DEBBIE ELLIOTT, host:
From NPR News, this is ALL THINGS CONSIDERED. I'm Debbie Elliott. For those of you shivering away through the long winter month of January, here's a hopeful note. The other day we got an e-mail for Candace Savage. She's our nature watcher in Saskatoon, Saskatchewan.
Even though the official start of spring is still almost two months away, she wrote I can't believe it. Yesterday at minus 19 degrees Celsius, or just below zero Fahrenheit, I heard a woodpecker drumming, not just pecking around for food, but pounding away rhythmically on an echoey, hollow trunk. It's the woodpecker equivalent of birdsong, and it means that the birds are getting in the mood for spring.
We have to admit that we found this pretty exciting, signs of spring in January, so we called her to find out more. She joins us now from the CBC studios in Saskatoon. Hello again, Candace Savage.
Ms. CANDACE SAVAGE (Nature Watcher and Author, "Crows: Encounters With the Wise Guys"): Hello there.
ELLIOTT: Tell us more about what you're seeing up there. Well, I was worried for a few days that you were going to think I was a complete fraud because it's been warm and puddley, but today we're back in the dominion of winter. Everything's hard and crunchy, and there's wind that makes it feel like minus 20 degrees centigrade.
But despite that, I've been hearing great horned owls dueting to one another. Now this isn't just something that they do all winter long. They're amongst the earliest birds to breed. They'll be on their nest in March, and this probably was a matted pair talking to one another, whoo-whooing at one another from different parts of their territory, starting to get in the mood. So it proves if, you know, even though we're still freezing to death here in the snow zone, spring actually is on its way.
ELLIOTT: Now how, exactly, do birds and animals know that spring is coming?
Ms. SAVAGE: Well, that is a very good question and one that puzzled people for a long time. Scientists used to think that birds must sense a change in temperature or maybe it was barometric pressure. You know, bird migration in the northern hemisphere was a particular mystery. How is it that a bird that's in Mexico or in Argentina picks up the pulse of spring and is able to get back to us at just the right time?
In about 1920, there was a person named William Rowan, he did some experiments with a group of birds called dark-eyed juncos. He was able to expose them, not to changes in temperature, not to differences in barometric pressure, but to different day lengths.
Birds actually have a special part of the brain itself that is sensitive to light, and the pineal gland, right in the middle of the brain, also receives light, not through the eyes but through the skull. There've been nasty experiments done with birds in which they were blinded, and they continued to go through their cycle in time with the seasons. But if their skulls were painted black so no light could go through the bone, then they, there reproductive cycle just fell apart. They no longer were able to tell time.
ELLIOTT: So those long, dark nights actually give birds some vital information.
Ms. SAVAGE: The long, dark nights of winter are what reset their biological clocks. More experiments, experiments were done with a group of birds called white-throated sparrows. Those are the lovely little Boreal-breeding birds. On this side of the border, we think they say, oh, sweet Canada, Canada, Canada. I don't know what they say in the United States.
But scientists have shown that if white-throated sparrows in the fall are immediately exposed to longer days, they don't go into breeding condition. They have to have a period when the nights are long to get them in the mood again, to reset their clocks.
ELLIOTT: What about other animals? How do they know the season is changing?
Ms. SAVAGE: It turns out that for microorganisms, for plants, for fish, for reptiles and for mammals, just as for birds, photoperiod, the change in day length, is the most important parameter, the most important phenomenon that we all track. So we're all keeping time by the sun.
ELLIOTT: Candace Savage writes about nature from Saskatoon, Saskatchewan. She's the author of more than 18 books, including most recently Crows: Encounters With the Wise Guys. Thanks for joining us.
Ms. SAVAGE: My pleasure.
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