White-necked Thrush (Turdus albicollis) are found in the understory of second growth and primary forest throughout the Amazon basin. Sexes are indistinguishable by plumage. The preformative molt (FPF) is partial, and definitive prebasic molts (DPBs) are complete. FPF includes less coverts, med coverts, and some inner-greater coverts.
FPF - First PreFormative
First cycle juvenal (FCJ) is characterized by buffy-tipped body feathers that are quickly replaced by feathers lacking buffy tips during a partial preformative (FPF). The partial extent of the FPF results in molt limits within the greater coverts (see FCF below). The picture above shows an individual just beginning the preformative molt where some formative feathers are found in the lesser coverts.
FCF - First Cycle Formative
First cycle formative (FCF) individuals retain several outer-greater coverts that are tipped buff, contrasting with the uniformly olive-brown (lacking buffy tips) inner-greater coverts. Replaced inner greater coverts are often several milimeters longer than retained outer greater coverts resulting in a molt limit "step". Buffy tips can be worn off resulting in a more cryptic molt limit. In addition to a molt limit in the greater coverts, FCF individuals have retained rectrices (outer rectrices noticeably more tapered when compared to DCB birds), primary coverts, and remiges.
DCB - Definitive Cycle Basic
Definitive cycle basic (DCB) birds underwent a complete prebasic molt resulting in uniform plumage of a single generation, with no molt limits in the greater coverts. Outer rectrices are truncate (relative to FCJ and FCF individuals).