Titi (sooty shearwaters) on Whero Island: Analysis of historic data using modern techniques

A reanalysis of titi (sooty shearwater, Puffinus griseus) banding data collected between 1940 and 1957 by Lance Richdale demonstrates that well-documented archival material can be usefully reanalyzed using newly developed statistical techniques. In this study, we compare the results obtained by Richdale using empirical techniques to those obtained using a multistate mark-recapture model. Although the two approaches produce similar estimates for some of the parameters, the multistate model additionally provides estimates of precision and can be used to answer biologically significant questions not raised by the original worker. Our analysis provides some evidence for two conclusions that Richdale put forward but could not justify rigorously: (a) nonbreeders have a lower survival rate than breeders, although the difference is not statistically significantly; and (b) nonbreeders are more difficult to capture than breeders. We argue that reanalysis should be carried out more frequently on historical data and lament the fact that it can be rare for such data to be made available for future scrutiny.