Sex and age determination of Creamy-bellied Thrush, Turdus amarochalinus, at Carijós Ecological Station, Santa Catarina, Brazil

Sex and determination using molt and plumage criteria are important tools for population demographic studies. We analyzed and determine the strategy and extension of molt individuals of Turdus amaurochalinus (n=31). According to data, the breeding season starts in September. Males, identified by the cloacal protuberance, exhibited an intensely yellow bill, while females/immatures presented partially yellow bills. The juvenile plumage is characterized by brown-spotted white feathers on the breast and rusty tips to the brown feathers of the head, body, and wing coverts, in addition to an evident gape/brown beak. In January, the preformative molt occurred while other birds were still breeding. Preformative and prebasic molts were characterized by a strong body molt, and prebasic molts also included sequential primary replacement. The preformative plumage was observed between April and September, with molt limits and incomplete skull ossification. Eight birds exhibited partial preformative molts including the replacement of all body feathers, lesser and median coverts, and 4-9 (6.9±2.2) inner greater coverts. Thus, the molt strategy of the species appears to follow the Complex Basic Strategy, consistent with the Turdidae. We found one individual with an eccentric preformative molt, replacing p7-10, along with two outer primary coverts, all alulas, and all secondaries and tertials. To our knowledge, this pattern is not known from other New World Turdus. Understanding the within- and between-population variation in the extent of the preformative molt is critical for developing accurate aging criteria and can reveal insights into the ecological and evolutionary pressures that drive this variation.