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Owls

A Feathered Visitor

For the past six winters a Barred Owl has been a daily visitor at my house.  For most of these years, he roosted (and slept) all day every day from December through February on a White Birch tree just outside my door.  Although I usually try not to interfere with the natural rhythm of things, one year when the snow was exceptionally deep, making hunting quite challenging, I decided to offer the owl a daily treat – one small rodent.  Enough to entice him but not to satiate him or make him dependent upon this source of food. (I once opened up the gizzard of a road-killed Barred Owl and discovered five small rodents – they average about this amount per day.) Thanks to the Listserv in my town, I could appeal to residents for small rodents (trapped, not poisoned) which they generously deposited in a specially marked box outside the Town Hall, freshly frozen.

 

Every afternoon like clockwork the Barred Owl would become alert and open his eyes.  If he had left his perch during the day, he would return at dusk, precisely at 4:30 p.m. His timing appeared to be in sync with the amount of daylight, as he arrived a bit later as the days lengthened.  Most mornings I would take a mouse from the freezer and let it thaw (when I forgot, the microwave came in handy!).  I would take the mouse outside, dangle it by its tail to alert the observing owl, and place it on the railing of my porch. Practically before my hand released the mouse the owl would fly in, grasp the mouse on the fly in its talons and disappear into the woods. More than once I felt the tips of his wings brush against me.

Six years, 60 days a year, comes to 360 days…this owl has spent nearly a year, one-tenth of its life, outside my door.  I came upon the remains of a Barred Owl not even a quarter of a mile from my house this week.  I can only hope it wasn’t my friend.

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Great Horned Owls Courting & Mating

Great Horned Owls are one of the earliest species of birds to breed in the Northeast. Their intense hooting begins in late December or early January, about a month before actual mating takes place. Males call during most seasons of the year, but the period when the males are hooting vigorously lasts for a month or six weeks. During the mating season the deep, rich tones of the males are occasionally interspersed with the higher and huskier notes of the females. The answering calls of the females are typically heard for only a week or two, toward the end of the six-week period.

Eventually, when a male and female approach each other, they do a sort of courtship “dance.” The male cocks his tail, swells his white bib (see photo), and with much bobbing and jerking utters a series of deep sonorous calls that elicit calling responses by the female. He cautiously approaches the female, continuing much tail-bobbing and posturing. The owls nod, bow, and spread their wings as well as shake their heads. Courting pairs have been observed engaging in high-pitched giggling, screaming, and bill-snapping. Mutual bill rubbing and preening also occurs. Copulation concludes the courtship ritual, with both owls hooting at a rate of 4 or 5 hoots per second throughout copulation, which lasts 4 – 7 seconds.

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Eastern Screech-Owls Basking

1-7-18 nc screech owl in cavity_u1a8484 Tree cavities serve not only as nesting sites, but also as winter roosting sites for many species of birds, including Eastern Screech-Owls. Here they perch and soak up the sun’s warmth on cold winter days,with their eyes open just enough to be aware of any activity in the immediate area.

Perhaps the most common owl east of the Rocky Mountains, the Eastern Screech-Owl is best known for its two main calls, which don’t really resemble a screech but are more of a descending “whinny” and a monotone trill. Their vocal repertoire also includes various barks, hoots, squeals, and screeches — hence the common name. Both sexes call, with the female’s call a bit higher than a male. You can hear these calls by going to https://www.allaboutbirds.org/guide/Eastern_Screech-Owl/sounds.

Eastern Screech-Owls come in multiple forms (polymorphic): rufous, gray and a more rare brownish form. These different forms are not directly tied to age or gender, but vary with region and climate. Gray morph owls are prevalent in colder, drier, more coniferous habitats in the northern and western part of their range. Rufous Screech-Owls are most common in eastern and southerly regions and in humid, deciduous forests. (Thanks to Marc Beerman and Howard Muscott for photo op.)

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An Owl’s Digestion Process

11-26-18 -barred owl coughing up pellet2 _U1A1839Most owls do not bother to tear small prey such as mice and voles apart but instead swallow them whole.  After eight to sixteen hours, all the nutrients available in the eaten prey have been absorbed by the bird.  Owls cannot digest the fur, feathers, bones, teeth and nails of their prey, so these parts remain in the bird’s gizzard (specialized organ that grinds up food in most birds but serves as a filter for holding indigestible parts in birds of prey).  This accumulation of indigestible parts takes on its pellet form (which is the shape of the gizzard) about eight hours after ingestion, but is sometimes retained by the owl for another six hours or so before being coughed up. As a rule, bones are on the inside of the pellet, and the fur and feathers form a soft coating on the outside.

The stored pellet partially blocks the entrance to the digestive system so it must be ejected before the owl can eat again.  This process takes anywhere from a few seconds to several minutes.  The owl appears to “yawn” several times before regurgitating the pellet.  Note that the pictured Barred Owl has prey (a Deer or White-footed Mouse) in its talons, but out of necessity is getting rid of a pellet before devouring it.

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Snowy Owl Gets Mouthful When Hunting In Tall Grass

12-8-17 snowy owl and meadow vole3 049A9802Only Naturally Curious readers would come up with flossing!

If lemmings are in short supply and you’re a Snowy Owl, head for tall grass where small rodents dwell. This juvenile female Snowy Owl successfully caught a Meadow Vole (along with a footful of grass) in its talons and proceeded to swallow the vole whole, along with some of the grass. However, most of the grass remained hanging from the owl’s mouth after the vole had been consumed, so it proceeded to grasp the grass with its foot and pull it out of its mouth (yesterday’s Mystery Photo).

Although many people are under the impression that hard weather forces Snowy Owls farther south some winters, the reason for Snowy Owl invasions or irruptions turns out to be linked to either prey population crashes in the north, high productivity breeding years (producing more predators than the prey can support) or a combination of the two. New research has shown that the abundance of Snowy Owls seen in the eastern U.S. during the winter of 2013-14 was the result of a particularly good nesting season on the Arctic tundra. A population boom of lemmings, the Snowy Owl’s primary food source, translated to a population boom of owls.

 

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Barred Owl Parents Providing Fledglings With Food

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Young Barred Owls are fed from the time they hatch (four to six weeks old) until late summer or early fall, months after they have fledged and long after they are capable of flight. When first out of the nest, the fledglings cannot fly, and thus are totally dependent upon their parents’ continued delivery of prey. The fledged young initially stay near one another and the nest site. The parents continue to feed them, and as the young become more mobile they slowly move away from the nest tree. Flight is attempted between the ages of 12 and 15 weeks. The first attempts are, as you would imagine, rather awkward, but as their wings strengthen, the young owls’ flying skills improve. Even so, the parents continue to feed them through the summer and often into the fall, when prey deliveries slow down and eventually cease, forcing the young to disperse. (Photo: Recently-fledged Barred Owl chick eyeing the Flying Squirrel its parent is delivering.)

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Barred Owls Parents Tending Chicks

5-12-17 adult owl in nest hole 241For about a month the female Barred Owl sits on her 1-5 eggs (usually 2 or 3) until her white, downy chicks hatch, usually around the end of April or beginning of May. At about two weeks (mid-May) their natal down is being replaced by a white-tipped gray-buff secondary down, and primary feathers are beginning to grow in.  They remain in their cavity nest for their first month.

It is pretty safe to assume that the adult owl in this photograph is a female as she is in constant attendance during the chicks’ first two weeks. The male brings her food which she tears into little bits so the chicks can swallow it. At the beginning of the third week, the female begins leaving the nest frequently to hunt. When she is at the nest, she often takes breaks from the kids and sits at the entrance surveying her surroundings.  At this point the chicks start consuming prey (that is delivered to them) on their own. In a week or two the chicks will also start appearing at the cavity entrance.  By their fourth or fifth week, the still-flightless chicks will leave the nest, but parental provision of food continues until fall.

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Feathered Fishermen

4-24-17 barred owl IMG_8141

Using their keen eyesight and sense of hearing, Barred Owls typically sit and perch on a branch, surveying the ground beneath them for whatever morsel appears, small mammals and birds being at the top of their list during the winter, with more emphasis on amphibians, reptiles, fish and invertebrates during the warmer months.

Several times I have observed a Barred Owl taking advantage of a vernal pool that was teaming with life, specifically Wood Frogs and Spring Peepers. Perched in a nearby tree, the owl kept an eye out for any sign of movement in the water.  When ripples appeared near the shore it would swoop down to the water’s edge in an attempt to grasp a frog with its talons. Although it met with repeated failure, success was inevitable due to the plethora of distracted mating frogs.

Because they lack hair and feathers, frogs may be underestimated when scientists dissect owl pellets to see what Barred Owls eat. Given the frequency with which I have observed these feathered fishermen, I would think that might be very likely.

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The Feathered Feet of Northern Owls

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Most owls have feathered legs, but the feet and toes of some owls, especially those living in colder, higher latitudes, are also densely feathered. The feathers keep the feet of these birds warm, allowing them to hunt where snow is on the ground and temperatures are very low. Great Gray Owls (pictured), Snowy Owls and Northern Hawk Owls are all examples of this phenomenon. Owls living in warmer climes, such as Barn Owls, have sparsely feathered feet and toes, and tropical owls have nearly featherless feet. This variation can also be found within a given species that has a range that extends over many degrees of latitude, such as the Barred Owl.

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Rare Winter Visitors – Great Gray Owls

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Great Gray Owls are impressive birds – at 27” in length, they are our largest owl (Great Horned Owl – 22”, Snowy – 23”) but at 2.4 pounds, not our heaviest (Great Horned Owl – 3.1 pounds, Snowy – 4 pounds). The feathers that make a Great Gray Owl look so massive are what keep it warm during winters in the northern boreal forests where it resides.

Most of a Great Gray Owl’s diet consists of rodents, and some winters, when prey is scarce, individuals wander south to southern Canada and northern U.S. to sustain themselves. Sometimes Great Gray Owls are highly irruptive, and the number of sightings in the Northeast is high. In the winter of 1978-79 there were over 150 sightings in New England and Quebec. While there were numerous sightings in southern Canada this winter, northern New England was visited by only a few individuals, including the one pictured (in central New Hampshire).

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Snow Conditions Making Life Challenging For Barred Owls

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There has been an unusually high number of Barred Owl sightings reported in northern New England and New York this winter, primarily from the road and near bird feeders. This phenomenon, particularly with owls, is usually attributed to either a current lack of food or an abundance of food during the most recent breeding season resulting in a dramatic increase in the owl population.

In the case of Barred Owls, it is the former. Unlike Snowy Owls, which vary the size of their clutch depending on food availability, Barred Owls typically have two young, regardless of the size of the rodent population. Thus, a plethora of progeny can be eliminated as a viable explanation for the abundance of Barred Owl sightings this winter, which leaves a scarcity of food as the primary reason.

For several weeks there has been a thick crust on top of the snow, which makes hunting for mice and voles difficult for raptors. Because they are very territorial, Barred Owls rarely wander outside of their territory, even when food is scarce. Thus, especially in the past few weeks, they have been desperate to find small rodents. Roads are one reliable spot where mice, voles and shrews are exposed, and bird feeders are most definitely rodent magnets. Hopefully weather conditions will allow birds of prey access to the subnivean layer (space next to the ground where small rodents travel, shelter and breed) before too many more Barred Owls starve to death. (Source: Joan Collins, NYS Ornithological Association, UV-BIRDERS List) (Photo:  Barred Owl with recent Northern Red-backed Vole catch.)

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Modern Technology Reveals Snowy Owl Winter Behavior

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With the arrival of this winter’s first Snowy Owls in New England comes a renewed interest in the winter ecology of these birds of prey. An organization called Project Snowstorm (www.projectsnowstorm.org ) gathers detailed information every 30 seconds on the movement of Snowy Owls that they have outfitted with a backpack harness containing a solar transmitter. These transmitters use the cellular phone network, not a satellite, and when they are out of range of a cell tower, they store information which is transmitted when the bird is back within cell coverage territory – even if it’s years later.

The information that has been gleaned from this modern technology is stunning, and has allowed us to know far more about the behavior of Snowy Owls in winter. Some Snowy Owls stay within a quarter mile of where they are banded; others cover hundreds of miles within a few weeks. Some Snowy Owls spend much of the winter out on the frozen Great Lakes, where they prey on waterfowl they find in the cracks in the ice that open and close repeatedly.   Not only has it been confirmed that Snowy Owls feed heavily on birds in the winter (especially ducks, geese, grebes and gulls), but their use of channel markers and buoys as hunting perches while they seek prey over the open ocean at night has been documented.

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How Owls Locate Prey Under the Snow

1-26-16  barred owl imprint  067An owl’s range of audible sounds is not unlike that of humans, but an owl’s hearing is much more acute at certain frequencies, enabling it to hear even the slightest movement of their prey under two feet of snow. When a noise is heard, the owl is able to tell its direction because of the minute time difference in which the sound is perceived in the left and right ear. If the sound is to the left of the owl, the left ear hears it before the right ear. The owl turns its head so the sound arrives at both ears simultaneously, at which point it knows its prey is right in front of it. Owls can detect a left/right time difference of about 0.00003 seconds.

Once an owl has determined the direction of its next victim, it flies towards it, keeping its head in line with the direction of the last sound the prey made. If the prey moves, the owl makes corrections mid-flight. When about two feet from the prey, the owl brings its feet forward and spread its talons, and just before striking, thrusts its legs out in front of its face and often close its eyes before the kill. (Photo: barred owl wings and feet imprints; inset: barred owl ear opening.)

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Great Horned Owls Courting

Great Horned Owls are staking out territories and beginning courtship rituals in northern New England. Their “songs” are typically given with their beak closed, as they lean forward and cock their tail up (see photo). When calling, their white throat feathers are pronounced as their throat swells.

The hooting of a Great Horned Owl can be compared to the sound of a distant foghorn – it is soft, and somewhat subdued, with no strong accent on any one hoot. Pairs often synchronize their deep sonorous territorial songs, a custom which is referred to as “duetting.” The higher-pitched female calls a six or seven-note song and the male responds with a deeper five-note song during or within a few seconds after the female’s song.  The chances of hearing a Great Horned Owl are somewhat greater after midnight than before. To hear Great Horned Owl territorial calls and duetting go to https://www.allaboutbirds.org/guide/Great_Horned_Owl/sounds. (Thanks to Vermont Institute of Natural Science for photo op.)

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Great Horned Owl Fledglings Still Being Fed By Parents

great horned owls-first year IMG_1616Great Horned Owls are one of the earliest nesting birds — you can find them on nests in January, February and March, even in northern New England. Eggs are incubated for about a month, typically in March or April with young usually hatching in May or June. The nestlings remain in the nest for six or seven weeks before fledging. Unable to fly until they are ten or twelve weeks old, the fledglings follow their parents around and continue to be fed and cared for by their parents until fall. In late summer, when they have fledged but are still begging their parents for food, you can hear their distinctive calls. To know what to listen for, go to http://langelliott.com/mary-holland/great-horned_owl.mp3 (Sound recording © Lang Elliott – langelliott.com & miracleofnature.org.)

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Barred Owl Chicks Fledging

6-18-15  barred owl fledged 155The fledging of flightless Barred Owl chicks takes place four or five weeks after they hatch. Typically they perch on the rim of the nest cavity before climbing to a nearby branch. If there are no branches close by, the chicks will drop to the ground and climb a nearby leaning tree, where they perch and are fed by their parents. Juvenile Barred Owls begin short flights at approximately 10 weeks of age, attaining longer flights by 12 weeks. They are now learning to hunt, but continue to be fed by their parents until late summer or early fall. (Thanks to Alfred Balch for photo op.)

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Barred Owl Chicks View The World For The First Time

6-4-15  barred owl chicks2  100 Barred Owl eggs (usually two or three) are often laid in a tree cavity, where the adult female incubates them for roughly a month. Fuzzy, white, downy chicks hatch and remain inside the tree for four or five weeks while being fed by both parents. When the young owls are two or three weeks old, their white down is replaced with gray-buff secondary down, and they gain the strength to climb up the inside of the tree and peer out at the outside world. In and out they go, perching on the rim of the nest hole for half an hour or so as they await the arrival of their next meal, and then retreating back to the safety and warmth of their nest. (Thanks to Alfred Balch, naturalist extraordinaire, for photo op.)

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Great Horned Owlets Soon To Fledge

great horned owl 454Great Horned Owls are said to have a wider range of nest sites than any other bird in the Americas. Most commonly they use tree nests of other species, particularly Red-tailed Hawks as well as other hawks, crows, ravens, herons (Great Blue Heron nest pictured), and squirrels.

These month-old young owls have grown rapidly, from a weight of roughly an ounce at birth to about two pounds. They will weigh approximately 2 1/2 pounds when they fledge. By six weeks of age, young Great Horned Owls are climbing out of the nest and perching on nearby branches, and by seven weeks they are taking short flights.

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Owls & Humans Share Trait

barred owl 194Birds have three eyelids – an upper eyelid, lower eyelid and a third semitransparent membrane called a nictitating membrane that sweeps across the eye much like a windshield wiper. This membrane keeps their eyes moist, and protects their corneas from being scratched.

In most birds, including owls, the upper and lower eyelids are used to close the eyes when sleeping, and the nictitating membrane is used for blinking. Humans close their eyes mainly by lowering the upper eyelid, where most birds do so by raising the lower lid. Owls (and a few other birds such as parrots, toucans, wrens and ostriches) are more human-like in that their upper lids are usually lowered to close their eyes. Owls also usually close their eyes, partly or entirely, when capturing and transferring prey, scratching their face, preening another owl and copulating. (Note the rows of feathers on this barred owl’s upper eyelids.)

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Patient (and Hungry) Barred Owls Visit Feeders

3-12-15 barred owl 152Barred owls are nothing if not resourceful when it comes to methods for finding food. Typically they sit on a high branch and scan the area for prey before dropping down to capture small mammals such as mice, squirrels as well as reptiles and amphibians. During summer months, they have been seen perched over water and swooping down to capture fish, as well as wading in shallow water to hunt for crayfish and fish. Barred owls have even been seen running along the ground and pouncing on amphibians.

Even with a myriad of hunting techniques, however, barred owls have had a hard time this winter, due to the depth of the snow (harder to hear and reach prey) and the time it is taking for it to melt. Small mammals, which compose the bulk of their diet, remain well hidden. Reports of barred owls perched patiently waiting and watching on or near bird feeders for unsuspecting rodents to expose themselves have become commonplace. Mice and voles that come out from under the snow to feed on spilled seed during the night are a life-saving source of food for these stressed birds. Warmer weather will hopefully soon improve hunting conditions for barred owls. Their gain will be our loss, for once again, as it should be, a sighting will become a far more rare occurrence. (Thanks to Emily and Joe Silver for photo op.)

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Barred Owls Courting

2-11 barred owl 057Barred Owls call year-round but their vocalizations increase and expand in February when courtship begins. No longer are their calls limited to their year-round “who-cooks-for-you — who-cooks-for-you-all.” Males and females engage in “duets,” as well as many other vocalizations, including cackles, hoots, caws and gurgles. Those who sleep with open windows may feel like they are in the middle of a jungle inhabited by hundreds of raucous monkeys.

Barred Owl courtship is not strictly vocal. Male Barred Owls display by swaying back and forth and raising their wings, while sidling along a branch in close proximity to a female. Courtship feeding and mutual preening also occur prior to copulation. The nights of February are filled with amorous avian calls and gestures.

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Great Horned Owls Courting

1-22-15  great horned owl IMG_5973The intense hooting of Great Horned Owls begins in late December or early January, about a month before actual mating takes place. Males call during most seasons of the year, but the period when the males are hooting vigorously lasts for a month or six weeks. During the mating season the deep, rich tones of the males are occasionally interspersed with the higher and huskier notes of the females. The answering calls of the females are heard for only a week or two, toward the end of the six-week period.

Eventually, when a male and female approach each other, they do a sort of courtship “dance.” The male cocks his tail, swells his white bib (see photo), and with much bobbing and jerking utters a series of deep sonorous calls that elicit calling responses by the female. He cautiously approaches the female, continuing much tail-bobbing and posturing. The owls nod, bow, and spread their wings as well as shake their heads. Courting pairs have been observed engaging in high-pitched giggling, screaming, and bill-snapping. Mutual bill rubbing and preening also occurs. Copulation concludes the courtship ritual, with both owls hooting at a rate of 4 or 5 hoots per second throughout copulation, which lasts 4 – 7 seconds. (Photo: Great Horned Owl, in captivity)

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The Effects of An Icy Crust on Wildlife

1-19-15  ruffed grouse snow cave IMG_8590This winter has brought us several storms that have ended in rain and were followed by plummeting temperatures. Just a few inches down into the powdery snow on top of the ground there is a ¼”-thick crust, and if you dig down several more inches, there is a second layer of ice, roughly 1/8”-thick. When a thick, icy layer of crust forms, it can have a dramatic effect on the lives of wildlife both above and below it.

Some animals are relatively unaffected by the presence of a crust but many predators and prey are significantly helped or hindered by it. Ruffed grouse cannot seek overnight shelter from the bitter cold and/or predators by diving into a foot of soft snow and creating a snow cave (see photo). On the other hand, small rodents have a distinct advantage — mice and voles have several layers of ice between themselves and hungry coyotes, foxes and owls. Snowshoe hares lose the advantage they usually have on deep, soft snow — “snowshoes” that keep them on top of the snow when the bobcat or fisher chasing them has to flounder through it. Turkeys don’t have the strength to dig down through one thick crust, much less two or more, in order to reach hidden acorns. If a deer is being chased, its pointed hooves will break through the crust, slowing the deer down, whereas the crust may well support a lighter predator, allowing it to outrun the deer. Red squirrels have to work much harder to reach their cached winter cones and to create tunnels.

What is a mere inconvenience to us humans literally is costing as well as saving the lives of wildlife this winter.

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Owl Night Vision

1-5-15  barn owlIMG_6003Like humans, birds have a sensitive retina in the back of their eyes that absorbs incoming light, senses it, integrates the information in it, and sends this information on to their brain. An avian retina is much thicker than ours and contains more rod cells (for dim light vision) and cone cells (for acuity and color vision).

As most owls are active at night, their eyes must be very efficient at collecting and processing light. The eyes of owls are disproportionately large compared to the size of their skull, and enable them to collect as much light as possible. In addition, the retina of an owl’s eye has an abundance of light-sensitive rod cells — owls have almost a million rods per square millimeter compared to humans which have only about 200,000. Barn owls can see a mouse at 6 – 7 feet with an illumination of .00000073 foot-candles – the equivalent of humans seeing a mouse by the light of a match a mile away. Eye size, an abundance of rod cells and additional neural mechanisms provide owls with vision greater than that of most of their prey.

Since owls have extraordinary night vision, it is often thought that they are blind in strong light. This is not true, because their pupils have a wide range of adjustment, allowing the right amount of light to strike the retina. Some species of owls can actually see better than humans in bright light. (Photo: barn owl, in captivity)

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