Lynx Recruitment during a Snowshoe Hare Population Peak and Decline in Southwest Yukon

Mowat, Garth; Slough, Brian; Boutin, Stan

We estimated litter size, birthrate (proportion of F with young in mid-Jun), and survival of young to winter for lynx (Lynx lynx) in southwest Yukon between 1990 and 1992. Radiocollared females were located shortly after parturition to count young, and relocated in winter to count the number of surviving young from tracks. Hare (Lepus americanus) density, as estimated by pellet transects, peaked at 7.4 hares/ha in 1990 and began to decline in winter 1990-91. Reproducing lynx faced a declining food supply in spring 1991. Litter size averaged 5.3 (n = 12) for adults (>2 yr) and 4.2 (n = 5) for yearlings in 1990, and all females monitored had litters in mid-June. Adult litter size was 4.9 in 1991 (n = 15) and 16 of 19 adult females (84%) had litters in mid-June. None of 7 yearlings retained litters in 1991. In 1992 none of 7 adult or 3 yearling females retained litters. Minimum survival estimated from track counts was 0.63 in 1990 and 0.75 in 1991 for kittens of adult mothers. Survival was 0.26 in 1990 for kittens of yearlings. Recruitment to 1 year of age was 2.8 kittens per adult female, and 0.55 kittens per yearling female in 1990. In 1991 recruitment was 3.2 from adults and 0.08 from yearlings. Lynx recruitment went from a peak in 1990 to zero reproductive output in 1992. Adult females managed to recruit young the year after the hare peak, but recruitment from yearlings virtually ceased in the first year of the hare decline. Recruitment from yearlings was surprisingly low, even in the peak hare year. If this observation describes other lynx populations, it has serious ramifications for trapped populations, which are often composed largely of yearlings. Population models which have based yearling recruitment on in utero data probably have overestimated recruitment and sustainable harvest.

Lynx Recruitment during a Snowshoe Hare Population Peak and Decline in Southwest Yukon

Series