Numerical 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 in North America. Populations of hares cycle in abundance, with peaks in density occurring every 8-11 yr, and experimental results suggest that predation is a necessary; factor causing these cycles. We measured the numerical 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 movements. 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 were associated with lower reproductive output and high emigration rates. Likewise, few to no kits were produced by lynx after the second winter of declining numbers of hares. High emigration rates were characteristic of lynx during the cyclic peak and decline, and low in situ survival was observed late in the decline. The delayed numerical responses of both ''generalist'' coyotes and ''specialist'' lynx were therefore similar, and would contribute to the cyclic dynamics.