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Birds of Prey

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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Juvenile Barred Owls Mastering Flight

barred owl-fractured wing 062Typically Barred Owls in northern New England hatch in May and fledge, or leave their nest, in June at approximately four to five weeks of age. Unlike most young birds, Barred Owl nestlings leave their nest before they can fly. They initially perch on the rim of the nest and then climb to a branch on the nest tree, eventually dropping to the ground and climbing a nearby leaning tree to perch. The parents feed their young from the time they hatch until late summer or early fall. The fledglings begin short flights at approximately 10 weeks of age, attaining longer flights by 12 weeks. The pictured Barred Owl may have been mastering flight when it fractured a wing and ended up on the ground, soaking wet and very vulnerable to predation. (Thanks to Bob Moyer for photo op and Vermont Institute of Natural Science’s Wildlife Rehab staff for setting wing.)

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Young Cooper’s Hawks Fledging

8-19-14 juvenile cooper's hawk2 306After a month of living in a nest that measures roughly 7 ½ inches across and 3 inches deep, Cooper’s Hawk nestlings are more than ready to stretch their wings. Although they’ve been dismembering prey (mostly birds and a few small mammals brought to them by their parents) since they were three weeks old, catching prey is a skill they have yet to acquire. For roughly ten days after they leave their nest, the young hawks return to it for continued prey deliveries (and for roosting). During this time the fledglings learn to catch their own prey and they become independent, but they continue to stay together near their nest for the next month or so. (Thanks to Marian Boudreault for photo op.)

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Broad-winged Hawks Become Empty-Nesters

8-7-14 broad-winged fledgling2 037Broad-winged Hawk nestlings typically leave their nest sometime in July or early August, at about five to six weeks of age. The fledglings tend to stay within their parents’ territory for up to eight weeks. Much of the first two weeks after fledging is spent perched close to the nest, often returning to the nest for food delivered by the parents, but by the time the fledglings are about seven weeks old, they are capturing their own prey. This leaves the adults free to hunt for themselves, as they fly overhead emitting their high-pitched, shrill whistle. (Photos: adult Broad-winged Hawk)

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Snowy Owls Headed North

4-21-14 flying snowy 046The record number of Snowy Owls that spent the winter in New England are turning up in all sorts of new locations now that they are on their way back to their breeding grounds on the open tundra and stopping to refuel along the way. Although many were young birds, and won’t breed this year, the adult owls will when they reach the Arctic in a few weeks. First, the males perform aerial and ground displays. After mating, the female selects a nest site. In addition to having a sufficient food supply, the site must be snow-free, not subject to flooding, and command a view of its surroundings. The latter is achieved by making their nest on a hummock, or slightly raised surface of bare ground. The female scrapes a shallow depression in the earth with her claws, twirling around to make a form-fitted hollow. No insulating material is added to this depression – no vegetation, no feather lining. Eggs and nestlings are totally dependent upon the mother’s warmth, transmitted via the large, featherless, pink patch of skin on her belly known as an “incubation patch.” The female alone incubates the eggs and broods the young chicks while the male provides food for his entire family.

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Barred Owls Frequenting Feeders

4-4-14  barred owl with suet IMG_5432The number of Barred Owls seen near bird feeders recently makes one question whether these birds are, in fact, in dire need of food. Certainly the extended period of deep snow this winter has made finding prey challenging. Fortunately, the local bird rehab center (Vermont Institute of Natural Science) has not been inundated with starving owls, which indicates that other factors may be involved in the increased number of sightings near homes and feeders. One of these factors could be that Barred Owls are currently laying and incubating eggs, and a few early nesters may even be providing food for young owlets. Whatever the reason, the accessibility of rodents that are attracted to feeders and the food itself that’s in the feeders allows us an all-too-rare glimpse of this common owl. (The mystery of repeatedly finding my suet feeder on the ground every morning was finally solved when I took this photograph – look closely at what the Barred Owl is clutching in its talons.)

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Snowy Owl Pellet

3-25-14 snowy owl  203Your knowledgeable ID skills regarding yesterday’s Mystery Photo were most impressive!

Snowy Owls are the heaviest owls in North America, weighing roughly 4 pounds (a Great Gray Owl is only 2.4 pounds). A lot of fuel is needed to power this magnificent raptor. In the Arctic, where they live, lemmings are their preferred prey — one owl may eat more than 1,600 of these small rodents in a single year. This winter the Northeast has experienced record numbers of visiting Snowy Owls. A banner year for the Arctic lemming population followed by prolific nesting success for Snowy Owls resulted in an unprecedented “irruption” of these owls further south this winter.

While we do have lemmings in New England, they are uncommon, so Snowy Owls have relied on our small rodent, squirrel, rabbit and hare populations for food. Those owls wintering on the coast, where dunes and moors closely resemble their tundra habitat, have also taken advantage of the large number of sea ducks. As witnessed and described by Nantucket ornithologist Edie Ray, the owls fly up to great heights over the sea, spot waterfowl and then plummet down to just above the surface of the ocean where they sink their talons into a “sitting duck.” As a result, the indigestible bones, teeth and nails of prey are protectively wrapped in feathers as well as fur in the large pellets coughed up by these owls. (Snowy Owl locators: Edie Ray and Sadie Richards; Snowy Owl pellet finder: Sadie Richards)

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