Friday, October 4, 2013

Fri-D: Molting Shorebirds

[Short-billed Dowitcher molting to winter plumage, Stone Harbor, NJ today. Click to enlarge photos.]

As autumn gets later, the shorebirds we see will trend more and more to winter plumage - which means they will look more and more like each other, with uniform gray upperparts and paler underparts. Many shorebirds begin fall molt at migration stopover sites and complete it on or near the wintering grounds, though there are exceptions. Late fall and winter is the time to hone your identification skills using structure, but also don't forget that bare part colors also still work.

Here we have two species in molt to winter plumage. Above, a Short-billed Dowitcher has replaced most of its back and scapular feathers with uniform gray winter plumage ones.

Below, a Dunlin has molted most of its feathers, but you can see a couple of retained breeding plumage feathers - the orangy ones that, when the bird is in full breeding plumage gave it its old name, "Red-backed Sandpiper." Dunlin, by the way, is an exception in that in "our" subspecies, adults molt to winter plumage on the breeding grounds, then come south, and most juveniles also molt extensively before they come south. That's why we don't see breeding-plumaged Dunlin on southbound migration, and rarely see fully juvenal-plumaged birds. It also explains why Dunlin is a late migrant compared to other shorebirds, with the bulk of them arriving in September or later, compared to the July-August migration of many other shorebird species.

Both birds were photographed from a kayak at Stone Harbor/Nummy Island today.
[Dunlin nearly all the way into winter plumage, Stone Harbor today.]

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