INDIVIDUAL AND GEOGRAPHICAL VARIATION IN AGE AT MATURITY IN FEMALE MOOSE (ALCES-ALCES)

Variation in age at maturity among 2764 female moose (Alces alces) in 14 populations in Sweden was investigated and related to patterns of b ody growth and characteristics of the environment. Data were collected from animals shot during the hunting season in 1989-1992, and all fem ales were aged and examined for previous pregnancy by inspecting the u terus. Individual variation was large; 10 (1.3%) out of 776 yearlings were classified as previously pregnant, and must have become fertile d uring their first year of life. Among 2-year-old females 31.2% were ma ture, while the majority (80.5%) of females became mature at 3 years o f age. Age at maturity, calculated as the age at which 50% of the fema les were mature, was also highly variable among populations and ranged between 2.06 and 3.17 years. Population-specific age at maturity was significantly related to mean yearling carcass mass among populations but not to juvenile, 2-year-old, or adult carcass mass. Approximately 50% of the variation in age at maturity among populations could be exp lained by the mean rate of body growth between juvenile and yearling s tages. High initial rates of body growth and early maturity in a popul ation were strongly associated with low rates of body growth after the yearling stage. No clear relationship was found between age at maturi ty and population density, amount of browse, latitude, or climatic con ditions among populations. This suggests that multiple factors are inv olved in shaping the geographical pattern of age at maturity and that additional factors such as nutritional quality and age-specific surviv al must be considered when explaining the mechanisms behind the appare nt variation in age at maturity among populations of female moose.