Thursday, August 15, 2013

Songbird Migration & a Warbler Hybrid

While birding in Prospect Park on Monday morning, Peter Colen and I had an interesting experience. Songbird migration has begun in earnest and I was hoping that we might find something unusual among the warblers that are now passing through the park. What we encountered was completely unexpected.

We had walked up Lookout Hill to the Butterfly Meadow where there seemed to be a bit of activity on and within the assorted sunflowers, buddleia and other wildflowers. In the weeds below an oak tree at the East end of the meadow I spotted a gnatcatcher chasing a mostly yellow bird. It turned out to be a the warbler hybrid known as a "Lawrence's" Warbler. We walked over to get a closer look, then spotted a Blue-winged Warbler in the oak tree above. The "Lawrence's" Warbler was subsequently chased across the meadow by one of many goldfinches in that area. A moment later the first blue-winged was joined by a second. I decided to circle around to the opposite side of the small meadow to track down the Lawrence's. As we walked the footpath on the North side of this opening on top of Lookout Hill I noticed a small bird feeding down low and just behind the meadow's surrounding fence. I think I may have made an audible noise when I focused in on a Golden-winged Warbler! I used to see this species in Brooklyn every year during migration, but in the last 15 years, I've only see it three times. My last Lawrence's Warbler sighting in Prospect Park was on May 10, 1997 and, ironically, in this same location. This is the only time in my 20+ years of birding that I've seen Blue-winged Warbler, Golden-winged Warbler and their bastard offspring, Lawrence, together. I'm glad that there was someone else present to share this rare family portrait.

The above paragraph (with a few edits) was what I quickly wrote up and posted to the NYS Birding list when I got home Monday. I didn't go into much detail as, I assumed, most subscribers were familiar with the Lawrence's Warbler. For this blog, I decided to do a little research and fill in some of the blanks as to why it was such a special experience.

Blue-winged Warblers are fairly common on migration around New York City. They breed in shrubby habitats, edges of forest and fields, and in what is generally referred to as early to mid-successional habitats. Beginning in the late-1800's, they expanded their breeding range, which now extends from the central Midwest to the East coast. This change has brought the blue-winged into close contact, and competition for territory, with the Golden-winged Warbler. Both species are in decline, however, as their preferred successional habitats revert to forest and human development eliminates upland and wetland habitats. In addition, Golden-winged Warblers have been hybridizing with Blue-winged Warblers where their breeding grounds overlap. The Golden-winged Warbler Working Group has created the Golden-winged Warbler Conservation Initiative in an attempt to save this species from extinction. In addition, the American Bird Conservancy has a project to try and save this bird. They summarize the challenge:

"The Golden-winged Warbler is one of the most seriously threatened, non-federally listed species in, eastern North America. Its decline is due primarily to habitat loss, particularly the loss of early successional habitats to suburban sprawl, regeneration of eastern forests, competition and hybridization with Blue-winged Warblers, cowbird parasitism, and potentially loss of wintering habitat."

The Cornell Lab of Ornithology's "Birdscope" newsletter describes a study by Frank Gill who used mitochondrial DNA to access the genetic integrity of Golden-winged Warbler. You can read about it here. In 2002 there was a similar study by John Confer and Shelagh Tupper of the Golden-winged Warbler population of New York's Sterling Forest. They found that "golden-wing population at Sterling Forest is holding its own against the influence of blue-wing hybridization". They theorize that the golden-wings in Sterling Forest nest in wetlands where blue-wings are rare.

Here is a link to 10 things you can do to help the Golden-winged Warbler.

Here are some photos I found online that show the typical male Blue-winged and Golden-winged, plus the two forms of hybrids that result from interbreeding:


Location: Prospect Park, Brooklyn
Date: Aug 12, 2013
Comments: Most time was spent around the Butterfly Meadow, but also birded in The Ravine.
Species seen: 36 species (+1 other taxa)

Red-tailed Hawk (1.)
Chimney Swift
Northern Flicker
Eastern Phoebe (1.)
Great Crested Flycatcher (1.)
Eastern Kingbird
Warbling Vireo (1.)
Red-eyed Vireo (1.)
Barn Swallow (6.)
Blue-gray Gnatcatcher (2.)
Northern Mockingbird (1.)
Cedar Waxwing

Ovenbird (1, In understory behind the Upper Pool.)
Northern Waterthrush (1.)
Blue-winged Warbler (3; 2 at Butterfly Meadow, 1 in Ravine behind Upper Pool.)
Golden-winged Warbler (1, foraging among dense weeds and wildflowers at Butterfly Meadow.)
Lawrence's Warbler (1, feeding at Butterfly Meadow.)
Black-and-white Warbler (5.)
American Redstart (4.)
Yellow Warbler (1.)

Indigo Bunting (2, Butterfly Meadow.)
Common Grackle
Baltimore Oriole (6.)
American Goldfinch

Other common species seen (or heard):
Mallard, Rock Pigeon, Mourning Dove, Red-bellied Woodpecker, Blue Jay, Black-capped Chickadee (1.), Carolina Wren, American Robin, Gray Catbird, European Starling, Northern Cardinal, Red-winged Blackbird, House Sparrow

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