You are not currently logged in.
Access your personal account or get JSTOR access through your library or other institution:
If You Use a Screen ReaderThis content is available through Read Online (Free) program, which relies on page scans. Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Foraging Ecology of Avian Frugivores and Some Consequences for Seed Dispersal in an Illinois Woodlot
Patti Katusic Malmborg and Mary F. Willson
Vol. 90, No. 1 (Feb., 1988), pp. 173-186
Published by: Cooper Ornithological Society
Stable URL: http://www.jstor.org/stable/1368446
Page Count: 14
Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Preview not available
A 3-year study of interactions between frugivorous birds (11 species) and fleshy-fruited plants with bird-dispersed seeds (eight species) documented the diffuseness of the mutualism between the taxa. We found considerable annual variation in degree of frugivory, principal fruits in the diet, and dietary diversity for most of the frugivores. There were no consistent correlations between fruit or seed size and gape width, body size, or diversity of consumers. Mutual dependency of bird species and plant species was very limited. The birds could usually obtain 1 to 2% of their metabolically effective body mass in fruit pulp/minute, but they did not concentrate their foraging on the fruits yielding the greatest intake rate. Subcanopy and understory foragers seldom changed foraging stratum and may constitute two guilds of seed dispersal agents, from the perspective of the plants. These guilds differed consistently in average body size, tendency to void seeds by regurgitation, occurrence in years of low fruit abundance, frequency of foraging on clumped fruiting displays, and in speed of movement away from a fruit source. However, three of the five subcanopy species have increased dramatically in abundance in the past 100 to 150 years, and so the dispersal regime for plant species whose fruits are eaten by these species may be different now from what it was. Most of the frugivores foraged preferentially in treefall gaps, and several species also shifted their foraging behavior toward increased fruit foraging in gaps. These observations reinforce other studies that have shown greater abundances of birds and greater rates of fruit removal in gaps. As a result of the preference for fruit foraging in gaps, bird-dispersed plants growing in gaps may achieve better seed dispersal than those in forest interior. Frugivores usually left a fruit source soon after feeding, so most seeds were carried some minimum distance away from the parent plant. However, the probability of departure varied with bird species and plant species, and bird species also differed in probable sites of seed deposition. The most efficacious dispersal agents were not necessarily the most common dispersers of any of the plants.
The Condor © 1988 Cooper Ornithological Society