Delmarva’s Neotropical Migrantsby Jim Rapp
April and May are exciting months for birders on Delmarva. Almost every day, we see new migratory species arrive from southern wintering grounds, and birds that winter with us take flight for breeding grounds to the north.
Waterfowl and loons on our bays are replaced by warblers and vireos in our forests. Each sunrise brings the promise of new spring bird song filling the air as our Neotropical migrants begin their ancient courtship rituals.
Our Neotropical migratory birds actually spend most of their year in the Caribbean, Mexico, Central America and South America. They arrive here to nest and raise young in the summer. Some nest with us here on Delmarva, while others migrate through the peninsula to breed in the northeastern U.S. and Canada.
The term "Neotropical" refers to migratory birds of the Western Hemisphere that winter south of the Tropic of Cancer and breed north of that same latitudinal line. There are close to 200 bird species that fit that definition, and most are small songbirds and shorebirds.
You might wonder why a warbler or sandpiper would leave the tropics and southern South America to breed and raise young in the North, when there is so much life south of the border. The answer lies in the incredible abundance of the food that Neotropical migrants need to raise their babies here and further north, such as caterpillars, small insects, fruit and nectar in our forests, and horseshoe crab eggs and invertebrates on our beaches.
Delmarva's forests, marshes and beaches are like a giant never-ending buffet for birds, and they have more daylight here for feeding in the spring and summer than they do near the equator. When that food disappears and the days begin to shorten in the fall, these same birds fly south with their young to survive the winter.
Many of these tiny birds migrate tremendous distances to get to Delmarva in time for the spring breeding season. A Scarlet Tanager migrating from Colombia or Ecuador may travel 3,000 miles to nest on Delmarva, while a Red Knot may travel almost 10,000 miles from the southern tip of Argentina to its breeding grounds in the Arctic.
Most small birds migrate at night when temperatures are cooler, the air is calmer, and predators are fewer. They stop to rest and feed during the day. Most fly between 20 to 40 miles per hour. A single non-stop flight between rest stops may last for several hours or several days.
Songbirds flying over the expansive Gulf of Mexico are known to rest on boats or oilrigs before completing their open water flight to the U.S. When they make landfall, they are exhausted and hungry. If they hit rough weather, a phenomenon known as a "fallout" occurs when hundreds and thousands of birds concentrate in an area to rest and feed before starting the next leg of their journey.
Several migrants have already arrived on Delmarva, and more are on their way over the next several weeks. Here are a few to look and listen for when you're exploring our parks and preserves.
Purple Martins have arrived from South America, and many have already started to nest in man-made martin houses along the Delmarva coast. Purple Martins are our largest swallow, and they are known for their aerial maneuvers when flying to catch insects on the wing. Males are a dark, glossy purple and females are mostly brown.
Native Americans hung hollow gourds to serve as Purple Martin nest houses well before Europeans arrived in the Americas. Purple Martins in the eastern U.S. now nest almost exclusively in birdhouses, while those in the West use tree cavities.
The Louisiana Waterthrush prefers Delmarva's bald cypress swamps and slow-moving streams. This large warbler looks more like a thrush or sparrow, with its drab brown back, white belly with dark stripes, and white stripe over the eye. It can be found walking between tree roots and cypress knees at the water's edge, constantly bobbing its tail up and down.
When the Louisiana Waterthrush arrives on its Delmarva breeding grounds from wintering in Mexico and Central America, males begin to sing immediately. He will sing almost non-stop all day until he acquires a mate. Here is an example of the waterthrush song from the Sibley Birds app: (song)
Another warbler of Delmarva's cypress swamps is the brilliant gold-yellow Prothonotary Warbler. It is one of only two Neotropical warblers that nest in tree cavities. The name "Prothonotary" refers to clerks in the Roman Catholic Church who wore bright yellow robes.
Known to some as the "Preacher Bird" for sermonizing all day, the Red-eyed Vireo is one of the most commonly seen -- and heard -- Neotropical migrants in Delmarva's forests. They have olive-green backs, white bellies, a gray cap, and black and white streaks near their red eyes. Over 12,000 different Red-eyed Vireo song types have been recorded. Here is an example of a typical song from the Sibley Birds app: (song)
Males will sing constantly from dawn to dusk. More than 20,000 individual phrases of the Red-eyed Vireo's song have been counted in a single day.
Male Scarlet Tanagers are one of the most beautifully colored Neotropical migrants in Delmarva's spring and summer forests. Males have electric crimson bodies with ink-black wings and tails, while females are yellowish-green with dark wings. Look for these birds high in the forest canopy from May until late summer, when they take off for northern South America.
Ruby-throated Hummingbirds are the only breeding hummingbird found in the Eastern U.S. They arrive on Delmarva after flying from Central America. During migration, many hummingbirds cross the Gulf of Mexico in a single, non-stop flight. You can find these tiny, iridescent green birds glittering in the sun as they feed on the nectar provided by red and orange spring flowers, or at a hummingbird feeder outside of your kitchen window.
If you want to explore Delmarva in search of Neotropical migrants, join the expert guides leading field trips during the Spring Delmarva Birding Weekend, which will be held April 21 through 24. For more information, please visit www.DelmarvaBirding.com.
Neotropical migrants fill our natural areas with color and song every spring and summer. Until next time, I hope this story inspires you to explore Delmarva's many natural wonders.
Find out more:
One of the world's great migrations: neotropical warblers and other songbirds
Maryland Department of Natural Resources
Birding in Worcester County
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