• age at first reproduction;
  • food quality;
  • food supplementation;
  • maturation;
  • Peromyscus maniculatus borealis

1. Five populations of Peromyscus maniculatus borealis (Mearns) were live-trapped in the Kananaskis Valley, Alberta, throughout the breeding seasons of 1996 and 1997, to test the hypothesis that growth and maturation of young-of-the-year (YY) females are limited by dietary protein.

2. In 1996, two populations received a high protein (30%) food supplement, one received a high energy, but low protein (14%) food supplement and two others were unsupplemented. In 1997, three populations received the protein (30%) supplement and two served as controls.

3. In 1996, control populations had high nestling growth rates and many (43%) YY females bred. In 1997, nestling growth rates were lower in control populations and no YY females bred.

4. Supplementation of high protein food resulted in consistently high nestling growth rates in both 1996 and 1997, and a significantly higher proportion of YY females bred than controls in both years.

5. Supplementation of high energy, but low protein food had no effect on YY growth or maturation.

6. Neither protein nor energy supplementation had any effects on the number of litters conceived per season, litter success, litter size or sex ratio of litters born to over-wintered females.

7. We conclude that growth and maturation of YY female Peromyscus maniculatus in this area are limited by the availability of dietary protein.