Feathered flyways: When, what birds to look for during fall migration

• This column by Environmental Communications Specialist Brett Peto is reprinted from "Horizons," the quarterly publication of the Lake County Forest Preserves. You can subscribe to receive the free magazine at lcfpd.org/horizons.

Scarlet tanagers weigh about an ounce and stand barely taller than the halfway point of a ruler. They've spent spring and summer eating and reproducing in the canopies of eastern North America's deciduous woodlands and, occasionally, backyards. But this isn't their permanent home.

When fall approaches, the male tanager's red feathers molt to resemble the female's olive-yellow plumage, though he retains his black wings and tail. Adults and juveniles fuel up for a cross-continental journey to wintering grounds in Central and South America.

By August and September, tanagers join millions of other birds undertaking fall migration, flying primarily north to south.

Fall migration is a partial misnomer. Birds migrate to and fro year-round, generally to find better food sources and nesting locations. Fall and spring are peak times.

"In Lake County, fall migration starts in July," said Restoration Ecologist Ken Klick. "It spans five months, involving millions of birds representing 200-plus species that appear in the Lake County Forest Preserves' 31,000 acres."

There are four flyways recognized nationwide. These are historic migration routes that provide food, shelter and a visual north-south orientation. Lake County is an important point along the Mississippi Flyway, which spans portions of eastern Canadian provinces, the Midwest and the Gulf Coast.

Some birds that nested in the upper Midwest, Canada and the Arctic rest and refuel in the forest preserves and other natural areas along their travels. Others that nested in Lake County leave, aiming for destinations as varied as southern Illinois to Argentina. Less commonly, Lake County is a destination for birds that fly south to overwinter there, such as dark-eyed juncos.

Preparing for takeoff

Declines in food availability, length of daylight and temperature can trigger migration. Flying up to thousands of miles is tough. To prepare, birds eat more in late summer, said Environmental Educator Mark Hurley.

"They eat berries, seeds, insects and occasionally fish, replenishing energy reserves."

Long distances expose birds to predators, bad weather and human-made obstacles. Deforestation and development of natural areas, power lines, cellphone towers, roaming cats, skyscrapers and bright lights can disrupt migration. Climate change, too, is increasingly shifting the timing and abundance of food sources. The 2021 drought affecting Lake County is one example.

Across the map

Short-distance migrants relocate within flitting distance of their starting point. Redheaded woodpeckers sometimes migrate 10 to 50 miles south of Lake County to follow the annual acorn crop in oak woodlands. Medium-distance migrants fly across the same state or several states. Long-distance migrants travel from the U.S. and Canada to Central and South America.

Lake County Layovers

July brings the first fall migrants: shorebirds. A visit to the Lake Michigan shoreline at Fort Sheridan Forest Preserve in Lake Forest finds sanderlings, sandpipers and yellowlegs. Many migrating shorebirds have just finished raising young in the Arctic Circle's perpetual daylight.

Near the end of August, swallows and common nighthawks congregate for South American destinations. Nighthawks sometimes catch the first cold front for a tail wind ride south. September brings the highest bird numbers and diversity. Passerines, or perching birds - think warblers, vireos, tanagers, grosbeaks and thrushes - are common.

Raptor Rapture

Lake County's position on the western shore of Lake Michigan provides stupendous hawk viewing opportunities. In October, strong winds blow migrating raptors - hawks, falcons, ospreys, eagles and other birds of prey - toward the Great Lake.

The water concentrates raptors along the shoreline, since there are no thermals, or rising columns of warm air, over the lake to improve flight.

On a given day, "thousands of raptors can pass silently at dizzying heights, some singly and some in groups called kettles," Klick said.

Navigating November

November delivers a recognizable scene, often heard before seen: sandhill cranes and Canada geese flying overhead in V-shaped formations. With luck, you could spot a federally endangered whooping crane. Look for a large, white crane with black wingtips among groups of migrating sandhills.

Some waterfowl, such as snow geese, move through in November. Bucking the north-south trend, tundra swans fly east to winter in the Chesapeake Bay area. Other waterfowl return to overwinter here. Look for buffleheads, common goldeneyes and common mergansers on lakes and rivers with open water through winter.

There are always oddballs and outliers during bird migration, but this annual event "unfolds in nature's rhythms and patterns," Klick said. "Each month provides unique birding experiences. Yet they're fairly predictable for those who look."

Finding feathered friends

If your bird-watching is taking flight, obtain some gear.

"A field guide to the birds of the eastern U.S. is key. You can purchase a copy or check one out from a library," Hurley said. "Buy or borrow a pair of 7- or 8-power binoculars."

Also consider using free bird identification and monitoring apps from the Cornell Lab of Ornithology, National Audubon Society and other organizations.

Increasing the complexity are species that seem to live locally year-round but are medium-distance migrants.

"The blue jays that nested in northern Wisconsin may appear at our bird feeders in winter, while the jays that nested in your backyard could spend the winter in southern Illinois," said Director of Education Nan Buckardt.

The pace of migration differs in fall.

"In spring, it's all about getting to the breeding grounds and reproduction," Buckardt said. "Fall migration is typically more casual and some species may stick around longer."

This can reverse the order in which birds arrived during spring. Yellow-rumped warblers and palm warblers land in early spring but are often the last warbler to leave Lake County in fall.

Spotting birds in fall can prove challenging. Most adults rarely sing and have molted into subdued winter colors. Foliage also interrupts lines of sight. Accompany other bird-watchers and become familiar with migration locations. Learn more at LCFPD.org/birdwatching.

• Kim Mikus is a communications specialist for the Lake County Forest Preserves. She writes a bimonthly column about various aspects of the preserves. Contact her with ideas or questions at kmikuscroke@LCFPD.org. Connect with the Lake County Forest Preserves on social media @LCFPD.