[EBB Sightings] Townsend's Warbler fledgling

Hi All,

I have a few thoughts on Judi Sierra's Townsend's Warbler.

1. I don't have any experience with young ToWa, but a fledgling that is
barely able to fly ought to show some traces of down, especially around
the head and vent, as well as a gape and stubby bill.  Any signs of
parents? Birds often have distinctive juvenile calls that differ from the
usual begging notes - anything heard?

2. Some birds are well known to occasionally breed well outside of their
normal range.  I've seen this mentioned a lot in European field guides,
particularly for the UK, which may be an effect of a more widespread
tradition of birding there.  This has also happened with waterbirds in
Hawai'i, such as Pied-billed Grebe (which even established a breeding
population) and Blue-winged Teal, which are normally just winter visitors.

3.  Does anyone know of sporadic breeding within the wintering range for
migratory passerines? A number of irruptives will stay to nest well south
of their normal range, but how about regular migrants? This may be how
disjunct populations form or it may just be an aberration that is not
repeated.

4.  My feeling is that one needs to be cautious about this report.  It
would be most unusual if it were correct, but unusual things do happen.  I
find the early date most troublesome, but if they were to have an odd
nesting down here, it may be timed for the local insect abundance, not the
calendar. But it still seems early to me. I think that if they did nest
here, it's highly unlikely to result in a new population, but that pair
just might do it again next year, so keep vigilant!

good birding,

Jaan Lepson
Livermore


On Wed, April 15, 2009 12:16 pm, Steve Glover wrote:

> Hi all,
> I would just like to add a few words of caution about the possibility of
> the bird in question being a fledgling Townsend's Warbler.
> First, while the species does nest in the Pacific Northwest, it isn't
> known to do so any closer than about central Oregon.
> Second, the Birds of North America lists the earliest egg date for the
> species as 24 May and young not expected until mid-June.
> As Phila correctly pointed out, many birds have expanded their breeding
> range to now include the East Bay. A partial list would include
> Red-shouldered Hawk, California Gull, Least Tern, Olive-sided Flycatcher,
> Chestnut-backed Chickadee, Pygmy Nuthatch, Northern Mockingbird,
> Dark-eyed Junco, Great-tailed Grackle, and Hooded Oriole. I think an
> important thing to remember, however, is that none of those species
> appeared suddenly and expanded their breeding range 500 or so miles in
> one fell swoop. Even with far fewer birders out and about, the spread of
> the species that apparently began to breed in the East Bay (or Northern
> California in general) during the 20th Century was well documented. First
> they reached this area, then they reached this area, etc. If the
> Townsend's warbler was expanding it's range down the coast I would expect
> that at least the very active Humboldt birding community would have begun
> to report them during the summer.
> Finally, and I have first-hand experience with this, adult birds can look
> like very much like fledglings, particularly when they are wet or cold.
> I think the most significant point to be made in a case like this is that
> the nesting of Townsend's Warbler in California would be an event that
> demands strong documentation. When I say "demands" I don't mean to say
> that Judi should feel compelled to go back out and obtain photos if she
> doesn't have the desire to do so. What it does mean is that for this to
> be of any use to future researchers there needs to be more.
> I hope this is taken in the spirit it was intended!
> Good birding,
> Steve Glover
> Dublin
> --- On Wed, 4/15/09, Phila Rogers  wrote:
>> From: Phila Rogers 
>> Subject: [EBB Sightings] Townsend's Warbler fledgling
>> To: "audubon mt.diablo" 
>> Date: Wednesday, April 15, 2009, 11:17 AM
>> Dear Birders:
>>
>>
>> I think Judi Sierra's posting this morning about seeing
>> a Townsend's Warbler fledgling along the lower fire trail in Strawberry
>> Canyon is entirely credible.  Judi is an
>> excellent birder and the cool mixed conifer forest on the north-facing
>> slope is a suitable nesting habitat for this species which usually
>> breeds further north along the coast in conifer forests.  It's important
>> to remember that once juncoes and chickadees (and probably certain
>> nuthatches) were only winter residents in the Canyon.  Birds commonly
>> expand their ranges (re:  Red-shouldered Hawks).
>>
>> This rich Strawberry Canyon habitat is another the reason
>> for opposing the proposed construction of two industrial-scale buildings
>> (totaling more than 200,000 sq.
>> ft) in the canyon!
>>
>> -Phila Rogers
>>
>>
>>
>>
>>
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-- 
Jaan Lepson

University of California
Space Sciences Laboratory
7 Gauss Way
Berkeley, CA 94720-7451