Thursday, July 12, 2012
Wrentits in northern Willamette Valley
This spring and summer there have been several scattered reports of Wrentits in NW Oregon outside their historic range. Could the sightings and heard-only reports be correct? Possibly. On the other hand some might just be weather balloons.
Reports have come from North Portland, Sauvie Island Wildlife Management Area, Hagg Lake, and Tualatin River National Wildlife Refuge. Thus far, all these reports from well-birded areas are unverified--descriptions are incomplete and others can't find them the same or next day. That's a problem for me. I'll tell you why.
Wrentits are sedentary to the extreme. Their home ranges are a tiny 2-1/2 acres--a few hundred feet across. Pairs of birds mate for life and are never far apart (Terres, 1980. The Audubon Encyclopedia of North American Birds). Both sexes sing throughout the year--a very loud and unique bouncing ball whistled trill. On the rare occasions when birds have been found pioneering new areas they are rather easily and repeatably detected.
The range of Wrentit in Oregon hasn't changed all that much in 200 years. Historically, they were found along the immediate coastline in salal bushes under the scrubby shore (lodgepole) pine, from California to the Columbia River. They have never crossed the Columbia into the state of Washington, even though regular on the Oregon side of the mouth of the river. In winter they sometimes can be found a few miles inland into clearcuts. They also occur in the SW area of the state near Medford in low-elevation chaparral of the Rogue Valley, and in low numbers into the Klamath Basin.
Recently (the past 50 years or so), their inland population has inched northward through the Umpqua Valley to the eastern edges of the southern Willamette Valley in Lane County. A population has also crawled northward on the western edge of the Willamette Valley, from Finely NWR near Corvallis in the 1970's to Grand Ronde of Yamhill County.
There are three known isolated outposts north and east of this range. Birds were detected in the late 1990's near Lebanon. Birds this century colonized the Sandy River delta near Gresham. Birds recently arrived at Minto Browns Island Park in Salem. Especially is this last location hard to fathom. Birds either hopped across miles of city streets or somehow crossed the Willamette River. This from a species that refuses to come out of cover and is loathe to cross a single lane dirt road!
Of course, birds had to get to these new outposts by crossing miles of unsuitable and even dangerous (for a Wrentit) habitat. Thus it is possible that some of this year's out-of-range reports may be correct. I take comfort in my present skepticism, knowing that if birds really are present at these new locations they won't stay undetected for long.