Kirtland's Warblers in Wisconsin, check-list changes, Bar-tailed Godwit migration, and feather-plucking palm-swifts
Birding Briefs -- October 2007
Published: August 24, 2007
|Kirtland's Warblers found nesting outside Michigan|
Three decades of intense habitat management and cowbird control in Michigan appear to be paying off for the Kirtland's Warbler, North America's most endangered wood-warbler.
For years its core breeding range was limited to a handful of counties in northern Lower Michigan, but the warbler's population has grown rapidly since 1990.
Record numbers of singing males have been tallied during the last five annual censuses. This year, census-takers counted 1,697 warblers in Michigan, 8 in Wisconsin, and 2 in Ontario. A total of 1,486 warblers were counted in 2006, and 1,415 the year before that. The surveys have been conducted annually since 1971.
The steady increase has led biologists to speculate that the warblers would eventually disperse from northern Lower Michigan in search of additional suitable breeding habitat, and that appears to be happening.
Kirtland's Warblers have been breeding in Michigan's Upper Peninsula since 1995. Males banded in Ontario last year returned this spring. And this summer, for the first time in six decades, the warbler nested outside Michigan.
In June it was announced that a birdwatcher had discovered three active nests on privately held land in central Wisconsin. One of the nests contained four eggs.
Kirtland's Warblers of both sexes were photographed near the nest sites in early July, around the time that adult warblers are typically busy feeding nestlings. One of the images captured is reproduced on the cover of this issue.
Another, showing a singing male wearing three bright orange plastic leg bands, appears above. According to a member of the Kirtland's Warbler Recovery Team, the bird was banded on the island of Eleuthera in the Bahamas on November 13, 2003, and was spotted there again the following winter. The island has been a focal point of Kirtland's Warbler research since early 2002, when, after a century of fruitless searching, an unprecedented number of the birds were found overwintering there.
Also photographed in Wisconsin in early July was a male warbler carrying insects. According to the photographer, the bird delivered the meal not to a young Kirtland's, but to a just-hatched Brown-headed Cowbird.
|Five species added to check-list|
The American Ornithologists' Union has added five species to the official register of the continent's birds. The total now stands at 2,046.
Three species -- Ringed Storm-Petrel, Intermediate Heron, and Red-footed Falcon -- were added because of new distribution information. The storm-petrel was spotted off California in early August 2005. The egret was found dead in Alaska the following year. And the falcon, as we wrote in February 2005 (p.26), delighted birders on Martha's Vineyard in August 2004.
The two remaining additions reflect splits in species already on the Check-list: Bean Goose was split into Taiga Bean-Goose and Tundra Bean-Goose, and Cuban Black-Hawk was split from Common Black-Hawk.
The additions were announced in the 48th supplement to the Check-list, which was published in the July issue of The Auk and is available at www.aou.org.
The AOU also added Sacred Ibis, a species of Africa and Iraq, to the appendix. Captive ibises escaped following Hurricane Andrew in 1992, and now a population of 40 birds "seems to be on the way to establishment" in South Florida.
|Satellite-tracked godwits fly 6,300 miles nonstop|
Thanks to satellite technology, ornithologists finally have a more complete picture of just how far and how fast the Bar-tailed Godwit migrates (see map below).
Scientists had long known that the annual wanderings of the 16-inch shorebird take it from New Zealand and Australia, south of the equator, to eastern Russia and northern and western Alaska, above and just below the Arctic Circle.
This year, researchers from the U.S. Geological Survey Alaska Science Center and other organizations attached satellite transmitters to 14 godwits in New Zealand to track their speed and routes. One bird stayed home, and six either turned around or their transmitters stopped working.
The other seven reached breeding areas in the north after resting on the Chinese and Korean coasts of the Yellow Sea. The flight to Asia was completed nonstop in about seven days, a distance of 6,300 miles. The birds remained for one to two months.
Five of the godwits then flew about 4,000 miles to the Yukon-Kuskowim Delta in Alaska. The sixth migrated 2,800 miles to eastern Russia.
The seventh bird was bound for Alaska but turned around about 275 miles from the coast. It flew 800 miles west to Russia's Kamchatka Peninsula, stayed for a week, and then winged more than 1,000 miles to the Yukon Delta. All together, it covered about 12,000 miles on its journey -- the equivalent of halfway around the earth.
Godwit flies nonstop to New Zealand
Shown here are the routes of seven Bar-tailed Godwits from wintering areas in New Zealand to nesting spots in Alaska and Russia.
|Feathers by the mouthful, plucked on the wing|
Many birds line their nests with feathers to conserve energy and insulate their chicks. Most find stray feathers or pluck downy plumage from their own bodies, but Fork-tailed Palm-Swifts of South America employ a very different strategy: They steal feathers directly from the backs of other flying birds.
Palm-swifts build their nests exclusively in the hanging leaves of palm trees, where nestlings are protected from predators but exposed to the elements. To shield the young, large quantities of feathers are required. Because palm-swifts spend most of their lives in flight and never stray far from palm groves, it was assumed that they collected windblown feathers discarded by preening birds or bird-eating raptors.
Instead, as tour guide Bret Whitney writes in the April issue of The Auk, the agile palm-swifts circle high over their nesting ground. Then, when a pigeon, parrot, or other bird passes below, they stoop from above and behind, "sometimes in tandem, striking their victim in the middle of the back and tugging at feathers with the bill for about 1-3 seconds to dislodge a mouthful."
Whitney calls the behavior kleptoptily. He suggests that other swift species may use the same technique to obtain feathers for their nests. -- Jessica Eskelsen