An Excuse to Walk in the Woods

Scarlet Tanager (Piranga olivacea)

(Note: The images illustrating this post are not mine; they are borrowed from the Web.)

Last Saturday morning, (June 30) I completed my 2012 series of censuses of the birds that are breeding in the largest forest in our natural area.  This is the 21st straight year that I have been marching through the woods, starting at the crack of dawn and finishing up about 9 a.m.

This project began in 1991 when the Cornell Laboratory of Ornithology asked birders nationwide to conduct a census of the birds breeding in deep woods in order to assess the population status of forest interior breeders like Wood Thrushes, Veerys, and Scarlet Tanagers.  Cornell's protocol required participants to establish a transect through their chosen woodland, and to locate stopping points spaced 50 meters apart along the transect.  Then, the birders were asked to walk the transect at least eight times during each breeding season, stand quietly for 10 minutes at each designated stopping point, and record the birds heard singing or observed within 50 meters of each stopping point.  After completing eight walks, the birders were instructed to review their observations and to try (to the best of their abilities) to map territories of individual breeding pairs.

I dutifully reported my results to Cornell for the first nine years, but after the 2009 census Cornell terminated the project.  By this point, I had invested a lot of time in the woods and had also come to realize that information about birds breeding in our forest could be a valuable, independent measure of the ecological integrity of our woods and a bellwether of our success in actively restoring forest in old-fields adjacent to the existing forest.  After all, birds can "vote with their wings," and if the habitat is not to their liking, they'll move on.  So, I have continued the censuses, even though there's no platform on which to share the data.  (I did hear from the researchers at Hawk Mountain Sanctuary in the Pennsylvania Appalachian Mountains a few years ago; they, too, had continued their census after Cornell terminated the project, and they were seeking information from others who had continued to collect data.)

Red-eyed Vireo (Vireo olivaceous)

I haven't carefully analyzed all of the information I've gathered over the years, but I do have some impressions.  First, a few species that had been fairly common when I began the censuses have declined, including Red-eyed Vireos (not so worrisome, at least in this context, because they aren't really forest interior breeders) and Veerys (Catharus fuscescens) (much more of a concern, because they do need large blocks of woodland to breed). 

Brown-headed Cowbird (Molothrus ater)

On a far more positive note, Brown-headed Cowbirds, which are nest parasites, have all but disappeared from the woods, though initially they had been numerous.  Also on the very positive side, Wood Thrushes remain among the most common breeders in the forest; many of my suburban ornithologist colleagues would be green with envy over the number of breeding Wood Thrushes in my woodland.

Wood Thrush (Hylocichla mustelina)

Another observation:  the forest topography is gently rolling, with two rills flowing through shallow valleys draining from the east to the west.  More birds select the south-facing slopes of these valleys than the north-facing slopes--I'm guessing because the south-facing slopes are a bit warmer.  I have two other observations that will ring true with every experienced birder.  First, the birds sing less frequently as the time after dawn lengthens, so I have to alternate the direction of my walks in the woods, starting one time at the north end of the transect to catch the north-end early morning singers, and then at the south end on the next walk to catch the south-end early birds.  Second, the woods become increasingly quiet as the breeding season progresses; the birds have established their territories, breeding, brooding and raising young are underway, and there's less and less need to defend boundaries.  So, for the human observer, the last few walks in the series of eight, especially the sections containing the "late morning" stopping points observed from 8-9 a.m., can become pretty tedious affairs because there's so little "action" to document.

And, as for last Saturday's final census.  Well, I was only in the woods for one hour from 7-8 a.m. observing six stopping points (instead of the usual 18) because this was a special "ninth" walk to make-up for the six stopping points I was unable to observe on May 25 when a ferocious early morning thunderstorm drove me out of the woods to seek cover under a neighbor's shed.