More Flycatchers
A Western Kingbird harassing a Red-tailed Hawk
A Western Kingbird harassing a Red-tailed Hawk
■ The Scissor-tailed Flycatcher has one of the most spectacular tails of any bird, but what is it for? Most birds have a tail because it improves flight performance: it reduces drag when folded (by smoothing the airflow behind the body) and increases lift at slower speed when fanned. A long forked tail takes these advantages to an extreme and provides two distinct high-efficiency modes: high-speed flight with the tail folded, and slow flight with the tail fanned. In the case of terns (see this page), this makes sense. Terns need to travel quickly and efficiently over long distances to reach foraging areas, and once there they need to patrol slowly and even hover to find fish. The Scissor-tailed Flycatcher’s long and flashy tail is less for aerodynamics and more for display and foraging. By flying slowly while dipping and waving its tail into the grass, it can “sweep” insects out and catch them in flight.
Scissor-tailed Flycatcher “sweeping” with its tail
■ All birds have extraordinary vision, but the needs of flycatchers are particularly extreme. Imagine flying twenty miles per hour, swerving and dodging to follow the movements of a mosquito in flight, then grabbing that mosquito out of the air with a pair of tweezers. This requires several visual adaptations beyond human eyesight.
•Increased visual acuity detects tiny specks at a distance.
•The ability to see ultraviolet light undoubtedly helps to distinguish insects against a background of mottled foliage and shadow.
•Colored oil droplets inside cone cells in the eye act as filters to enhance color definition—for example, making it easier to pick out other colors against blue and green backgrounds.
•An ability to track very rapid movements of insects and surroundings during high-speed flight. Other birds process images more than twice as fast as we do, making high-speed motion less of a blur, and flycatchers have the fastest processing of any birds tested. A newly discovered type of cone cell unique to flycatchers may be the key to this ability.
A Black Phoebe catching an insect
■ Rictal bristles are a set of modified whisker-like feathers around the base of the bill. These are well developed in most flycatchers and prominent in several other families of birds. Because these birds rely on capturing small, fast-moving insects in midair, a common assumption is that the bristles function as a sort of net to help scoop up flying insects or sense the location of insects near the mouth. But flycatchers always capture flying insects between the tips of the mandibles, and the bristles are not involved. Experiments have shown that the bristles act as eye protection, a safety net that deflects insects (and their legs and wings) away from the eyes during high-speed capture.
A Willow Flycatcher with rictal bristles around the base of the bill