Is What Comes out the Same as What Goes in? A Preliminary Investigation of the Isotopic Impacts of Digestion by Red‐Tailed Hawks ( Buteo jamaicensis ) and Eurasian Eagle Owls ( Bubo bubo )
Brooke Erin Crowley, Madison Laurel Greenwood, Rachel Elizabeth Brown Reid

TL;DR
This study examines how digestion in predatory birds affects isotopic signatures in their excreta and prey remains, providing correction values for more accurate diet and environmental reconstructions.
Contribution
The paper provides the first evaluation of isotopic diet-excreta offsets and digestion effects in predatory birds, offering tentative correction values for isotopic analysis.
Findings
Diet-excreta isotopic offsets vary slightly between individual birds and depend on tissue type and acidification of excreta.
Digestion significantly affects bone δ13C and 87Sr/86Sr isotopes, which could impact diet and environmental reconstructions.
Researchers should use caution when using digested bone to infer diet or environmental conditions due to significant isotopic shifts.
Abstract
We investigated isotopic diet‐excreta offset (Δdiet‐excreta) for predatory birds, and the isotopic influence of bird digestion on consumed prey tissues. Foraging ecology of predatory birds can be non‐invasively monitored using excreta or regurgitated prey. However, one must account for Δdiet‐excreta and any influence of digestion on prey tissues. Neither of these has been previously evaluated for predatory birds. We worked with a captive Eurasian eagle owl ( Bubo bubo ) and red‐tailed hawk ( Buteo jamaicensis ) fed frozen murid rats. We collected rat feet, as well as regurgitated pellets and excreta from each bird's enclosure. We analyzed carbon (δ13C) and nitrogen (δ15N) isotopes in undigested rat muscle, undigested and digested fur, and bone collagen (extracted from pellets), δ13C, oxygen (δ18O), and strontium (87Sr/86Sr) isotopes in rat bone bioapatite, and δ13C, δ15N, and 87Sr/86Sr…
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Taxonomy
TopicsIsotope Analysis in Ecology · Mercury impact and mitigation studies · Marine animal studies overview
