Wood Warblers
A male Black-throated Blue Warbler in mountain laurel
Like most birds, each species of wood warbler is specialized for a certain habitat, and can successfully build a nest and raise young only in that setting.
A male Black-throated Blue Warbler in mountain laurel
Like most birds, each species of wood warbler is specialized for a certain habitat, and can successfully build a nest and raise young only in that setting.
■ Scientists are still working to sort out the remarkable details of the magnetic sense of birds. There is evidence that songbirds have two different systems for detecting the orientation of the magnetic field as well as the slope of the field (which varies with latitude from horizontal at the equator to vertical at the poles). They can also detect polarized light, which gives valuable clues to the position of the sun even when the sun itself is not visible. All of these senses might be linked to the birds’ vision, so it is possible that a songbird sees some sort of compass guide all the time. This information is critical for orientation during migration, but it could also be very useful for a bird navigating locally. Imagine seeing a compass reading all the time as you walked through your house or the supermarket. Birds could use this information as they navigate their own breeding territory, to help remember the locations of stored food, and more.
A Black-and-white Warbler with a totally hypothetical artist’s rendering of what the bird might see in the sky: a blue band of polarized light, and a reddish band oriented with the magnetic field with a stronger dot showing the slope of the magnetic field
■ Filoplumes are a specialized kind of feather, tiny slender plumes growing in clusters around the base of most feathers. The follicle where they enter the skin is packed with nerve endings. Like telltales on a boat’s sail, they apparently act as sensors to allow a bird to monitor the movements of individual feathers. Birds know when a feather is out of place, when two feathers are stuck together, when a fly has landed on a feather, etc. In flight filoplumes allow birds to sense lift, drag, turbulence, updrafts, downdrafts, and other forces over the entire wings and body. The birds can use this information to make the constant tiny adjustments of wing and tail position necessary for efficient flight.
Filoplumes growing next to a typical feather
■ One of the riskiest aspects of migration is the days off. Imagine flying all night and landing in an unfamiliar place at dawn. Finding water, shelter, and food while avoiding predators is a huge challenge, and even more so when much of the landscape is covered with human structures and lawns. In urban and suburban areas, especially, small parks and gardens can be a magnet for migrating birds. You can make your yard bird-friendly by planting native shrubs and trees and offering water. The biggest benefit of using native plants for birds is that those plants have evolved over millennia to coexist with a whole ecosystem of insects and other organisms. Exotic plants are not integrated with the local ecosystem, and fewer insects are able to use them. For example, in the eastern United States native oak trees host more than five hundred species of moth and butterfly larvae, exotic Norway Maples fewer than ten species. For insectivorous birds, obviously, an oak tree is much more attractive. Furthermore, if you want your yard to provide food for birds, you should not use insecticides. Let the birds control the insects.
A Black-throated Green Warbler foraging in a spring oak tree