Field Populations of Deermice with Supplemental Food

A description is given of a field experiment from winter through fall in which excess artificial food was provided in some areas with Peromyscus maniculatus, but not in others. Population size and production of young increases, and adult but not juvenile survival improves slightly with additional food; hence the hypothesis that no differences in breeding and survival would exist between experimental and control areas is rejected in part. The numbers of adult males in experimental and control situations are similar, suggesting that the male portion of the breeding population may, as hypothesized by Sadleir (1965) and Healey (1967), be held relatively constant during breeding by behavioral mechanisms. Attention is drawn to the different numerical responses of males and females, and the possibility of different regulating mechanisms for the sexes.