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Bird Migration

Lingering Great Blue Herons

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Most fish-eating birds that breed where most bodies of water freeze over in the winter migrate further south in the fall, including Great Blue Herons.  Movement of this large wading bird takes place largely from September to mid-October. According to Christmas Bird Count data, the Great Blue Heron has the widest wintering distribution of any heron species in North America.

While the number of Great Blue Herons in the Northeast is greatly diminished in November and December, it’s not uncommon to spot lingering birds at this time of year.  Come January, when most bodies of fresh water are inaccessible to herons, sightings become rare until they begin returning in March.

Where open water remains in the Northeast, those Great Blue Herons braving the cold continue to consume fish, insects, amphibians and crustaceans.  Small mammals, especially voles, and birds remain a warm-month delicacy, when mammal hair is cast in pellets and bones are digested.

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Semipalmated Plover Migration Winds Down

10-31-18 semi-palmated plover_U1A1025During the peak of their migration in the fall (August and September), Semipalmated Plover sightings occur inland but are especially concentrated along the East coast.  Sightings are decreasing now as we approach the tail end of their flight from their Arctic and sub-Arctic breeding grounds to their wintering grounds which range from the southern U.S. through southern South America.

In general, plovers (Charadriidae) are small to medium-size, plump shorebirds with long wings and short necks and rounded heads.  The Semipalmated Plover, during the breeding season, has a black crown, eye patch and single breast band.  These areas are brown in nonbreeding adults (pictured).

Fortunately, there is no evidence that the estimated breeding population of 200,000 birds is diminishing. According to the Cornell Lab of Ornithology, “The Semipalmated Plover is among the few plovers whose numbers are apparently increasing, perhaps owing to its versatility in food and habitat choice, its wide-spread coastal winter distribution, or its habitat expansion in the sub-Arctic as a result of disturbance by both humans and arctic geese.”

For those curious about this shorebird’s name, “semipalmated” in a wading bird’s name indicates that its toes are webbed for part of their length (barely detectable in photo, but if you look hard you’ll see partial webbing in the left foot).

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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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Dark-eyed Junco Numbers Increasing

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Although Dark-eyed Juncos can be found year-round in New England, their numbers increase dramatically at this time of year, and they become much more noticeable. In addition to our year-round residents, many individuals that have bred further north migrate to the Northeast and even further south to overwinter. For this reason they are sometimes referred to as “Snowbirds.” From late September through October their numbers build and remain high until next May, when many return to their Canadian breeding grounds.

During the winter Dark-eyed Juncos can often be found in flocks, hopping and scratching on the ground as they forage for the seeds that make up 75 percent of their diet. Their two-toned white and gray plumage, and their white outer tail feathers are distinctive.

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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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Snow Geese Migrating

11-10-17 final snow geese2 049A7452The eastern population of Snow Geese, one of the most abundant species of waterfowl in the world, migrate in very large flocks from their high Arctic breeding grounds to their wintering grounds along the Atlantic coast during October and November. Their migration is characterized as a combination of long stopovers with rapid and distant flights between areas. Birds from the same breeding population use many of the same stopovers sites, or staging areas where they rest and refuel, each year. Here they forage and eat the stems, seeds, leaves, tubers and roots of grasses, sedges, rushes in addition to waste grains such as wheat and corn in fields where crops have been cut.

Most of the eastern Snow Geese stage on the St. Lawrence estuary and many then migrate over Lake Champlain and fly southward along the Hudson River to their wintering grounds along the east coast, where the highest numbers occur along the shore of Delaware Bay. Those of us lucky enough to live near a staging area keep our ears tuned this time of year for the sound of baying hounds, for that is what an approaching flock of thousands of Snow Geese sounds like. (Photo taken at Dead Creek Wildlife Management Area, Addison, VT)


Hooded Merganser Numbers Increasing

10-23-17 hooded mergs 011The number of Hooded Mergansers (Lophodytes cucullatus) is beginning to build as their fall migration from eastern Canada breeding grounds to southeastern U.S. gets under way. Late migrants, Hooded Mergansers won’t reach the peak of their migration until mid-November. They will not completely vanish from sight, however, as many Hooded Mergansers remain in New England on open marshes, ponds, rivers and creeks where they can find fish and crustaceans to feed on throughout the winter.