Responses of coyotes and lynx to the snowshoe hare cycle

Coyotes and lynx are the two most important mammalian predators of snowshoe hares throughout much of the boreal forest. Populations of hares cycle in abundance, with peaks in density occurring every 8-11 years, and experimental results suggest that predation is a necessary factor causing these cycles. We measured the numerical and functional responses of coyotes and lynx during a cyclic fluctuation of hare populations in the southwest Yukon, to determine their effect on the cyclic dynamics. We used snow-tracking, track counts, and radio telemetry to directly examine changes in the numbers, population dynamics, and foraging behaviour of the predators. Numbers of coyotes varied 6-fold and those of lynx 7.5-fold during a 26-44-fold fluctuation in numbers of hares, and the abundances of both predators were maximal a year later than the peak in numbers of snowshoe hares. Cyclic declines in numbers of coyotes and lynx were associated with lower reproductive output and high dispersal rates, and low in situ survival of lynx later in the decline. Coyotes and lynx both fed mostly on hares during all winters except during cyclic lows, when the main alternative prey of coyotes was voles, and lynx switched to hunting red squirrels. Both predators showed clear functional responses to changes in the densities of hares. Kill rates of hares by coyotes varied from 0.3 to 2.3 hares/day, with the most hares killed one year before the cyclic peak, while those of lynx varied from 0.3 to 1.2 hares/day, with the highest one year after the peak. Coyotes killed more hares early in the winter, and cached many of these for later retrieval. Based on these estimates, the combined effect of predation by coyotes and lynx ranged from 9.1% to 46.5% of the total winter population of hares killed. There were several changes in foraging behaviour of the predators over the cycle. Habitat use by coyotes and lynx varied, and roughly paralleled trends in habitats used by hares. Lynx increasingly used hunting beds for ambushing both hares and red squirrels during the cyclic decline and low. Lynx also hunted in adult groups for the first time during the decline and low in hare numbers.Science, Faculty ofZoology, Department ofGraduat