Population Dynamics of the Willow Ptarmigan Lagopus lagoups alleni L. in Newfoundland 1955 to 1965

A study of the population dynamics of the willow ptarmigan (Lagopus lagopus alleni L.) was carried out in southeastern Newfoundland from 1955 through 1965. The adult population in spring increased from 1955 to 1961, then decreased in each of the four remaining years, 1962-65. Clutch size varied independently of population trend, being larger in early nesting seasons than in late nesting seasons. Nesting success, by contrast, and chick survival in the first three weeks of life, varied in a non-random sequence, tending to be greater in the years before the peak than in the years immediately after. Changes in population density were associated with changes in the number of young alive per hen in August. Survival after August was about the same each year for all age groups, roughly 28 per cent per year. These observations were consistent with the idea that there was a self-regulatory population process in which the probability of survival of the chicks varied with the stage of population growth.