Hi all: David Leatherman posted the following recently:
"Yesterday I reported seeing what I was thinking was a young-of-the-year Swainson's Hawk out on its own at Crow Valley. ?In the Clark and Wheeler hawk field guide the authors state (photo and caption on page 199 in my second edition) many young birds arriving back on the breeding grounds for their second summer show up with whitish heads. ?After arriving in spring, juveniles then do a complete molt into Basic 1 Plumage. ?A second molt into Definitive Basic Plumage occurs late in summer or fall (sometimes on the wintering grounds). ?The bird I saw was still in Juvenile Plumage and apparently misinterpreted. ?FYI, the CO Breeding Bird Atlas 1 book lists May 29 as the onset of fledging and since everything seems to be getting earlier and earlier, maybe a two-week extension of this phenomenon wasn't that big of a stretch. ?The latter interpretation seems the less likely, although it will be interesting to see what BBA II discovers." I agree that it will be interesting to see what BBAII discovers, but I wanted to expand on David's comments and bring him (and everyone else)?into the current age, plumage terminology-wise. First off, one-year-old Swainson's Hawks should be just arriving in CO from the winter grounds to do their duty of chasing grasshoppers around for the next few months, as they have little else to do (they will not breed this year).? But, also arriving are birds in second basic plumage (birds that are almost two years old).? These two age classes of youngsters and the incredible individual variation inherent in the species make for a bewildering array of plumages.? These birds can look like Rough-legged Hawks, Red-tailed Hawks, and who knows what else, and are the source, I believe, for a host of erroneous reports of the former (I covered this topic in a recent In The Scope column in Colorado Birds). Now, onto new plumage terminology.? Steve Howell (and others) published a paper a few years back on plumage terminology that laid out his rationale for changing accepted plumage terminology.? The rationale was based on his work on gull molt, as he had found that juveniles of various arctic-breeding species (e.g., Thayer's and Iceland) do not conduct a molt in fall/early winter as do most other gull species.? This made for some awkward terminology and to make things not awkward required changing which plumage was the starting plumage for the Humphrey-Parkes plumage-terminology system.? That is because H-P starting plumage was first basic and since those arctic gulls didn't conduct a first pre-basic molt, they didn't have a first basic plumage, so.... Howell et al. suggested changing the starting plumage to what is known as juvenal plumage, the first set of "hard" feathers that birds wear.? Thus, juvenal plumage is now equivalent to first basic plumage (it is the first basic plumage worn by birds).? This change, then, solves all the problems that those arctic-breeding gulls illustrated with the origional HP system and makes things hunky-dory, groovy, and all-around copasetic! But, now we have to rethink things a bit.? So, the just-less-than-one-year-old Swainson's that are just arriving are still (for the most part) in juvenal plumage -- also called first basic plumage.? They will molt while here into second basic plumage, a plumage that is not the definitive basic plumage that adults wear.? They will then migrate south for the winter (probably southern South America, though more and more birds are found wintering farther north, e.g., in Mexico, CA, and s. TX).? Come early spring (northern hemisphere spring), they will begin their return to the breeding grounds still in second basic plumage and will spend the summer on or near the breeding grounds and will conduct another pre-basic molt that will put them into, finally, definitive basic (or adult) plumage. That's it.? For a more thorough treatment of the new plumage (and molt)?terminology, check out the relevant sections in the introductive material in the Howell and Dunn Gulls book or the recently-published Part II of Pyle. Later, Tony Leukering Villas, NJ --~--~---------~--~----~------------~-------~--~----~ Join us at the 2009 Convention in Alamosa: http://cfo-link.org/convention/index.php You received this message because you are subscribed to the Google Groups "Colorado Birds" group. To post to this group, send email to cobirds@googlegroups.com To unsubscribe from this group, send email to cobirds+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.as/group/cobirds?hl=en -~----------~----~----~----~------~----~------~--~---
