Overwinter changes in urea nitrogen:creatinine and cortisol:creatinine ratios in urine from Banks Island Peary caribou

Abstract

Over 200 snow urine samples were collected from Banks Island Peary caribou between March 1993 and May 1998. Most (n = 146) samples were collected during 3 time periods in 5 successive years: early winter (3 November-3 December), mid-winter (9 February-1 March), and late-winter (23 April-2 May). We determined the ratios of urea nitrogen:creatinine (U:C) and cortisol:creatinine (C:C) for each sample. U:C ratios had significant year, time, and year x time interaction effects. Mid-winter ratios were higher than early or late-winter ratios. U:C ratios ranged from 0.53 to 19.05 mg/mg, and were lowest in 1997-98. Five calf caribou sacrificed in February 1994 had significantly (P 60-fold higher than those indicative of prolonged undernutrition in barren-ground caribou were common. This difference is likely because the winter diet of Peary caribou has a higher crude protein content than that of barren-ground caribou. C:C ratios had significant year and year x time interaction effects, and were highest in 1996-97 and 1997-98. C:C ratios of sacrificed caribou were similar to those of other animals during early and mid-winter. C:C ratios for Peary caribou ranged from 0.0120 ug/mg to 0.2678 ug/mg; ratios indicative of morbidity in mule deer were common. C:C and U:C ratios from the same individuals were not correlated (R = -0.073). Monitoring U:C ratios of Banks Island Peary caribou may provide useful management information.

Keywords

• caribou
• Banks Island
• Peary caribou
• Rangifer tarandus pearyi
• snow urine analysis