EFFECTIVENESS OF 3 TURACOS AS SEED DISPERSERS IN A TROPICAL MONTANE FOREST

We studied the effectiveness of three species of turacos, the Great Bl ue Turaco, the Ruwenzori Turaco, and the Black-billed Turaco, as seed dispersers in a tropical forest in Rwanda. For each species of turaco, we examined two factors affecting the effectiveness of seed dispersal : (1) the proportion of ingested seeds dispersed away from the parent tree and (2) the distances seeds were dispersed. To estimate these mea sures of effectiveness, we systematically observed the foraging activi ties of focal birds over a 14-month period. We also fed six species of tree fruits to captive Ruwenzori Turacos to determine the gut retenti on times for seeds of various sizes. Based on these measures, we calcu lated the seed shadows generated by each turaco species for tree seeds with either long or-short gut retention times. The gut retention time of seeds was not correlated with seed size, but was positively correl ated with the time interval over which seeds were defecated. Seeds wit h a long gut retention time were not only dispersed farther away from the parent tree, but were also deposited over a longer time period and were thus likely to be dispersed over a greater variety of habitats. Of the three turacos? the Ruwenzori Turaco deposited the highest perce ntage of ingested seeds away from the parent tree because it had the s hortest residence time in feeding trees. However, the Ruwenzori Turaco also dispersed seeds for the shortest distance, partly due to its sho rt flight distances. The Great Blue Turaco on average dispersed seeds the farthest due to its long flight distance and long gut retention ti me. The Black-billed Turaco, which fed least frequently, deposited see ds more evenly among perching sites than did the other two species. Al l three species of turacos dispersed over 80% of ingested seeds away f rom the parent tree.