Sunday, August 18, 2013

The Fall Warblers Begin to Arrive

The first Canada Warbler came through last week
Though it seems too early, but by this point in the summer fall bird migration is well underway. Many warblers, swallows, bobolinks, orioles and shorebirds are on the move - and some have been for several weeks. These birds aren't flying directly to their wintering grounds. Instead many will linger in places along the way - in habitats with good food reserves. There they will fatten up as best they can before proceeding on the next leg of their long journeys south.

The Blue-winged Warbler is most often gone by September
In fall the adult Chestnut-sided Warbler molts into less ornate plumage
About a half dozen species of warbler came through today. Most breed locally, but a few are migrants from the north country - from the Adirondacks and Canada.
The Northern Waterthrush (a warbler) looks much the same in fall as it does in spring
An immature Black & White Warbler needs to fatten up before its flight to the tropics
It's interesting that family groups often break up and make separate journeys south. The immature Chestnut-sided Warbler and Black and White Warbler have never embarked on this journey before, but still they know right where to go. With no guidance from their parents, they will fly thousands of miles to the tropics and to a wintering ground that they've never seen before.
The Warbling Vireo (not a warbler) sometimes shows yellow on its flanks
The immature Yellow-rumped Warbler (Myrtle Warbler) perches briefly over a stream
At this time of year warblers and other migrant songbirds can be difficult to find. After the breeding season, most songbirds cease singing territorial songs, and quiet birds are generally harder to find than noisy ones. Interestingly, when some of them do attempt to sing, often what comes out is a jumbled song that is barely recognizable. I heard one such "song" today. Rhythm wise, I thought that it resembled the song of a Warbling Vireo, but I couldn't be sure. In a case like this, in order to properly verify the species, all you can do is hope catch a glimpse of the singer or hear one of its more distinctive call notes.
The adult male American Redstart looks much the same in fall as it does in spring
This immature American Redstart is completely independent from its parents
Plumage wise, many of the warblers look much different in fall than in spring, but this is not universal. Some, like the adult male American Redstart, retain the same bold pattern and colors throughout the year. Also, often enough, when the Redstart sings in late summer, the song remains recognizable.
The adult male Black-throated Blue Warbler also looks the same in the fall
The female Black-throated Blue Warbler looks like she belongs to a different species than the male
Immature warblers can be hard to identify. It's not unusual for birders to mistake an immature Mourning Warbler for a Connecticut Warbler. The later species is a rarely seen migrant in our area, so legitimate sightings are of particular interest. Both species are shy and often skulk in heavy brush. With both the Mourning and Connecticut, a short glimpse is usually all you can hope to get. Both species are yellow and have a complete dark hood, but in immature Mourning Warblers the hood does not extend over the throat. An obvious white eye ring (absent in the adult) is the feature that causes the most confusion. A close examination, if possible, reveals that the young Mourning Warbler’s eye ring is incomplete and shows a gap by the bill.    
The immature Mourning Warbler shows an incomplete eye-ring and shorter undertail coverts
The adult male Mourning Warbler has no eye-ring
The Nashville Warbler always shows a distinct white eye-ring and a yellow throat
An immature Magnolia Warbler lacks the adult's heavily barred breast
Warblers and their neotropical allies will continue passing through upstate New York until November, but by the end of that period there are only one or 2 species likely to be observed. Warblers only infrequently overwinter in the area; in early winter the most likely species to be encountered  is the Yellow-rumped Warbler – also known as the Myrtle Warbler. Locally I have seen a few in winter – usually in areas that are rich in poison ivy. The small waxy berries that grow on those infamous vines can be a staple food for these warblers in wintertime. So indeed yes, Poison ivy is good for something!
The adult male Wilson's Warbler has a black cap

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