Spring Migration Underway: A Bird’s-Eye View

The annual spectacle of spring bird migration has begun, bringing with it a flurry of avian activity across the continent. Utilizing advanced radar technology, researchers are tracking the movements of millions of birds as they journey to their summer breeding grounds. This incredible migration, driven by the availability of food and suitable nesting locations, represents a crucial phase in the life cycle of numerous species.

"On a big night in the spring, you’re talking 450 to 500 million birds flying under cover of darkness," explains Andrew Farnsworth, a migration ecologist at Cornell University’s ornithology lab. These impressive numbers highlight the scale of this natural phenomenon, a testament to the resilience and adaptability of birds. The migration season sees a diverse array of species on the move, including those returning from their winter retreats and those making temporary stops to refuel before continuing their journey.

Currently, significant bird movement is being observed in Florida, the Southeastern United States, and several Midwestern states. The ruby-crowned kinglet, swamp sparrow, and eastern phoebe, having spent their winter months in the southeast, are now venturing northwards. In regions like Kansas, waterfowl and various sparrow species, such as the fox sparrow, American tree sparrow, and dark-eyed junco, are actively migrating. The red-winged blackbird and common grackle are also among those taking to the skies.

For those eager to follow the migration’s progress, Cornell University’s BirdCast Migration Dashboard provides daily summaries of radar-based nocturnal bird migration. This innovative tool allows users to observe the movement of birds across the nation and even track the number of birds that flew over their specific county the previous night. The use of radar is essential due to the nocturnal habits of most migrating birds, which often fly at altitudes as high as 15,000 feet, rendering them invisible to the naked eye.

The peak spring bird migration in the contiguous United States generally occurs between March 1 and June 15, with some species migrating earlier or later. Fall migration typically spans from August 1 to November 30. Peak migration is defined as the period during which approximately 50% of nighttime bird migration traffic passes through a given area. Maps illustrate a wave of peak migration progressing from the southernmost United States to the far north as temperatures gradually rise throughout the spring.

"It’s not until April that you really start to get the big bang of bird diversity," Farnsworth notes. The peak migration resembles a wave sweeping across the United States, starting from the south and moving towards the north. BirdCast offers live, local bird migration alerts, providing real-time information on the species flying through specific areas.

Currently, bird numbers are particularly high in New Mexico, Texas, Oklahoma, and to some extent in the Maryland-New Jersey region. A migration prediction map forecasts upcoming nocturnal migrations. For instance, on the night of March 10 to 11, an estimated 20 million birds were projected to be migrating across the United States, with high migration activity expected in Iowa, central Texas, and Oklahoma.

That night, Des Moines County, Iowa, witnessed an estimated 158,700 birds crossing its borders, including snow geese, dark-eyed juncos, killdeers, white-throated sparrows, yellow-bellied sapsuckers, northern shovelers, and buffleheads.

In North America, birds typically migrate south for the winter, seeking regions with ample food resources during the colder months. In the spring, they return north to capitalize on burgeoning insect populations, flourishing plant life, and optimal nesting sites. As winter approaches, the cycle repeats, with birds migrating south once again to escape the cold and ensure access to sufficient food.

Birds exhibit diverse migration strategies, categorized into five main types, with larger birds generally undertaking longer journeys:

• Permanent residents: These birds do not always migrate, often due to sufficient food availability in their habitat. Examples include the American crow, common raven, mourning dove, wild turkey, and various heron species in Florida.
• Altitudinal migrants: These birds migrate vertically, changing altitude rather than location, typically moving up or down mountains. Examples include Clark’s nutcracker, the mountain chickadee, and rosy finches in the Rocky Mountains.
• Short-distance migrants: These birds migrate relatively short distances, such as the eastern phoebe, yellow-bellied sapsucker, and song sparrow.
• Medium-distance migrants: These birds migrate a few hundred miles, often breeding in the Northeastern U.S. and wintering in the Southeast. They may also breed in eastern deciduous forests and migrate to Central and South America or the Caribbean. Many shorebirds fall into this category, along with various warbler species, the western tanager, and the snow bunting.
• Long-distance migrants: These birds undertake journeys spanning thousands of miles, often from the northern United States and Canada to wintering grounds in Central and South America, sometimes traveling as far as 8,000 miles. Shorebirds are frequently long-distance migrants, including those breeding on the tundra and wintering in southern South America. Examples include the arctic tern, Hudsonian godwit, long-tailed jaeger, and the bobolink. The blackpoll warbler songbird can migrate from Alaska to the Amazon.

The mechanisms underlying bird migration, particularly how birds navigate and determine when to migrate, remain a subject of ongoing research. Factors such as day length, smell, the position of the sun and stars, and even the Earth’s magnetic field are believed to play a role.

Climate change poses a significant threat to bird migration patterns, as shifts in plant budding and insect availability disrupt the synchrony between migration and food sources. This mismatch can lead to food shortages during crucial breeding periods.

To assist migrating birds, ornithologists encourage individuals to turn off nonessential lighting from 11 p.m. to 6 a.m. during peak migration periods. Artificial lights can attract and disorient nocturnal migrants, increasing the risk of fatal collisions with buildings.

"These simple steps can help protect them," emphasizes Farnsworth. "And please make sure any glass in your house is bird friendly." By taking these measures, we can contribute to the safety and survival of these remarkable creatures as they undertake their arduous journeys.