[CT Birds] sharp-tailed sparrow (longish)
elphick at sbcglobal.net
Fri Feb 8 21:45:32 EST 2013
Sorry to chime in so late on this issue - it's been a busy week and like Dave, it seems my kids are on the computer doing homework (really!) constantly. I wrote Bill about the sharp-tailed sparrow pictures he took at East River this morning and he asked if I would post those comments to the list. Now that I've found some time to catch up on what has been written by others, I've added a couple of additional things to that original message:
First, I should say that the East River marsh is, I think, the best place in CT to watch
tidal marsh sparrows without getting into the marsh itself. So, if you want to study them, it's the place to go.
Regarding the mystery bird, I have
emailed with a PhD student in my lab who studies sparrows on the wintering grounds. She is probably the only active researcher who has
daily experience, both of birds in the field and in the hand, with saltmarsh
sparrow during summer, fall migration, and winter. At her winter study sites she
routinely catches sharp-taileds that fit all five described subspecies, plus a couple of
subspp of seasides - when I was down there last winter, we had all 7 in one morning! She handles many 100s of sharp-tailed sparrows a year.
Her immediate reaction was much like Mark's and mine - that if it's a saltmarsh,
it's a strange one. It's clearly not a typical subvirgatus Nelson's either. And, I don't think
it's a classic nelsonii (though I am much less familiar with that subspecies). But
there's a lot of variation within interior Nelson's, there also is considerable within-population variation across the year due to feather wear, and, of course, there's the issue of
hybirds (more on this below).
Having seen the additional photos, I can see that there is a
stronger argument for saltmarsh than initially, but in my view it is far from
airtight. Even if the additional photos look good for saltmarsh, and we can
find ways to explain away the apparent plumage discrepancies in the first photo,
one still needs to explain the small bill. Perhaps it's a camera angle issue,
but perhaps not. Bill size does overlap, but it's limited overlap and in my experience when handling birds
in CT, Nelson's always jump out and it's generally the bill that I notice first.
The real problem I see is that (in my view) none of us has a really good handle on
the plumage variation within species and within the hybrids - and that variation can only
be assessed by studying them on the breeding grounds and/or by studying birds for
which genetics confirm the origin. Consequently, there's nothing to be done
with birds that do not fit nicely into either group except speculate.
Personally, I lean towards caution in IDs and would just call this a
"sharp-tailed" sparrow and move on.
All is not completely lost. Along
with collaborators in ME, NH, DE and SC we have begun to try to get a handle on
the variation. We systematically photograph all of the birds we capture, score
their plumage, take a detailed set of measurements (especially of the bill), and
also a DNA sample. Our colleagues in other states do the same, so that between us we have
all this information for birds across the range of saltmarsh sparrow and across
the hybrid zone. A PhD student at the University of New Hampshire has
been studying population genetics and hybridization in these birds and can use this information to determine which birds are hybrids. By bringing together the genetics with the photos, plumage scores, and measurements we hope to be able to say just how variable the
hybrids can be, and put some limits on which birds can be reliably
There is a legitimate concern about invoking the "hybrid option" whenever a hard-to-identify bird appears, and in many cases that concern is especially valid. A lot of odd-looking individuals are just the result of natural variation within species (just look at me!). But, hybrids in sharp-tailed sparrows are not at all uncommon. The hybrid zone extends from Mass up into Maine, and at least in some areas a sizable proportion of the population appear to be hybrids. Breeding birds with Nelson's genes have been found as far south as Rhode Island. Given that the entire world population of saltmarsh sparrows is (we think) only a few 10,000 individuals, the fact that there are almost certainly 100s of hybrids means that the odds of seeing one is quite high.
So, a long-winded and inconclusive answer to a simple question. But hopefully
elphick at sbcglobal.net
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