Lynx Demography during a Snowshoe Hare Decline in Alberta

Abstract

Demographic changes in lynx (L. canadensis) populations in Alberta were studied by examining 1108 lynx carcasses collected from trappers during winters 1971-1972 through 1975-1976. Both snowshoe hare (L. americanus) and lynx populations declined during this interval from their cyclic peaks to low levels. Indices of consumption rates by lynx decreased with declining hare population levels. Concomitant decreases in indices of body fat of lynx during late winter suggested that lynx experienced a negative energy balance during hare scarcity. Lynx pregnancy rates and litter sizes decreased during the population decline. Annual finite rates of reproductive increase fell 38%. Kittens were underrepresented in trapped samples. The proportion of kittens in adjusted age ratios dropped from 66% during 1971-1972 (year of hare abundance) to 3% during 1973-1976 (years of hare scarcity). Postpartum mortality of kittens, ranging from 65-95%, was the predominant cause of lowered recruitment to winter populations. Rates of trapping mortality were positively related to average pelt value and appeared additive to nontrapping mortality. By curtailing lynx trapping during 3 yr of population decline, the total Alberta lynx harvest during 5 yr of subsequent increase would be greater than that of a continuously trapped population. Curtailment of lynx trapping for 3-4 yr starting with the 2nd yr after the peak in fur harvests.