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Wednesday, June 12, 2013

Kirtland's: Our Rarest Warbler and an Amazing Conservation Success

[Grayling, MI. June 2013]

Any serious student of American Ornithology and Bird Conservation will surely be aware of Kirtland's Warbler and its brush with extinction -- its total population was a perilous 400 as recently as 1990 -- think about it -- 400 Kirtland's Warblers on Earth; about the same number of Dunlin (or Starlings) you might see in a single day wintering in SW Florida.

Fortunately, in a comeback story, eloquently detailed in The Kirtland's Warbler: The Story of a Bird's Fight Against Extinction and the People Who Saved It by William Rapai, the population today is now estimated to be almost 10 times that number per the census graph of singing males (courtesy of Michigan Dept of Natural Resources):

The graph also shows that starting in 1991, the population trend finally becomes positive after decades of stagnation in the low hundreds.

Formerly a breeder endemic to Michigan, it now has a small breeding presence in Ontario and Wisconsin as well. However, its stronghold continues to be in Michigan and the prospect of seeing this rarest of warblers attracts people from all over the country to a few pockets in this state. One of which is the Grayling area where these photographs were taken.

Fortunately, unlike Bachman's Warbler which is surely already extinct (the last confirmed sighting was in Louisiana in 1988), excellent field work, relentless conservation and good science all played a role in preventing a similar fate for the Kirtland's.

Had a similar mix of forces come together to aid the Bachman's Warbler, birders in America would be ticking off 57 warbler species and not the 56 that are possible today.

The key factors to the population recovery of Kirtland's Warbler were:
  • Realizing that forest fire prevention worked against the warbler -- Kirtland's is a very picky breeder and will only nest in young (~5 foot tall) jack pine trees. Natural fires rejuvenated the forest with the growth of young jack pines; when naturally occurring forest fires were prevented, availability of breeding habitat declined.
  • Understanding that breeding territories (upto 6 acres per male) need to exist in large swathes of jack pine habitat (at least 80 acres). Michigan DNR's goal is to maintain 40,000 acres of suitable habitat for this species.
  • Realizing that brood parasitism by the Brown-headed Cowbird had a catastrophic effect on breeding success; unlike the Yellow Warbler, the Kirtland's does not have a coping mechanism to nest invasion by Cowbird-laid eggs.
Of course, the above conclusions were arrived at due to the hard work of many dedicated scientists and conservationists over decades of trying to understand the fascinating natural history of this little-understood warbler.

The male Kirtland's Warbler shows a lemon-yellow breast with a grey face and upperparts. Additionally, an incomplete white eye-ring, black streaking on the flanks, and black lores [absent in the female] serve as key identification characteristics.

Kirtland's Warbler -- showing all key identification characteristics

Kirtland's Warbler -- as was the custom of the era -- was "collected" [shot and skinned] by Charles Pease on May 13th, 1851 when the bird was in migration passing through Ohio. He turned the "specimen" over to his father-in-law Dr. Jared Kirtland who in turn gave it to Spencer Baird. And, it was Baird who then published a paper scientifically describing the warbler as a species new to science and named it after Dr. Kirtland.

However, it was 28 years later that the wintering grounds of the Kirtland's were located in the Bahamas. And, a full half-century since its discovery was the first nest of the Kirtland's discovered in Oscoda County, Michigan.

This discovery resulted in a frenzy of "collecting" -- the warbler's rarity prompting collectors and museums to pay up to $25 [a princely sum in those days] per specimen. This phenomenon -- shooting rarities for private or public collections -- is known to have contributed to the extinction of the Ivory-billed Woodpecker.

Kirtland's Warbler is an indefatigable songster -- documented to sing up to 2.200 times a day during Spring. And, its song is rich and complex; almost defying description.

To my ear, the song has finch-like notes in the beginning but ends in a whistling "wit-weet" akin to the call of a curve-billed thrasher.

 And, while the tonal complexity of the song renders transliteration difficult and ambiguous; one thing that all, however, can agree to, is that when the Kirtland's sings, every muscle, every fiber of the bird's body is in song.

All of our 56 warbler species are unique and delightful in their own right; however, none, perhaps, has as fascinating a history as the Kirtland's. Coupled with its incredibly melodious song and extreme requirements for successful breeding, the Kirtland's Warbler stands taller than the rest of its family in its uniqueness and significance to conservation.

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