An experimental study of male adornment in the scarlet-tufted malachite sunbird: I. The role of pectoral tufts in territorial defence

Scarlet-tufted malachite sunbirds (Nectarinia johnstoni) are endemic to the alpine zones of East African mountains. On Mount Kenya they feed almost exclusively on the nectar of Lobelia telekii flowers. Males are resident on their territories all year and defend L. telekii inflorescences from conspecifics. Males are bright iridescent green, with scarlet pectoral tufts which are displayed prominently during aggressive interactions with other males. We investigated the role of pectoral tufts in territory defence using natural variation and experimental manipulation. Males with naturally large pectoral tufts defended more L. telekii inflorescences than males with smaller tufts, and achieved a higher reproductive success. Males were subjected to one of three experimental treatments - having their pectoral tufts enlarged, reduced or manipulated but kept at the same size. Males with reduced tufts spend more time in aggressive interactions than the control males, the interactions lasted longer and they lost a number of inflorescences to neighbours. Males with enlarged pectoral tufts increased the number of inflorescences defended. These results indicate that the pectoral tufts of male scarlet-tufted malachite sunbirds are used as a means of male-male assessment during aggressive interactions.