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Birds of Prey

Ospreys Migrating

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Banding birds, and the retrieval of these bands, has provided valuable information on the movement of birds. Today we also have the benefit of satellite telemetry, in which a bird carries a tracking device and its location is calculated via satellites that orbit the Earth.  The following is just a sample of what this tracking technology has revealed about the migration of Ospreys.

There are significant differences in male and female timing of migration (females leave up to a month before males), distance traveled and overwintering locations.  There is strong fidelity to overwintering sites as well as to migration flyways.  Breeding pairs of Osprey do not migrate or overwinter together, and adults do not migrate with their offspring.  Ospreys rarely migrate at night over land but inevitably migrate at night when undertaking longer (more than 12 hours) water crossings.

Subtle insights into migratory behavior can be gained by the findings of satellite telemetry, as well.  Their first flight south by juvenile Ospreys is often largely over water. A majority of juveniles migrating over the Atlantic Ocean from Massachusetts to the Bahama Islands flew as many as 1,500 miles over a period of up to 58 hours. The fact that no adults or 2nd year birds took this route over water suggests that juvenile Ospreys learn the coastal migration route during their first trip north.

Overwintering habitat preferences have also been assessed.  Of 79 Ospreys tracked by satellite, 30.4% overwintered on coasts, 50.6% overwintered on rivers, and 19% overwintered on lakes or reservoirs, with differences based on both sex and region of origin.

These few facts don’t begin to exhaust the information gathered from banding and satellite telemetry on Ospreys, much less many other species. They just serve to illustrate how modern tracking technology compliments and increases the information formerly gathered by firsthand observation and banding.

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Broad-winged Hawk Migration Peaking

9-17-18 juv. broadwing_U1A7043The migration of raptors has begun, and one of the first species to migrate in the fall is the Broad-winged Hawk (Buteo platypterus). While it is quite secretive when nesting, it is one of the more conspicuous species of birds when migrating.  This is for two reasons. They are one of the few North American raptors that flocks during migration, and much of their migratory behavior is concentrated in the Northeast in a two-week period around the middle of September.

Migrating Broad-wings conserve energy by frequently soaring in thermals and mountain updrafts. Flocks of birds, or “kettles”, soar up the heated columns of air, peel off and glide to the next thermal where they repeat the process. Very little wing-flapping is necessary in order to cover a lot of ground. The flocks, or “kettles,” range from several individuals to thousands of birds (larger kettles generally occur nearer their Central and South America wintering grounds).

The number of birds migrating often grows following a cold front, when winds die down and thermals increase. Fall migration of Broad-wings in the Northeast is associated with good visibility, moderate favorable winds, high temperatures, and afternoons (vs. mornings). (Photo: juvenile Broad-winged Hawk)

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American Kestrel Chicks Fledging

 

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The American Kestrel is the smallest, most numerous, and most widespread North American falcon. Roughly two months ago these birds (formerly known as Sparrow Hawks) were mating and laying eggs in nesting cavities (natural tree cavities, woodpecker holes, nest boxes), most of which are located near open fields with low growth (to facilitate finding insects to eat).  The female kestrel does most of the incubating of her four to five eggs (one month), and all of the brooding (one month).  The male rises to the occasion and feeds the newly-hatched chicks for the first 7-10 days, and then the pair shares the feeding.

After 26 – 28 days in the nest, American Kestrel chicks are ready to fledge.  Their first flight, consisting of alternate fluttering and gliding, can be quite short or as long as 200 yards, and typically ends with an awkward landing.  After the chicks have fledged, the parents continue to feed them for up to 12 days. During this period young American Kestrels have been observed returning to their nest cavity to roost.

(Photo:  Male American Kestrel nestling, roughly 22 days old. Note feathered “eye” spots on back of head (serve to ward off predators) are already showing. Thanks to Joan Waltermire, John Douglas, David Merker, and Sebastion and Carter Lousada for photo op.)

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Barred Owls Fledging (But Not Flying Yet)

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If you heard Barred Owls calling this winter, and have occasionally spotted one in the same vicinity this spring, now is the time to start looking up at the canopy to see if they produced any young owls. Having spent four or five weeks in a tree cavity being fed and cared for by their parents, Barred Owl nestlings get the urge to spread their talons (and eventually their wings) and leave their nest about this time of year. It will be roughly another month before they begin short flights; until then the fledglings are referred to as “branchers,” as that is where you will find them, perched and begging for food from their parents, who will continue to feed them until late summer or fall. (If you know a youngster who is captivated by owls, they might enjoy reading Otis the Owl by yours truly!)

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Bald Eagles On Eggs

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Thanks in large part to the Vermont Bald Eagle Restoration Initiative, seeing eagles in Vermont is not all that unusual these days, even in winter. The open water of Lake Champlain (as well as ice fishermen and White-tailed Deer carcasses in other parts of the state) allow them to survive here during our coldest months. Vermont’s mid-winter Bald Eagle Survey documented 84 eagles in January, 2018.

Equally as encouraging is the growing breeding population of eagles in this state. This past year 21 adult Bald Eagle pairs successfully produced 35 young in Vermont. The return of eagles to their nest site is always a much- anticipated event, which often coincides with the opening up of the Connecticut River for at least one pair that nests on its banks (see photo).

Eggs have been laid and eagles (both male and female) are engaged in incubating them for the next month.  One can’t help but be impressed by their perseverance — recently they endured three Nor’easters in 10 days while incubating their eggs (note snow on rim of nest)!

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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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