By Robin Meadows
Having a relatively simple way to assess the effects of conservation corridors is critical to determining whether they are working as intended. Now, new research shows that corridors do work for bluebirds and the seeds they disperse in South Carolina: the birds dispersed about one-third more seeds to habitat patches that were connected by corridors than to those that were isolated.
“Our results provide a landscape-level demonstration that habitat corridors substantially increase the movement of birds and seeds between connected patches,” say Douglas J. Levey of the University of Florida, Gainesville, and four coauthors in Science.
This work was part of the Corridor Project at the Savannah River Site National Environmental Research Park near Aiken, South Carolina. The researchers compared eastern bluebird (Sialia sialis) movements and dispersal of wax myrtle (Myrica cerifera) seeds in experimental habitat patches that were either isolated or connected by corridors. The patches and corridors were cleared from pine forest, creating the open habitats favored by bluebirds and wax myrtles. There were eight sets of habitat patches, each with five patches: the central patch was encircled by the other four, one of which was connected to the central patch via a corridor. The remaining three patches in each set were isolated.
The researchers placed fruiting wax myrtle bushes in each central patch and then tracked the bluebirds that ate this fruit as well as the seeds they dispersed in the four surrounding patches. Using their data on bluebird movements over short distances (less than 20 m), the researchers developed a model of seed dispersal over long distances (more than 250 m). The model predicted that foraging bluebirds were 31 percent more likely to move to connected patches than to isolated patches.
To test their model, the researchers sprayed fluorescent powder on the wax myrtle fruits in the central patches and then tracked the dispersion of fluorescent seeds to the surrounding patches. The model accurately predicted the relative distribution of more than 11,000 seed dispersions to the connected and isolated patches. Specifically, the birds dispersed 37 percent more seeds in the connected patches. “Our study shows how models based on easily observed behaviors can be scaled up to predict landscape-level processes,” say the researchers.
Levey, D.J. et al. 2005. Effects of landscape corridors on seed dispersal by birds. Science 309:146-148.
Photo by Dave Menke/NFWS