EARLY MATURATION BY NORTHERN PEROMYSCUS-MANICULATUS

Female Peromyscus maniculatus rarely breed as young of the year in the Kananaskis Valley, southwestern Alberta. We monitored breeding by you ng-of-the-year females in unmanipulated sites from 1985 to 1991 and on manipulated sites (females removed, males removed, and food added) fr om 1989 to 1991. Breeding by young females was uncommon on all manipul ated sites (16% when food was added, 3 % when females were removed, 0% when males were removed). Females that matured as young of the year t ended to have relatively high growth rates as nestlings. We conclude t hat individual quality is more important than social cues in regulatin g maturation by young females in this population.