An isotopic approach to measuring nitrogen balance in caribou

Nutritional restrictions in winter may reduce the availability of protein for reproduction and survival in northern ungulates. We refined a technique that uses recently voided excreta on snow to assess protein status in wild caribou (Rangifer tarandus) in late winter. Our study was the first application of this non-invasive, isotopic approach to assess protein status of wild caribou by determining dietary and endogenous contributions of nitrogen (N) to urinary urea. We used isotopic ratios of N (?15N) in urine and fecal samples to estimate the proportion of urea N derived from body N (p-UN) in pregnant, adult females of the Chisana Herd, a small population that ranged across the Alaska-Yukon border. We took advantage of a predator-exclosure [...]