On Monday I wrote about cats and windmills as threats to bird life but neither of them are the leading reason why birds die. The number one cause of bird death worldwide is habitat loss.
The Laysan rail, pictured above, went extinct in the 20th century because of habitat loss with a bizarre twist.
Laysan is a small, isolated island in the middle of the Northwestern Hawaiian Island chain. Only 1 by 1.5 miles across its land area is 1,016 acres, about twice the size of Schenley Park.
Laysan is famous for its bird life, a nesting island for many Pacific seabirds and home of the rare Laysan albatross and even rarer Laysan duck. It was also the home of the Laysan rail, a fearless, flightless bird less than 6 inches long.
Unfortunately, in 1903 Max Schlemmer released rabbits on the island as a money-making venture. Instead of making money it was the beginning of the end. The rabbits on Laysan had no predators and in short order they overran the island. (Keep in mind that a rabbit can bear 35 young per year.) The rabbits ate everything. Everything.
By 1918 Laysan was a barren dustbowl on which only 100 rabbits survived. With little to eat and no cover the Laysan rail population was hanging on by a thread. Meanwhile a few rails had been introduced to other islands in the northwestern Hawaiian chain in hopes they could survive elsewhere.
In 1923 the Tanager Expedition eradicated Laysan’s rabbits but it was too late for the rail. The last two on the island died that year. A few hung on at other islands in the chain but the final blow fell in 1944 when a World War II ship drifted to shore on Eastern Island, Midway and the ship’s rats swam ashore. The rats ate the last Laysan rails on earth. That was that. Extinction.
In the broadest sense, loss of habitat killed the Laysan rail. In a narrow sense it was a case of extinction by rabbit.
(drawing by Walter Rothschild from Wikimedia Commons. Click on the image to see the original. Today’s Tenth Page is inspired by page 640 of Ornithology by Frank B. Gill.)
On Tuesday morning, amidst fog and drizzle, four intrepid men from the University of Pittsburgh, PixController, and the National Aviary visited the Cathedral of Learning to replace the peregrines’ streaming nestcam.
Last year the old camera stopped displaying color in bright sunlight. Ideally its replacement would have been installed in January when the peregrines weren’t territorial but scheduling was a problem. High winds a week ago postponed the trip until February 5.
At first the peregrines were nowhere to be seen, probably because the fog kept them drowsy at their roosts.
Dave Marti (Pitt), Bill Powers (PixController) and Chris Gaus (National Aviary) worked undisturbed in the photo below. Mike Faix (National Aviary) was on the ledge too but not visible in this picture. The work area is so small that everyone has to stand in a row.
The effort took longer than expected and Dorothy got tired of roosting. Even though it was drizzling she dropped by to see what was happening (above) and Chris held out the broom so she would keep her distance.
The new camera is now in place and will start streaming in a few weeks. Thank you to everyone who made this peregrine nestcam possible. To…
- The University of Pittsburgh for hosting the peregrines’ nest and cameras.
- Phil Hieber of Facilities Management who makes all the arrangements and keeps the peregrines in mind whenever there’s Cathedral maintenance … and to Dave Marti & his toolkit.
- Bill Powers and and PixController for camera expertise.
- The National Aviary’s Urban Peregrine Program that hosts the falcons’ website (that’s Teri Grendzinski, Chris Gaus and Mike Faix).
- And to everyone who donated to the National Aviary to make this camera possible.
By the end of February, Dorothy will drop by more often.
(peregrine/broom photo by Mike Faix, installers’ photo by Kate St. John)
Heavily hunted for meat and feathers, trumpeter swans nearly went extinct in the early 20th century, disappearing from all but a small range in Alaska and Canada.
When the swans were at their low ebb, states and provinces established reintroduction programs in the 1970’s and 1980’s in Ontario, Minnesota, Wisconsin, Michigan, and (an introduction program in) Ohio.
Because of the Ohio program we now see trumpeter swans occasionally in western Pennsylvania, but if you want to see a really large flock the place to be is along the Mississippi River at Monticello, Minnesota in mid-winter. They’re there because the water is ice free, thanks to a nuclear power plant upstream.
Sparky Stensaas, the Photonaturalist, visited last month and produced this video.
Read his blog for more information about the Monticello trumpeters.
(video by Sparky Stensaas)
How do you survey a population of owls who are afraid to make noise? Dogs to the rescue!
In 1990 northern spotted owls were listed as Threatened under the Endangered Species Act. Since then their population has been surveyed year after year, but despite changes in logging practices northern spotted owls continue to decline 3.7% per year.
Part of the problem could be that some owls have fallen silent and are impossible to count. The typical survey method is to play an owl recording and listen for the owl to respond. But barred owls have infiltrated the old growth forest, displaced northern spotted owls, and sometimes killed them. Some northern spotted owls would rather not respond when the tapes are played. They don’t want to give themselves away.
So how do you count these owls?
Researchers at the University of Washington trained two dogs, Max and Shrek, to identify owl pellets by species! Amazingly, the dogs can smell the difference in regurgitated mouse bones from a barred owl versus a northern spotted owl.
The team takes the dogs out for a spin in the forest. They don’t use recordings at all. The dogs sniff for pellets below owl roosts and are so good at identifying the species that they have a 30% better success rate at finding northern spotted owls than the recordings do.
Here’s Max triumphant. See the northern spotted owl in the tree above him?
Read more about Max in the Science Daily press release.
(photo of Max, a member of the University of Washington’s Conservation Canines program, by Jennifer Hartman, Univ of Washington)
How do owls turn their heads this far without killing themselves?
Trauma experts know that when humans turn their heads too far or too fast the arteries to the head are stretched or torn, cutting off the blood supply or producing blood clots that can kill.
Why doesn’t this happen to owls? A team at Johns Hopkins decided to find out.
Led by medical illustrator Fabian de Kok-Mercado, they used imaging technology on barred, snowy and great horned owls who had died of natural causes. The researchers found four adaptations that make the owls’ wide range of movement possible:
- As in humans, the major arteries that feed the brain go through bony holes in the vertebrae but in owls these holes are 10 times larger than the arteries, allowing them to move within the hole without pinching.
- The owls’ vertebral artery enters the neck higher up than in other birds — in the 12th vertebrae rather than the 14th. This provides more slack.
- When an owl turns its head the arteries at the base of the head balloon to take in more blood. In humans the arteries get smaller and smaller.
- Owls also have small vessel connections between the carotid and vertebral arteries so if one path is blocked the other still works.
A simple turn of the head that’s so hazardous to us is all in a day’s work for an owl.
Read more about the study here in Science Daily.
(photo of a barred owl by Steve Gosser)
In case you missed it last week, the numbers have changed.
The Smithsonian Conservation Biology Institute and U.S. Fish and Wildlife Service developed a mathematical model, used data from 21 of the most rigorous cat-wildlife studies, and ran the numbers on cats.
The results were quite surprising. 2.4 billion birds are killed by cats every year in the U.S. That’s two to four times the old statistics.
Compare this new data to other human-induced causes of bird mortality(*) and cats are now on top.
- Cats: 2.4 billion
- Windows: 1.0 billion
- Power lines: 0.174 billion
- Communication towers: 0.051 billion
- Windmills: 0.0004 billion
So you can stop worrying about windmills.
If you want to save birds’ lives, keep your cat indoors. I do.
Read more about this study including information on feral and pet cats in the New York Times.
(photo of windmill and a former stray cat named Lilith, both from Wikimedia Commons. Click on the imbedded links to see the original photos)
(*) p.s. I’m not sure where habitat loss fits in now, but it has always been the leading cause of human-induced bird mortality.
p.p.s. I love both birds and cats. Here are two posts about my beautiful indoor cat, Emmalina: Mouse in the House and Animal, Vegetable.
This female ring-necked pheasant looks wary as she steps out across the snow in the last hour before sunset.
The snow was five to six inches deep when Cris Hamilton, Bobby Greene and Don Weiss found this and another female pheasant at the Volant Strips on January 5.
The pheasants weren’t bothered by the birders but they were certainly watching for predators.
And this bird was watching her step. Despite her light weight she occasionally punched through the snow.
(photo by Cris Hamilton)
What’s black and white and red all over?
This crimson-breasted shrike (Laniarius atrococcineus) from southern Africa is an unbelievably beautiful bird.
(photo by Hans Hillewaert from Wikimedia Commons. Click on the image to see the original and its location data)
A bird’s lifestyle is written in its wings.
Birds who fly fast and maneuver quickly, such as peregrines and swifts, have narrow pointy wings built for speed and agility. They need this equipment to capture prey in the air.
Birds who soar slowly in search of food, such as red-tailed hawks and turkey vultures, have broad wings with a lot of surface area.
Broad, blunt wings create a lot of wingtip turbulence (remember those vortices?) so soaring birds have feather slots at their wingtips. This confers two flight advantages.
First, each feather stands alone like a tiny pointy wing with a high aspect ratio (ratio of length to breadth) that’s more like a peregrine’s wing. The winglets create less turbulence and therefore less drag.
The second advantage is in the gaps. As air is forced upward between the feather slots, it expands on the upper side creating low air pressure on top and therefore more lift.
Turkey vultures are masters of slow speed flight. They turn and teeter without flapping — not even once!
The slots help them fly.
(Photo by Chuck Tague. Today’s Tenth Page is inspired by page 120 of Ornithology by Frank B. Gill.)