Aboveground Activity of Merriam's Kangaroo Rats (Dipodomys Merriami) in Relation To Sex and Reproduction

Sixty-seven male and female Merriam's kangaroo rats (Dipodomys merriami) were radio-tracked over four study periods between November 1980 and mid-March 1984 on two study sites near Palm Desert, Riverside County, California. Animals were located once per hour yielding data representing 10,996 animal hours and 1232 animal days. The reproductive condition of animals during the tracking periods was also monitored. This paper describes the general surface activity patterns of D. merriami in terms of the mean distance moved in meters between successive hourly fixes (called MHD) with particular emphasis on movements in relation to sex and reproductive condition. It was found that during non-breeding periods (study periods 1 and 3), males and females exhibited similar surface movement patterns, although during period 1, between-male variance was significantly greater than between-female variance. During the breeding season (study period 2), however, males moved significantly more from one hour to the next than did females, and again between-male variance was significantly greater than between-female variance. Movements were also found to be related to reproductive condition in both females and males. During study period 2, females that were estrous, pregnant, or lactating moved signficantly more than when they were nonreproductive. One female in study period 2 and two females in study period 4 moved their day burrows over exceptional distances precisely at the time of estrus. In study period 3, there was a significant positive correlation between testis length in males and surface movements. These results indicate that surface activity by D. merriami reflects different behavioral strategies by individuals in relation to sex and reproduction; and that analyses which attempt to balance the costs of surface activity must consider the social functions of such activity and not simply the foraging returns.