Nectar and flower production of Lobelia telekii inflorescences, and their influence on territorial behaviour of the scarlet-tufted malachite sunbird (Nectarinia johnstoni)

Abstract

The alpine zone of Mount Kenya is a typical equatorial, high-altitude habitat with a harsh environment, large fluctuations in physical conditions and an impoverished flora and fauna. A common flowering plant is Lobelia telekii, which has large inflorescences with up to 2000 flowers. The long hanging bracts of this plant ameliorate the physical environment around the flowers, damping the fluctuations in temperature and relative humidity. The scarlet-tufted malachite sunbird (Nectarinia johnstoni) is a highly active nectarivore that obtains most of its food from the nectar of L. telekii, Sunbirds are more likely to visit the younger, male flowers at the apex of the inflorescence, which are larger and contain twice as much sugar as the older, female flowers lower down the spike. Male flowers will gain from multiple visits by exporting more pollen, while female flowers probably need to be visited only a few times for successful fertilization. Male sunbirds were resident on their territories all year and vigorously defended them from conspecifics. All territories contained about four times the number of flowers visited by the territory occupants in a day. Males on territories with a large number of flowers suffered more intrusions than males on low quality territories and spent more time in flight. After an intrusion the resident male frequently fed near where the intrusion took place. Males that subsequently attracted mates defended about twice as many flowers as males that did not breed, although undefended inflorescences were present. Some males apparently defended territories suitable for a pair, others only for a single bird. © 1996 The Linnean Society of London.