Migration Mysteries

The mystery of bird migration has filled people with a sense of wonder and amazement for thousands of years. Consider, for example, the mystery of a Tennessee warbler which, after a journey of 3,000 miles, will often return to the same tree to nest year after year. Greater shearwaters migrate 8,000 miles annually, and mallards have been observed by jets at an altitude of 21,000 feet. Hummingbirds can fly 500 miles in 25 hours at an average speed of 20 mph. How and why do these birds migrate?

The following eight examples, generated from eBird data, describe the migration patterns of some Iowa birds:

1. American Robin - Most robins spend the winter in the southern United States and migrate each spring to the northern states and southern Canada where they nest and spend the summer. Although most leave Iowa in the fall, every year a few robins winter in Iowa. Robins that nest in Iowa typically winter in Missouri, Arkansas, Louisiana, Kansas, Oklahoma, Texas, Tennessee, and Mississippi.

2. Dark-eyed Junco - Juncos nest from far northern United States north into Canada. In fall, they migrate south where many will winter in Iowa and surrounding states. In spring, they leave Iowa to go back north to their nesting grounds in northern Minnesota and Wisconsin, as well as Manitoba and Ontario in southern Canada.

3. Ruby-throated Hummingbird - This hummingbird nests in the central United States and southern Canada. In late fall, it migrates south, eventually crossing the Gulf of Mexico and winters in southern Mexico, Guatemala, Honduras, Nicaragua, and Costa Rica. In spring, it reverses this migration pattern and returns to Iowa in May.

4. Upland Sandpiper - This bird nests on grasslands in Iowa and other prairie states. In fall, it migrates south, eventually reaching Argentina and Paraguay in South America where it spends the winter. The next spring, it returns to Iowa in April. It has one of the longest migrations of any Iowa bird.

5. Tundra Swan - This swan has an unusual migration pattern because it moves not only in a north-south direction but also from west to east. The birds nest in the far north of Canada and Alaska near the Arctic Ocean. In fall, they migrate to the southeast and usually winter along the Atlantic Coast from Maryland to North Carolina. In spring, they fly back northwest to their breeding grounds. In Iowa, we most often see wild swans in the northeast part of the state along the Mississippi River. One of the best places to see tundra swans in Iowa is on the Mississippi River near Harper's Ferry.

6. Bobolink - The bobolink nests in tall grasses, flooded meadows, and prairies in the Midwest. In the fall, it starts its journey to South America, staying mostly east of the Andes Mountains. It winters in South America from southern Brazil through Bolivia and Paraguay to northern Argentina.

7. Red-winged Blackbird - This bird signals the arrival of spring in Iowa. The males show up as soon as the snow melts in late February or March to stake out their territories here in Iowa. Even in snowstorms, the red-winged blackbird is seen in many of Iowa's road ditches. In early August, large flocks of blackbirds can be seen congregating to get ready for their flight to southern United States. Most blackbirds from Iowa winter in Missouri, Arkansas, Kansas, Oklahoma, Texas, Kentucky, and Tennessee. During migration and on the wintering grounds, these birds form flocks of hundreds of thousands or even several million birds. These flocks are a nuisance because they feed on grain that farmers have fed to their livestock. The birds also are a problem because of their droppings; the droppings that accumulate below the roosts are messy and they may cause health hazards.

8. Baltimore Oriole - The oriole winters from southern Mexico south through Central America (Guatemala, Honduras, Nicaragua, Costa Rica, and Panama) and into northern South America (Colombia).