Gut retention time in captive brown bears Ursus arctos

Abstract

Knowing animals' gut retention time (GRT) for important food items is critical when using non-invasive studies based on faecal remains, e.g. when analysing nutritive quality of food, or relating diet or behaviour to movements. We analysed GRT in six captive brown bears Ursus arctos, after feeding on either berries (a mixture of bilberry Vaccinium myrtillus and lingonberry V. vitis-idaea) or animal carcasses (either reindeer Rangifer tarandus, European rabbit Oryctolagus cuniculus, domestic pig Sus scrofa domestica, cattle Bos taurus or horse Equus ferus caballus). Median GRT50% (i.e. when 50% of all faeces containing experimental food had been defecated) was 5 hours and 47 minutes (1st and 3rd quartiles = 4 hours and 36 minutes and 7 hours and 3 minutes; N = 20) after feeding on berries and 14 hours and 30 minutes (1st and 3rd quartiles = 10 hours and 9 minutes and 16 hours and 57 minutes; N = 20) after feeding on carcasses. Median GRTmin (i.e. first defecation comprised of experimental food) was 3 hours and 5 minutes (1st and 3rd quartiles = 1 hour and 51 minutes and 4 hours and 12 minutes; N = 21) for berries and 8 hours and 2 minutes (1st and 3rd quartiles = 6 hours and 14 minutes and 10 hours and 44 minutes; N = 20) for carcasses. Median GRTmax (i.e. last defecation comprised of experimental food) was 15 hours and 27 minutes (1st and 3rd quartiles = 11 hours and 36 minutes and 17 hours and 16 minutes; N = 21) for berries and 16 hours and 16 minutes (1st and 3rd quartiles = 12 hours and 11 minutes and 17 hours and 27 minutes; N = 20) for carcasses. A carcass diet had 6 hours and 26 minutes ± 1 hour and 56 minutes (SE) longer GRT 50% than a berry diet (N = 39), despite low variation in food intake. Activity level, feeding time (midday/midnight), sex, age (subadult/adult), ingested amounts of food, prior food remains processed by the gut (i.e. cumulative faeces weight) and defecation rate did not influence the GRT 50%. Our reported GRT estimates are reliable values to be used within research and management to relate diet based on faecal remains to habitat use for common and important food items used by Scandinavian brown bears. © 2013 Wildlife Biology, NKV.