Lessons from the CBC,I: Small is Beautiful

jenningsmap

It’s a tiny patch of green, really. Unless you were tuned into it, you’d walk right by it and never give it a second glance. In fact, thousands of OSU students do just that. The Jennings Hall habitat restoration is a half-acre with some native plantings smack dab in the middle of the main campus. But to the Columbus CBC, this tiny patch of habitat wedged between Jennings & Aronoff Halls turned into a gold mine. Paul Hurtado and several other OSU students and staff discovered and kept tabs on a quartet of rare lingering migrants for Ohio: a Common Yellowthroat, an Ovenbird, a Northern Waterthrush, and a Lincoln’s Sparrow. All but the waterthrush stayed into December and were relocated on Count Day (Dec 16), and in one fell swoop elevated this year’s CBC from memorable to remarkable.

jenningsmap

Notice Jennings Hall highlighted on the O.S.U. map above; note that Mirror Lake (bottom center-left) is the only nearby ‘natural’ habitat.

How do you get a concentration of rarities like this? “They were probably window-strikes that survived, got disoriented, and forgot to migrate”, opined Paul. There is certainly some validity here. All 3 are species that are ground-loving, making them likely window-strikes.  Dave Slager, another student, has documented over 100 window-strike kills on main campus over the past few years, and all 3 species are common in the tally. These individual birds are uninjured and free-flying, so what keeps them here?  Most of their compatriots have moved on and safely settled into winter territories in Mexico and central America.  Perhaps by the time they recovered fully, their migratory urge had passed, and they looked for the nearest patch of good habitat here.  Water & food are found around the native plantings at the site, and predators are relatively rare here.  The mild late Fall also has probably been a big aide in helping these birds survive.

 

This group of rarrities, though remarkable, is not wholly unprecedented.  Central Ohio has a long history of unusual early winter birds, chronicled by our observers in several long-established Christmas Counts. Our CBC records are flecked with late, out-of-range migrants, including some records for these species. Ovenbird has been on the Hoover CBC just last year, and was almost a count period bird several years back for Columbus. There is an old (1984) record of Lincoln’s Sparrow here, and an older one for Hoover. Both Hoover and Buckeye Lake have several records of Common Yellowthroats. Other late records include Redstarts, Palm Warblers, Orange-crowned Warbler, Pine Warblers, Dickcissel, Savannah Sparrows, Chipping Sparrows., and Baltimore & Bullock’s orioles. If you add in January records, the list expands to even more migrants. All of these are birds that should’ve migrated south, but didn’t. This suggests a small but stable number of birds that stray here through the early winter.

 

Can this occurrence tell us other things about winter-lingering rarities? It’s certainly not a common process, or we would find many more birds. All of the records that I mention above come from an enormous database of local CBCs back to 1960, which might generously average out to 1-2 stray migrants every year for our 5 local area CBCs. That’s 2 per approx. 400 party hours. Can we increase our odds of encountering these birds? If they are window-strike or predator-attack survivors, we might expect to find them in late Fall/early winter in isolated patches of habitat with a water source & few predators. There aren’t very many locations that map to those criteria, perhaps 2-3 on the OSU campus and another 3-4 downtown. Dave Slager realized this point very quickly and checked several downtown areas on Count Day, with no success. The birds at Jennings are very secretive, though. It took almost ‘saturation birding’ by several birders to accumulate the handful of sightings that indicated they were still around..  If other lingerers are equally secretive, it might take multiple visits just to detect them.

 

So perhaps we’ve been looking in the wrong places for some of our early winter rarities. We’ve often focused our efforts on urban ‘islands’ of habitat, but on bigger islands like Blendon Woods, Greenlawn Cemetery, and Waterman Farms. While we do find rarities there, they usually take much effort, and are not often such small migrants as were found at Jennings.  In fact, at Blendon many of the rarities were associated with their great bank of bird-feeders.  Maybe, we’ve looked at the wrong islands and need to think ‘smaller’.  Much smaller.  Perhaps the model spot would be more like the Statehouse Grounds, a small isolated patch of green with some native shrubs surrounded by a sea of windowed high-rises. There aren’t that many of those in central Ohio, and it might pay good dividends to check those sites in late Fall & early Winter.