramatically alter the feather morphology did not substantially affect δ2H values of feathers from these songbirds. However, higher temperatures induced charring and reduced δ2H values. Therefore, severely charred feathers should be avoided when selecting feathers for δ2H-based assessment of geographic origin.