Northbound Flight

Several studies, as well as backyard observations, document a northward shift of bird populations.

By Sue Smith-Heavenrich

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Climate Change and birds: Purple FinchFaced with ever-warming global temperatures, some birds are changing their migratory flight plans. They’re heading north earlier in spring, arriving in the northeastern United States up to 6 days ahead of schedule.

It’s not just migration patterns that are changing with the climate, says Frank La Sorte at the Cornell Lab of Ornithology in Ithaca, New York. Some birds are adjusting their ranges—the regions where they live—in response to global warming. The black vulture now spends winter in parts of Massachusetts, where the coldest temperatures match those in Baltimore, Maryland, some 35 years ago. David Bonter, assistant director of the lab’s citizen science initiatives, notes that the range of the tufted titmouse has moved northward to include Ithaca, and local birders have reported more sightings of Carolina wrens—a bird rarely seen in the area 25 years ago.

A 2009 study by the National Audubon Society found that purple finches now spend winters 430 miles north of their previous range; the range of American robins has moved 206 miles north. In fact, 177 of the 305 bird species monitored in the Audubon study registered significant northward movement over the previous 40 years.

Moving north as conditions warm makes sense, says La Sorte. Birds fly, so are more mobile than other animals. But northward relocation depends on a host of factors, including the dispersal behaviors of individual species. Some species take decades to move.

Other birds seem to be stuck. The red-cockaded woodpecker chisels its nesting cavities in the longleaf pines found in southeastern forests. It’s not adapted to other pines and has what La Sorte calls “tight habitat association.” So, while the woodpecker could potentially expand its range to keep pace with the warming climate, it hasn’t. Birds do have ways to adjust to changing climate, says La Sorte. But even if they adapt to the demands of warming temperatures, the woodpeckers face other challenges: Northbound species moving into the longleaf pine forests will increase competition for food, nesting sites, and water.

For birds that can emigrate northward, expanding their range often means long flights over sprawling metropolitan regions. One of the problems they face, says La Sorte, is the lack of “green corridors”—parks and other patches of bird-friendly habitat where they can land for a rest stop and a meal. This is where gardeners come in. By taking a few simple actions, we can help birds weather climate change:

  • Mow less, or let a patch of yard go wild over the summer, to provide food and shelter for birds. The birds will return the favor by eating insects in your garden.
  • Let flowers go to seed and leave them for the birds. Asters, bachelor buttons, cosmos, coneflowers, marigolds, sunflowers, and zinnias work well.
  • Tolerate weeds that offer food for birds: dock, goldenrod, and even ragweed.
  • Plant trees and shrubs that provide shelter and edible fruit, such as blackberries, crabapples, elderberries, serviceberries, and sumacs.
     

Learn More: Attracting Songbirds to the Garden

Originally published in Organic Gardening Magainze April/May 2013.

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