Regulation of a large herd of migratory caribou: summer nutrition affects calf growth and body reserves of dams

Abstract

The range used for calving and for the first month of lactation by the Rivière George Caribou Herd (RGH), which peaked at over 600 000 individuals in the mid-eighties, showed signs of overgrazing, in contrast to that used by the adjacent Rivière aux Feuilles Herd. Density of females in the tundra habitat below 600 m asl averaged 11.2 animals/km2 on the overgrazed range in 1988, in comparison with ≈0.5/km2 on the other range. Inadequate foraging conditions during the first month of lactation caused complete exhaustion of fat reserves in females on the poor range; milk production was seemingly insufficient, as calves were lighter and grew at a slower rate than calves born on the better summer range or born in captivity from dams fed ad libitum. Moreover, females on the poor range were shorter and lighter than their counterparts on the good range, illustrating that priority goes to reproduction rather than to growth under suboptimal foraging conditions. Accretion of body fat and protein in RGH females was rapid in autumn, but individuals with a calf at yield accumulated smaller fat reserves than nonreproductive adult females. Condition did not affect ovulation. However, interruption of gestation was suspected in females that were unable to accumulate enough body reserves in autumn or early winter, judging from the progressive decline in the pregnancy rate and in the autumn cow:calf ratio observed for the RGH since 1984, concomitant with the levelling off of the herd. Summer nutrition seemingly regulated the RGH through a combination of decreased fecundity and survival.

Causes and Consequences of Broad-Scale Changes in the Distribution of Migratory Caribou (<i>Rangifer tarandus</i>) of Southern Hudson Bay

“…Skeletal size in ungulates is unaffected by ephemeral, seasonal changes in resource availability, but it is a particularly useful gauge of forage resources during development (Huot, 1988;Crête and Huot, 1993;Gerhart et al, 1997;Knott et al, 2005;Mahoney et al, 2011). In SHB, we found no significant differences in body size through time in the West.…”

“…Caribou may shift ranges in response to reductions in forage quantity (Messier et al, 1988;Couturier et al, 1990) or quality (Klein, 1970;Gordon and Illius, 1989;Wolfe, 2000). A decline in the quality of the summer range can result in delayed arrival, reduced calf survival, and earlier departure from summering areas (Crête and Huot, 1993;Mahoney and Schaefer, 2002b;Couturier et al, 2009). Over decades, body size and population size can also reflect density-dependent fluctuations in available forage biomass (Crête and Huot, 1993;Mahoney and Schaefer, 2002b;Couturier et al, 2010;Mahoney et al, 2011).…”

Reproductive Rate and Calf Body Mass in a North-Boreal Reindeer Herd: Effects of NAO and Snow Conditions

“…Furthermore, even dwarf shrubs and dead grass that reindeer eat from the first snow-free patches might be important (Ryd 2001, Fauchald et al 2004. Availability of green forage improves milk production of females, which affects growth rate and survival of calves (Créte & Huot 1993, Post & Klein 1999, Tveraa et al 2003.…”

Predation risk and optimal foraging trade-off in the demography and spacing of the George River Herd, 1958 to 1993

“…More recently a news release at this conference showed 5 of 23 satellite George River animals associated with Leaf River satellite animals (April 17-22) and Couturier et al (this conference) gave a paper titled "Is the meta¬ population theory useful in conservation?--A test with the Quebec-Labrador caribou". When we have two large adjacent migratory herds that winter in the same areas at high numbers, one with a severely degraded low risk calving range and the other with a much larger above treeline, low risk calving habitat, (Crête & Huot, 1993;Crête et al, 1990;Bergerud, 1988b;Manseau et al, 1996), might not we expect exchange?…”