Sexual character intensity and its relationship to breeding timing, fecundity and mate choice in the great cormorant Phalacrocorax carbo lucidus

Reproductive success and the intensity of five separate seasonal sexual characters, expressed similarly in both sexes and likely to be dependent on age and/or individual condition, were documented at a colony of great cormorants at Lake Naivasha, Kenya (00°46′ S, 36°22′ E) in 1996. The characters assessed were head filoplumes, thigh patch feathers, colour of cheek, neck and upper breast plumage, colour of gular skin, and colour of suborbital skin. More intensely developed sexual characters at the time of pair formation were associated with significantly earlier breeding. Pairs that bred earlier fledged significantly more chicks than those breeding later. However, correlations between the number of chicks fledged and the intensity of the parents’ sexual characters at pair formation were generally weak and not significant. An exception was the colour of the cheek, foreneck and upper breast plumage: males (but not females) with the darkest plumage in these areas fledged significantly more chicks than others. Correlations between paired male and female sexual character intensity were weak, and significant only in the case of suborbital skin colour. Other factors may have been more important than these characters in influencing mate selection.