Thursday, August 9, 2007

PS 67-134: Patch size and tree species influence the number and duration of bird visits in restoration plots in southern Costa Rica

Rebecca D. Fink, Duke University, Catherine A. Lindell, Department of Zoology, Emily B. Morrison, Michigan State University, R. A. Zahawi, Organization for Tropical Studies, and K. D. Holl, University of California-Santa Cruz.

Efforts to restore tropical forest in abandoned pasture are likely to be more successful when seed dispersal is promoted by increasing seed disperser visitation; this in turn requires a clear understanding of the effect of different restoration strategies on bird behavior. We measured the likelihood of visitation, number of visits, and duration of visits for all birds and for Cherrie’s tanager, Ramphocelus costaricensis, a common seed disperser, in five sizes of mixed-species restoration patches (ranging from 2.7 m2 to 283.7 m2), planted with four tree species in southern Costa Rica. Based on optimal foraging theory, we predicted that the largest patches and individual tree species with the greatest canopy cover would have the most and longest visits. We found that birds were most likely to visit large patches and the tree species with the highest canopy cover, Inga edulis. Birds visited Inga trees more often and stayed in Inga and Erythrina poeppigiana trees for longer periods of time than other tree species. Similarly, we found Cherrie’s tanagers were more likely to visit large patches and Inga trees, and to visit Inga trees more often than other tree species. Thus, we identified two factors, tree species and patch size, which may be manipulated to increase bird visitation. Further investigations should clarify why birds prefer trees with greater canopy cover and whether more bird visits to large patches explains previously documented cases of increased seed rain under large tree patches.

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