Mechanism for decline in a woodchuck population [Mécanisme du déclin d'une population de marmottes américaines].

Résumé

Etude menée dans un dépôt de l'armée dans le centre sud de la Pennsylvannie : diminution de 80% de la population de 1955 à 1970. Rôle des ressources alimentaires. The number of woodchucks on an army ordnance depot in south central Pennsylvania decreased by 80% from 1955 to 1970. The depot contained 4,000 ha of former agricultural land taht provided excellent sites for burrows. The birth rate was initially low (1,3), but increased and remained high (1.7) after 1958 due primarily to an increase in the percent of yearlings pregnant. The death rate of adults changed little, but the loss of young during summer 1964-1967 and during hibernation 1962-67 was high. Movements increased after 1962. Changes in habitat after 1960 resulted from cessation of leasing land for crops of corn, wheat and barley. A dought occured from 1961 to 1969, and decreased the quantity of natural vegetation. Thus, a great decline in food supply occured after 1962. The mechanism for the decrease of woodchucks was failure of young to gain the weight neccessary to survive the hibernation period and subsequent emergence. During 1957-60, 50% of young males and females reached a weight considered adequate for survaval, compared to only 1-10% during 1962-66, during 1967, 50% of males and 80% of females achieved adequate weight.