Annually many bird species migrate as their food supply disappears, water sources freeze, shelter options lessen, and daylight hours reduce. Migration cannot begin, however, until the young birds have fledged in their breeding range and all birds have eaten extra food for the long journey. Many species double their weight to fuel their migration. Purple Martins, as an example, eat three times their weight in mosquitoes in a day in preparation for the trip.
Generally, birds migrate when the weather and atmospheric structure are good. This means winds are blowing in the direction that they are headed and tail winds are available to increase their speeds. Navigational options for birds include use of the stars, sun, and internal sensitivity to the Earth's magnetic field as their compass(es). They also learn routes from other birds. Often they will use one of the four major flyways in the USA: Atlantic, Central, Mississippi, or Pacific. For information on flyways click here and here.
Birds using powered flight that involves continuous flapping and a level course through the air are often nocturnal migrants. At night the air is calmer or more stable and predators are fewer. These can be viewed with a telescope as they pass by the light of a full moon. Soaring birds, on the other hand, prefer daylight when they can ride thermals of rising hot air.
Most birds need stopover sites during migration for re-fueling and rest. Familiar stopover sites are disappearing as forests are denuded and wetlands destroyed by over development. Pollutants destroy the quality of soil and water. Habitat fragmentation delays finding needed food and rest from the exhausting flight. Some birds die in the effort to find suitable rest areas.
Hunters take advantage of the large flocks in the air and can destroy thousands of birds in a season of hunting.
Tall buildings with reflecting glass, lights at night, and wiring into the building add still other obstacles. Birds run into these and die.
Automobiles maim or kill other migrants attempting to cross highways to better fueling stations.
COMMUNICATION TOWERS
Communications towers are killing an estimated 4-5 million birds per year which violates the spirit and intent of the Migratory Bird Treaty Act and the Code of Federal Regulations at Part 50 designed to implement that Act. Some of the species affected are protected under the Endangered Species Act and Bald and Golden Eagle Act.
Audubon, Defenders of Wildlife, and the American Bird Conservancy filed a petition to the Federal Communications Commission for expedited rule making to prevent needless bird deaths at communication towers.
In 2000 the U. S. Fish and Wildlife Service issued science-based guidelines on the siting and operation of communication towers. Their website www.fws.gov has a section on publications and reports such as this one as well as on migratory birds.
Bird Migration Audio Stories
Two fascinating audio stories on bird migration are available at National Public Radio's web site. Click here for the first one and here for the second one.
Blackbirds migrating south.
ACTION ALERT
MIGRATING SHOREBIRD SLAUGHTER
Hunters are shooting migrating neotropical shorebirds in Barbados. The wild fowlers in Barbados lure migrating birds to managed swamps and shoot from 15,000-30,000 every fall.
Fortunately BirdLife International (a global partnership of non-governmental and non-profit bird and biodiversity organizations), is now working with swamp owners and hunters to persuade them to adopt bag limits, to avoid species of special concern such as the American Golden Plover, and to stop using taped calls to lure birds to the swamps. All the signs are that reason will prevail. However, BirdLife’s program manager in Barbados has his salary secured only until September 2009. Our Audubon chapter has begun a fund raising campaign to help. If you would like to help please send contributions to West Pasco Audubon Society, PO Box 1456, Elfers, FL 34680. Make check payable to West Pasco Audubon Society, reference “Barbados Rescue”. (100% of funds donated will go to the rescue program).
Cornell Lab of Ornithology, the American Bird Conservancy, and The Johnson Foundation at Wingspread hosted a meeting of top wildlife scientists in Racine, Wisconsin. By the end of the meeting scientists from industry, government, non-governmental organizations, and universities had agreement on research priorities related to the safe passage of birds during migration and the growing alternative of wind energy. Click here to see details.
Fall Migration Hot Spots
Kenn Kaufman's recommended hot spots for viewing migrating birds in the fall are:
- Bill Baggs Cape Florida State Park, Florida www.floridastateparks.org/capeflorida
- Cape May, New Jersey http://birdcapemay.org
- Great Salt Lake, Utah www.fsw.gov/bearriver/birds.html
- Monterey Bay, California creagrus.home.montereybay.com/MtyBay.html
- Izembek Lagoon, Alaska http://izembek.fws.gov
- Hawk ridge, Duluth, Minnesota www.hawkridge.org
He published his recommendations in the Fall 2009 issue of the Audubon magazine.
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