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The purpose of egg speckles, tower lights that help prevent bird deaths, Blackcap evolution in action, a Cave Swallow invasion, and an Ivory-bill update
The purpose of egg speckles, tower lights that help prevent bird deaths, Blackcap evolution in action, a Cave Swallow invasion, and an Ivory-bill updateBirding Briefs -- February 2006
Published: December 22, 2005 Blinking Tower Lights May Reduce Collisions
Reducing mortality caused by collisions with television, radio, and cell-phone towers has been a challenge for decades. Now a study suggests that birds could be saved by changing the type of lights that illuminate towers.
Joelle Gehring, a biologist with Central Michigan University, started out investigating whether towers supported by guy wires were deadlier than self-supported towers. She has organized technicians to search for dead birds at 24 towers around Michigan during each migratory period since fall 2003. In the first three field seasons, 96 percent of carcasses found were collected beneath towers with guy wires.
When she factored tower lighting into the study last spring, she found that guyed towers with white or red strobe lights or red blinking incandescent lights led to far fewer bird deaths than guyed towers with non-blinking red lights. Towers with non-blinking lights accounted for 83 percent of carcasses, those with blinking and strobe lights 17 percent.
Gehring says she'll gain more confidence in last spring's results if the phenomenon is repeated in subsequent migration seasons. "But preliminary results do suggest that we can greatly reduce the numbers of birds colliding with towers by altering these light systems," she says.
Such changes would require action by federal aviation-safety agencies.
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Egg Speckles Provide More than Just Camouflage
Speckles on eggs may serve as more than camouflage. They might also reinforce a shell's weak points.
According to a paper published in the October 2005 issue of Ecology Letters, speckled sections of Great Tit eggs from a woodland near Oxford, England, were thinner than non-speckled sections, and the darker the speckle, the thinner the underlying shell.
Also, tits nesting over calcium-deficient soil had more speckles than tits with nests over calcium-rich soil. A low-calcium diet can cause birds to lay thinner, more porous eggs.
"For open ground-nesting species, it is obvious that the eggs are cryptic," says study co-author Andrew Gosler of Oxford University. "The issue for the small passerines that lay essentially white eggs with speckles is that we can't reasonably say that the pigmentation exists to camouflage the egg."
The speckles do not make thin spots thicker. Instead, Gosler thinks that the speckles, made from chemicals called protoporphyrins, protect eggs two ways: by acting as shock absorbers and by sealing thin spots, thereby reducing water loss.
- Michael Campbell
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Bringing NEXRAD Into Sharper Focus
For several years, next-generation radar, or NEXRAD, has dramatically improved researchers' understanding of migrating birds.
Now a partnership consisting of the U.S. Geological Survey, the U.S. Fish and Wildlife Service, and academic researchers is working to refine the radar's echoes to reveal even more details of migratory behavior, thereby deepening the scientific underpinnings of land-management decisions. (Contributing editor Paul Kerlinger described the technology in our February 2004 issue. See "Birds on the Move," page 62.)
Janet Ruth, informal coordinator for the venture, says she and her collaborators are working on several initiatives.
They intend to pick out bird echoes from other targets, to better understand how topographic obstructions cause blind spots, and to link data with geographic information systems applications. In addition, they hope to make NEXRAD easier to use. Presently, not all of the needed studies are funded. - Dan Risch |
One Migrant, Two Destinations
Researchers studying stable hydrogen isotopes from a warbler's claws have found a change in migratory behavior so extraordinary it could foretell the evolution of a new species.
The Blackcap is a warbler in the genus Sylvia and one of Europe's most common songbirds. Since the 1960s, the number of Blackcaps wintering in the British Isles has increased dramatically.
The warbler also spends the winter in southern Spain, Portugal, and northern Africa, its ancestral home.
Blue squares and circlesin the map below show the winter locations of warblers that researchers captured in southern Germany. Birds that winter in the British Isles rarely mate with the warblers that winter farther south.
The so-called assortative mating process, enhanced by the Blackcap's new migratory route to Britain and Ireland, could eventually lead to a new species.
Stuart Bearhop of Queen's University Belfast and colleagues published the findings in the October 21 issue of the journal Science.
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This Just In
All of the estimated 240 Wood Stork nests at the Corkscrew Swamp Sanctuary were abandoned last spring, and the total number of wading bird nests in South Florida fell 41 percent from 2004, according to a report published by the South Florida Water Management District. Wetlands that wading birds rely on were inundated by rain early in the nesting season, causing the decline.
The Ivory-billed Woodpecker received the federal government's lowest "recovery priority number" - an 18 on a scale of 1-18 - in a recovery plan published last September. The U.S. Fish and Wildlife Service uses the priority system to direct its efforts "toward the plants and animals in greatest need."
Possibly the largest invasion of Cave Swallows ever into the Great Lakes region occurred in early November. Birders in Rochester, New York, spotted nearly 600 swallows, and observers reported handfuls to hundreds of the birds in Ohio, Indiana, Michigan, Illinois, Ontario, and Wisconsin.
The Upper Bay of Panama, visited by up to two million shorebirds each year, was recently named the first site in Central America to join the Western Hemisphere Shorebird Reserve Network. It is a globally important site for Western Sandpipers and at least six other shorebird species.
The number of Black-faced Spoonbills rose 22 percent in 2005 to 1,475 birds, according to a recent census. The Asian species has recovered from a low of 294 birds in 1990. In our April 2003 issue, we reported on an avian botulism outbreak in Taiwan that killed 71 spoonbills.
See our Birding Briefs Special Report: The Truth About Bird Flu
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