To Migrate or Not? That is the Question.

WILDER SIDE OF OAKLAND COUNTY

The classic image of bird migration at the approach of winter is the sight of Canada Geese flying high above our lakes, parks, towns and cities in V-shaped flocks. As winter fades, local television newscasters sometimes bubble with excitement at an alleged sign of spring’s return, robins on a snow speckled lawn. They salute the American Robin as the first returning bird of spring when robins are reported stalking about sunny suburban lawns searching for worms between patches of melting snow. These romanticized images of bird behavior and migration are less than accurate.

Facts on the ground often contradict long assumed beliefs that are passed on by both casual Facebook posts and well-respected writings in historic journals. In 1859, Henry David Thoreau wrote, “The bluebird comes and with his warble drills the ice and sets free the rivers and ponds and frozen ground.” Times change, food sources change, habitats have been altered, and our climate has warmed. Established patterns of bird migration and behavior that were once accepted as fact are getting a closer look.

Many local Eastern Bluebirds no longer migrate and are frequent visitors to bird feeders if they are stocked with suet. Some Canada Geese are still grazing on Oakland County golf courses that have been laced with snow. Although most Sandhill Cranes have departed, others still stalk about the stubble of corn fields, even as snow swirls and cold winds rattle the dry stalks. Walk quietly along the edge of a wetland and a motionless Great Blue Heron might be spotted as it waits for the movement of a fish. As for American Robins, you won’t spot one on a frozen lawn when worms can’t be tugged from the earth. But that does not mean all robins migrated to warmer climates. A walk through the wildlands of our county on a wintry day often reveals robins feasting on old berries and fruits and foraging for grubs in clusters of dry sumac seeds.

Migration is more than a flight of fancy to bask in Florida sunlight and warmth until winter wanes, like human “snowbirds” may do. To migrate or not to migrate—that remains the question. Who stays, who goes, and why? The answers are not set in stone. Migration remains something of a mystery, triggered by a combination of factors and events, including food supply availability, diminishing hours of daylight and lower temperatures. Although cold is often perceived as the primary motivating factor, it is not so much that birds get cold. Birds tend to seek shelter in swales and shrubs and ‘fluff’ up against biting winds, but it is the cold that often kills off their food supply. No food means death, and the only alternative is migration, unlike many reptiles and amphibians and some mammals that hibernate.

The Cornell Lab of Ornithology, looks at four categories of migration. It’s important to remember that there are no firmly defined lines in their categories. Categories overlap and can change due to habitat alteration, habitat destruction, weather conditions and predatory pressures.

  1. Permanent Residents: They do not migrate. The Oakland County list is very long, and includes commonly seen species such as chickadees, blue jays, turkeys, woodpeckers, house finches, owls and hawks. Turkeys move into woodlands with abundant acorns and other fallen nuts. Red-tailed Hawks wait for rabbits or squirrels to pass by, while Cooper’s Hawks often perch near a bird feeder to feed on their favorite prey, smaller birds.
  2. Short Distance Migrants: They migrate a short distance from one habitat to another, or from a higher elevation to a lower elevation. Their migration may only be a few hundred yards, or a few dozen miles, but some follow categories three or four. The American Robin and Eastern Bluebirds fit that variable category. Robins can’t locate worms in frozen lawns, nor can bluebirds find live grubs and insects, so they both retreat to shrubs and areas where they can find old fruits and berries as seasonal substitutes.
  3. Medium Distance Migrants: They travel a relatively short distance that might span from one state to another. Many of our Canada Geese would fall into medium distance migrants, as would many of the Bald Eagles of Michigan. Sudden severe weather can fuel a medium distant migration.
  4. Long Distance Migrants: They may go thousands of miles from breeding ranges in the United States and Canada to wintering grounds in Central and South America. Birds that feed mostly on flying insects or nectar are long distance migrants, including tree swallows, chimney swifts, and nighthawks, and of course, the smallest bird that breeds in Oakland County, the Ruby-throated Hummingbird.

Migration is full of risk, for it’s an arduous journey of thousands of miles that will tax the bird’s physical capabilities and may expose it to unknown hazards and rapid weather changes such as hurricanes. Climate change is presenting a clear and present danger to many migratory songbirds. “New research shows climate change is altering the delicate seasonal clock that North American migratory songbirds rely on to successfully mate and raise healthy offspring, setting in motion a domino effect that could threaten the survival of many familiar backyard bird species.” Here’s the rest of that story in a news release posted by Science Daily and the Florida Museum of Natural History.

With all the risks, why would a tiny bird such as our Ruby-throated Hummingbird, weighing only a fraction of ounce, undertake such a journey, while much larger, powerful birds including Great Horned Owls, Barred Owls, Red-tailed Hawks, and Cooper’s Hawks stay in town? As you have realized by now, it’s mostly about food and the ability to adapt to changing conditions. Ruby-throated Hummingbirds sip nectar, and there is no nectar to be found for almost six month and no way to adapt to a substitute meal. Owls and hawks feast on small mammals. Small mammals are abundant, and so they are year round residents.

Common wisdom makes it rather clear that water wading birds, such as our Great Blue Heron must migrate. Common wisdom is not always correct. The presence of Great Blue Herons in winter makes some believe the heron must be sick or unable to fly. Although the majority of the great blues in our county wing southward before water freezes, many over-winter in Oakland County. Great Blue Herons may be found in our county as long as water with their favorite food—fish, remains opens. Although they stand four feet tall, these skilled fishers often escape detection because they stand motionless in the shallows scanning for fish. Sometimes, even after their water-world feeding grounds freeze over, a few will not migrate and switch to a diet of meadow voles and other small animals. Adaption is the key to their survival. Perhaps by staying here all winter they also earn the right for the best nesting spots high up in their rookeries.

Bald Eagles are becoming increasingly common in Oakland County, and one pair has nested successfully for the past five years at Stony Creek Metropark. They are primarily fish eaters but will also take ducks, muskrats and other small creatures. That adaptability helps them thrive in new habitats, and limits the need for a long distance migration. Some of the Bald Eagles that nest in Michigan fly just far enough south to reach shallow waters for fishing. One of those southern locations is in Southeast Michigan, at the landscape of the DTE Monroe Power Plant. The Detroit River International Wildlife Refuge, along with the International Wildlife Refuge Alliance and DTE Energy of Southeast Michigan, will host their eighth annual Eagle Tour at the DTE Monroe Power Plant on January 27th. This event has become so popular that a lottery takes place to give visitors a fair chance to win a spot to view gatherings of bald eagles in their local winter fishing grounds at the power plant. Visit the Detroit River International Wildlife Refuge website for information on the refuge and a link to enter the lottery.

For more information on birds, bird migration and secrets of migration, explore the Cornell Lab of Ornithology website and the Oakland Audubon website.

Jonathan Schechter is the Nature Education Writer for Oakland County Government and blogs weekly about nature’s way, trails, and wildlife on the Wilder Side of Oakland County.


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