I've just read an interesting draft document by D.A. James and A.R.
Green on the eastern form(s) of Bewick's wren. This used to be a pretty
common bird in our region, but its numbers dived in the mid-20th
century. The last verified nest in Ohio was in Adams Co in 1995; the
last accepted sighting came from Pike Co. in 1998. Now this eastern
population is being considered for Endangered Species status, and this
document is a step along the way to application.
        Bewick's wren maintains healthy populations in the west, but in the
east ours (of the two subspecies Thryomanes bewickii bewickii and T.b.
altus) are disappearing. "A Status Assessment Investigation of the
Eastern Subspecies of Bewick's Wren" looks at trends in 35 eastern
states for these birds.
        The steep decline of Bewick's wren in the east is easy enough to
document. The reasons are harder to define: this paper discusses habitat
change, competition with certain other species, climate change, cowbird
parasitism, etc. as possible factors. Lots of interesting expert
opinions are brought to bear, some of them at variance with one another.
The authors do a commendable job of research. They agree with some
authorities that the two accepted subspecies of Bewick's are really only
one, and that all the more rufous birds of the east, extending from
Texas plains to Appalachian mountain habitats, are one and the same. One
interesting reason they adduce is that the extensive use of coal for
heating in the East stained and darkened the feathers of birds so much
that they were reckoned to be a different subspecies (altus); this seems
to be confirmed by museum curators, who find that many of their
specimens from the era are remarkably dirty.
        Other interesting aspects of the research involve the habitats of our
local form, which seemed to be dominated by rural sites with discarded
automobiles, deteriorating outbuildings, and trash-piles, which Bewick's
wrens found convenient for nesting and roosting. Such habitats have a
fairly brief history in Ohio: Audubon did not see a Bewick's during his
stay in Cincinnati over two hundred years ago, but with the clearing of
land and subsequent failure of small farmsteads across the state a
hundred years later, Bewick's wrens reached their peak in population.
Since then, the return to forest in many of these sites, as well as
cleaner agriculture, suburbanization, etc. have not been so inviting to
Bewick's.
        Competition with other species, especially the house wren, whose
nesting range expanded south during the last century, is widely cited as
a reason for Bewick's decline, but in the aggregate the evidence is not
so clear. Many studies are described, and many contradict one another.
The situation resembles that for some other birds that have disappeared
from Ohio--Bachman's sparrow is a good example--in that the precise
reason for their endangerment is unclear, and just as unclear is what we
might to do reverse it.
        I can't find this interesting and quite readable document on the Web,
but I can send it to interested persons on request (it's an 118-page
pdf, 2.5 MB).
Bill Whan
Columbus


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