Introduced predators are a leading threat to seabird populations world-wide and cats (Felis catus) have probably had the most universally damaging effect (Moors & Atkinson, 1984). Eradication of feral cat populations from seabird colonies is a conservation priority (Tershy et al., 2002) and there are many studies that demonstrate the benefits of these actions for seabirds (e.g. Forsell, 1982; Cooper et al., 1995). However, detailed estimates of the effects of cat predation on seabird population viability are lacking in spite of the fact that such data could provide important support for land managers attempting to promote eradication programmes for seabird restoration.