Spillover of avian seed dispersers between secondary forests and degraded areas in a tropical island

Abstract

Seed arrival to degraded areas often represents a limiting factor to forest regeneration, but seed-dispersing birds able to move into such areas may help to overcome such constraint. As the number of degraded areas prone to regeneration is increasing in the tropics, it is important to know which bird species and associated traits make such spillover movements. We studied the interactions between frugivorous birds and eight plant species in contiguous degraded and secondary forest areas in a Brazilian land-bridge island, evaluating the potential of avian cross-habitat spillover to disperse seeds to degraded areas and thus contribute to their vegetation recovery. We recorded 21 and 17 bird species removing fruits in degraded areas and secondary forests, respectively. Avian communities dispersing seeds in both habitats are dominated by habitat generalist species. Visitation and fruit removal rates did not differ between the two habitats. Avian cross-habitat spillovers were more frequent from secondary forests to degraded areas than the reverse. A few bird species (Dacnis cayana, Elaenia flavogaster, and Turdus spp.) stood out in the spillover between habitats due to their generalist habitat occupancy and capacity for foraging in disturbed areas. We likewise identified the plants that most attracted birds (including an exotic palm, Livistona chinensis) so as to pinpoint the plant species that may occasionally be the focus of management actions to enhance the arrival of seeds to degraded areas. We conclude that the spillover dynamics reported herein shed some light on how tropical forest regeneration could benefit from native species’ spatial behaviour, offering a biological alternative to overcome practical issues, such as seed limitation in degraded environments.