SEED DISPERSAL BY CERATOGYMNA-HORNBILLS IN THE DJA RESERVE, CAMEROON

Seed dispersal is a process critical to the maintenance of tropical fo rests, yet little is known about the interactions of most dispersers w ith their communities. In the Dja Reserve, Cameroon, seed dispersal by the hornbills Ceratogymna atrata, C. cylindricus and C. fistulator (A ves: Bucerotidae) was evaluated with respect to the taxonomic breadth of plants dispersed, location of seed deposition and effects on seed g ermination. Collectively, the three hornbill species consumed fruits f rom 59 tree and liana species, and likely provided dispersal for 56 of them. Hornbill-dispersed tree species composed 22% of the known tree flora of the site. Hornbill visit lengths, visit frequencies, and seed passage times indicated that few seeds were deposited beneath parent trees; in five hornbill/tree species pairings studied, 69-100% of the seeds ingested were deposited a way from the parent trees. Germination trials showed that hornbill gut passage is gentle on seeds. Of 24 tre e species tested, 23 germinated after passage by hornbills; of 17 plan ted with controls taken directly from trees, only four species showed evidence of inhibition of germination rate, while seven experienced un changed germination rates and six experienced enhanced germination rat es. Results suggested that Ceratogymna hornbills rank among the most i mportant seed dispersers found in Afrotropical forests, and they deser ve increased conservation attention. Ceratogymna hornbills are likely to become increasingly important in forest regeneration as populations of larger mammalian seed dispersers (such as forest elephants and pri mates) diminish.