(This exceedingly long post is broken into separate radio/podcast episodes. Part 1, Part 2, Part 3, and Part 4.)
My birding buddy Michael Bernstein recently made a reservation for his family and a friend to visit Hawk Ridge Bird Observatory’s owl banding station this past Saturday night and generously invited me to come along. The Hawk Ridge Bird Observatory traps somewhere between 600 and 1,700 or so tiny Northern Saw-whet Owls every fall; they provide opportunities for small groups (like us) to observe the banding and public programs for larger numbers of people to learn about owl banding and see banded birds just before they’re released. (Details about both opportunities are here.)
Unlike hawk banding, owls caught at night are not lured in with what looks like potential prey. The banders capture only those owls who just happen to be flying in the area and get caught in the mist nets. In hopes of drawing curious owls from a wider area, banders were playing recordings of Long-eared, Northern Saw-whet, and Eastern Screech-Owls while we were there. They never play recordings of larger owls—on the very rare occasions that a Great Horned or Barred Owl does appear on site, it may try to grab one of the little owls from the net, hurting or even killing the little bird as well as getting itself entangled. Fortunately, this hardly ever happens. When a larger owl is caught, the banders usually take it somewhere else to release it.
The largest push of migrating saw-whet owls up here is in October, but they start moving in September, after the young of the year are fully independent and the adults have finished molting. Owl banding at Hawk Ridge starts on September 15, and during the first 7 nights of banding this year they caught a respectable 32, but then it picked up enormously—on just the five nights from September 23 through 27, they caught 250. (You can see the totals from this and past seasons here.)
As usual, the only owls they’ve caught as of September 27 were saw-whets. All but seven of these are now wearing a new U.S. Fish and Wildlife Service leg band; the exceptions were already wearing a band when they got caught. A great deal of information can be gleaned from those rare encounters with previously banded owls.
On Saturday, we arrived at 7:30, just as the banders were setting up their mist nets. They check the nets every half hour; when they checked at 8:00, they’d caught one, and at 8:30, three more. Our group stayed until they’d released the last of those and the banders were heading out for the 9:00 net check. Through the night, they caught 31 more.
It’s of course a crapshoot whether any owls at all show up on a given night—owl migration is very weather-dependent, heaviest when winds are light or from the northwest and pretty much non-existent when it’s raining hard. Ideal conditions can’t be predicted in advance with any certainty, but the Hawk Ridge staff provides a lot of valuable information so on the few nights the experience falls short of superb because of a dearth of owls, it’s still pretty darned good.
I’ve observed saw-whet owl banding at Hawk Ridge and other banding stations several times over the years, and it’s always a treat. Once in a while, one of these tiny owls shows its displeasure by clacking its bill, but they never bite or claw at the people handling them1, and their curiosity always exceeds their annoyance, making it a genuine joy to watch them watching us.
When an owl is ready for release and has had time to adjust to the darkness, very often the banders allow one of the visitors to hold the bird in their flattened hands until it flies off.
On Saturday night, one flew off almost instantly, two remained for several long seconds, and one remained for over a minute. They’re so light, their feathers so soft, and their eyes so bright that holding one for even the briefest moment is one of the sweetest experiences a person can have.
Seven TONS!
The owl banding project at Hawk Ridge was started in 1972 by David Evans, who banded raptors there every autumn through 2010. Since 2011, Frank Nicoletti has been the lead bird bander, then the Research Director, and now the Senior Research Associate. I can’t find a total number of saw-whets banded at Hawk Ridge over the past half century, but 11,359 were banded over the past 10 seasons. Extrapolating suggests that over the 54 years they’ve been banding these owls, they’ve handled more than 60,000. Saw-whets average about 4 ounces, which means that in the past half century, the Hawk Ridge banders have dealt with a good 7 TONS of Saw-whet Owls. Imagine that.
The banders place a numbered, aluminum U.S. Fish and Wildlife Service leg band on each bird and record its weight and wing-chord length to determine its sex.
Females average larger than males but there’s some overlap in wing chord length so only the longest and shortest indicate sex accurately. The heaviest of the ones of intermediate wing length are females and the lightest are males, so using both measures determines sex in virtually all of them.
The banders examine how faded or fresh the flight feathers are to determine the bird’s age.
The precise shading of the color can be a little tricky to distinguish in low light, but that is much easier now that we know that one of the pigments on the underside of a saw-whet owl’s wing feathers is porphyrin. This pigment is visible only at the ultraviolet end of the spectrum so we mere humans can’t see it under natural light, but it glows pink under a black light. Porphyrin degrades and fades over time, most quickly when exposed to sunlight, so while fresh new saw-whet feathers are rich in porphyrin and appear brilliant pink under a black light, older feathers are not pink at all.
By fall, young saw-whets molt out of their adorable juvenile plumage…
…into their even more adorable adult plumage.
Banders can easily recognize the birds hatched this year because every one of their flight feathers is new and unfaded, all appearing uniformly dark under regular lighting and pink under black light.
This year’s young owls (called “hatch year” or HY birds) will start molting their flight feathers next summer, replacing them in a specific pattern, never all in one year. After a couple of old flight feathers drop out up until new ones grow in, flying ability is slightly compromised, which would be a minor hardship when an owl is provisioning young or when it’s migrating, and growing new feathers takes a lot more nutrients than these little guys can afford to expend while giving most of their prey to their chicks or in winter. So their molt is limited to the brief period after they’ve finished raising their chicks in July or August until they start to migrate in September or October. Their body feathers are replaced every summer, but growing in new flight feathers takes significantly longer, so many older primary and secondary wing feathers remain on the bird after that limited molting period.
The year after their hatch year (called their “second year” or SY), they replace their outermost primaries and innermost secondaries. The new feathers appear more darkly colored under regular lighting or bright pink under black light, while the central section (the innermost primaries and outermost secondaries) is faded—not pink under black light. This simple pattern accurately identifies these birds as second year.
Aging birds in these two categories is easy and straightforward, but it gets more complicated after that. The sequence of molting feathers is regular and consistent, the birds replacing their primaries one at a time from the outermost inward and the secondaries from the innermost outward. (You can see the color pattern for owls of different ages at the McGill University owl banding website.)
Depending on food availability, successful or unsuccessful nesting, and other factors, some individual birds may molt more or fewer flight feathers than average in any given year. Some third year (TY) and fourth year (FY) birds fit the predicted patterns perfectly, but many don’t. We know this because Hawk Ridge’s David Evans and some other banders carefully documented the wing-color pattern for birds who were originally banded as HY or SY and then recaptured years later. Using the original banding information, the bander could verify an older bird’s precise age to see how well its plumage pattern fit the prediction. They found that 95 percent of the birds whose feathers showed the typical third year pattern in fall really were third year birds, but only 59 percent of the known-to-be third year birds showed this pattern. And 95 percent of the owls showing the fourth-year pattern really were in their fourth year, but only 63 percent of the known fourth-year birds showed that expected pattern.
After the fourth year, saw-whets can’t be accurately aged at all, so most banding stations designate birds older than second year as “after second year” or ASY. One second-year female originally trapped in 2009 in Ohio was recaptured and released in 2022 in Pennsylvania when she was over 14 years old! (Longevity records set by retrapping banded birds of all American species are available on the Bird Banding Lab longevity page.)
A Closer Look at Owl Bodies
Visiting an owl-banding station when they’re capturing Northern Saw-whet Owls is thrilling, and also intriguing. Jamie Tigges and Ivy Houts, the naturalists on duty when we visited Hawk Ridge, were very knowledgeable and approachable for all of us, from Michael’s young children through his parents and me.
The Hawk Ridge naturalists have all kinds of teaching tools to explain owl features. Jamie showed us a rope with tags along its length showing the wingspan of a variety of owls, from the tiny Elf Owl of our own Desert Southwest (about 10 inches) to Blakiston’s Fish Owl, native to China, Japan, and Russia’s Far East (more than 6 feet).
We intuitively understand that owls must fly silently to sneak up on their prey, but there’s an equally important reason for their silent flight. After they detect a mouse, they need to keep listening to its tiny sounds as they fly in to capture it—any whoosh of their wings, so close to their ears, would make it hard to hear the mouse. Owl feathers are soft and loose, muffling sounds in the way that new-fallen, fluffy snow can make a winter night so magically silent. But even more important, the leading edges of the first two primaries on each wing have a “comb”—a fairly stiff fringe that breaks up whatever soft whoosh the wing would make into a great many much less audible whooshes. Jamie showed us an owl wing so everyone could see this unique and important feature.
Owl eyes are huge and fixed in place, so they must move their heads to look in different directions. How do they do this so quickly and smoothly? Unlike us mere mammals with 7 neck vertebrae, owls have 14. (Swans have even more—24 or 25!) When sitting still, an owl’s scrawny neck, hidden under very thick feathers, is held in a position shaped something like a question mark, allowing them to easily move it in any direction. Owls cannot rotate their heads all the way around, but larger species can easily move the neck 270º, or three-quarters of the way around.
When some owls are alarmed, they may raise the neck into more of an exclamation point, making themselves look long and thin like a broken branch. If they sense even more imminent danger, they may crouch low, moving their face from side to side in an eerie Egyptian head-slide movement while they widen their eyes and pull back their feather tufts as a threatening cat holds its ears, hissing and clacking their bill to enhance the threat.
Owl retinas are huge. They have cone cells to see color and a huge number of rod cells to discern shapes and movement in the dark. Unlike many birds, the upper eyelid on an owl’s eye is the larger, so they blink down the way we do, protecting their huge pupils from too much sun from above while focusing on potential prey and predators on the ground below. Their pupils can dilate enormously but cannot contract to be as small as ours, so under what would otherwise be uncomfortably bright light, they can close their eyelids. When we see owls in daytime, they often appear to be asleep, but if you look very carefully, you can see that the eyelid is open a crack. When our eyes are mostly closed, our vision seems smushy, but owls can see perfectly well with mostly closed eyelids.
When flying, owls seldom blink—at least, they don’t blink their outer eyelids. Instead, their translucent inner eyelid, the nictitating membrane—sweeps across so they don’t have even a split second’s loss of vision. Banders do their best to minimize the amount of stress on the birds they capture, releasing them as quickly as possible, so visitors can’t usually scrutinize their eyes. I got these photos of a captive Snowy Owl’s eyelid and nictitating membrane in 2012 during a program at the International Owl Center’s annual festival.
Owl ears are huge and in many species asymmetric, one higher (and in some species further back) than the other. Sound reaches the lower (and sometimes further forward) ear a split second before it reaches the higher ear, allowing the bird’s brain to calculate the distance even as it flies toward the sound. Several species can hunt in total darkness because their brain calculates the distance so precisely that the owl never grabs too soon, missing its prey, nor too late, crashing to the ground.
Long ago, banders often pulled forward the stiff feathers on one side of an owl’s face to show people the huge ear underneath. But owls consider that the height of rudeness, and whenever I’ve observed this, the owls seem uncomfortable, so banders no longer pull those feathers forward unless there’s a compelling reason. But of course people want to know what these huge ears look like under the feathers. After Duluth’s mega-snowstorm on Halloween in 1991, someone brought me a dead Long-eared Owl they found while shoveling—it had still been migrating through when suddenly the snow was just too deep for hunting. Since the poor thing was already dead, it didn’t mind my opening the stiff cheek feathers (called the “facial disk”) to expose the ear. I didn’t tear any tissue—owls can move and control those cheek feathers to focus precisely on sounds. Had the bird been alive or at least warm, the moment I let go of the feathers, they’d have snapped right back into place, but the body was still quite frozen. (After my husband Russ took these photos, I brought the bird to the University of Minnesota Duluth biology department’s collection.)
Owl beaks are longer than they appear, because the base is hidden under the facial disk feathers. The feathers near the mouth can easily get gooped up with blood, so when possible, owls swallow their prey whole or in clean bites.
Owls have specialized feet with two normal front toes, one normal hind toe, and a “reversible” toe—the outer front toe is opposable, so when perched or grasping prey, an owl can hold on whichever way feels best in that situation.
More to learn
Studying owl bodies and the data gathered here and at other banding stations has taught us a lot about these tiny predators, but there is ever so much more to be learned, and the more we learn, the more we realize we still don’t know. For example, females usually outnumber males at banding stations whether or not the station is playing owl recordings. Do females outnumber males, or are males just less likely to migrate?
Saw-whets are known to migrate over large bodies of water—some have washed ashore on the Great Lakes, and some have alighted on fishing boats. In October 1999, one landed on a fishing vessel 70 miles from shore in the Atlantic Ocean near Montauk, New York! How regular are these over-water flights?
Saw-whets migrate throughout the night, with many stations catching the largest numbers in the four hours before dawn. Some stations capture fewer saw-whets on nights with a full moon, while the moon phase doesn’t seem to affect the numbers caught at other stations.
During irruption years, 82 percent of all the owls banded at one station in Virginia were hatch-year birds, while in non-irruptive years, only 33 percent were. Was that because more young had been produced in the irruption years so there was more competition for food, or was it because a food shortage forced the young to move? During irruption years, both the adults and young birds average lower body mass and poorer body condition.
The “advertising call” of saw-whets is a monotonous series of whistled notes on a constant pitch. I once got a call from a person who had been camping in the Boundary Waters Canoe Area Wilderness, miles from the nearest motorized vehicles, when he was awakened in the middle of the night by what sounded like a truck backing up. He was bewildered until he saw the little owl calling away. This call is understood to serve a territorial function, though there is also a courtship component, with females giving a similar call. Researchers studying nesting birds learned that individual males can be recognized by the frequency of these notes. When I’ve watched saw-whets calling, they seem to move their body forward with every note like a real-life cuckoo clock.
We may start hearing this call in April up here, the males already on territory warning away those males still passing through even as they try to attract a mate. Like Boreal Owls, once Northern Saw-whet Owls commence nesting, they pretty much stop calling; both tiny species are vulnerable to predation by larger species of owls.
Owls don’t have access to black lights, but it’s hard to imagine that they’d produce a pigment that they themselves couldn’t see, especially since we already know that many species see ultraviolet wavelengths. But what is the value to them of porphyrin if it fades with time? Saw-whets might be using the intensity of the color of their inner wings as a signal of fitness in a potential mate. How could that help?
The pigment degrades fastest when exposed to sunlight, so individuals skilled at finding and defending daytime roosts in cavities and within deep foliage almost certainly retain the pigment longer than owls who are more exposed or forced to fly around in daytime.
During courtship, males have been reported circling a female about 20 times in flight, exposing those inner wings, before landing beside her. Saw-whets may be looking at more than the intensity of the color—they may well be judging the age of potential mates by the color pattern, exactly the way bird banders do. In most avian species, the older a bird is, the more desirable it becomes as a mate—older birds have more experience and proven survival skills. We humans must know this intuitively—why else would the expression be “wise old owl” rather than “wise young owl”?
Banders at Whitefish Point in Michigan have been studying Long-eared Owl feathers, which are also pigmented with porphyrin. In their case, the amount of fluorescent pigment is related to size, age, and sex, being noticeably more intense in females than males and in heavier birds than lighter ones. Fluorescent pigments in eggshells are known to help regulate heat by reflecting infrared wavelengths, and the Whitefish Point researchers speculate that the pigment in the females’ inner wing feathers may limit heat loss while nesting. If so, it’s possible it serves a similar function in saw-whets.
Finding Saw-whet Owls
Up here in Duluth, we think of winter as being the season for finding owls, but late September through mid-November can be pretty darned wonderful if we’re paying attention. Crows yelling their heads off (living up to the expression “a murder of crows”) often are mobbing one of the large owls, so those “cacawphonies” are always worth checking out. Chickadees and nuthatches mob the smaller owl species. Except in late spring when saw-whets are calling, I’ve found virtually all the ones I’ve ever seen in daytime when chickadees were mobbing them. In summer, robins and Red-eyed Vireos join the mobs, and year-round, nuthatches and Downy Woodpeckers do. Whenever you hear agitated little birds, check it out!
We’re especially likely to find many owls in autumn, when the young of the year are still figuring out life, the universe, and everything, and owls of all ages, passing through unfamiliar areas during migration, don’t know the best hiding places in the area. I’m sure at least a few saw-whet owls have visited my yard this fall, though I haven’t detected any so far. But at 5 am on Monday the 29th, a Great Horned Owl was hooting from somewhere across the street when it was still too dark to see. When I heard crows and jays make a fuss about 8:30, I expected them to be mobbing that Great Horned Owl, but no—a Barred Owl was in the dead-end path right next to my yard.
Paying attention to sounds for the past 44 years is how I’ve brought my yard list of owls up to 7 species: Great Horned, Great Gray, Barred, Long-eared, Boreal, Saw-whet, and Eastern Screech-Owl. Of those species, the screech-owl was the least likely up here—we’re slightly north of its natural range. I found that one late on September 8, 2004, thanks to my education owl Archimedes. He must have heard the one outside and started calling to beat the band, so I went outside and checked.
Archimedes was also calling up a storm late at night after the Cubs won the World Series, only this time he was alerting me to a Boreal Owl calling away in the backyard! I’ve seen Boreal Owls at least a dozen times in my yard in the 44 years we’ve lived here, but that was the only one who was calling—proof that Nature itself was celebrating. (Well, okay, some extremely knowledgeable people think the owl was calling because the Hawk Ridge banding station was playing recordings less than a mile away, but I refuse to believe that.) Tragically, I was so thrilled about the Cubs that it didn’t even occur to me to run in and grab my camera.
One of my all-time favorite saw-whet owl experiences happened in October 1994, involving our springer spaniel puppy. Betsy was mostly liver-colored with one conspicuous half-dollar-sized white spot right in the middle of her back. I took her out at midnight, and WHOA! While she was nosing around, a little saw-whet owl flew in, its tiny talons extended as it headed straight for that little white spot which the tiny predator must have mistaken for a mouse. When it realized the mistake, barely millimeters from the spot, it put on the brakes and fluttered to the spruce tree next to the house, where it studied the two of us as hard as I studied it. The owl looked adorably animated, looking not just back and forth between me and Betsy but also in every other direction, apparently picking up tiny sounds I was oblivious to.
Saw-whet owl experiences like this are etched permanently in my memory, and a brain dancing with visions of saw-whet owls is a happy brain, indeed.
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Oops! Robert Mulvihill made an important comment:
I loved reading this, but I have to take one very small issue with something you said—“Once in a while, one of these tiny owls shows its displeasure by clacking its bill, but they never bite or claw at the people handling them, and their curiosity always exceeds their annoyance,….”
At my station outside of Pittsburgh, PA, we get only a tiny fraction of the number banded at Hawk Ridge and other major stations, but even with a sample that typically does not exceed 50 Saw-whets in a fall season, we always DO get a couple of biters and often quite a few talon grabbers, too!!! 😉
It’s possible, I suppose, that the birds at Hawk Ridge have a case of “Minnesota nice,” but more likely that the banders here DO experience some of this, and only allow their educators to hold and release the ones that are more docile.
I loved reading this, but I have to take one very small issue with something you said—“Once in a while, one of these tiny owls shows its displeasure by clacking its bill, but they never bite or claw at the people handling them, and their curiosity always exceeds their annoyance,….”
At my station outside of Pittsburgh, PA, we get only a tiny fraction of the number banded at Hawk Ridge and other major stations, but even with a sample that typically does not exceed 50 Saw-whets in a fall season, we always DO get a couple of biters and often quite a few talon grabbers, too!!! 😉