Hugh et al,
I always regarded "shrub" birds like green-tailed towhee to be one of the big winners in the aftermath of what ecologists call "disturbance events". When forest overstories are removed by beetle epidemics and fires, birds that like early succession plant communities have the world come their direction. So, yes, I think your assessment of "habitat change" as a major factor in BBS number changes near the Hayman Fire is probably correct. I also think, as Paula suggests, there are seasonal shifts in populations in response to weather issues, food abundance, condition of a particular area when migrants first arrive, etc. The amazing data set that BBS constitutes is invaluable in helping sort out these changes of both a short and long-term nature.
Interestingly and perhaps related, when I helped Nat Warning (now working for State of Maryland DNR) with his very interesting graduate studies of Canyon and Rock Wrens up at Horsetooth Reservoir west of Fort Collins, we found that even when the two species nest in very close proximity, they forage differently. The Canyon Wrens came to the nest with prey that obviously mostly came from rocks and caves (lots of spiders, centipedes and crane flies), the Rock Wrens more often went out in the meadows near the rocks to find the majority of their nestling fare (more moths, flies, grasshoppers and beetles).
Dave Leatherman
Fort Collins
Sent: Monday, July 3, 2017 2:40 PM
To: redstart.paula@gmail.com; cobirds@googlegroups.com
Subject: [cobirds] Re: green-tailed towhees and rock wrens - Jefferson
The Green-tailed towhees sing from fire-tinged hillsides which have some shrubs.
The Hammond's Flycatchers used to inhabit the ponderosa woodlands along the first part of the route, the part that the Hayman fire changed drastically into Rock Wren habitat. Their habitat is gone gone gone.
Franktown, CO
From: Paula Hansley <redstart.paula@gmail.com>
To: ouzels8 <ouzels8@aol.com>; CObirds <cobirds@googlegroups.com>
Sent: Sun, Jul 2, 2017 10:10 pm
Subject: Re: green-tailed towhees and rock wrens
Sent from my iPhone
A miscellany of observations:
A Rufous Hummingbird visited the Denver Audubon Nature Center July 2. Seen by the Denver Audubon group on Walk the Wetlands.
A Lark Bunting seen east of Castle Rock on Upper Lake Gulch Road, June 30, by Sharon Hines. Apropos of Jared Del Rosso's 2 observations in western Arapahoe County the same day.
On our Cheesman Lake BBS route, June 30, we heard/saw
23 Green-tailed Towhees -- 5 times the previous high count -- and
16 Rock Wrens, 3 times the previous high count.
Why the high towhee numbers I'm not sure (unless I've improved at identifying its song) but Rock Wrens have increased due to Habitat change. They have burgeoned in the aftermath of the 2002 Hayman Fire, and to a lesser extent, the 1996 Buffalo Creek Fire.
We also counted 31 Western Tanagers, not a record but still a high count and 30 Broad-tailed Humm.--
Hugh Kingery
Franktown, CO
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