Euplectes progne

Abstract: Darwin's1 hypothesis that male secondary sexual ornaments evolve through female preferences is theoretically plausible2–7, but there is little experimental field evidence that such preferences exist8–10. I have studied female choice in relation to male tail length in the long-tailed widowbird, Euplectes progne, and report here that males in which the tail was experimentally elongated showed higher mating success than males having normal or reduced tails. The possibility that intrasexual competition among males maintains the long tail was not supported: males with shortened tails held their territories as long as did other males. These results suggest that the extreme tail length in male long-tailed widowbirds is maintained by female mating preferences.

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.

Abstract: -Sexual wing dimorphism in relation to tail ornaments and body size was studied in the strikingly sexually dimorphic widowbirds and bishops (Euplectes) of the African tropics. Seven widowbirds grow long tails, varying from 7 cm in Fan-tailed Widowbird (E. axillaris) to 0.5 m in the Long-tailed Widowbird (E. progne). Aerodynamic drag increases with tail length, and adaptations to compensate for this cost might be expected (e.g. increasing wing length), a prediction that was supported among the widowbirds. After controlling for overall size dimorphism (estimated by tarsus length), 70% of the variation in residual wing dimorphism among the widowbirds was explained by tail dimorphism. Bishops were more dimorphic in wing length than expected, which may be related to their slow display flight. The results suggest caution in using wing length alone for interspecific comparisons of sexual size dimorphism. Based on tarsus length, the lekking E. jacksoni is more size dimorphic than the average of its congeners, in contrast to what has been concluded in previous studies based on wing length. Received 13 May 1993, accepted 2 July 1993. SEXUALLY SELECTED characters, such as the elongated tails or the exaggerated displays of some birds, are expected to evolve until their mating advantages are balanced by costs (Fisher 1930), like predation or physiological constraints (Harvey and Bradbury 1991, Andersson 1994). At this dynamic equilibrium, morphological or behavioral adaptations that reduce the costs (hence, improve survival and allow further exaggeration of the trait) can be expected to evolve. Two such indirect effects of sexual selection on avian morphology have recently been reported. Hedenstrom and M6ller (1992) used aerodynamic theory to predict morphological adaptations to the demands of song flight. Consistent with their predictions, they found greater sexual dimorphism in wing span and wing area in eight passerines with song flight than in related species without this (supposedly sexually selected) behavior. Evans and Thomas (1992) estimated the aerodynamic costs of elongated tails in three species of sunbirds (Nectarinia spp). An increased tail area was shown to affect the aerodynamics in several ways, but most importantly increase the drag on the bird, which is a major component of flight cost (Norberg 1990). This cost should be particularly strong for birds with graduated tail ornaments (i.e. in I Present address: Department of Biology 0116, University of California at San Diego, La Jolla, California 92093, USA. which all rectrices are elongated) compared to pin tails and fork tails (Balmford et al. 1993). As predicted based on higher energy costs of flight, sunbirds with experimentally elongated tails spent less time flying than controls (Evans and Hatchwell 1992). Based on a correlation between wing length and tail length in one of the species (Nectarinia johnstoni), Evans and Hatchwell (1992) suggested that the sunbirds compensate for the energetic costs of a long tail by increasing wing span. Likewise, intraspecific relationships between ornamental tail length and wing length have been found in the Long-tailed Widowbird (Euplectes progne; Craig 1989) and Jackson's Widowbird (E. jacksoni; Andersson 1992a), suggesting similar compensations for the cost of carrying long tails. In particular, the exceptionally long wings of the Long-tailed Widowbird have made it an outlier in comparative studies of sexual size dimorphism based on wing length (Payne

Abstract: No evidence for sexual selection in the evolution of tail-length or wing-length in widow birds and bishopbirds (genus Euplectes) was found when the methods used by previous authors were applied to a larger set of data. Nuptial tail-length dimorphism scaled with body size dimorphism except in Euplectes progne, and interpopulation variation in taillength could be explained by genetic drift alone. Wing-length appears to be under stabilizing selection and scales allometrically with body size, with no relation to tail-length unless E. progne is included in the analysis.

Abstract: Summary Nuttall, R.J. 1993. Seasonal changes in the birdlife of a pen-urban grassland community. Ostrich 64: 1–7. Visits to a grassland habitat near Pietermaritzburg, Natal, South Africa were undertaken over a period of ten months (March-December) to document changes in avifauna, and to investigate possible reasons for any changes. A total of 72 bird species was recorded. Monthly species totals showed considerable fluctuation, with species diversity highest in spring-early summer (n=53) and lowest in winter (n=14). Terrestrial insectivores were the best represented fin terms of number of species) during the course of the study. The influence of rainfall on food availability and on vegetation is considered important in determining the structure of this avian community. Observations of the assumption (and loss) of nuptial plumage in euplectines showed that Longtailed Widows Euplectes progne developed breeding plumage earliest, and retained it for the longest period of time. Both Whitewinged E. albonotatus a...