I am also very interested in identifying and describing molt (=feather loss and replacement) limit patterns which can be used to determine the age of tropical birds. Studies in the north-temperate region (where most work to date has been done; Pyle 1997, Svensson and Hedenström 1999, Howell et al. 2003) indicate that many passerine (landbird) species undergo predictable molting "strategies" (defined as patterns of plumage succession, timing, feather replacement order, and extent in individual molts). The "stereotypical" passerine will undergo a limited (=few body feathers), partial (=most to all body feathers), or incomplete (=most/all body feathers plus some, but not all, flight feathers) molt within a few months of fledging, known as the preformative molt (Howell et al. 2003). Subsequent annual definitive (post-breeding) molts are essentially complete, with all body and flight feathers replaced. Of course, there are many exceptions, but the typical molt cycles and extents have been determined for most resident and migratory species in North America and Europe (Jenni and Winkler 1994, Pyle 1997).

This pattern results in predictable molt-limits (boundaries between retained and replaced feathers) in young birds who have not yet completed their first definitive molt, which can be used in combination with presence of "tapered" remiges and rectrices to age individuals to the hatching-year/second-year age class (before/after January 1, respectively; Pyle 1997). After-hatching-year birds grow "truncate" flight feathers and undergo complete pre-basic molts following breeding, and can thus be assigned to the after-hatching-year/after-second-year age class based upon absence of molt-limits (Pyle 1997).

However, tropical molt research to date is scarce (see reviews in Pyle et al. 2004 and Pyle 2006). Until recently, tropical molts were considered to be protracted seasonally with highly variable timing and extents (making age determination difficult), due to the lengthy breeding season, small photoperiod oscillations, limited seasonality, and lack of extended migrations (Stutchbury and Morton 2001, Wikelski et al. 2003, Pyle et al. 2004, Barta et al. 2006). However, Pyle (2006) found that 85% of tropical landbirds studied (N=201) undergo definitive pre-basic molt between June and September following strategies similar to north-temperate species, making age determinations possible in the tropics. However, this conclusion is based upon a limited sample size drawn primarily from dry and seasonal habitats, e.g., Cuban thorn-scrub (Pyle et al. 2004). Observations on wet-forest species are urgently needed in order to develop generalizable guidelines.

I am collaborating with Peter Pyle and other Neotropical banders to resolve outstanding questions regarding the timing, extent, and replacement pattern of tropical molts. I am collecting extended-wing photographs, like those shown here, of many species of tropical birds to contribute to a proposed online database documenting molt patterns in tropical birds.


Literature Cited
Barta, Z., A.I. Houston, J.M. McNamara, R.K. Welham, A. Hedenström,
     T.P. Weber, and O. Feró. 2006. Annual routines of non-migratory
     birds: optimal moult strategies. Oikos 112:580-593.
Howell, S.N.G., C. Corben, P. Pyle, and D.I. Rogers. 2003. The first basic
     problem: a review of molt and plumage homologies. The Condor
     105:635-653.
Jenni, L., and R. Winkler. 1994. Moult and ageing of European
     Passerines. Academic Press, London.
Pyle, P. 1997. Identification Guide to North American Birds, Part I. Slate
     Creek Press, Bolinas, CA.
Pyle, P. 2006. Molt strategies and age determination in Neotropical
     landbirds. In: Conference Abstracts, IV North American
     Ornithological Conference; October 3-7, 2006; Veracruz, Mexico.
Pyle, P., A. McAndrews, P. Veléz, R.L. Wilkerson, R.B. Siegel, and D.F.
     DeSante. 2004. Molt patterns and age and sex determination of
     selected southeastern Cuban landbirds. Journal of Field Ornithology
     75:136-145.
Stutchbury, B.J.M., and E.S. Morton. 2001. Behavioral ecology of tropical
     birds. Academic Press, San Diego, CA.
Svensson, E., and A. Hedenström. 1999. A phylogenetic analysis of
     moult strategies in Western Palearctic warblers (Aves: Sylviidae).
     Biological Journal of the Linnean Society 67:263-276.
Wikelski, M., M. Hau, W.D. Robinson, and J.C. Wingfield. 2003.
     Reproductive seasonality of seven Neotropical passerine species.
      The Condor 105:683-695.