Molt limits, counting primaries and more

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Posted by Don Roberson ( on March 05, 2000 at 23:39:25:

Rather than giving an "off the cuff" answer on the bluebird, the photo was so great that I decided to try using Pyle's 1997 banding guide. It separates female bluebirds mostly on size, weight, and tail length, none of which are useful here. However, it also explains how to age female bluebirds -- look for the presence or absence of molt limits in the greater coverts. The quiz bird has obvious molt limits -- worn dusky outer greater coverts clearly separable from new blue inner greater coverts. Accordingly, this is a HY female (i.e., a bird in its first calendar year). Since it seems to be carrying nesting material, this is presumably its first spring or early summer. Interestingly, work at Hastings Reserve in Monterey Co. has shown that first-year Western Bluebirds are often "helpers" at the nest the next year after they hatch, and this female could be an example (although generally it is young males who are helpers; I've just heard a talk by Janis Dickinson on the exciting stuff coming out of her banding work). In any event, the young age of the bird may account for how pale it looks.

As to counting primaries, I believe there are five (5) beyond the tertials since one rarely sees the shorter outermost primary hidden beneath the longer penultimate one. I do think a five-primary projection is short in bluebirds -- Mt. Bluebird has 8-9 primary projection in photos I've just checked. Ergo, all fits a first-year (HY) female Western Bluebird helping at the nest. I don't know if Eastern Bluebirds help at the nest, but I suspect not given differing ecological strategies, and, in any event, Eastern Bluebird has never been documented in California beyond a couple single-observer records (one which may be good); but they have never been photo'd. The big-eyed look produced by the eyering also looks more like Western/Eastern Bluebirds than a Mountain.

The thrasher is surely a Bendire's. I think the base of the lower mandible IS pale (not a lighting artifact) but, anyway, the bill is much too short for anything but very young Curve-bills. No such young birds have ever been in California, let alone photo'd this well. Indeed, none of California's few vagrant Curve-bills have been photographed this well. This could be one of the wintering Bendire's in n. Calif. (e.g., the Sacramento area bird some years back?) as the tail looks freshly-molted to me, consistent with a bird completing a molt prebasic molt.

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