Listening for signs of spring
A black bird with brilliant bands on his shoulders, like the blossoms of tulip trees, lights on a cat-tail with a low, rasping cry. Some of the first signs of spring come by ear.
"Among the early returners are red-winged blackbirds, males in the marshes," said Rene Laubach, director of Mass Audubon's Berkshire Wildlife Sanctuaries. "Within two weeks, the phoebes will be back -- they nest on shelf-like structures on buildings, and on lights."
House wrens will return, he said, and brown creepers will sing high-pitched melodious ripples in the woodlands. The main migrations will come in mid to late April, but bluebirds and robins are here already -- some overwinter. And chickadees, tufted tit-mice and white-breasted nut-hatches, visiting backyard feeders, will begin to shift from winter calls to spring breeding songs, especially on sunny days.
On a rainy spring evening, a walker in the Berkshires will hear the first spring peepers -- or a bat waking from hibernation.
Bats talk to each other. A mother can find her babies by sound in a roost of millions of bats, said Craig Langlois, education and program manager at the Berkshire Museum. They squabble, and they recognize each other by voice.
But they are best-known for another aural skill: echolocation. Bats make a series of clicks through the mouth and nose and hear the echoes of the clicks coming back to them, said Emma Kerr, natural science education specialist at the museum. They hunt insects in the dark by echo.
Humans can't hear these sounds -- bats can hear a greater range of frequencies than people do. The chittering of a bat flying at dusk is not echolocation.
It may be the sound of one bat talking to another or the sound of their flight.
What does a rainy spring night sound like to a bat?
Rob Mies, director of the Organization for Bat Conservation, visited the museum this month with a "bat detector" -- a machine that makes the frequency of the echolocation into a sound people can hear. When he brought a meal worm close to the bat, the clicks speeded up.
New York artists have begun playing with the sounds of bats, Langlois said, and remixing them with music.
But what sounds like a series of clicks to a human eavesdropper means something to the bat. Based on the echo bouncing off a moth or a maple bud or a rock, the bat can tell how far away something is, how large, whether it is moving and how fast, Langlois said.
The response is based on folds in the ear and on what part of the ear intercepts the vibrations, he said. The structure of a bat's ears is finely developed. They have delicate folds to increase surface area, and increasing surface area increases sensitivity. And relative to their size, their ears are large.
The big-eared bat may be 2 inches tall and have ears 2 inches long, Kerr said.
Bats can detect an object the size of a hair.
They can "hear" an object a quarter of a mile away, Langlois said, and they interpret movement and changes in direction as instinctively as a human reaches out to catch a ball.
"When we walk around, we're planted on the ground," Langlois said. "In the air, they're in three dimensions, and they're not running into each other. Birds use murmuration, when they all gather together and move as one cluster. Bats don't."
They live in colonies of hundreds of thousands, Kerr said, and they pour out of their home cave together at dusk, through they may spread out to hunt.
"We hear more than we process," Langlois said. "Our minds filter out repetitive sounds. I wonder whether bats do the same thing."
When they hunt on a rainy night, do they hear echoes of the rain drops?
Sounds of the Berkshires:
A March medley of local sounds, natural and manmade --
What: 'Bats: Creatures of the Night' exhibit
Where: Berkshire Museum, 39 south St., Pittsfield
When: Through May 12
Information: (413) 443-7171, berkshiremuseum.org
What: Bird walks in Canoe Meadows with Mass Audubon
When: Friday mornings in April and May
Information: (413) 637-0320 www.massaudubon.org
To learn about birdsong: www.birds.cornell.edu/AllAboutBirds/studying/birdsongs
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