Migrating: A Stressful Time for Birds
By Wilma Young
The writer celebrated her 90th birthday in November. In the late 1980’s, she served as a volunteer and intern at several national parks, including the Chincoteague National Wildlife Refuge on the Eastern Shore of Virginia. Along with her volunteer duties, she found time to make use of her research and writing talents. This is one of a number of articles and trail guides she wrote. Following a chance meeting with Wild Pony Tales publisher, Robert Boswell, four years ago on the Chincoteague Refuge tour bus, she made this article and others available to the website.
Chincoteague National Wildlife Refuge was created for migratory birds in 1943 and is suitably located on the Atlantic flyway. The refuge is a major stopover and wintering area for waterfowl and spring migrations of shorebirds are tremendous, with the peak migration of songbirds through the area occurring during April. People often think of waterfowl, shorebirds and wading birds as the most important of the migratory birds, and these birds are, of course, seen in large numbers at Chincoteague Refuge.
Songbirds, also neo-tropical migrants, visit the refuge in huge numbers in spring and fall. Prairie Warblers, Red-eyed Vireos, White-eyed Vireos, Yellow Warblers, Indigo Buntings and all manner of colorful, fascinating song birds spend time feeding and resting in the shrubs and maritime forest of Chincoteague National Wildlife Refuge.
Neo-tropical migratory birds are those species whose breeding areas and wintering areas span the Arctic and temperate areas of North America and the semi-tropical and tropical areas of Mexico, Central and South America and the Caribbean.
Some of our migrants do not go to the tropics, wintering instead at the southern limit of their range and to the Gulf of Mexico. The golden and bald eagles and the Black Crowned Night Heron make these shorter, though potentially hazardous, trips.
Migration is a particularly stressful time for birds; therefore, food and shelter take on added importance. Storms can lead to the deaths of migrants. Power lines can be killers of owls and raptors. Oil spills kill or endanger water birds. Poisons such as lead and mercury cause indirect or accidental death. Birds collide with spot lighted buildings, and TV and radio towers. Migrating birds are adversely affected by the destruction of stopover sites. Development on the coasts and the filling in of , wetlands have been contributing factors. As these staging areas dwindle, birds are more densely concentrated in small areas. The food supply must then be shared by more birds and the high concentration of birds increases the possibility of disease spreading among the avian population and also increases the opportunity for predation.
Even shore birds that appear to be abundant (Sandpipers, Ruddy Turnstones. Sanderlings, Dunlins) may be in jeopardy because of their dependence upon a few sites that supply super-abundant food
resources.
The long distances between presently existing rest areas may be prohibitive for such birds as the Piping Plover and many of the sandpipers. Disturbance of the migratory pattern may cause some birds to arrive so late that they can raise only one brood although ordinarily they might be able to raise two or even three.
Although all species of birds do not show the same rate of decline, it is known that at least one hundred and fifty species of North American birds are in jeopardy. There is no quick and easy solution to the diminishing of neo-tropical birds as each species may present a slightly different problem. These varied needs suggest the importance of attempting to maintain as diverse a habitat as possible.
Neo-tropical migrants make up sixty to eighty percent of all the breeding birds in the forests of eastern North America. These songbirds play a critical role in the eco-system both as consumers and as prey. Their breeding range consists of over fifteen million square miles, yet their wintering grounds comprise only two and three tenths million square miles.
Deforestation of this winter range has certainly been responsible for a percentage of the decline of many species. It is estimated that the tropical forests are being lost at a rate of one to three percent a year. Some countries such as Costa Rica and Cuba have lost eighty percent of their original forests.
While this can account for some of the decline of our song birds, we in North America must bear some of the responsibility. The Breeding Bird Survey has reported continuing decline of song
birds over the past twenty-seven years. The decline appears to fall under the categories of out-right habitat loss as well as the degradation of habitat. Prairie fragmentation in North American has caused us to lose numbers of grassland birds such as the Bobolink and Dickcissel. Fifty-four percent of our wetlands have been drained, filled and converted to other uses. It is possible that the Midwest has lost
as much as seventy to ninety percent of its wetlands.
Fragmentation of the forests results in birds being forced to nest in small woodlots where they are vulnerable to predators such as skunks, raccoons, jays, grackles, snakes and house pets as well as to the parasitism of cowbirds. Predators thrive on the edge of the woodlands.
Brown-headed cowbirds once favored open country west of the Mississippi using the open prairie for feeding and social display. As forests were cleared, their range extended. Now they range over the entire United States. They are not nest builders, choosing instead to lay their eggs in the nests of song birds. Cowbirds parasitize at least one hundred and forty-four species of birds, most commonly Vireos, Warblers and Flycatchers.
Although they depend on other birds to raise their young, they are an extremely successful species, doubling their population in eight years.
The refuge, created in 1943 to provide habitat and protection for migratory birds is an excellent site for both migrating and nesting birds. The fresh water impoundments on the refuge are managed for the benefit of waterfowl, shorebirds and wading birds. Water levels in some of these impoundments are slowly lowered in April and May to provide ideal conditions for the germination and growth of plants suitable as food for waterfowl which migrate through the refuge in the fall and those which remain on the refuge all winter. The receding water levels provide excellent feeding opportunities for shore and wading birds.
A recently completed habitat enhancement project on the refuge involved the planting of Wax Myrtle shrubs along a portion of the Beach Road. This grassy area is regularly frequented by brown-
headed cowbirds. The wax myrtle will eventually provide additional habitat for neo-tropical migrants and reduce the feeding area for cowbirds. This effort may reduce the number of parasitized nests in the adjacent Loblolly Pine forest.
Since 1973, we have had an Endangered Species Act which allows the USFWS to classify a species as Endangered when there is imminent danger of its extinction. Those species likely to be in danger
soon are considered Threatened. There are also candidates for Special Concern: those known to have suffered losses but still awaiting formal recognition of the severity of their decline. The National Audubon Society recognizes the un-official impairment to a species. This group, thought to be in a decline, is named in a Blue List. Some birds appear to be doing well in many regions of the country, but are of local concern.
Plans for the recovery of breeding populations include the effort to restore habitat, the use of captive breeding programs with release as a goal (as in the peregrine falcon programs), the introduction of nesting boxes for purple martins and blue birds and the closing of areas to public use at breeding time for such birds as the piping plover. There is also an effort to assist developing countries in the use of their natural resources without the concomitant effect of destroying wetlands, grasslands and woodlands.
There is no quick and easy solution to the diminishing of our birds as each species may present a slightly different problem. These varied needs suggest to us that we should attempt to maintain as many diverse habitats as possible.
So why do we care whether we lose a few species of bird? People come first, right? Remember that canaries were taken into the mines. If the birds died, the miner knew that his own life was endangered. We are now looking at birds’ reactions to give us a clue about our general health as related to the environment. What threatens the birds also threatens us. Ozone depletion may cause Cancer and it may damage food production. Our water sources are already showing the effects of acid rain. Fish productions are limited by this. Rapid climate changes damage our agricultural systems.
WHAT CAN WE DO?
On a global and national level, we can support projects which fight against environmental destruction and encourage environmental diversity.
On a local level, homeowners who are responsible for small yards may contribute by providing shelter and feeding sites. A bird bath is a simple addition to the yard. Pools or clean stream beds large enough to support plants that grow in and around water are an even greater asset. If your municipality has no local “weed” ordinance, and if you have no driving desire to own a “perfect” lawn, you might plant native wild flowers and shrubs. Standing dead tree trunks also offer nest sites and shelter.
WHY DO BIRDS MIGRATE?
Over the centuries, people have been fascinated by bird migration. Why do birds migrate? How do they manage to locate breeding and wintering sites? In fact, for many years the mystery was where they went. Aristotle firmly believed that some birds hibernated in hollow trees or perhaps buried themselves in mud. One of the more fanciful notions was that they flew to the moon for the winter.
A theory held until fairly recently was the transmutation of species. People thought that one species disappeared and a different one appeared in its place.
Most people found it easy enough to believe that large, obviously strong birds, could fly long distances; but they doubted that small birds would be able to endure long flights and so assumed that the little fellows must hitch rides on the backs of larger birds or on ships going in the general direction of their destination.
Some birds make spectacularly long flights. some manage remarkable continuous flights without rest as others achieve unusual speeds.
Dr. Robin Baker, in his book “The Mystery of Migration”, makes this startling observation: “Every year, as the summer wanes, willow Warblers weighing only a few grams undertake a journey of 8000
kilometers (5000 miles) to escape winter’s rigors. In human terms, this is equivalent to traveling ten times the distance from the earth to the moon or 38,625,000 kilometers (24,140,000 miles)”.
Weather may be a triggering factor in migration but the underlying reason is surely to ensure food supply. Birds do not migrate unless they are ready to do so.
HOW DO BIRDS KNOW WHERE THEY ARE GOING?
It cannot be assumed that young birds follow older birds during migration because in some species, the young migrate at different times. Sometimes preceding the adults.
Although birds have excellent vision and could possibly remember landmarks, this doesn’t explain how young birds can find their winter homes on their first unescorted trips. It is probable that birds use a number of clues including sight, smell, and the earth’s magnetic force. Possibly they take bearings from sun, moon and stars and even have an ability to recognize home after an absence of as much as eight years. Beyond these things they may use a number of clues that we do not even suspect.
If migration is so stressful, why do birds persist in repeating this hardship? Migration makes it possible for birds to have the best of all worlds: abundant food in an agreeable climate while they raise their families and warm homes in winter, with rich food sources during their resting period.
