Effects of Exurbanization on the food and habitat of Pileated Woodpeckers (Dryocopus pileatus)
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Subjectexurbanization; birds; development; pileated woodpeckers; ecology; conservation; Sewanee, Tennessee
AbstractDryocopus pileatus (Pileated Woodpeckers) are the largest woodpeckers in the United States. They require large trees for roosting, nesting, and feeding that must be dead or dying for ease of excavation and presence of the woodpeckers’ main prey of ants and beetle larvae. Because of these specific habitat requirements, Pileated Woodpeckers have often been used as an indicator species for mature forests. However, their status in exurban areas, or places of low-density rural development beyond the suburban fringe, is poorly known. Because exurbanization covers a large and growing portion of the eastern U.S., I decided to use the Cumberland Plateau in southeast Tennessee to examine how exurban development affects the habitat and presence of Pileated Woodpeckers. From previous literature I made the assumption that Pileated Woodpeckers would prefer habitat with larger diameter trees, a larger volume of more decayed dead wood, and a greater abundance of food (ants and beetle larvae). By using proportion impervious cover as a proxy for exurbanization, I hypothesized that as exurbanization increased, the following habitat characteristics preferred by Pileated Woodpeckers would decrease: (1) average tree diameter and number of large trees, (2) volume and rot class of standing dead and fallen dead trees, and (3) ant and beetle larva abundance in the soil and leaf litter. Concurrently, I hypothesized that along with these habitat characteristics, the likelihood of Pileated Woodpecker presence would decrease with increasing exurbanization. I conducted the study in Sewanee, Tennessee, U.S.A., establishing 30 stratified random sample points evenly divided between exurban and forested areas. At each point I assessed Pileated Woodpecker presence through visual and vocal surveys; habitat structure through measures of downed and standing dead wood and standing live trees; and food availability through presence of ants and beetle larvae in soil cores and pitfall traps. I found no difference in the amount of dead wood, degree of decay of dead wood, ant and beetle larva abundance, nor presence of Pileated Woodpeckers as exurbanization increased. These data suggest that some exurban areas may provide suitable habitat for Pileated Woodpeckers. Tree diameter was the only habitat factor that changed along the gradient and it increased with increasing exurbanization, probably a result of human preference for large trees. Such overall statistically insignificant results suggest that more studies are needed to examine the breeding success and survival rates of Pileated Woodpeckers in exurban and forested areas to determine if exurban areas truly are suitable long-term habitat and not just ecological traps. Because the mature forest characteristics that Pileated Woodpeckers prefer can be found in exurban areas, it is possible that other species requiring these characteristics could also find suitable habitat in exurban areas. This could apply most specifically to those secondary cavity-nesting species such as the northern flying squirrel, owls, and bats that use old Pileated Woodpecker nesting cavities. More studies should be conducted to further explore the effects of exurbanization on these secondary cavity-nesters as well as other species that are thought of as indicating mature forests.
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