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November 5 - November 28, 2023
Pick up a pair of owl feathers and rub them together, and you won’t hear much. That’s because the feathers are coated with a fine layer of plush fibers called “pennula,” which shroud sound and give owl wings that soft, velvety feel that Graham noted. An owl’s wing feathers separate slightly from one another in flight, so air flows over each feather, with the pennula providing a gap between adjacent feathers so there’s none of the friction or rubbing there is in most birds. The wispy vane fringes at the tips of both wings and tail also help to prevent wind eddies. Collectively, the serrated
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Owls that depend less on hearing when they hunt, such as Mountain Pygmy Owls, have noisier flight.
They’re masters of camouflage—streaked like grasses; mottled, speckled, and striped like tree bark; pale like snow—to befuddle the eye of both predators and prey. They wear the look of the land around them to meld into it, a strategy known as crypsis.
Barred Owls had invaded the home range of the spotted owls, and the presence of the aggressive invaders suppressed the smaller owls’ own hooting. If the spotted owls did vocalize, the Barred Owls would attack them, sometimes with lethal force. So the smaller birds started to go silent, and the traditional method of hooting to find Northern Spotted Owls stopped working.
Enter Max, a “detective dog.” Hartman trained the blue heeler mix to use his 250 million olfactory cells (more than twenty times the number we possess) for the highly specialized task of detecting the pellets owls eject at roosting or nesting spots.
Hartman and Max participated in a study showing that dogs specially trained in this way could detect the owls better than vocalization surveys and could cover a much bigger area. The probability of detecting Northern Spotted Owls after six vocalization surveys was 59 percent. After three dog searches, it was 87 percent.
The day Max found a family of four owls using only his nose, Hartman knew this was an important way of locating these owls. And it was completely noninvasive. “We didn’t have to see the owls or elicit hooting from them and attract unwanted attention.”
When a team of conservation biologists was tasked with surveying for Barred Owl and California Spotted Owls throughout the northern Sierra Nevada, “the prospect was overwhelming,” says team member Connor Wood. “We looked at the logistics and realized there’s no way we can do this with traditional methods.” So the team devised a system for “passive acoustic monitoring,” planting 200 audio recording devices across thousands of square miles of mountainous terrain to collect owl calls for two years.
“These two species just can’t coexist. They’re too similar ecologically, and it’s the spotted owl that loses because Barred Owls are bigger, more aggressive, and more flexible in what they eat—just all around competitively superior.
Wood was deeply surprised by what he discovered in the recordings: First, the density of Barred Owls was still fairly low in the Sierra Nevada. And where the bigger owls were present, California Spotted Owls were making more territorial calls—the opposite of what had been found in the Pacific Northwest.
Even passive acoustic monitoring won’t work in the most remote places on the planet—like the old-growth forests of northeast Asia and Russia, home to the Blakiston’s Fish Owl. The terrain is too difficult and hard to access. So scientists are turning to other high-tech monitoring strategies—satellite imagery and drones.
Typically, Burrowing Owls use ready-made burrows dug by prairie dogs, woodchucks, skunks, badgers, armadillos—really any fossorial mammal—and even tortoises, which spares them the trouble of excavating their own holes.
In this region of Brazil, with its fertile red soil, their natural environment has been transformed into pasture and farmland, forcing the owls to seek a less desirable breeding habitat.
So it’s these two conditions, stability of climate and landscape and variety of topography, that have allowed owls to diversify in these regions.”
The geotags, tiny data loggers and transmitters, are a great way to collect an owl’s location several times a day, providing abundant data about its activity, where and when it’s resting, moving, hunting, or migrating. But the tags are costly, and while some of these devices transmit the data to a satellite or receiver station, like a cell phone tower, others require recapturing the bird to download all the information—which can be a gamble.
At first Johnson thought there was something wrong with his data. Why would males choose to winter in a frigid area where food is scarce? He realized there could be only one reason: “Because they want to be first back to their burrows! Their strategy is, ‘If I can survive in the north, I get to be first back. And if I’m first back, I get dibs on the best burrow and the best territory.’ For a male, real estate is worth putting your life on the line.”
Johnson knows the owl is female because she’s bigger than her male counterpart would be, and darker. During the nesting season, the feathers of males bleach out in the sun as they stand guard over the nest.
There are greeting hoots and territorial hoots and emphatic hoots. And owls don’t just hoot. They shriek, yap, chitter, squeal, squawk, warble, and wail plaintively, most often in courtship songs—love songs made of odd and uncouth sounds generally unappreciated except by the ears for which they are intended. Some owls sing with the full power of their lungs; others coo softly. Some chirrup like a cricket. Some chuckle or roar with maniacal laughter.
In general, body size for a bird dictates the pitch of its vocalizations. The bigger the bird, the lower its pitch. Smaller birds usually have higher, twittery voices. The tiny Flammulated Owl explodes these formulas. It slows the vibrations of its call by loosening the skin around its throat, creating a low-pitched, husky hoot more suited to a Great Horned Owl,
Unlike songbirds, which learn their songs through vocal learning, just as we learn to speak—by listening, imitating, and practicing—owl calls and songs are hardwired, genetically fixed.
“Owls don’t want to fight because the risk of injury is so high,” says David Johnson. “If you catch a talon in the eye or something, it’s game over, so you’re willing to do everything you can do to avoid that. When you vocalize, if you want to be a tough guy, you’ll lower your voice and project it.”
And sure enough, if a nesting Great Horned Owl is threatened by a dog or other predator, it will fluff up its feathers and throw itself to the ground, flapping around as if its wing is injured and squealing once or twice—a highly risky move and an indicator of what good nest protectors these birds can be.
Why would owls have distinctive voices? Most bird species have at least some individuality in their calls and songs. It’s useful in identifying kin and communicating with mates, allies, and rivals.
The team members studied various regions with different densities of Little Owl populations. In Hungary, they found that where males are living on isolated farms, far from other neighbors, territorial calls have less individuality. But where the population is denser, where there are as many as five males at a single site calling to one another as little as one hundred meters apart, calls are more distinct and distinguishable—likely to enhance individual recognition within the community.
In the bird world, divorce is defined as one breeding individual partnering with a new mate while the previous mate is still alive. A study in barn owls suggests it occurs when breeding isn’t going well for a pair, and new pairings benefit both partners. But not much is known about divorce in eagle owls. Savelsberg discovered that those at the quarry seemed to swap partners as often as Great Horned Owls.
Parent owls don’t chase away their young at the end of the breeding season, as was previously believed. The owlets hang around, sometimes for months. This developmental pattern—a long juvenile period before becoming independent from parents—is considered by some scientists a prerequisite for intelligence in birds.
It seems counterintuitive. But many bird species rear offspring that are not theirs, especially if they’re captive bred or cooperative breeders (birds that routinely raise young collectively).
Sometimes owls will adopt orphan chicks when they lose their own, which appears to have been the case with these eagle owls. But the behavior seems remarkable, nonetheless.
What does it take to make an owlet? It’s the mystery and the enterprise for which all owls live. The different species do the job differently, but for all, it’s hard work with tough odds. And for all, it starts with finding a mate.
can see why these owls are known as “glaring gnomes.” They even glare from behind, or so it seems. On the back of the Northern Pygmy Owl’s head is a pair of dark, white-ringed feathered eyespots, “false eyes” that are quite convincing. For years it was thought these eyespots functioned solely to confuse predators, but research suggests they may also confound mobbing songbirds.
Early in the breeding season, in late winter, males sing their strange, loud, repetitive toots from a high perch to attract a mate. If the female shows interest, then comes duetting, alternating single toots from a distance, male at a lower pitch and female at a higher pitch.
When the pair is bonded, they’ll hunt apart during the day, but they always know where the other is by swapping toots of call-and-response.
Courtship in owls is like this. No strutting around or flashing of splashy, colorful feathers, mostly just mutual hooting.
Once a male owl gains the interest of a female, he may start showing off in other ways. He might display his feathers by fluffing them out. He might stretch his head to the full length of his neck, then swing it to one side and drop it at least as low as his feet, then swing to the other side and raise it again.
The Snowy Owl is the only owl species with distinct sexual dimorphism in its adult coloring and plumage patterning.
But in Snowy Owls, females are dramatically darker than the pure white males.
Why would owls pick mates their own size? It has to do with energetics, says Johnson. “It’s only advantageous to be big during a good food year. If it’s not a good food year, it’s better to be smaller because you need less energy to succeed.”
Most owls don’t construct their own nests at all, but rather they appropriate structures built by other animals. The male usually finds a territory with abundant prey and some good nesting possibilities, but the female selects the actual nest sites.
While cavity nesters like Northern Pygmy Owls need natural tree holes or the drilled holes of woodpeckers, Great Grays rely on large broken-topped snags or the abandoned nests of other big birds.
With that huge influx of food and no cleaning up—you know, they don’t take the trash out—all of this recycling is going on inside the hollow by invertebrates, fungi, and bacteria. So I don’t think we can replicate in a nest box that really special dynamic environment offered by a tree hollow until we really understand it.”
Dave Oleyar and his graduate student Kassandra Townsend are also looking into the thermal properties of hollows in different tree species and thinking about the effects of global climate change on the cavities themselves and on the owls and other animals that depend on them. “Will the same suite of animals use these cavities when (or if) the temperature range within falls above or below certain thresholds?”
Here’s one way that Northern Pygmy Owls are rebels in the owl world. The females in most species of owls start incubating as soon as they lay an egg. Not a female pygmy owl. She’ll lay an egg every day or day and a half, with a total, usually, of five to seven eggs. But only after she has laid all of her eggs will she settle in to incubate.
their development. The number of eggs she lays, as with all owl species, relates to her condition, says Holt, and how much food is available, both where the owl is nesting and—in the case of migratory species—where she came from.
area that makes the most of their camouflage. Only birds that lay in places hidden from view have white eggs—woodpeckers, bee-eaters, kingfishers, owls. The eggs are concealed, so there’s little reason to expend precious energy producing pigments for them.
The eggs of birds that are airborne most of their lives—murres, sandpipers, albatrosses—are elliptical, the theory goes, streamlined to fit through the pelvis of the birds’ smaller, lighter, and more compact skeletons. Owls, which tend to fly only in short glides, have a heavier skeleton and a wider pelvis that can accommodate more spherical eggs. (But there are exceptions, of course. Barn owl eggs are decidedly conical or ovoid. The eggs of Great Grays are “egg-shaped,” too, but they’re smaller than a hen’s egg and can fit through the bird’s pelvis.)
Some chicks might already look like small adult owls, still downy but with the dark facial disk of adults and flight feathers already growing in, while others look like tiny balls of white downy fluff.
just seems amazing. How do they gain the strength to fly that way? How do they develop their wings when they’re still inside the cavity?”
Scientists have found that nestlings with live-in blind snakes grow 50 percent faster and experience lower mortality than broods lacking serpentine company.
Successfully raising young is such an energy-demanding task that the adults routinely lose as much as a third of their body weight during the nesting season. In pouring their resources into their offspring, they also forgo molting their feathers—a process that consumes significant energy.
“this big female came barreling in. For whatever reason, we didn’t detect her until the last minute, and she got me in the back of the head. It was like being hit with a two-by-four with nails stuck in it. One of the talons dug deep into the back of my skull, and the tip broke off in there.
