Responses of caribou and reindeer (Rangifer tarandus) to acute food shortages in spring

Abstract

Migratory caribou and sedentary reindeer (Rangifer tarandus (L., 1758)) can encounter acute food shortages during spring. We examined the response to short-term food restrictions by measuring individual food intake, body mass, and activity of 2-year-old unbred female caribou and reindeer from 25 April to 29 May 2011. Caribou lost 2%–3% of body mass on days when mean dry matter (DM) intakes (60 ± 6 g DM·kg−0.75·d−1) were restricted up to 75%. Caribou regained body mass as intake increased to 98 ± 8 g DM·kg−0.75·d−1 following restriction without a change in digestibility (82%–83%). In reindeer, digestibility increased (78%–83%) as intakes decreased (67–45 g DM·kg−0.75·d−1). Food restriction did not affect activity for either subspecies. We suggest that, at high digestive efficiency, Rangifer have “spare capacity”, to increase DM intake to compensate for lost foraging opportunity or to use patches of emerging high-quality forage. Furthermore, caribou with large fat reserves lost proportionally more body mass, consumed less food, and were less active than leaner caribou. Our data indicate that Rangifer use flexible responses of food intake, digestion, and body condition to maximize survival and reproduction in both migratory and sedentary ecotypes at the end of winter.