Reconstructing time-specific diet composition in greater sage-grouse chicks using feather stable isotopes.
Ecology and Habitat Relationships of Birds
Wednesday, Oct 17, 2012, 1:30 PM - 5:20 PM
Wednesday, Oct 17, 2012, 1:30 PM - 1:50 PM
Erik J. Blomberg
, Simon R. Poulson, James S. Sedinger, Daniel V. Nonne, University of Nevada Reno, Reno, NV, Contact: EJBlomberg@gmail.com
Diet during early stages of growth can have profound direct effects on young birds, as well as carryover effects to later life stages. Many diet studies for precocial birds rely on sampling crop contents; an approach that is limited because it is lethal to the animal and only provides a snapshot of diet that cannot be connected to other values of interest (e.g., survival). We developed a novel, non-lethal method for analyzing diets of greater sage-grouse (Centrocercus urophasianus) chicks using stable isotope composition of feather tissue, which allowed us to quantify contributions of diet items and reconstruct a post-hatch dietary timeline. We collected secondary feathers from greater sage-grouse chicks in Eureka County, Nevada, at 28 days of age. Feathers were sectioned into subsamples that corresponded to sequential multiday periods, isotopic composition of carbon (δ13C) and nitrogen (δ15N) was analyzed for each subsample, and Bayesian mixing models were used to estimate the relative contributions of invertebrate versus plant materials to diet during 1-week periods. We found δ15N to be a robust predictor of diet composition, whereas results for δ13C were more ambiguous. Bayesian mixing models using δ15N estimated the mean contribution of invertebrates to chick diet as 33 ±6% for week 1, 23 ±3% for week 2, 17 ±3% for week 3, and 14 ±0.3% for week 4. These results are consistent with previous studies that suggest a shift to a greater herbivory as chicks aged. We also show chicks that maintained a more intermediate diet were larger at 28 days, compared to individuals that consumed greater proportions of either plants or invertebrates throughout growth. These methods are well-suited to dietary assessment for grouse, and provide a new tool for evaluating sage-grouse response to management that can compliment studies of habitat use and survival.
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