A Species-By-Species Look at Forest Fragmentation

Preliminary findings

By Stefan Hames and Jim Lowe

For the past four years, participants of the Birds in Forested Landscapes project have helped the Cornell Lab of Ornithology to collect data on more than 40 forest bird species that are of high or moderate conservation concern. Results from a preliminary analysis are revealing valuable information about the unique habitat requirements of different species and the ways they respond to forest fragmentation.

For example, based on data from 95 sites, the Yellow-bellied Sapsucker was significantly more likely to be found in larger, less-isolated patches of forest, and farther from the forest edge. Additionally, participants found sapsuckers more frequently at higher elevations than at lower elevations.

In contrast, the Eastern Wood-Pewee was more likely to be found in low-elevation sites with a relatively tall canopy of deciduous trees in areas with moderate forest fragmentation (Figure 1). At the 208 sites that were sampled, participants were more likely to find wood-pewees in landscapes with less forest. However, at the smaller scale, wood-pewees were found more often in larger forest patches.

Figure 1. Eastern Wood-Pewee

Eastern Wood-Pewees showed an unexpected pattern: they were more likely to appear in landscapes with less forest (indicated by raised area on graph). Within those landscapes, however, they were more likely to occur in large patches of forest than in small patches.

Illustrations (2) by Evan Barbour, fromThe Birds of Sapsucker Woods

The Black-throated Blue Warbler was similar to the Yellow-bellied Sapsucker because it was more likely to be found breeding in larger, less-isolated patches, and farther from the forest edge (Figure 2). However, it was more likely to be found at sites with a well-developed deciduous shrub layer.

Figure 2. Black-throated Blue Warbler

Black-throated Blue Warblers had a decreased probability of breeding in small patches and in landscapes with little forest (indicated by low areas on graph), a pattern similar to that shown by other species sensitive to forest fragmentation.

These results show that responses to the many effects of forest fragmentation can be similar overall, but may vary in the details because of each species’ idiosyncratic responses to fragmentation and other key factors in the environment. This is not surprising, since theory suggests that each bird species should have unique dietary, habitat, and other ecological requirements as a result of evolutionary pressures to avoid competition with other species. However, these differences among species do provide a good illustration of how a detailed understanding of the natural history of a species is key to its conservation. That’s what makes research like Birds in Forested Landscapes so important and why the contribution of our participants is crucial.

We are just beginning to mine this very valuable data set, and we will complete more detailed analyses soon. As we move forward, we encourage our loyal participants to continue their efforts on the birds’ behalf. As more years of data are added for each study site, we can use that information to perform ever more sophisticated analyses of how individual bird species respond to their environments. In addition, a high level of participation will provide the crucial scientific underpinnings for new projects such as this year’s effort to study mercury exposure (see the Spring 2005 Birdscope article on Birds, Mercury, and Acid Rain), as well as our ongoing work on the impact of acid rain on breeding birds. Birds in Forested Landscapes continues to be a valuable tool for understanding the extremely complicated issues facing forest birds. We owe a great debt of gratitude to our invaluable past participants, and we encourage new participants to join our network of forest-bird enthusiasts. For additional information see the website (Birds in Forested Landscapes), send email to forest_birds@cornell.edu, or call 607-254-2413.

Stefan Hames is a research associate and Jim Lowe is a research biologist with the Birds in Forested Landscapes project.

For permission to reprint all or part of this article, please contact Miyoko Chu, editor, Cornell Lab of Ornithology, 159 Sapsucker Woods Rd., Ithaca, NY, 14850. Phone: (607) 254-2451. email: mcc37@cornell.edu