[CT Birds] Tennesse Warbler questions
ghanisek at rep-am.com
Fri Aug 16 22:05:15 EDT 2013
A few people have asked me about the juv. Tennessee Warbler I saw today, regarding both seasonal timing and ID.
First, once we hit mid-August a fairly wide range of passerine migrants begin to arrive, but it's not the easiest time to find them. They're not singing and many are juveniles (more about that later). Regarding Tenn Warblers specifically, mid-Aug is well wihin their expected southbound schedule, which is quite protracted and extends into Oct. Conn has a banding record from Aug. 14 (Zeranski & Baptist), and CT and surrounding states all have sight records in the first 10 days of the month. At Cape May, NJ, where fall migrants can accumulate in amazing numbers, there's a record of 120 Tenn Warblers on an Aug 19 date in 1980s.
ID: This species is a poster bird for the Confusing Fall Warbler category created by Roger Tory Peterson in his classic field guides. (As an aside, that photo plate heading alone has probably scared off many beginning birders from tackling this group). So why was I confident in my ID? The most important point is that the bird gave me an excellent look in good light, feeding rather low in scrubby growth. On first glance a juvenile Tenn Warbler is about as devoid of notable markings as a warbler can get (lacking the gray head of an adult), although it is a rather bright greensih-yellow overall that catches the eye. The first thing to do is use the minimal markings to your advantage. The fact that the bird lacks streaks of any kind eliminates a large percentage of expected warblers (although it doesn't rule out vireos). The first thing to do here is make sure it's not a vireo, with Philadelphia/Warbling the species closest in appearance. A good place to start is the bill, since vireos have stouter bills than warblers. Fortunately Tenn Warblers have very small, thin bills even by warbler standards, and this bird had a nice little bill. Another structural clue, which the bird cooperatively showed, is the very short tail of the Tennesse, proportionally shorter than most warblers and all local vireos. This one made it even easier by feeding for a short time next to a juv Red-eyed Vireo, which was obviously bigger. There were also plumage details of importance, such as very weak wingbars, a pale supercillium, dusky eyeline and white undertail coverts. The latter eliminates the most similar species, Orange-crowned Warber, which is also seasonally unexpected in Aug. Tenn might have some yellow tinge to the undertail, but that's always the whitest part of the underparts; on Orange-crowned it's always the yellowest. The juv Tenn's facial markings can be pretty indistinct and require good looks. Yellow Warblers can be remarkably drab and confusing, but they should usually show yellow undertail coverts, a plain face without a supercillium and a stouter bill and longer tail. Juv Nashvilles are close in size and can also be quite plain, but they too have yellow undertails.
It's also worth noting that in spring Tenn Warblers are usually singing hidden high among the leaves of deciduous trees, but in fall it's not unusual for them to be feeding in lower scrubby growth and even weedy fields.
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