Interestingly, a recent thread on the Oklahoma Listserve made mention of
Bewick's Wren advancement and retreat in areas to the east of that state.
The discussion was related to the cold weather that they had been having,
the heavy ice storms, and the weather's effect on the populations of
Carolina Wrens. It seems that when there is an extreme die-back of Carolina
Wrens after an extreme winter weather year, the Bewick's Wrens tend to be
the first to make the move into the vacated habitat of the Carolina Wrens in
the range that was clobbered by the extreme cold and ice. This only happens
when there is an extremely high mortality rate of the Carolina Wrens and
their territories remain open for a lengthy time. Once the Carolina Wrens
make a recovery, the Bewick's Wren retreat again until the next major
kill-off.
If this information is indeed factual, then to me it brings up an interested
hypothesis for a contribution to the loss of Bewick's Wrens in the east. I
haven't had to time to look at the historical data for the last century but
to my understanding the early part of the 20th century had far colder
winters that the later half did; we all know that the last 25 years were
especially mild. Not only would this have affected the Piedmont with more
extensive outbreaks of deep cold and ice, but the Appalachians would have
had winters even colder still. If the Carolina Wren population was a
benefactor of increasingly warm winters by expanding their range and range
density with fewer and fewer die-off years, and their impact on the
populations of Bewick's Wrens are as described on the Oklahoma Bird
Listserve, this could have been one of the causes for this species' retreat
from the east.
It's funny that this topic just came up on MDOSPREY because after reading
this thread on the OK List, I had this very discussion with Jim Stasz and
Bill Hubick on Sunday while we were out birding on the eastern shore. I have
no supporting data on this since I have not had the time to even brush the
surface of investigating winter weather data from the last 100 years, nor
the status of Carolina Wren populations during this same period. If someone
does have the time and resources to investigate this scenario, I sure would
like to know the results of their investigation.
Regards,
Ed Boyd
----- Original Message -----
From: "Pfaffko, Mary (DDOE)" <>
To: <>
Sent: Tuesday, January 23, 2007 8:16 AM
Subject: [MDOSPREY] What happened to the Bewick's wren?
> Dear Birders,
>
> I am reviewing a status report on Bewick's wren & am seeking thoughts from
> anyone who might have expertise on the status of the wren in MD/DC & the
> reason for it's population decline. While the wren was considered common
> in
> western portions of MD in the 1940s, it has become a rarity.
>
> Has anyone spotted a Bewick's wren in/around DC or eastern portions of MD?
> Any suspicions on the reasons for its decline? I welcome your thoughts if
> you'd like to weigh in.
>
> Here is the history I have so far:
> During the late 1940s, Hampe and Kolb stated that T.b. altus was a summer
> resident & common breeder in western Maryland and that it was rare in the
> eastern part of the state. There were no breeding records for Baltimore-DC
> &
> Eastern Shore & only casual breeders in the Piedmont region near
> Cooksville
> and Millers. By the 1970s, it was rarely reported nesting anywhere but
> western MD from Garrett through Baltimore counties.
>
> The Atlas of breeding birds of Maryland and the District of Columbia shows
> declines in populations of Maryland and DC in the 1960s. By the late
> 1990s,
> Bewick's Wren had disappeared in most places it had once occurred as a
> breeding bird and was now considered a rarity (Robbins and Blom 1996).
> They
> note two possible causes of decline: the coinciding population explosion
> of
> the House Wren in these areas & cold weather in recent years.
>
> Thanks!
> Mary
>
> Mary Pfaffko
> Wildlife Biologist
> Fisheries & Wildlife Division
> DC Department of the Environment
> 51 N St., NE, 5th floor
> Washington, DC 20002
> 202.535.1739
> |