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Birds of Prey

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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Small Birds Beware of Sharp-shinned Hawks

coopers-and-blue-jay-by-jeannieShort, powerful, rounded wings and a relatively long tail enable Sharp-shinned Hawks to maneuver in dense cover in pursuit of small birds, which compose 90% of their diet. Small mammals and insects are consumed, but not nearly as frequently as birds. The size of the birds eaten range from hummingbirds to Ruffed Grouse. Long legs and toes (especially middle toes) enable individuals to reach into vegetation and large eyes enhance its ability to catch fast-moving prey.

Sharp-shinned Hawks are familiar sights to those of us with bird feeders – this species is responsible for 35% of 1,138 predation incidents reported at feeders in continent-wide survey. In this photograph, a Blue Jay is successfully warding off an attack by a juvenile Sharp-shinned Hawk. (Photo by Jeannie Killam.)

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Bald Eagle Eyesight

7-26-16  juv. bald eagle2 026The eyesight of a Bald Eagle is impressive.  Part of the reason for their excellent vision is that these birds of prey have two centers of focus (foveae), which allow them to see both forward and to the side at the same time. Cone cells, one of three types of photoreceptor cells in the retina, perceive color, fine detail and rapid movement.  In a human, the fovea has 200,000 cones per millimeter; in the central fovea of a Bald Eagle’s eye, there are about a million cones per millimeter. An eagle’s eye is almost as large as a human’s, but its sharpness is at least four times that of a person with perfect vision.

Bald eagles are capable of seeing fish in the water from several hundred feet above, while soaring, gliding or in flapping flight.  (They locate and catch dead fish much more rapidly and efficiently than live fish, because dead fish float with their light underside up, making them easier to see.)  It is very likely that a Bald Eagle can identify a rabbit moving almost a mile away. This would mean that an eagle flying at an altitude of 1000 feet over open country could spot prey over an area of almost 3 square miles from a fixed position. (photo: recently fledged, juvenile Bald Eagle)

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Carrion a Vital Food Source for Bald Eagles

3-1-16 eagle3 036Eagles obtain food mainly in three ways — by direct capture, scavenging for carrion and stealing food from other birds and mammals. When securing their own live prey, they hunt from perches or soar over suitable habitat, taking most prey on the wing. Bald eagles’ preferred food is live fish, but they are opportunistic foragers that select prey based on availability. Twenty studies from across their range found that the composition of bald eagle diets averaged the following: fish-56%; birds-28%; mammals-14%; and other 2%.

In addition to capturing live prey, eagles rely heavily on fish, bird and mammal carrion, especially during the winter. Ice fishermen’s leftover bait and/or rejected catches, roadkills and deer that have slipped and died on ice-covered ponds and lakes are three heavily-used sources of food at this time of year. If the carrion is small enough, it is often carried to a perch (see opossum in photo) where it is inconspicuously consumed. Larger carrion, such as white-tailed deer, salmon and waterfowl, that are too big to carry off, are eaten on site and repeatedly visited until consumed.

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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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