For the Birds Radio Program: Questions Not Answered in Books

Original Air Date: Jan. 31, 2005 Rerun Dates: Nov. 14, 2012; Nov. 25, 2011; Dec. 10, 2010; Nov. 21, 2008; Dec. 27, 2006; Feb. 10, 2006; Oct. 19, 2005

Some questions about birds aren’t answered in the bird books.

Duration: 5′03″


People have been recording their bird observations at least since early cave-dwelling times, when a primitive but accurate pair of Snowy Owls and their chicks were painted on a cave wall in France, 32 – 34,000 years ago. But so many centuries later, we’re still discovering a lot about birds. Just a few fairly simple questions about which we still seek answers:

Why do waxwings pass berries back and forth before eating them? I think I figured out the answer to this one when I was caring for an injured Bohemian Waxwing one winter. At the time I had the bird, there were dozens of waxwings feeding in my mountain ash, so I went out and retrieved a few berries to feed my bird. He ate them eagerly, but 10 or 15 minutes later, out they came the other end, completely undigested. I’d been watching the outside birds mouthing and passing berries to one another, and how a single berry could pass through the beaks of 10 different birds before one finally swallowed it, and I suddenly had an inspiration. I brought in another handful of berries, but this time before feeding the waxwing, I rolled the berries between my thumb and index finger for a few minutes. This time the waxwing digested them completely. Apparently mouthing the berries and passing them from bird to bird not only cements social bonds but also helps soften the berries to make them more digestible. Though, come to think of it, I did mention this in my first book, so now this actually is something you could learn from one book.

Back in 1946, Edmund Jaeger discovered what he called a hibernating Poorwill in the Chuckwalla Mountains of California. That individual was found hibernating, or in extended torpor, the following three winters as well. He wasn’t the first to discover a hibernating Poorwill—Meriwether Lewis also found one on the Lewis and Clark expedition, which he could not rouse. He wrote in his journal thatwhen he picked up the bird, “It appeared to be passing into the dormant state”. His log entry for Oct. 18: “on the 18th the mercury was at 30. The bird could scarcely move. I run my penknife into its body under the wing and completely destroyed its lungs and heart yet it lived upwards of two hours. this I could not account for unless it proceeded from want of circulation of the blood.” Native Americans had long noted the habits of Poorwills—their name for the species was Hölchko, which means “the sleeping one.” But after his discovery, ornithologists have never been able to find more than a handful of hibernating Poorwills, and they are currently teasing out information about how many other species in this or other bird families undergo hibernation or extended torpor—this state has been observed in some swifts and hummingbirds. I’ve been studying nighthawks, in the same family as Poorwills, for a long time, at first curious about why once a day when they pooped it was yucky and smelly, quite different from the rest of their droppings. In books I learned that nighthawks have two blind offshoots of the intestines called caeca, and what I was teasing out when I was in graduate school was how bacteria in the caeca affect digestion. Apparently in nighthawks these bacteria produce an enzyme called chitinase that helps the nighthawks to digest the thick exoskeletons of beetles and other hard-bodied insects, in the way that Ruffed Grouse caeca produce cellulase to help them digest the woody tissue in tree buds in winter.

Now, thanks to dozens of observant northlanders, we’re teasing out how Great Gray Owls eat rabbits and squirrels. One day books about Great Grays will include information about how their primary food is mice and voles, but that many individuals are effective at killing and eating animals as big as snowshoe hares. Most of the observations indicate that the owls can’t carry this heavy prey far or high in the air, and eat it on the ground. They don’t take many bones, rather ripping off the meat while sitting over it for many hours, which seems to both guard it from other predators and scavengers and to keep it thawed. And w ho knows what question will next occur to someone, who will seek out the answer, which will eventually find its way into a book?