ECOLOGICAL CORRELATES OF INDIVIDUAL VARIATION IN AGE AT MATURITY IN FEMALE MOOSE (ALCES-ALCES) - THE EFFECTS OF ENVIRONMENTAL VARIABILITY

1. Large variation was found in age of onset of reproduction among radio-collared female moose (Alces alces) in a population in northern Norway (69-degrees-N). Eight (50%) of the individuals matured at 2.5 years old, whereas age of maturity was 3-5 years or older for eight females. 2. Onset of reproduction was closely correlated with body weight. Both calf and yearling weight was significantly higher for those females that matured as 2.5 years old, compared with the other females. 3. Average calf weight differed significantly among females; however, this variation was not significantly correlated with the mother's body weight. 4. Calf weights were significantly correlated with the biomass of the herb species in the mother's summer home-range. A close relationship was found with the availability of some important forage species such as Lactuca alpina. 5. Calf body weight varied independently of birth date. Single calves of experienced mothers were significantly heavier than twins. 6. Yearling weight was significantly higher among females that stayed in the areas used as winter grounds (the central area) after they had become independent of their mother in their second summer. Females that moved to the surrounding areas had significantly lower weight gain and a delayed age at maturity, indicating a cost of dispersal. Thus, the distribution of age at maturity in a cohort will be strongly influenced by the proportion of females that succeed in establishing a home range in these areas.