Tuesday, June 09, 2009

The 2009 Breeding Bird Survey season

I completed my fourth and final Breeding Bird Survey route for 2009 last weekend; it's quite nice to have them all done only a week in to June. My most notable find was a Worm-eating Warbler in Obion County in the far northwest part of Tennessee where they are not supposed to be breeders; thi was the second time in three years I have had a singing bird at the same stop. A synopsis here of the season as a whole:

Opening day of BBS season in Tennessee is May 27th, and on that day I ran the Campbellsville route in Giles County. This is my most rural route overall, with the least vehicle traffic, so it seemed like a good choice for a mid-week date. I just acquired this route last year in a bit of a rush, when I discovered that it was still unassigned and un-run with only a few days left in the season. As it is only about 40 miles from my front door I arranged to dash out and cover it ASAP. The way the BBS works, data is far more valuable when the route is run by the same observer over multiple continuous years. So, when you volunteer to cover an orphan route one year, you've adopted it for the duration (much like when you feed a stray puppy). Last year I ran Campbellsville on July 1, by far the latest I have ever run a BBS. I was interested to see the comparison between 2008 and this year with it being run in May. Surprisingly, there was not a dramatic difference. Numbers of woodland singers were slightly higher this year than last, but not markedly so and probably not to a statistically significant degree. The only major change was the Orchard Orioles. In July in 2008 I found none; in May 2009 I had 9 of them. One thing I found curious about this route last year was the relatively low numbers and diversity of wood warblers compared to the other routes I run in the western Highland Rim. I had only 5 species as compared to the 12-16 I had come to expect in this area. The historical data from the previous observer also showed this paucity of warblers; but there are often substantial differences in the individual biases between two observers (hence the need for data from the same observer year after year) and I knew from past experience that I tend to bias on the high side for warblers. This left me wondering if it was a function of the route or the late run date; 2009 data would tell. Well, this year I only had 7 species of warblers, adding only a single Worm-eating and two Prairie Warblers to the 2008 list. Apparently the Western Highland Rim "motherload" for Middle Tennessee warblers does not quite reach as far as Giles County!

Next up on the list were Wrigley and Collinwood. This was my third year on both of these runs. These routes are fairly similar, being forest- and warbler-rich runs through hill-and-holler country of the Highland Rim, with enough open farmland to add diversity and help wrack up impressive species totals. I scheduled Wrigley first, on Saturday May 30, as it has more vehicle traffic issues and I was going to be in Dickson close to its start point over the weekend already. The Wrigley route starts in Hickman County and travels east across the northwest tip of Maury County before ending a few miles over the line into Williamson County. It has been run continuously since the inception of the BBS in 1966, with not a single missed year. Ideally one is supposed to scout one's routes in advance to avoid having road construction, etc. issues come up on the count day; but in the case of these routes where the start points are less than an hour from my front door I forgo the scouting trip. I just figure that if something arises on count day that I can't resolve on the fly, it would be simple enough to rerun the route a day or two later after checking with the Mothership in Pautuxent and working out a solution. The Wrigley route has had some pretty significant road changes in its 43 years of existence, especially when the Natchez Trace Parkway was constructed and bisected it, causing quite a few stops to be relocated. I narrowly dodged the bullet this year: as I approached stop 50 (out of 50), I was presented with orange "ROAD CLOSED AHEAD" signs. The barricades were sitting exactly at the point where the BBS route ends! It seems that Highway 840 construction into Williamson County has resumed and reached Leiper's Creek, after many years of delay. Fortunately this will make no changes to the route; though who knows what it might do to the traffic issues?

The Wrigley route was its usual warbler-filled self, with a run total of 15 warblers and a hefty 79 species. Some year the planets and birds will align just right and this route will break the 80 species mark! The only disappointment was the absence of any audible or visible Cerulean Warblers at their usual haunts along Lick Creek or anywhere else on the route; however these were balanced by singles of Blue-winged Warbler and American Redstart, both of which are often missed. I would be tempted to blame the missing Ceruleans on the fact that the February 2008 tornado cut across the route right at the spot where they have been most reliable recently; however there was a bird singing there last year still after the tornado so hopefully it was just bad luck this year.

I chose to run Collinwood on Tuesday, June 2nd. This route often gets run on a weekday as the traffic is not too bad; though last year I ran it on a weekend and I have to say by comparison the passing cars were pretty annoying in parts this year. I will probably try to move it back to a weekend for the future. For this one we start out just east of the Natchez Trace Parkway in southern Wayne County, wind through the hollers eastwards into southern Lawrence County through "downtown" Westpoint and north of Loretto, and finish up in the high, flat, open farmland and hayfields of the barrens near Center Point. It has some memorable stops, such as the one in Westpoint that is almost right on the front porch of a friendly old lady who you hope has remembered to fill her hummingbird feeder; and the stop that is right in the middle of the Shoal Creek bridge with the Cliff Swallows swarming around you. In the first stops it passes through large regenerating clearcuts that have reached perfect Blue-winged Warbler stage. This year I tallied 7 of these beauties, along with 12 Prairie Warblers and 25 Yellow-breasted Chats. The shifting numbers of birds as the forests are cleared, regenerate, and close in again are one of the things the BBS is intended to document. Sometime in the distant future these same stops will probably be recording Ovenbirds, Acadian Flycatchers, and Hooded Warblers again; of course by then I will have probably long since lost my hearing and passed the route on to someone else! The missing Ceruleans from Wrigley were found at Collinwood, with singles at two stops. One of these was heard from the aforementioned Shoal Creek Bridge, where there was also an American Redstart singing for the second time in three years. The Barrens added only a single Dickcissel this year; sometimes they yield Loggerhead Shrikes or Grasshopper Sparrows but it's always hit-or-miss for these species. All told I had 77 species including 14 warblers.

A curiousity -- after acquiring Campbellsville, I now run 3 of the 4 BBS routes in this southwestern highland rim area. It reminds me of the South Carolina Breeding Bird Atlas, where I wound up covering all the Georgetown County and most of the Horry County blocks myself for the same reason: paucity of local birders. I'm not sure if this is a good thing statistically, but it does get these remote rural areas covered which is better than having missing data. Of course the only local route I do not run is the one that begins only 9 miles from my front door: Lewis Forest. I don't know who does cover this, but looking at their data for past years it is clear that route is in very good hands.

To finish out the season I made the long trek to the far northwest corner of Tennessee for Tiptonville. This is the first Tennessee BBS route I acquired. 2009 marked my fourth year on it -- almost enough for some meaningful statistics to start coming from my data! Though this route is cursed with heavy traffic on the early stops regardless of the day of the week (commuters on the weekdays, fishermen on the weekends), it is also probably the most exciting of my four routes. It begins on the delta flatlands north of Tiptonville just south of Black Bayou, then skirts right along the south shore of Reelfoot Lake before climbing the bluff in to the Obion County uplands. In the Reelfoot portion you never know what might fly over, and up in the hills and creeks on the second half you never know what you might glimpse or hear. Just in my four years I have come across unexpected-in-summer-in-far-west-Tennessee woodland birds there such as Worm-eating Warbler, Scarlet Tanager, and Broad-winged Hawk. This is also the only BBS route I have ever broken the 80-species mark on (81 on 2007). Over the decades the route has racked up a cumulative species list of 111; individual year totals usually run in the 70s so you can see how much year-to-year variation and luck-of-the-flyover-draw there is.

There was an additional factor this year that had me intrigued: the extensive forest damage from an intense ice storm last winter than hit Lake and Obion Counties. The impacts are massive. It looks very much like what I have seen near the coast in the aftermath of major hurricanes, except that it lacks the "blown sideways" effect. The branches and tops of all these trees were dropped straight down and remain piled in great heaps throughout the woods. The trees are resprouting in that clumpy, stunty way that looks like the aftermath of a bad pruning job, just as you would see following a tornado or hurricane. Overall I'd guess the tree canopy leaf area is reduced by an average of 50% or more across the landscape. It is hard to say from just my one route what effect this tree damage had on the bird totals. In general the numbers for woodland birds seem lower than average; but there is always substantial year-to-year variation so it is hard to say much for certain. My species total was 73, which is a bit low but not markedly so. Tiptonville is the only Tennessee BBS route within the ice storm footprint, but there are many others in Kentucky that were also walloped by the storm. I will be especially interested to see what happens over the next couple of years as the underbrush explodes in these opened up woods -- what might move in, and what might move out? Will we see huge increases in chats, towhees, and catbirds? Time will tell.

After a week and a half of getting up at 3:00 a.m., I finally have time to weed the garden again...


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