Hi all: Since I seem to be getting a variety of questions concerning the aforementioned Rose-breasted Grosbeak, I thought that I'd expand a bit on the topic.
First off, there are grosbeaks and then there are grosbeaks. Recall that some bird species called "grosbeak" are cardinals, that is, are members of the family Cardinalidae, and these include Rose-breasted, Black-headed, and Blue (among others). Other beasts called "grosbeak" are finches (Fringillidae), including Pine and Evening. All ABA-area grosbeak members of the Cardinalidae exhibit delayed plumage maturation (DPM) -- that is, they do not attain definitive (read, adult) plumage in their first fall. This character is true of most of the cardinalids, except (of course, just to be annoying) the cardinals (Northern Cardinal and Pyrrhuloxia). So, the grosbeaks and the buntings in that family (also recall that there are other species called "bunting" that are NOT cardinalids -- e.g., Lark and Snow buntings) all exhibit DPM. The ABA-area Fringillid grosbeaks are split, with Pine Grosbeak exhibiting DPM and Evening Grosbeak not. Thus, first-year male Evening Grosbeaks look virtually like adult male Evening Grosbeaks (there are very minor differences that can be used with a bird in the hand, but which are difficult or impossible to use on birds not being handled). Now, here's where things get a bit tricky. The cardinalid grosbeaks have two molts per year -- a pre-basic molt and a pre-alternate molt (the related buntings are even trickier, having 2-3 molts per year), while the finch grosbeaks go through only one molt (pre-basic) every year. This enables young male cardinalid grosbeaks to start bringing in adult-like plumage in their first spring (when roughly 9-11 months old) during their first pre-alternate molt -- this explains the partly-blue, partly-brown buntings one sees in spring and early summer. Conversely, since the finch grosbeaks don't have a pre-alternate molt, they, obviously, cannot start looking adult-like until their second fall (when roughly 14-16 months old) and conducting their second pre-basic molt. Both cardinalid and Pine grosbeaks have immature males becoming adults -- achieving definitive plumage -- after completing their second pre-basic molt in their second fall: cardinalid grosbeaks conduct the transition in two molts, finch grosbeaks in one molt. Remember that male Evening Grosbeaks always look like male Evening Grosbeaks. One of my recent In The Scope columns (in Colorado Birds, the journal of the CFO) dealt with molt and plumage and is a good primer on the subject. However, if you really want to dig into the subject -- and birders really ought to, as it impinges on ability to correctly ID birds in very many situations -- then the two-part Identification Guide to North American Birds (by Peter Pyle) is the reference par excellence. Enjoy, Tony Leukering Villas, NJ -- You received this message because you are subscribed to the Google Groups "Colorado Birds" group. To post to this group, send email to cobi...@googlegroups.com. To unsubscribe from this group, send email to cobirds+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/cobirds?hl=en.
