Demography, Breeding Biology and Predation of Willow Ptarmigan at Anderson River Delta, Northwest Territories

Abstract

Observations on the willow ptarmigan (Lagopus lagopusa lbus) were made during the breeding season from 1958 to 1985 at the AndersonRiver delta, N.W.T. Numbers of territorial males on a 65 ha study area have fluctuated between 7 and 28 over this time, with numbers peaking in1961-62, 1969 and 1980. Peaks in ptarmigan numbers appear to be fairly synchronous over a large geographical area. Large flocks of males wereobserved in some years. In 1978, these males, mainly yearlings, had similar wing lengths to, but weighed slightly more than, territorial males. Thereappeared to be a shortage of hens in 1978, possibly caused by differential mortality during the winter. Mean clutch size ranged from 8.7 to 10.4 and meannumber of fledged chicks per brood ranged from 6.3 to 6.9. Within North America clutch size of willow ptarmigan does not appear to increase withincreasing latitude. As in other localities, raptors and foxes appeared to be the main predators of ptarmigan. More males than females were killed on thebreeding area, but this could have been because more males were present.