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Posts tagged “Strix varia

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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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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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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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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Contents of One Barred Owl’s Stomach

11-7-14 vole, shrews and mouse 027Fantastic guesses, given you had no measurements to work with. Very creative, indeed. Yesterday’s mystery photo was a packed version of the bodies displayed today.

Owls swallow small prey, such as mice and voles, whole, while larger prey is torn into smaller pieces before being swallowed. Once eaten, prey goes directly into the owl’s stomach, as owls have no crop, and thus no ability to store food for later consumption.

Like other birds, owls have a stomach with two chambers — one is the glandular stomach, or proventriculus, (yesterday’s mystery photo) which produces enzymes, acids and mucus and begins the process of digestion. (Because the acids are weak, only the soft tissues are digested.) The second stomach is the muscular stomach, or gizzard, also called the ventriculus. The gizzard lacks digestive glands – it serves as a filter, holding back bones, fur, teeth and feathers that are difficult to digest. The soft parts of the food are ground by the gizzard’s muscular contractions, and allowed to pass through to the rest of the digestive system.

Several hours after an owl has eaten, the indigestible parts remaining in the gizzard are compressed into a pellet the same shape as the gizzard. The pellet travels back to the proventriculs and remains there for up to ten hours before being regurgitated. Because the stored pellet partially blocks the owl’s digestive system, new prey cannot be swallowed until the pellet is ejected. If more than one prey is eaten within several hours, the remains are consolidated into one pellet. (In this case, one very large pellet!)

Update: I left the contents of the deceased Barred Owl’s proventriculus outside last night, and a resident Barred Owl recycled the Meadow Vole and Masked Shrew.

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