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Migration

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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Green Herons Starting To Migrate

8-24-18 green heron2 20160916_0770Green Herons breed throughout the eastern half of North America.  After their nesting season is over they tend to wander, often to more favorable foraging areas. This dispersal merges gradually into a protracted fall migration for birds in the Northeast, beginning around the end of August, with most birds having left by mid-October.

Most Green Herons from eastern United States migrate south to winter along the Gulf of Mexico, Florida, Caribbean islands, Mexico, through Central America to northern South America.   We usually see our first Green Herons returning in mid-April, earlier than other herons.  This may be due to their crepuscular feeding habits, which gives them a longer span of time to feed each day.

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Eastern Gray Squirrels Swimming

e-gray squirrel swimming by Erin 2_H6A2563 copy (002)Imagine coming upon a stick floating in a large pond only to discover the “stick” had a head and tail and was making a beeline for the shore.  The fact that an Eastern Gray Squirrel (Sciurus carolinensis) had paddled half a mile to get from one shore to the opposite shore of a pond shouldn’t have come as such a surprise, as this rodent has a long history of migratory swimming behavior, but it’s such an incongruous and unexpected event that it made my companion and me initially question our eyesight and then laugh out loud.

Historical reports suggest there have been many massive Eastern Gray Squirrel migrations in the United States, beginning in 1749 in Pennsylvania.   Records show the state paid three cents for each squirrel killed; over 640,000 squirrels were turned in for bounty.  One migration from Wisconsin in 1842 lasted four weeks and involved a half billion squirrels. Because of the numerous squirrel migrations, John James Audubon was erroneously convinced that the squirrels on the move were a separate species from the Eastern Gray Squirrel and gave them the scientific name Sciurus migratorius. (This proved to be inaccurate.)

During the 1800’s, thousands of squirrels would periodically move en masse across roads, fields and forests, and swim across lakes and rivers (including the Mississippi and Connecticut Rivers) in an effort to disperse. The consensus is that these mass movements were a response to local food conditions. They occurred mostly during the month of September following a year in which there was a large production of food (acorns).

The most recent mass migration of Eastern Gray Squirrels in eastern U.S. occurred in 1968, when a bumper crop of acorns in 1967 was followed with a corresponding bumper crop of young squirrels in 1968. By fall, as the first litter of the year left the nest, there was a severe shortage of food. As a result, massive numbers of acorn-eating squirrels dispersed in search of food.

One Eastern Gray Squirrel swimming across a New Hampshire pond does not a migration make, but it might not be a bad idea to keep an eye out for excessive numbers of paddling squirrels and/or road-killed rodents come September. (Photo by Erin Donahue)

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Male American Redstarts

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Warblers — small, active, insect-eating birds — are often referred to as the “butterflies of the bird world” due to the striking breeding plumage of many of the males.  One warbler that’s hard to overlook due to its brilliant orange and black plumage is the male American Redstart.  Like most warblers, it is a very active feeder, flitting from branch to branch looking for insects.  However, it also occasionally feeds like a flycatcher — perching and flying out to capture insects in mid-air, giving you the opportunity to get a good look at it.

The breeding behavior of the American Redstart is of particular interest, in that not only is the male occasionally polygamous, as are many other bird species, the two females he mates with at the same time do not nest in the same territory.  The male holds two separate territories that can be separated by as much as a quarter-mile.  The male begins attracting a second female after the first has completed her clutch and is busy incubating the eggs.  Perhaps the bird world would benefit from a “Me Too” movement.

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A Vagrant Brant

12-1-17 pale-bellied brant 049A7777Brants are small geese that travel long distances (up to 3,000 miles) several thousand feet up in the air between their Arctic breeding grounds and their coastal wintering grounds. No other species of goose nests as far north, and few migrate as far. The subspecies that overwinters off the middle of the East Coast, the Atlantic or Pale-bellied Brant, typically migrates from northern Canada to James Bay, where it remains for several weeks building up fat reserves. From there most birds fly nonstop to their wintering grounds in Jamaica Bay and other nearby estuaries of greater NYC and New Jersey, arriving in late October and early November.

Occasionally migrating birds, often juveniles, veer a bit off course (often due to weather-related causes) and end up where they don’t belong. Brants are common winter residents in coastal areas during the winter, but are not often seen far from salt water. This fall a lone juvenile vagrant Pale-bellied Brant appeared one day on the shore of a lake in central Vermont, giving inlanders the opportunity to view a Brant up close. While adult birds have a very sophisticated mechanism for plotting their migration from one point to another and for getting back on course if they are displaced because of weather, first-year birds often lack this skill.

Had this Brant been blown off course in this manner 75 years ago, there would have been concern for its survival, as Brants used to feed almost exclusively on intertidal seagrass during the non-breeding season. However, in the 1930’s a disease devastated eelgrass and consequently the Brant population dropped. Brants that survived adapted to an alternative diet which included sea lettuce, saltmarsh grass and lawn grass, making it possible for a 21st century Brant to exist just fine in the interior of New England, at least long enough to refuel before continuing on its way.


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.