Tuesday, September 29, 2009

Warbler Guy: Do warblers migrate over the ocean or was this bird (below photo) confused and lost?


Thanks for the question, Kevin.

Here's my answer, though it's a simplified one to your question that deserves more ink than this digital retorte provides.

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Given your interesting photo of the Black-Throated Gray Warbler that landed on your boat’s deck while amid the Pacific Ocean, it’s 100% certain that your unfortunate friend is lost and wayward from its normal southern migration route. More exact, no wood-warbler species on the West Coast have yet been discovered to migrate to non-breeding/wintering grounds via an oceanic route.

On the West Coast, only disoriented and/or wind blown wood-warblers show up on offshore islands, such as those often seen by bird banders/researchers stationed at the central California chain of islands called the Farallones. Here, banders have captured in their nets various species of so-called eastern wood-warblers. Others, like the Black-Throated Gray in the photo, below, are wayward sojourners desperate for a wayside to rest upon while fighting to survive in a pelagic habitat that offers no food resources.

Unfortunately, the vast majority of wood-warblers seen resting on boat decks, buoys, and rip-rap along coastal and deep water habitats typically are hatch year birds. Most will either perish while traveling over the Pacific ocean before reaching island refugia such as the Farallones or incur high mortality after being set free by banders that discover them. Some researchers suggest eastern wood-warblers found on the West Coast (including Farallone Island individuals") are inherently "dyslexic" in the sense they do not have the orientation design necessary to complete the classic migration routes that their brethren successfully negotiate each spring and autumn on their north and south peregrinations.

Beyond the West Coast, trans-oceanic migration by songbirds is rare -- and, in the wood-warblers seen in N. America north of Mexico, it is only documented to occur in a few species.

One of them, for example, the Blackpoll is known to contain populations that in autumn perform the high-octane feat of an ocean migration route that totals more than 2,150 miles (NE USA/Maritime Provinces to northern South America).

How do researchers know the Blackpoll performs such a magician's stunt annually?

It's because bird bander's in Bermuda (an island east-southeast of the southeastern USA) band birds in the autumn, and, thereby, sometimes catch Blackpoll in their nets. Evidently, Bermuda is in line with the route over which Blackpoll travel during their southbound migration and this small island serves as a stopover wayside area for Blackpoll that wish to stop and "refuel" before leaving to migrate south again at night.

High-octane is an apt description of the Blackpoll's Herculean task because many leave their "staging" grounds en masse with other Blackpolls and fly en route together as heavyweight butterballs while weighing as much as 26 grams (nearly an ounce) at the beginning of their air treks.

By the end of the Blackpolls' long-distance trip, however, they have been documented to have lost half their starting weights. Emaciated and Twiggy-Thin Blackpoll, therefore, in some cases, are known to digest their muscle to serve as a last resort energy source.

While winging south, researchers have figured Blackpolls burn .08 grams per hour during their three to four days of travel, a process that is a non-stop direct flight, if the Blackpoll does not stop at island refugia such as Bermuda. In comparison, such a weight loss program for club members and gym rats on two legs would mean a 20-pound or more evaporation of girth per day (for the typical weight of 6' tall male or 5'6" female).

Now there's a weight loss program that would attract headlines and lead to a manic panic for (I imagine) a best-selling book titled: "Migrating With a TailWind To A Fat-Free Lifestyle." :-)

Friday, September 18, 2009

Warbler Guy: To help me with my warbler identification skills, can you tell me which warblers look the same year-round and don’t seem to become drab?

Among the 52 wood-warbler species typically seen annually in North America (north of Mexico), only 11 wear their flashy, bright, high-definition (alternate) plumage year-round. The vast majority — the other 41 species — undergo a molt before they migrate, so the males turn drab and less colorful after the breeding season.

Which11 warbler species look similar year-round?:
According to two sources I carefully checked — “Field Guide to Warblers,” (Jon Dunn & Kimball Garrett) and “Identification Guide to North American Birds (Part 1)” (Peter Pyle) — the answer is Golden-Winged, Yellow-Throated, Pine, Prothonotary, Worm-Eating, Swainson’s, Ovenbird, Louisiana Waterthrush, Red-Faced, Painted, and Yellow-Breasted Chat.

Expanding upon the basic facts presented above, most North American birds replace all their feathers during a complete molt that occurs in late summer or fall. The new feathers that develop before the birds leave on migration create an appearance that will be present throughout the fall and into winter. The technical word for this appearance is “basic plumage” because it usually persists longer throughout the year than the breeding (or alternate) plumage stage.

As indicated above, the majority of wood-warblers undergo a second molt that may occur progressively throughout the winter on the non-breeding grounds or as a more rapid molt before they leave to migrate north. This molt is called the peralternate molt and results in alternate plumage (or breeding plumage). In simple terms, think of this molt as providing birds the ability to “alter” their appearance to be colorfully attractive for the breeding season.

Of course, it is the males that most benefit from shedding their basic, non-breeding, drab (basic) plumage and transform into a brighter fa├žade. That’s because the females pick their male partners when nesting occurs on the breeding grounds, a process that begins after migrating males arrive and preceded by the prealternate molt that occurred for them in their non-breeding grounds.

If you’re lucky enough to see warblers performing breeding and courtship displays, then you’ll see first-hand how the pretty males attempt to catch the eye of their female suitors (that are typically slightly more drab in appearance). Courtship poses include various wing gyrations and diving/hovering displays, among other behaviors.

As a closing note, it’s a good idea to remember that not all prealternate molts result in a prettier, more colorful appearance among male birds. Consider three ptarmigan species in the western USA and Alaska that molt from a majestic snow white basic plumage appearance to a more mottled, camouflaged expression that matches their tundra (and other habitat) surroundings and is, thus, more suitable for the ptarmigans’ survival in their summer environs.

Thursday, September 3, 2009

Wisconsin Kirtland's Warbler Nesting Update


(Above, Kirtland’s warbler male at a new Adams County site, June 12 2009.
Photo by USFWS; Joel Trick)

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Want to know how many Kirtland's Warbler individuals were seen in WI this past 2009 breeding season?

Which counties?

How the Kirtland's third consecutive year of documented nesting in the state suggests this federally endangered songbird is now an annual nester in Wisconsin? -- in addition to, of course, nesting yearly in at least 12 Michigan counties (where at least 1,803 individuals were confirmed in 2009).

If so, please feel free to visit the following WI DNR link:

http://www.fws.gov/midwest/GreenBay/kiwa/2009Summary.html