Wheeler NWR is a haven for migratory birds. Each year, millions of birds migrate to or through the Refuge. While we do not know the exact number of migrants the Refuge supports, we can get a feel for the magnitude of migration. Scientists estimate that over five billion birds migrate across North America each season.
When we talk about bird migration, everyone knows what we mean. But what is migration? Migration is defined as movement from one place to another. In birds, we generally think of migration as the seasonal movement of large numbers of birds from one place to another and then returning. In reality, bird migration is much more complicated. It is not an all-or-none proposition. For instance, every American robin that nests in North American and their offspring do not migrate in the fall to a wintering area in the southern United States or Mexico. While a majority of them do, a few will linger across the northern United States. In fact, robins that nest at Wheeler NWR will often remain in the area during the winter and their numbers will be augmented by robins migrating to the Refuge from more northern areas. Many migratory birds exhibit this migratory behavior.
In general, there are three types of migrants: Diurnal migrants, nocturnal migrants and altitudinal migrants.
Birds that migrate during the day are known as diurnal migrants. These birds are usually strong fliers that can travel long distances each day. Some birds, like ducks and geese, do not feed while flying. Once they find suitable habitat at the end of the day, they will often feed late in the evening, through the night and during the early morning before continuing their migration. Other birds such as swallows and swifts capture food in flight as they migrate during the day.
Nocturnal migrants, such as warblers and sparrows, travel during the night and feed during the day. Most small birds that migrate are nocturnal migrants.
Altitudinal migrants move from high elevations to lower elevations. Western species such as Clark's nutcracker, dark-eyed junco, Steller's jay, and Arizona or Strickland's woodpecker move down slope in the fall to escape the harsh winters in the high mountains. While only a few North American birds are altitudinal migrants, scientists estimate that a fifth all tropical birds in the Central American highlands are altitudinal migrants.
Bird Migration at Wheeler NWR:
Wheeler NWR is the easternmost refuge along the Mississippi Flyway, one of four major North American flyways. The importance of the Refuge to migratory birds can be gauged by the diversity of migratory species that use the Refuge. Of the 286 bird species that have occurred on the Refuge, 262 species or 90%, are migratory in at least a part of their range. Let's look at the migratory patterns of some of the birds common on Wheeler NWR.
The Canada Goose is a common migrant across North America. Based on banding studies and neck collar observations we know that most of the Canada Geese wintering on Wheeler NWR are from the Southern James Bay region of Hudson Bay in Canada, with many nesting on Akimiski Island. In the late 1960's, up to 60,000 migrant Canada Geese wintered on the Refuge. In the late 1980's the Southern James Bay Population (SJBP) began to decline, resulting in a decline in the number of geese wintering on the Refuge. That decline has continued and now approximately 2,000 Canada Geese winter on the Refuge.
Most of the SJBP birds arrive back along Southern James Bay in late April. Nesting begins as soon as snow melt is compete, usually by late May. Canada Goose pairs construct depression nests on the arctic tundra and line them with goose down. Incubation of the 4-10 egg clutch takes 25-30 days. Young are usually capable of flight in 40-75 days depending on rate of development. Southward migration is well underway by September and the first migrants usually reach the Refuge by late September or early October. Migrant Canada's use the Refuge extensively as a feeding and resting area through February. By March many have started their northward migration, moving as far north as the snow melt allows them. By April they are back near their Southern James Bay nesting grounds.
There are some 750,000 Sandhill Cranes in North America. They are stately gray birds standing four feet tall with a six foot wingspan. Most nest from western Quebec to British Columbia and from the Great Lakes north to the Arctic and Alaska. Up until about 1990, they were almost unheard of at Wheeler NWR. About that time, they started showing up in small numbers. They usually arrive in November and leave in February on their way back to their nesting grounds. Since 1990, their numbers have grown to around 8000 during the winter of 2009-2010. We see them most often on Beaverdam Peninsula and Limestone Bay where the feed and roost. Until recently, we had no idea where birds wintering on the Refuge came from. On February 1, 2002, Steve McConnell, a local birder, photographed a color-banded Sandhill Crane on Limestone Bay. Based on the color band combination, the Bird Banding Lab and crane banders in Wisconsin were able to identify the banded crane. It had been captured as a flightless chick in central Wisconsin in 2001.
How many times have you heard someone ask "What bird looks like a cigar with wings in flight?" The Chimney Swift is one of America's most well-known birds, nesting in chimneys and other similar structures. It can be seen flying in small groups over every city in eastern North America during spring and summer. Yet, for over a century and a half, the wintering grounds of this neotropical migrant remained completely unknown. In 1940, Winsor Marrett Tyler remarked "From its unknown winter quarters, somewhere in Central America or on the South American continent, the chimney swift comes northward in spring and spreads out over a wide area, which includes a large part of the United States and southern Canada." The mystery was not solved until May 23, 1944, when the American Embassy in Lima, Peru received a report listing 13 bands turned in by a group of indigenous people who had killed the 13 banded birds along the Yanayaco River near the boundary between Peru and Columbia. Records at the Bird Banding Lab indicated these 13 bands had been placed on Chimney Swifts in Ontario, Connecticut, Illinois, Tennessee, Georgia, and Alabama.
Imagine a bird that weighs 1/4 ounce flying 600 miles across the Gulf of Mexico. That's just what the Wood Thrush. In spring, returning males arrive before females and begin to establish territories ranging in size from one-fifth of an acre to two acres. They spend the summer months across eastern North America where they nest in suitable habitat. In August, Wood Thrushes begin to migrate south, flying primarily at night. After stopping over on the Gulf Coast for two to three days, or longer in inclement weather, they fly across the Gulf of Mexico to winter in the lowland tropical forests of southern Mexico and Central America. The return trip brings them to the Gulf Coast beginning in early April, and from there they move rapidly north.
You are along Blackwell Swamp, Dancy Bottoms, White Springs Dike, or any of the many wooded swamps and creeks on Wheeler NWR when you hear a loud, ringing "sweet-sweet-sweet-sweet" and see a flash of golden yellow. You have just had an encounter with a Prothonotary Warbler. Prothonotary Warblers nest in cavities in trees in wooded swamps and along streams. They have such an affinity for wooded swamps that at one time they were known as the "Golden Swamp Warbler". After nesting and raising their young across much of eastern North America, they begin to travel south in late July and early August to their wintering grounds. Like many small neotropical migrants, they make the 600-mile flight from the northern Gulf Coast to the Yucatan Peninsula at night. They winter in mangroves and freshwater swamps in parts of Central and South America and the West Indies. Unlike most neotropical migrants, they roost communally on the wintering ground, and pair bonds between males and females persist.
Frequently Asked Questions About Migration:
Why do Birds Migrate?
The reasons birds migrate are complex and not well understood. One factor may be that reduced food supplies in late fall and winter force birds to migrate to warmer climates where food is more readily available. Other factors may include drastic changes in temperature during fall and winter and reduced hours of daylight.
How do Birds Navigate During Migration?
How birds find their way during migration is not well understood. One theory is that birds use the sun during the day and stars at night to guide them. But what about when skies are cloudy and the sun or stars can't be seen? Some scientists think that birds can use the Earth's magnetic field to navigate. Another theory is that young birds learn the migration route from older birds. While we may not know how birds find their way to their wintering grounds and back, we do know that they do it every year.
How Far do Birds Migrate?
Some birds, like the red-tailed hawk, may only move a few miles. Many birds only travel a few hundred or a few thousand miles during migration. The Arctic tern is probably the longest distance migrant. We know from banding studies that in the fall most Arctic terns migrate from their nesting grounds in the high arctic to their wintering grounds along the south polar ice pack near Antarctica. In spring, they make their return flight to the high arctic, a round-trip of up to 22,000 miles.
North America's long distance endurance champion has to be the small blackpoll warbler. This tiny warbler completes an annual migration route of 12,000 miles. It is a common spring migrant across much of eastern North America. On almost any late April day you can usually find several Blackpoll Warblers in the forests of Wheeler NWR. However, in fall it takes a much different migratory path, completely bypassing much of eastern North America as Scott Weidensaul tells us in his book "Living On the Wind":
"The Blackpoll Warbler is only about four inches long. It weighs less than half an ounce. You could mail two of these things in an envelope for one 39 cent stamp. They're barely heavier than air. In fall, those particularly from western Canada and Alaska first migrate east, completely across the top of Canada for 1500 or 2000 miles, until they wind up along the Atlantic seaboard of Canada, New England, and the mid-Atlantic states. Then they wait for strong north-west winds, which will carry them out to sea, across the western Atlantic and they finally make landfall on the coast of South America, the northern coast of South America. It's about an 80 to 90 hour journey, during which they will beat their wings three to four million times; they will have no rest, no food, no water. If they touch the water, they're dead. These birds are not waterproof; they can't float. And yet it works."
How does a Blackpoll Warbler prepare for the journey?
"What they're fueling themselves with is fat. A blackpoll warbler is going to weigh about 15 grams, and it will add a little bit of extra weight in fat before it leaves-- and that fat is the fuel that will carry it across the Atlantic. If they were burning gasoline instead of fat, they'd be getting about 720,000 miles to the gallon."