how many birds fly south for the winter

Geese winging their way south in wrinkled V-shaped flocks is perhaps the classic picture of migration—the annual, large-scale movement of birds between their breeding (summer) homes and their nonbreeding (winter) grounds. But geese are far from our only migratory birds. Of the more than 650 species of North American breeding birds, more than half are migratory.

Origins of long-distance migration

Long-distance migration patterns have far more complicated origins than short-distance migration, which most likely evolved from a fairly basic need for food. They have developed over countless years and are influenced, at least in part, by the genetic composition of the birds. They also take into account reactions to other elements such as the day’s duration, food sources, geography, and weather.

It seems strange to tropical birds that spend the winter months there to think about moving north and starting a migration. One theory for why these birds make such a difficult journey north in the spring is that their tropical ancestors dispersed from their tropical breeding sites northward over many generations. Compared to their stay-at-home tropical relatives (two to three on average), they were able to raise an average of four to six young due to the seasonal abundance of insect food and longer days. The birds continued to migrate back to their tropical homes during periods of glacial retreat, as the harshness of winter and diminishing food supplies forced them to do so. The majority of North American vireos, flycatchers, tanagers, warblers, orioles, and swallows have evolved from forms that originated in the tropics, which lends credence to this theory.

The mechanisms that trigger migration are diverse and sometimes poorly understood. A combination of shorter days, colder weather, altered food sources, and genetic predispositions can cause migration. Cage bird keepers have observed for centuries that migratory birds experience periods of restlessness every spring and fall, fluttering repeatedly toward one side of their cage. This behavior was named zugunruhe (migratory restlessness) by German behavioral scientists. Diverse bird species, and even subpopulations within a single species, may exhibit distinct migratory behaviors.

The BirdCast project is developing the capacity to forecast when, where, and how far birds will migrate; it’s almost like receiving a weather report.

It’s a treasure for bird watchers and important information for conservation efforts. Knowing the locations and times of birds’ migration allows for the prevention of millions of bird deaths by informing conservation decisions like the positioning of wind turbines and the dimming of building lights on particular nights.

More broadly, accurate migration models enable researchers to study the behavioral aspects of migration, the ways in which migration pathways and timing adapt to changing climatic conditions, and whether there are any relationships between variations in migration timing and ensuing shifts in population size.

Range maps This animated map shows where Common Yellowthroats occur each week of the year. The colors indicate the numbers of birds: darker or more purple colors indicate higher numbers of birds, lighter, yellow colors indicate fewer birds. Map from

Using the range maps in your field guide to ascertain whether and when a specific species might be present is always a good idea. Range maps are especially useful when working with migratory species. They can be confusing, though, as bird ranges can change from year to year, especially for invasive species like redpolls. Furthermore, some species’ ranges can change fairly quickly, sometimes even within the time it takes for a field guide to be republished. (The Eurasian Collared-Dove is the best example of this problem. ).

Digital range map versions that are driven by data are starting to address these limitations. The hundreds of millions of eBird observations that birdwatchers from all over the world have submitted have made the maps possible. Scientists can now create animated maps that depict a species’ ebb and flow across a continent over the course of a year thanks to “Big Data” analyses, which also help them understand more general patterns of movement.

Migration is a fascinating study and there is much yet to learn. Songbird Journeys, by the Cornell Lab’s Miyoko Chu, explores many aspects of migration in an interesting and easy-to-read style. The Cornell Lab’s Handbook of Bird Biology provides even more information on the amazing phenomenon of bird migration.

What is a migrant trap?

how many birds fly south for the winter

Certain locations appear to possess a talent for drawing migrant birds in greater quantities than usual. These “migrant traps” often become well known as birding hotspots. Usually, the local topography, an abundance of food, or the weather are to blame for this.

For instance, tiny songbirds that are migrating north in the spring cross the Gulf of Mexico straight and land on the states that border it. When headwinds are brought on by storms or cold fronts, these birds may be almost exhausted by the time they reach land. When this occurs, they flee to the closest area that provides food and shelter, which is usually live oak groves on barrier islands, where a large number of migrants can congregate in what is referred to as a “fallout.” Birdwatchers have taken a great interest in these migration traps, and they have even gained international recognition.

Additionally, as migratory birds follow the land and then pause before launching over water, peninsulas can concentrate them. This explains why areas with a strong reputation as migration hotspots include Point Pelee, Ontario; the Florida Keys; Point Reyes, California; and Cape May, New Jersey.

For those who feed birds in their backyard, spring migration is a particularly good time to attract species they would not typically see. Migrating songbirds may find a backyard appealing if it provides water, a range of food sources, and natural food sources integrated into the landscaping.

FAQ

What percentage of birds fly south for winter?

Not all birds migrate, but the majority of birds do. In fact, in North America about 75% of birds migrate. They do this for various reasons, for example, to find a more abundant source of food or a better climate. The Baltimore Oriole, one of our focal species found along the east coast, migrates south in the winter.

What birds fly south for the winter in USA?

In the most basic sense, birds migrate south for survival and return north to reproduce. They go to where there is sufficient food and protection. Geese, ducks and most waterfowl migrate south to seek open water where they find food and protection. If open water remains through the winter, some waterfowl may stay.

What bird doesn’t fly south for the winter?

Which birds do not migrate? The list of non-migrating birds includes some specific, well-known species – Blue Jays and Northern Cardinals – and also includes large groups of birds including black birds, chickadees, doves, finches, nuthatches, sparrows and woodpeckers.

What percentage of birds migrate?

At least 40 percent of bird species migrate in some form. But it’s simplistic to think of these trips as only annual flights south in fall and north in spring.