MOLT PATTERNS, BIOMETRICS, AND AGE AND GENDER CLASSIFICATION OF LANDBIRDS ON SAIPAN, NORTHERN MARIANA ISLANDS

摘要

Molt strategies and plumage development by age and gender are poorly understood for resident tropical landbirds. We used data from six banding stations on Saipan, Northern Mariana Islands, and examination of 267 museum specimens to describe patterns of molt and to establish criteria for assessing age and gender of nine native resident landbird species on the island. Feather replacement sequences in the majority of Saipan's resident landbirds were typical of related species. Preformative molts occurred in at least eight of the nine species; these and definitive prebasic molts were incomplete to complete, and prealternate molt appeared to be absent for all species. We developed criteria for classifying gender of sexually dimorphic species using plumage cues, presence of brood patch or cloacal protuberance, and biometrics. We confirmed whether or not both brood patch and cloacal protuberance were reliable indicators of gender during breeding in monomorphic species. Distinct periods or seasons of molt are not well defined and can vary between years. Age classification of first-cycle birds based on molt limits, feather shape and condition, and extent of skull pneumatization is possible for most landbird species sampled on Saipan.