Sexual Selection, Sperm Competition and Sexual Conflict - An Introduction to Behavioural Ecology - page 190

(b)

(a)

50 25

40

30 15

20

10 5

0

20 40 60

0 10 20 30 40 50

Repertoire size Repertoire size

Fig. 7.6 (a) Male sedge warblers with the largest song repertoires are the first to acquire
females in the spring. The size of song repertoire is estimated from sample tape recordings
of each male. The results were collected in such a way as to control for the possibilities that
older males, or males in better territories, both mate first and have larger repertoires. From
Catchpole (1980). (b) The mean ± s.e. response score of five females to repertoires of
different sizes. The response score measures sexual behaviour. From Catchpole et al . (1984).
Reprinted with permission from the Nature Publishing Group.

BOX 7.2 MULTIPLE ORNAMENTS IN WIDOWBIRDS AND BISHOPS
( EUPLECTES SPP.)
The red-collared widowbird, Euplectes ardens , lives in grasslands of eastern and
southern Africa. Females and non-breeding males are drab brown and have
short tails. Prior to the breeding season, males moult into a striking black
plumage, with a crescent-shaped red collar on the chest and they grow a long
tail, too (Fig. B7.2.1). Why have multiple ornaments?
During courtship, males display their tails in a slow flight over their territories.
Males with longer tails pair up sooner and attract most females (up to nine).
The colour and size of the collar does not correlate with mating success, but is
correlated with a male's success in territory defence against rival males (Pryke
et al ., 2001, 2002). Therefore, the red collar functions in male-male competition
while the long tail functions in female choice. Furthermore, there is a trade-off
between investment in the two ornaments; males with larger or redder collars
have shorter tails. This may reflect a physiological trade-off between resources
allocated to tail growth and to the red patch, which is produced by carotenoid
pigments acquired entirely from the diet.
Across the Eupletes species, too, there is an inverse correlation between tail
length and carotenoid colouration. Widowbirds tend to have elongated tails