The role of the Velvet Asity Philepitta castanea in regeneration of understory shrubs in Madagascan rainforest

Abstract

In the Madagascan rainforest, the role of the Velvet Asity Philepitta castanea, an endemic frugivorous bird, in the regeneration of five understory shrub species (Myrsinaceae and Rubiaceae) was examined during the dry season (August to October). Effective dispersal distance was 33.3 m/h. Based on seed retention time in captivity, more than 85.7% of regurgitated seeds and all defecated seeds were estimated to be transported outside the crowns of mother plants. Seeds passed by the Velvet Asity germinated less successfully than unmanipulated (control) seeds in four out of the five species of shrubs. The reduced germination rate of processed seeds was partly due to the non-adapted morphology of the Velvet Asity as a seed disperser, in particular its voluminous, thick-walled, muscular gizzard. The narrow, slightly decurved bill and the semi-tubular tongue with vibrissae at the tip of this bird are normally features of insect- and/or nectar-eaters. Moreover, since manual removal of fruit pulp decreased the germination rate of seeds, the shrub species studied may not have developed adaptations for seed dispersal by animals. The most probable explanation for this situation is that the Velvet Asity has shifted relatively recently to occupy the niche of a fruit-eater of the understory and as yet insufficient time has passed for a sophisticated relationship with fruiting plants to have coevolved.