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The Marvel of Migration

by Liz Magnanti

The four major migration routes in North America. Image courtesy U.S. Fish and Wildlife Service

The days are getting shorter, the temperatures are getting cooler, and insect populations are becoming increasingly scarce. For many birds that means one thing—it’s migration time! More than half (about 350 of the 650+ species) of the birds in North America are migratory. Migration is defined as a large-scale movement of a population of animals. Birds migrate to their breeding grounds in the spring and summer from their non-breeding winter grounds, and vice versa. The main reasons birds migrate is to “breed and feed.” They will travel to locations that have a larger breeding and foraging area as compared to their overwintering sites. As the fall approaches many species of birds are getting ready to make their epic trip south.

Migration has evolved over millions of years. Scientists believe that as glaciers in North America retreated, birds moved further north where nesting sites and food were seasonally more prolific. With this expanded habitat they most likely had better breeding success Over time the offspring of these birds would have increased success with breeding and continue the migration process northward. 

There are different types of migration. Some birds don’t migrate at all. They are known as resident or non-migrating species. Many of the birds you see at your feeders in the winter are resident birds. Cardinals, chickadees, nuthatches, goldfinches, and most woodpeckers fit into this category. Partial migrants are birds that migrate short distances, sometimes only spanning a state or two. Blue Jays, Red-tailed Hawks, Robins and Bluebirds are birds that make this kind of migration. The Blue Jays you have at your feeders in the spring are probably different from the individuals that will be there in the winter. As fall approaches, be on the lookout for flocks of blue jays and robins making their medium-distance migration. Irruptive migrators are birds that have unpredictable migration events that don’t always follow the rules. Their movement can be attributed to food shortages or food abundance in an area, or can be seemingly at random! Typically this type of migration is found in northern birds that will venture further south than normal. Great gray owls, snowy owls and redpolls are examples of irruptive migrators. And then there are the long-distance migrants. The long-distance migrants we are most familiar with are the neotropical migrants that will travel all the way to Central and South America to spend the winter. They stick to a schedule and will arrive to their breeding grounds north at the same time each year. Orioles, hummingbirds, grackles and warblers will make this type of migration. The tiny ruby-throated hummingbird will make the trek by flying completely over the Gulf of Mexico on a 25-hour nonstop flight!

In North America there are four major migration routes birds will take. These are the Pacific Flyway on the west coast, the Central Flyway in the Midwest, the Mississippi Flyway, and the Atlantic Flyway. Lake Erie and Lake Ontario are popular local stopover points for birds migrating along the Atlantic Flyway. In the fall, look for waterfowl in bodies of water and along the lakeshore where birds fuel up on berries, seeds, and remaining insects. 

You may see more birds coming to your feeders this time of the year. Birds that are making a migration of any type will begin to fuel up for the journey. Don’t be surprised if you see more hummingbirds drinking nectar, and a large array of species visiting mealworm feeders. Species like grackles, red-winged blackbirds, and rose-breasted grosbeaks will eat a large amount of seeds to bulk up for the journey. Birds will typically increase feeding by 25 to 30 percent this time of year in a process called hyperphagia. 

No one is quite sure what ultimately prompts birds to leave their breeding range, but there are several factors that have been linked to the urge to migrate. The shortening of daylight, food availability, and changes in the weather cause a transformation in a bird’s endocrine system, which changes their hormones. Birds, even some kept as pets, will undergo a migratory restlessness in the spring and fall named zugunruhe, which makes them more active and less likely to sleep. Many birds, like ducks and birds of prey, will migrate during the day, while most songbirds migrate overnight. 

How birds find their way to their destination is still a mystery. Studies have found that some species of birds have a navigation system coded into their DNA so they can find their way even when blown off course by a storm or other natural disaster. Other studies show some species learn their migratory route from their parents, and once they have completed the route they can perform it with accuracy year after year. The whooping crane is an example of a bird that has this type of navigation system. Birds are also known to be sensitive to the earth’s magnetic poles, and may use them in some way to navigate. Visual cues are also important. Birds will use the stars and land formations as guides when they are migrating. 

All in all, the process of migration is an amazing feat. Although it’s sad to see that some of our favorite backyard birds have flown the coop for the winter, it’s impressive to know that we can rely on them to show up at almost the same exact time each spring!

Liz Magnanti is the manager of the Bird House in Pittsford.

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