When Birds Use Wildlife Corridors, Plants Benefit
GAINESVILLE, Fla. — Wildlife corridors, intended to help animals move between otherwise isolated natural areas, may aid plants in the same way.
A University of Florida study at a massive outdoor experimental landscape has found that bluebirds, which eat berries, transfer more seeds in their droppings between habitats connected by corridors than between those that are unconnected. They did so despite their propensity to travel not in the corridors themselves, but rather in the woods parallel to the edges – a habit that could easily spur the wrong conclusion that the birds don’t use corridors.
An article about the research will appear Friday in the journal Science.
The study is important because it suggests the greenways that many urban and rural communities have spent public dollars to preserve in recent decades not only help animals but also plants. It’s also noteworthy because the researchers’ computer models proved adept at extrapolating their records of how bluebirds moved over small areas to how they moved over a large landscape — painting a much broader picture than available strictly through observation, said Doug Levey, a UF professor of zoology and the lead author of the paper.
“The model did a great job of predicting how birds move on a large scale by using data on movements at a much smaller scale,” he said.
That’s key to those trying to assess the worth of corridors “because birds and mammals can be very difficult to follow across these large, often inaccessible areas and because it’s critical to figure out the details of how corridors work,” Levey said.
Levey and several colleagues collaborated with the U.S. Forest Service in 1999 to set up the experimental landscape, which lies within the Savannah River Site National Environmental Research Park on the South Carolina-Georgia state line.
Loggers carved out eight sets of roughly 2-acre central and peripheral clearings in the forest. In each set, a corridor of the same habitat connected the central clearing to one
peripheral clearing, with the others remaining separated by the forest. These “patches” provided what Levey called “black and white” habitat types, with distinct plants and animals flourishing in the clearings and forest.
The experiment’s scale is unique in the history of corridor research, which has tended to focus on much smaller sites because of the difficulty of creating experiments large enough to match the scales at which animals typically move. One frequently cited experiment, for instance, focused on insect distribution on 20-by-20-square-inch plots of moss.
In the winters of 2001 and 2002, the researchers placed cut wax myrtle branches with ripe berries in the center patches, marking the berries with a harmless florescent dye so that they could track their whereabouts. Three-member teams equipped with voice-activated radios then watched the branches, noting when bluebirds ate the fruits and following their movements for as long as possible. Each time a bluebird landed, a team member would note the location with a stake, giving the researchers a physical record of the bird’s movement.
The highest percentage of birds followed the cleared corridor rather than entering the deep woods — but they moved along the corridor’s outside edge.
The researchers also placed seed traps under perches placed in the connected and unconnected peripheral patches, counting the seeds defecated by the birds. Using the florescent markers, they were able to identify all seeds originating in the center patches. A much higher percentage wound up in the connected than unconnected patches.
The researchers were able to follow the birds only for short distances in and near the center patches, usually less than 60 yards. The traps, however, were typically located hundreds of yards from the center patches. The researchers were delighted to find that their computer models, which were based only on short distance flights, successfully predicted the “seed rain” in the most distant traps.
Ilkka Hanski, a professor in the department of biological and environmental sciences at the University of Helsinki in Finland, said the results highlight the power of modeling to extend or broaden observational results. “Combining small-scale empirical studies with modeling is a potentially powerful approach to predict dispersal and consequences of dispersal at the landscape scale, and this study provides one such example,” he said.
The research was funded with a $350,000 grant from the National Science Foundation. The other authors of the Science paper are Ben Bolker, a UF associate professor of zoology; Joshua Tewksbury, of the University of Washington; Sarah Sargent, of Allegheny College in Pennsylvania; and Nick Haddad, of North Carolina State University.