Last night’s radar was a great example of the “migration window”, something I’ve mentioned in previous posts, but rarely get to see play out. Here’s the radar from 7:00pm last night through 5:00am this morning.
Frames are every 1/2 hour. Click on the thumbnail to view the full-sized animation.
The “migration window” I’m referring to is the time period between which birds will migrate, given favorable conditions exist. Several formal studies have shown this to be between sunset and around midnight, and it’s from my experience posting the radar that the times hold up pretty well.
At sunset last night most of the region was under light to moderate WSW winds, as the latest cold front pushed across the region. Migration was minimal, at best, for the first few hours after dark. But, checking the regional composite, you can see the areas behind the frontal boundary (NY and western PA) showed strong migration signals given the northwest winds. As the front pushed eastward over the mid-Atlantic, the migration signals began to strengthen as birds began taking flight. The winds over northern New Jersey didn’t turn northerly until after 10:00pm, which is supported by the increasing level of migration on the reflectivity images, as well as the overall trajectory of migration on the velocity images after 10:00pm. As the night progressed, the winds across the entire region turned northerly (and eventually northeasterly), triggering migration in quick succession. Had this change in wind direction taken a few hours longer, it’s unlikely we would have seen the same intensity of migration, as the migration window theory suggests that birds observe a cutoff time after which they will “lay over” until the following night of favorable conditions.
Based on the migration intensity and wind shift to northeasterly along the coast, expect inland migrant traps to be best this morning. Coastal areas will still see new birds given the northwesterly component late last night, but will experience some attrition due to the easterly wind at daybreak.
Another good reason to head inland? RAPTORS! We’re approaching peak Broad-winged Hawk season here in the mid-Atlantic, and northeast winds will definitely favor inland ridges. This might just be the day to skip work in favor of a little hawk watching
Whatever you decide, make sure you stop back and let us know what you saw.
Good Birding
David
P.S. Come check out my migration forecast for the Mid-Atlantic on Birdcapemay.org
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2 responses to “Birds on the move as cold front clears mid-Atlantic”
I wish I could have stayed later to test David’s theory on the Broad-winged Hawks, but work does
beckon! Gloucester County – just Wheelabrator.
2 1/2 hours of birding. Winds were light NE when I started. Mostly cloudy to mostly sunny when I left.
Birds were less in number, but greater diversity than Monday. But I spent more time here also today than Monday. I think most of what I had was new.
1 ALDER
2 EASTERN KINGBIRDS
1 VEERY
1 SWAINSON’S THRUSH
2 WARBLING VIREOS
1 RED-EYED VIREO
1 BLUE-WINGED WARBLER
1 PARULA
1 YELLOW WARBLER
2 MAGNOLIA WARBLERS
1 CAPE MAY WARBLER
1 BLACK-THROATED BLUE
1 BLACKPOLL
3 REDSTARTS
15 at least COMMON YELLOWTHROATS – some could be breeders.
0 Gnatcatchers – I heard they were coming through Cumberland County.
0 Mockingbirds – I’ve had a dozen there last week. Less Monday. None today. They moved on.
Some pre-work birding at 6 Mile Run today – many redstarts and yellowthroats, 1 B&W. Not too much else, though there were a lot of twitterings in the bushes.