Trap-Response Heterogeneity of House Mice (Mus musculus) in Outdoor Enclosures

Abstract

We studied extrinsic and intrinsic factors affecting trap-response heterogeneity in house mice ( Mus musculus ) in eight 0.1-ha outdoor enclosures. Changes in density did not significantly affect proportions of mice captured. Overall, greater proportions of males than females were captured. Adults were captured more often than subadults, and subadults were captured more often than juveniles. Extrinsic factors including relative humidity, temperature, and decreased vegetative cover affected proportions of mice captured for various age and sex classes. Two measures of individual trap-response heterogeneity were used: percentage of times an individual could have been captured that it actually was and mean number of trap sessions between captures. Significant yearly variation occurred in both measures. Trap response heterogeneity among sexes did not emerge until the mice were subadults or adults. There was significant yearly variation in proportions of recruits entering traps as juveniles, subadults, or both. Our findings indicate that there is substantial intrinsic heterogeneity, modified by external factors, in capture rates of the house mouse. Data collected to assess population size, survival rates, home range, and other life-history characteristics collected by live trapping warrant cautious interpretation.