From south-bay-birds-bounces+south-bay-birds-archive=[[email protected]] Fri Nov 1 12:13:00 2002 Received: from www.plaidworks.com (localhost [127.0.0.1]) by plaidworks.com (8.12.2/8.12.2) with ESMTP id gA1K8d7r002403 for <[[email protected]]>; Fri, 1 Nov 2002 12:08:39 -0800 (PST) Received: from falcon.mail.pas.earthlink.net (falcon.mail.pas.earthlink.net [207.217.120.74]) by plaidworks.com (8.12.2/8.12.2) with ESMTP id gA1K7Ake002319 for <[[email protected]]>; Fri, 1 Nov 2002 12:07:10 -0800 (PST) Received: from pool0375.cvx22-bradley.dialup.earthlink.net ([209.179.199.120] helo=earthlink.net) by falcon.mail.pas.earthlink.net with esmtp (Exim 3.33 #1) id 187i4S-00043c-00 for [[email protected]]; Fri, 01 Nov 2002 12:07:09 -0800 Message-ID: <[[email protected]]> Date: Fri, 01 Nov 2002 12:08:19 -0800 From: Rosalie Lefkowitz <[[email protected]]> X-Mailer: Mozilla 4.79 (Macintosh; U; PPC) X-Accept-Language: en MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Subject: [SBB] Some more stuff on White-throated Sparrows X-BeenThere: [[email protected]] X-Mailman-Version: 2.1b4+ Precedence: list Cc: South Bay Birding <[[email protected]]> List-Unsubscribe: , List-Id: South Bay Birding List-Post: List-Help: List-Subscribe: , To: [[email protected]] Sender: south-bay-birds-bounces+south-bay-birds-archive=[[email protected]] Errors-To: south-bay-birds-bounces+south-bay-birds-archive=[[email protected]] Hello everyone, I just found this piece dated Oct. 9,1995, but don't know where it came from. I suspect it was someone on the SBB list, but apparently not Bill Bousman. However, I think it's very interesting and worth passing on. Rosalie Lefkowitz The dimorphism in crown color in WTSP results from the presence of a chromosomal inversion (a certain chromosome can have one arm in either of two configurations). In individuals with the arm in one configuration, brown pigment is added to the pale areas on the crown, producing a tan-striped bird; in individuals with the arm in the other configuration, no pigment is added. There is no intermediate configuration, so pigment is either added or not. Studies show that 90% of matings of WTSP are between white-striped and tan-striped birds, the offspring having one crown type or the other once they reach their first nuptial plumage. According to Bent, juveniles usually molt into their first-winter plumage by September, so on the wintering grounds and in fall migration (when we see them), they look similar to adults but sometimes duller, often (but not always) with more vague brownish streaking on the underparts. In this first-basic plumage, the pale supercilium is usually "light tan" on all immatures, and only a small percentage of immatures (11 of 209 that Bent examined) have a white median crown stripe during winter, the rest having an "olive gray buff-tinged" median crown stripe. In spring, the immatures acquire their adult head patterns. Bent also says that although some white-striped adults retain the white head stripes during winter, most white-striped adults have a buffy tinge to these areas until new white feathers are acquired in spring. Other plumage characters may be of some help in determining whether an adult is white- or tan-striped. White-striped birds are "generally brighter colored and less streaked; they have more black on the lateral crown areas [rather than dark brown], less streaking on a wider and grayer chest band, less intense black on the malar markings of the white throat patch, and brighter yellow on the superciliary stripe." Of course, in applying these characters to a bird, one must first determine whether the bird is an adult or an immature (which may be difficult or impossible to do with 100% accuracy); if the bird has vague streaking below and tan crown stripes, is it a tan-striped adult, a tan-striped imm., or a white-striped imm.? Conclusions: if a bird has pure white head stripes and/or bright plumage with no streaking below, it is a white-striped bird. If a bird has tan or buff head stripes and is dull with some vague streaking below (and it is not spring or summer), it might be of either morph. _______________________________________________ Do not post admin requests to the list. They will be ignored. south-bay-birds mailing list ([[email protected]]) Help/Unsubscribe/Update your Subscription: http://www.plaidworks.com/mailman/options/south-bay-birds/south-bay-birds-archive%40plaidworks.com This email sent to [[email protected]]