Toward reliable estimates of seed removal by small mammals and birds in the Neotropics

Abstract

Birds are often considered seed predators of less importance when compared to rodents or granivorous ants in studies of seed predation using selective exclosures. However, it is possible that the role of granivorous birds interacting with seeds on the floor of Neotropical forests is being underestimated, if the selective exclosures designed to allow exclusive access to small rodents do not work properly in the Neotropics. We used an experimental approach to evaluate whether birds could remove seeds from selective exclosures designed to allow exclusive access to rodents. We compared seed removal from two paired treatments in the field: an open treatment (control) allowing the access to all vertebrates, and a selective exclosure treatment, where seeds were placed under a cage staked to the ground and covered on top and on the laterals by wire mesh of varying sizes. Treatments were placed in the center of a sand quadrat in order to record the visit of vertebrates from their footprints. Although the selective exclosures are used to tell apart the small mammal seed removal from that of other animals, birds could persistently remove seeds from selective exclosures. Thus, the role of birds interacting with seeds on the floor of tropical forests may be underestimated for some plant species, due to an artifact of the exclosure method employed. Exclosures of 40 x 40 x 40 cm should be efficient to deter the removal of seeds by birds, allowing the consumption of the seeds by small mammals at the same time.