Sexual Selection, Sperm Competition and Sexual Conflict - An Introduction to Behavioural Ecology - page 191

and little carotenoid pigmentation while the bishops have short tails but
extensive yellow or red plumage (Fig. B7.2.2). An energetic trade-off between
the two signals may, therefore, have influenced evolution of plumage diversity
in the genus, perhaps reflecting the balance between the forces of male-male
competition and female choice. Bishops tend to breed in colonies, where
males defend small, densely-packed territories, leading to intense male-male
competition (hence emphasis on carotenoid colour displays). By contrast,
widowbirds have larger, dispersed territories, where female choice of males
may be more important (hence emphasis on long tails) (Andersson et al ., 2002).

Fig. B7.2.1 Red-collared Widowbird. Photo © Warwick Tarboton.

Fig. B7.2.2 Red bishop. Photo © Oliver Krüger.

Finally, a phylogeny of 33 subspecies (all 17 species) of Euplectes shows that
long tails and brighter red colours have evolved at least twice from ancestors
with short tails and yellow colour signals. This suggests that during evolution
there has been sexual selection for increased advertisements. In addition,
long-tailed widowbirds (the species with the longest tail) have shown recent
losses of carotenoid pigments, further supporting the idea of a trade-off
between colour and tails (Prager & Andersson, 2009).