Male caribou sparring, Photo courtesy of Jim Winstead Jr.

Mating Behavior

The woodland caribou differ from other subspecies of caribou in much of their mating behavior. Barren-ground caribou form loose groups of females to breed with (Thomas and Gray, 2002). Conversely, woodland caribou males gather harems containing approximately twelve to fifteen females (Banfield, 1974). These numbers do not apply to all populations though, as other studies indicate that the number of females per harem depends on the specific population. Chichowski et al. (2004) determined that the boreal woodland caribou tend to have smaller group sizes with numbers less than five. Mountain caribou numbers resemble those reported by Banfield (1974) with groups as large as twelve.

The polygamous males only feed occasionally during the rut.  Instead, they spend the majority of their time displaying for the females. Their displays include running about, sparring with other males, panting, bellowing, and threshing foliage with their antlers (Banfield, 1974). The hoarse grunt of the bulls is most often heard early in the morning, though it is occasionally heard during the day as well (Elliot, 1903). The males also spar to establish dominance and control, and to defend their harem from other males (Banfield, 1974). However, sparring is never violent and often serves as a means for self assessment. Animals of smaller stature and with smaller antlers often challenge larger animals with larger racks, but these smaller caribou terminated the matches more often than not (Barrette and Vandal, 1991). Another study also suggests that male antler size serves as an indicator for breeding ability in males (Butler, 1986).

A woodland caribou calf, Photo courtesy of Kyle C. Joly

Calf Information and Survival

Females only produce one calf per breeding season, a likely contributor to their inability to adapt to and withstand the added pressures placed upon their habitats in recent decades (Thomas and Gray, 2002).  Additionally and unlike most ungulates, caribou do not breed until the age of two- or two-and-a-half years (Rasmussen).  For comparison, many species of deer mate at the age of one- or one-and-a-half years.  Woodland caribou calves are most vulnerable during the first few months of their lives and their survival rates are low within populations.  Some populations experience mortality rates near and above 50% (Chichowski et al (2004). Stuart-Smith et al (1997) reports a calf survival rate of only 21.9%.  On a slightly more positive note, observations of an expanding population of woodland caribou in northern Quebec yielded pregnancy rates of 43% for female yearlings, and 90% and 95% for two- and three-year-old females, respectively (Parker, 1981). 

The caribou calves are remarkably precocial and can run a few miles about 90 minutes after birth (Banfield, 1974).  Calves remain with their mother throughout the summer and rely on them for food and protection.  Some observations have yielded peculiar calf-cow relationships.  For example, it appears that woodland caribou calves exhibit calf-hiding behavior when separated from their mother (Chubbs, 1993).  This most likely serves as a possible anti-predation strategy.  In observations of such behavior, caribou calves retreated to designated areas in the forest upon dart tranquilization of their mother and approach by the observer. The observations following cow arousal indicated that the mother immediately looked for her calf in the location where it was hiding.  Impressively, this behavior was observed in calves as young as three or four weeks (Chubbs, 1993).