We used Cormack–Jolly–Seber capture–recapture analyses to investigate differences in monthly survival of the southeastern beach mouse (Peromyscus polionotus niveiventris) between sexes, between juveniles and adults, and effects due to the presence of transients that can bias survival estimates. We accounted for transients (e.g., nonresidents) by distinguishing survival for the initial month after an individuals' 1st capture from monthly survival after the 1st recapture. Survival estimates for 1st captures and recaptures of females were 0.70 and 0.78, respectively. Survival estimates for 1st captures and recaptures of males were 0.74 and 0.80, respectively. Our results showed that a comparably small proportion of transients (females = 0.10; males = 0.08) can bias survival estimates.