Where Do Birds That Leave Maryland for the Winter Go?

 Documenting the journeys of the birds who travel away from the Free State each year

Baltimore orioles can be found throughout much of Maryland in the summer months. In the winter, Baltimore orioles fly as far south as Venezuela. Photo by Jeff Dyke, submitted for the 2018 Maryland DNR photo contest.

In recent summers on Maryland’s “tern raft,” a man-made conservation platform that serves as habitat for state-endangered colonial nesting waterbirds, scientists found a common tern with a distinctive orange tag on its leg.

The tag indicated that Argentinian researchers had banded the tern in the winter at Punta Rasa, a coastal area just south of Buenos Aires. That means this common tern—and at least five others there with similar tags—traveled some 5,000 miles between summers spent in waters of Worcester County’s coastal bays and winters deep in the southern hemisphere.

Maryland, especially the coastal areas along the Chesapeake Bay, attracts many migrating northern birds during the winter, but that migratory pull goes in both directions. While these common terns are some of the farthest traveled, they’re hardly the only birds that clear out of Maryland for more temperate climes in the colder months.

“Migration is very dynamic and changeable by species,” said Dave Brinker, a Maryland Department of Natural Resources avian conservation  ecologist who studies bird movement. “They all have their different strategies to make it through the winter.”

Common terns at the “tern raft.” Photo by By Kim Abplanalp

Some of the birds that leave Maryland are other nesting waterbirds, like the small and speedy piping plovers, which nest on Assateague Island before following the southern Atlantic coastline in the winter, with some making their way into the Bahamas.

A number of songbirds also fly south from Maryland, including the state bird, the Baltimore oriole. While Baltimore orioles inhabit most of the state in their breeding season, they fly down to Florida, Cuba, Central America, and even Colombia and Venezuela for the rest of the year. Yellow-throated vireos follow a similar migration pattern, while cerulean warblers go as far as Bolivia.

This doesn’t necessarily mean the oriole eating an orange at your birdfeeder in July is kicking back in Bogotá or Caracas in January. Brinker noted that many bird migration patterns follow a “leapfrog” pattern, where birds that summer higher north tend to travel the farthest south, leapfrogging over birds that summer more southerly and don’t migrate as far. Maryland is toward the southern edge of Baltimore oriole’s summer range, so they may not travel quite as far as their Canadian cousins.

Regardless of how far they fly, many birds while away in the winter in a place that may seem enviable to Marylanders making do in a polar vortex. Chimney swifts, known for their dramatic aerial acrobatics and their ability to cling to chimneys and hollow logs, split the seasons between the continents, wintering from Colombia to Peru and Brazil. Barn swallows, another dynamic aerialist, summer throughout the states and spread out through Central and South America for the rest of the year, while ruby-throated hummingbirds stick mostly to the Yucatán through Costa Rica.

Most Maryland migrators don’t have as firm evidence of their travels as the tag on the common tern, but there is considerable information on many migratory species. The Audubon Society and the Cornell Lab of Ornithology compile data from tracked observations gathered from GPS transmitters, reported sightings, and other sources.

While many people assume that birds fly south for warmer weather alone, Brinker noted that shifting food sources are the driving factor for many migrations. That’s especially true for insectivores like black-throated green warblers, which nest in the forests of western Maryland and need to go south once the “insect load in the forest canopy has declined,” he said.

Many of the birds that remain in the state all winter are seedeaters, like cardinals and finches, and have a more reliable food source throughout the winter. Being in the Mid-Atlantic, Maryland has a number of year-round resident birds, and southern states tend to have more that don’t migrate.

A barn swallow feeds an insect to a juvenile. Barn swallows are insectivores that catch bugs in the air and raise young in places like Maryland before wintering from Mexico to Patagonia. Photo by William Pully, submitted to the 2023 Maryland DNR Photo Contest

Some birds go south in pursuit of other prey—even other migrating birds. Some arctic peregrine falcons follow shorebirds south, but Maryland’s peregrine falcons tend to remain in the area all year, Brinker said. But other predatory raptors—like broad-winged hawks and osprey—do migrate from Maryland to Central and South America. 

Adding to the complications of migration, there are some bird species that follow what’s known as “facultative migration,” Brinker said. This is when a bird will conditionally migrate based on environmental conditions, such as the red-necked grebe, which migrates to this area when Lake Erie freezes—so, if cold temperatures hold in the Great Lakes, Marylanders may see more red-necked grebes this winter.

But one near constant in migration is that individual birds usually do return to the same place every year, winter and summer. Brinker said “the bulk of our songbirds follow that model.” Like anadromous fish that return to the river they were spawned, birds follow a number of environmental and sensory cues to come back to the same location. (An exception is snowy owls, which come back to the same areas consistently in the winter—including Assateague—but crisscross the arctic in the summer in search of lemmings.)

Knowing as much as we can about bird movement ultimately helps us to best protect birds, Brinker said. More stationary species might need more landscape protections in one area, while migrating birds might need a “string of pearls” of protected habitats along their route.

“At both ends of the spectrum, knowing that mobility and migration is essential,” Brinker said. “It can help us keep all of our birds stable in the state of Maryland.”

An osprey catches a fish. The Chesapeake Bay has the world’s largest breeding population of osprey, which go into Central America down to Brazil during the winter. Photo by J. Sal Icaza, submitted for the 2020 Maryland DNR Photo Contest.

By Joe Zimmermann, science writer with the Maryland Department of Natural Resources