Migration Outlook May 21-23

Female Bay-breasted Warbler at Magee Marsh Wildlife Area, Ohio, on May 19, 2011. During the latter part of the migration we see fewer adult males of most species, more females and young males. photo/Kenn Kaufman.

Friday, May 20: The pattern of the last few days has been distinctly unusual. The extreme chilly conditions of May 15-17 apparently were stressful for many migrants, which appeared to be struggling to find enough food. Unable to build up their fat reserves until the weather warmed up, many stayed longer than usual. At the same time, when conditions improved and the wind shifted a little on Wednesday night, quite a few new birds came in that night and joined the numbers that were already present. On Thursday, May 19, birds were unusually numerous and easy to see (even for here!) along the edge of the woods at Magee Marsh, continuing to feed relatively low, for outstanding views. By today (Friday), with temperatures warming further, the birds had moved higher in the trees. Numbers from the BSBO research station, and my impressions from the field, were that Friday’s numbers were about half those of Thursday.

Looking ahead, the weather pattern for the weekend is far from obvious. Winds tonight (Friday night) will be shifting around, mostly easterly but swinging northerly and southerly during the night. I expect that we’ll see some continued turnover, with many of the current crop of migrants moving out and a few birds moving in. The recent abundance of Magnolia, Chestnut-sided, and Bay-breasted warblers may diminish, and we may see larger numbers of Canada and Wilson’s warblers, Red-eyed Vireos, American Redstarts, and various flycatchers.

According to current forecasts, the winds will shift to a strong southerly flow sometime late on Saturday and continue that way through to Monday, and I think we’ll see a big arrival of birds on Sunday May 22 and Monday May 23. By this date, of course, they’re becoming harder to see as the trees and shrubs become fully leafed out, but still there should be plenty to look for. Females tend to migrate later than males for most species, so in the latter part of the migration we hear less singing and we see more subtly patterned birds.

Short prediction: Good variety but only moderate numbers on Saturday May 21; probably bigger numbers on Sunday May 22 and Monday May 23.

Mourning Warblers should be present for most of the next ten days; they stay low, often around fallen logs and dense thickets, but periodically coming up above eye level. Connecticut Warbler is less reliable: it seems to be found after every big push of migrants in late May, but often for only a brief period. For examples, a couple appeared along the Magee Marsh boardwalk on Thursday the 19th, but I don’t believe they were seen again on the 20th. So for this species, it pays to look on the big migration days, rather than waiting until the day after one is reported. Connecticut Warblers are secretive and very easy to overlook, as they walk slowly on the ground inside the forest.