Annual apparent survival rates from 323 marked immature Magnificent Frigatebirds (Fregata magnificens) were estimated using mark-recapture models for live encounter data in a six-year study (1998–2003) at Isla Isabel, the largest breeding colony in Western Mexico. A time and age immature apparent survival pattern was found: high and variable as yearling-juveniles (mean 1998–2000 = 9.78 ± 0.22) and, later, moderate and constant as juvenile-subadults and subadults (mean = 0.62 ± 0.11). Whereas resighting rate (p) increased with time (range = 0.00 [± 0.04] – 0.87 [± 0.11]). The results suggest variation in true survival and emigration during the juvenile life phase, high true survival and high site fidelity of juvenile-subadults and subadults during the interval after marking, and constant and either low true survival or high emigration in the subsequent intervals. Frigatebird apparent survival was predominantly higher in yearling juveniles than in subsequent age classes, an uncommon occurrence in other seabirds but likely with important demographic implications for species with long post-parental care and delayed maturity.
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Vol. 33 • No. 4