Dennis A. Meritt

Foraging by parrots ( Amazona autumnalis ) on fruits of Stemmadenia donnell-smithii (Apocynaceae) in the tropical rain forest of Los Tuxtlas, Mexico

Quantitative data on predispersal seed predation by avian non-dispersers are few for tropical plants (but see Howe 1990, Janzen 1983). Parrots (Psittacidae) are ubiquitous in Neotropical rain forests, but published data on seed predation by these seed-eating birds exist only for a few plant species such as Brosimznun utile (H.B.K.) Pittier (Higgins 1979), Tetragastrispanametisis (Engl.) 0. Kuntze (Howe 1990) and Ficuis ovalis (Liebm.) Miq. (Janzen 1981). A conspicuous mid-level tree of both the forest interior and the forest-edge is Stemmadenia donnell-smit/iji (Rose) Woodson (Apocynaceae). This tree produces capsulated fruits which hang in pairs from the distal end of the branches. The fruits mature very slowly and after several months the capsules dehisce along their sagittal plane exposing seeds enclosed in a bright orange aril which contrasts markedly with the light creamy colour of the open capsule. These arillate seeds attract numerous birds and some mammals. Many of these animals ingest the seeds while attempting to consume the lipid-rich aril and hence disperse the seeds (Cant 1979, McDiarmid et al. 1977, Muskin & Fischgrund 1981). McDiarmid et al. (1977) in Costa Rica observed no pre-dispersal seed predation by parrots on S. donnell-smithii, although a small proportion (0.01%) of fruits with parrot beak marks were detected after censusing 700 fruits. They hypothesized that predation by arboreal vertebrates was reduced by a tough outer husk and the position of the hanging paired fruits at the outer part of the branches. Cant (1979), however,