Seed dispersal effectiveness by oilbirds (Steatornis caripensis) in the Southern Andes of Colombia

Oilbirds are specialized frugivores that disperse seeds; however, no study has evaluated their seed dispersal effectiveness (SDE). We estimated SDE for nine plant species and tested if high-altitude plants are more effectively dispersed than lowland species and if there are high SDE scores in non-breeding periods of oilbirds. The quantity factor was estimated from seed rain data in the main cave of Cueva de Los Guacharos National Park (Colombia). The quality component considered germination chance, the probability that seeds reach suitable habitats (using data from GPS devices on three birds) and the probability of establishment in different habitats (literature review). Our model showed that the habitat with more seedrain was the cave (41%), followed by dense forest and mosaics of crops and forests (both ca. 20%). Seed germination was evidenced in 7 of the species, and the other two indicated viability (using tetrazolium tests). The most dispersed species corresponded to palms (Prestoea acuminata and Geonoma undata), but, in terms of biomass, P. acuminata and Dacryodes olivifera (Burseraceae) were the top species. D. olivifera, G. undata, and P. acuminata showed the highest SDE values. No relationship was found between the probability of arrival to suitable habitats and the altitudinal level of the species, but the oilbirds were more effective dispersing seeds in non-breeding periods. Despite a large amount of seeds dropped at the caves, oilbirds disperse seed to suitable habitats, move seeds long distances, and disperse large seeds. As some of these ecosystem services are unique, oilbird's conservation seems imperative. in Spanish is available with online material.

Automated summary

Oilbirds show high effectiveness in seed dispersal, especially during non-breeding periods; they mainly disperse seeds to caves, dense forests, and mosaics of crops and forests, facilitating the dispersal and growth of plants; the unique ecosystem services provided by oilbirds highlight the importance of their conservation efforts.