Delmarva’s Visiting Winter Songbirdsby Jim Rapp
Delmarva is welcoming to a number of tiny, delicate-looking songbirds that are only found in our forests during the winter months.
When most people think of birds that winter on Delmarva, the image is likely that of rafts of ducks bobbing on our bay waters, massive flocks of white Snow Geese blanketing our farm fields, or chunky sea birds cruising low over the waves off our Atlantic beaches. We tend to associate winter with big, thick-bodied birds that nest in the Arctic, and are built to handle the bitter cold with warm downy feathers under a slick waterproof shell.
But Delmarva is also welcoming to a number of tiny, delicate-looking songbirds that are only found in our forests during the winter months. Many of these species are fairly common this time of year, and several make appearances at backyard bird feeders.
You might think these little guys would just keep flying south for more tropical temperatures, but there's a reason Delmarva is a better winter home for them than Central America and the Caribbean. The reason has to do with why birds migrate in the first place.
All birds migrate to move from areas with few or diminishing resources to areas with more opportunity. In the spring, most songbirds fly north for better nesting sites in forests with loads of protein-rich insects and fruit-producing plants. In the winter, the birds -- young and old -- are just looking for food, and Delmarva's winter forests have more bounty than you might think. As long as food resources are present, most tiny songbirds are incredibly well adapted to tolerate temperatures that drop well below freezing. And, with many of their competitors far off in the tropics, they'll have better luck finding food here on Delmarva.
Songbirds have several adaptations to help them survive winter. Their stick-thin legs and feet have a counter-current circulation system that moves warm blood through arteries from their heart next to veins carrying cold blood away from the feet. The system chills the artery blood so that by the time it reaches the bird's toes it's already cool. This keeps their core body temperature from dropping to dangerous levels. Songbird feet and legs have very little blood or moisture in them, so they can perch on an open branch or metal perch and not freeze.
Their feathers help keep them warm, too. Downy feathers act as insulation under their outer feathers by trapping warm air next to the body.
During a winter storm or heavy snowfall, songbirds seek shelter in evergreens and thick, tangly hedges. The little birds fare better when they can stay out of the wind and freezing rain. Woodpeckers and chickadees hide out in tree cavities to escape winter storms. If the birds know of a steady food supply, such as your backyard seed and suet feeders, they'll gorge themselves to fatten up. Chubby birds can survive on fat reserves until the snow melts and exposes feeding areas.
The songbirds that are found on Delmarva only in the winter are survival specialists. Each has a food resource or feeding strategy that gives them the edge when it comes to competing with other similar species. The goal over the winter is simply to stay alive, so they can fly north in the spring to nest and raise young.
Warblers are colorful, musical songbirds that are found in great abundance on Delmarva in the spring and summer, but are largely absent in the winter. There is one warbler species that is only found here in the winter, and it is one of the most numerous birds you'll find on a hike along forests near the coast.
The Yellow-rumped Warbler's winter plumage is streaky, pale brown with flashes of bright yellow on the sides and a distinctive yellow rump patch just above the tail. Some birders lovingly refer to them as "butter butts."
Large flocks of busy Yellow-rumps can be seen feeding at the lower, outer edges of forests. They are the only warbler capable of digesting the waxy coatings of bayberries and wax myrtles, two plants that are plentiful at the high ground edge of Delmarva's coastal marshes. Taking advantage of this food resource allows Yellow-rumped Warblers to winter much farther north than their tropical wintering cousins.
Another bird with a yellow body part can also be found on Delmarva in the winter, and this species has a truly specialized feeding strategy. The Yellow-bellied Sapsucker does just that: it sucks sap from holes it drills in trees.
These woodpeckers are mostly black and white, with white or pale yellow bellies. Males and females have red foreheads, and males also have red throats. It is the only woodpecker in the Eastern U.S. that is a true migrant. Our other woodpecker species reside here year-round.
The Yellow-bellied Sapsucker makes two kinds of holes in circular patterns around tree trunks. Round holes are made deep in the tree, and the sapsucker inserts its brushy-tipped tongue into the well to suck up the sugary sap. Rectangular holes are shallow scratches in the bark, and must be maintained often for the sap to keep flowing. As wells dry up, new holes are made in parallel rings above the old ones. If you see circles of neat, orderly holes on a tree during a winter hike, this is likely the work of a sapsucker. They also eat insects and spiders that get stuck in the oozing sap, or forage for them under flaking tree bark.
Another insect and spider specialist is the Brown Creeper. As their name indicates, these mousy birds creep up tree trunks searching for invertebrates tucked in bark crevices. They have brown, white and tan streaks on their backs, which provides excellent camouflage when pressed tight against the tree bark. Their bellies are mostly white.
Brown Creepers search for insects and spiders by spiraling upward around thick tree trunks and branches, using their tails for support much like a woodpecker. They use their thin, down curved bills to investigate crevices in the bark for food. When they begin hunting on a new tree, they fly to the base of the trunk to begin their climb to the top.
To conserve energy during the lean winter months, Brown Creepers survive by burning less than 10 calories each day -- this is equivalent to about 2 almonds. When bugs are scarce, creepers augment their diet with small amounts of seeds.
If you spot a Brown Creeper moving up a tree trunk, another insect-eating winter visitor may pass by going down. Red-breasted nuthatches have bluish-gray backs and a buffy belly, with bold black and white stripes on their heads. In addition to searching tree bark for invertebrates, these energetic feeders also eat the small seeds found in pine cones. They are known to visit backyard feeders, too. If they choose a seed too big to eat in one bite, they will jam the seed into a crevice and hammer it open with their long, sharp bill.
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