On the Tails of Birds

Abstract

rations in some sexually dimorphic species (Andersson 1994, Balmford et al. 1993a, 1994, Evans and Thomas 1992, Norberg 1995, Winquist and Lemon 1994). For example, the long-tailed widow bird Euplectes progne, a bird a little larger than a starling, has a tail more than 1 m long; the lyre-tailed nightjar Uropsalis lyra has a tail eight times as long as its body, giving it-in relative terms-the largest tail of any bird; and the marvelous spatule-tailed hummingbird Loddigesia mirabilis has a tail that is elongated into bizarre crossed wirelike structures with flags at the ends that are as long as its body (Figure 1). Other species, such as the spinetail swifts (Neafrapus cassini), have tails consisting of just a few spiny barbs. Between these extremes, bird tails exhibit a wide range of morphologies (Figure 2; Norberg 1989, Thomas 1993a, Thomas and Balmford 1995). In this article, I describe recent work that uses aerodynamic analyses to investigate the evolutionary forces responsible for the morphologies of birds' tails.