Tuesday, October 2, 2007

Nocturnal migrants, and a note on pre-dawn re-directed flight by Gray-cheeked Thrushes

I started a little study this morning, armed with a clicker in each pocket, a red-beam flashlight, a notepad, and a can of Dr. Pepper. The right clicker was for Gray-cheeked Thrushes, the left for Swainson's Thrush; the rest I hoped to record on the notepad.

Standing on the Delaware Bayshore near a salt marsh, I counted nocturnal migrants and other birds from 5:37 to 6:37 a.m. Almost no warblers were flying, which is just as well since I can only identify a few of them by flight note, but quite a few thrushes were. I clicked 97 Gray-cheeked notes, and 46 Swainson's, but my sense was that the Gray-cheeked's were calling more often, so I was probably hearing each bird 4 times on average.

Everything was flying south, based on changing position of the calls, until about 6:15 when a group of 6 or so Gray-cheeked Thrushes came over very clearly heading northeast, towards land. This was very interesting, because the thrushes are not part of Cape May's diurnal morning flight, wherein warblers and others are seen flying northward in an apparent effort to find suitable habitat for the day before continuing migration. The thinking is that the thrushes engage in this re-directed flight, too, but they do it before dawn. If this is true, and it seems to be, I wonder if it is because thrushes, with their big dark eyes, see better at night? Or perhaps because the thrushes are faster fliers than warblers, they realize they are not where they want to be as light begins to lift, the same as other birds, but the thrushes make it back to suitable habitat faster.

The morning's list is below.

Location: Norbury's Landing
Observation date: 10/2/07
Notes: Began observations at 5:37, last nocturnal migrant heard was at 6:15, daytime calling began at 6:25 with mockingbird, winter wren and house wren, sunrise was 6:56. Tide low at 7:56, 66% of moon visible and waning, stationary high since front 3 days ago, winds light and tending to be from the nnw, less than 5% cloud cover.
Number of species: 22
Canada Goose 10
American Black Duck 1
Mallard 5
Great Blue Heron 5
Great Egret 5
Snowy Egret 3
Black-crowned Night-Heron 38 flyovers heading south along bayshore pre-dawn, probably to a roost rather than migrating
Clapper Rail 5 all in the marsh, not flyovers.
Semipalmated Plover 1
Great Horned Owl 2
House Wren 1
Winter Wren 1
Veery 5 nocturnal migrants, all apaprently going south, pre-6 a.m.
Gray-cheeked Thrush 25 Clicked 97 call notes, figure heard each bird average 4 times. Nocturnal migrants, most going south, but at 6:15 a group of about 6 passed definitely headed northeast, apparently pre-dawn re-directed flight.
Swainson's Thrush 15 clicked 46 call notes, but seemed to call with less frequency than Gray-cheekeds. Nocturnal migrants, all apparently heading south. Last one heard 6:15 a.m.
Hermit Thrush 2 Nocturnal migrants
Wood Thrush 2 Nocturnal migrants
Northern Parula 1 Nocturnal migrant
Blackpoll Warbler 1 Nocturnal migrant. Also 5-6 Warbler sp., this could have been one of the other zeeps, too
Savannah Sparrow 5 nocturnal migrants
Rose-breasted Grosbeak 5 nocturnal migrants
Purple Finch 3 nocturnal migrants
This report was generated automatically by eBird v2(http://ebird.org)

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