Tracking tubes offer an efficient alternative to live-trapping for studies that require very large sample sizes. However, it is necessary to know how small mammals change in their tendency to enter tracking tubes with time. We measured this change in response in a region of boreal forest in northern Nova Scotia, Canada, in 1994–1998. Over 4 weeks, small mammals increased in their tendency to enter tubes, with no difference in response among species. Thus, when designing studies using tracking tubes, one needs to adjust for differences in duration—one cannot simply calculate a tracks/tube-night measure. We show how to statistically remove the effect of duration.