Apparent survival of adult magnificent frigatebirds in the breeding colony of Isla Isabel, Mexico

Abstract

Annual apparent survival rates of the Magnificent Frigatebird (Fregata magnificens) were estimated from 1998 to 2003 using a capture-resight model with 870 marked adult birds on Isla Isabel, México (21°51′N, 105°54′W). The most parsimonious model was a time since marking model (or two age class model) with constant resighting rate for males and females (pm and pf), constant apparent survival rate for males in both age classes (φ1m and φ2+m), and time-dependent apparent survival rate for females (φ1f and φ2+f) in both age classes. We found higher resighting rates in males than in females, a tendency of higher apparent survival in females than in males in 1999, a clear higher apparent survival rates in females than in males in 2000, nearest the same apparent survival rates of the two age classes of males throughout, and differences in apparent survival between age classes of females showing considerable annual variation within age classes. The results suggest permanent emigration of females from the breeding colony, whereas males showed site fidelity.