Robustness of survival estimates from radio-telemetry studies with uncertain relocation of individuals

Traditional methods of estimating survival from radio-telemetry studies use either the Trent-Rongstad approach (Trent and Rongstad 1974, Heisey and Fuller 1985) or the Kaplan-Meier approach (Kaplan and Meier 1958; Pollock et al. 1989a,b). Both methods appear to require the assumption that relocation probability for animals with a functioning radio is 1. In practice this may not always be reasonable and, in fact, is unnecessary. The number of animals at risk (i.e., risk set) can be modified to account for uncertain relocation of individuals. This involves including only relocated animals in the risk set instead of also including animals not relocated but that were seen later. Simulation results show that estimators and tests for comparing survival curves should be based on this modification.