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Owls

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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