Spring migration timing varies across the U.S. and even within regions, according to radar data analyzed by BirdCast.
We know that catbirds migrate to different places in the fall after mating, based on tracking data, including light-level geolocator tags. Even among birds that migrate from the same breeding site, the paths they take are not all the same. For instance, a few of the catbirds from Washington, D.C. that we have tracked C. some traveled along the foothills of the Appalachian Mountains, a long mountain range extending from Georgia to Maine, while others followed the Atlantic coastline.
The winter habitats of gray catbirds are fairly similar to those in which they spend the summer. The majority of the catbirds that we have monitored spend the winter in areas with lots of shrubs. These environments typically feature lots of cover to help catbirds evade predators as well as lots of berry-producing plants and insects to provide food for the birds. The majority of catbirds would not survive if they spent the winter in the north due to a very limited food supply.
The nestlings depart the nest when they are large enough and have developed the feathers necessary for flight. This process is known as fledging. The young catbirds are now referred to as fledglings, and they will go on a quest with their parents to find insects to consume. The fledglings must put on a lot of weight in order to survive because they are still very weak. Additionally, they are still learning how to fly and are still getting acclimated to the new environment they have entered. Because of this, predators—particularly outdoor cats—find it easy to prey on fledglings. These cats frequently spend time hunting birds in suburban gardens. The majority of fledglings won’t live longer than a week. When they are strong enough, which will be in a few more weeks, the fledglings that make it will leave their parents and go exploring.
Catbirds begin arriving in Washington, D. C. , in late April and early May. There are a lot of catbirds when they first arrive, and their songs fill the city. A large number of the catbirds that we observe are migrating through the area from far north of the city. Only the birds that will remain for the entire summer remain in the area after a week or two. The remaining catbirds mark out areas with their songs so they can construct nests.
As spring approaches, the catbirds start to become restless. They undergo a shift in their sleep patterns and begin searching for food later in the day. Once more, the catbirds put on a lot of weight to fuel their migration back north. They will return to their summer range to breed if they survived the winter in good health, managed to store enough energy as fat, and made it north.
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Eager birders in the West will be able to enjoy their peak bird migration bonanza in late April and the first week of May, while birders in the Northeast and Upper Midwest may have to wait a few more weeks, according to a new BirdCast analysis that mapped out the periods of highest aerial bird density across the United States from March to June.
Scientists at the Cornell Lab of Ornithology, Colorado State University, and University of Massachusetts Amherst have teamed up to create a project called BirdCast that tracks and forecasts bird migration using weather radar and machine learning. BirdCast has been using radar to track nightly bird migration throughout the United S. since 1999. In this new analysis, 143 radar systems from coast to coast were used to measure aerial bird densities every ten minutes between 2013 and 2022. The goal was to determine the peak periods of the spring bird migration, which is defined as the times when the nightly average of birds in the night sky was at its highest.
According to Cornell Lab research associate Adriaan Dokter, senior researcher for BirdCast, variations in the timing of bird migration can be observed not only throughout the continent but also in specific areas.
Dokter notes that one observation that caught his attention is the later peak migration date in the western Gulf of Mexico and Texas compared to the eastern Gulf. He attributes this difference to the species composition of bird migration in those two regions. “By far the longest-distance migrations [of birds migrating from overwintering grounds in Central and South America], such as warblers and orioles, arrive in the United S. much fewer enter the East via Mexico and the western Gulf states. Many common short-distance migrants, like blackbirds and sparrows, migrate to the Southeast for the winter, often departing several weeks early. ”.
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Dokter observes that the same pattern can be seen in the Central Valley of California, where a short-distance migratory bird island’s overwintering grounds are encircled by long-distance migratory birds’ flight paths. Furthermore, he notes that, in comparison to nearby regions, a corridor extending northward from western Texas to the Dakotas records comparatively earlier peak bird-migration periods.
The Great Plains serve as a major migration route for birds, allowing them to enter the nation, travel north, and then disperse west and east, he says.
While weather radar scans can’t be used to identify the bird species on the move—radar just detects the biomass of birds in the air—another project by some of the scientists involved with BirdCast will delve deeper into bird-migration patterns. A study published in the journal Methods in Ecology and Evolution in January, and spearheaded by researchers at UMass Amherst and the Cornell Lab, describes a new machine-learning computer model called BirdFlow that shows exactly which species are specifically going where on migration.
To accurately predict the movement of specific bird species from place to place, week to week throughout their migrations, BirdFlow processes multiple data sources, combining past studies of birds equipped with satellite-tracking tags with weekly estimates of bird numbers from eBird data submitted by birdwatchers.
“With BirdFlow, we won’t need to catch birds and affix tracking devices in order to decipher the paths that birds take—from their breeding grounds to stopover locations to wintering grounds and back.” says Dokter. It will be essential to comprehend these relationships in order to understand why certain bird populations are doing well while others are not. ”.
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