Widowbirds

Exaggerated Traits and Breeding Success in Widowbirds:

A Case of Sexual Selection and Evolution

by

J. Phil Gibson

Department of Zoology and Department of Botany and Microbiology

University of Oklahoma

Part I— Introduction

Natural selection is the evolutionary force that shapes the traits of a species in response to the various

demands of its environment. Any process or event during the life of an organism that influences the number

and/or quality of offspring produced by an organism due to a heritable trait(s) of that organism can act as a

selective force. Selective forces can be produced by either the biotic or abiotic components of an organism’s

environment. Hence, natural selection is manifest as not a singular action, but rather as many different

events occurring over the life of an organism. In this case study, the different and potentially conflicting

manifestations of natural selection will be explored and studied.

The Study Species

Widowbirds are small, finch-like birds in the genus Euplectes.

They are striking members of the bird community in grasslands

and shrubby savannas of southern and eastern Africa. This

group is noted for the pronounced sexual dimorphism between

males and females. During the non-breeding season, both male

and female widowbirds have a brownish or buff coloration that

blends with the grass and other vegetation. During the breeding

season, however, males molt and produce black feathers on most

of their body. Males also produce characteristic bright red and/

or yellow epaulets and chevrons on their wings. Additionally,

males of several widowbird species grow elaborately long tail

feathers that can be up to half a meter in length (see Figures 1

and 2).

During the breeding season, males secure and defend a territory

from other males where they then build multiple nest frames.

Males then perform a flight display that has a “bouncy rowing”

appearance with loops and exaggerated wing beats to attract

females to their territory. Females...