Patch, Landscape, and Soundscape Effects on the Forest Bird Communities in the National Parks of the National Capital Region.

Goodwin, Sarah

The National Parks of the mid-Atlantic are under constant human pressure from the surrounding urban / suburban matrix. With accelerated development over the past 20 years and population increases predicted during the next 20 years, these National Parks are increasingly critical habitat for forest breeding birds. The assessment of bird community integrity is an important first step in the management of these conservation areas. To this end, I applied previously developed bird community indices (BCIs) to National Park Service avian Inventory and Monitoring Program data. This technique uses proportional species representation across a suite of avian guilds with specialist guilds ranked more favorably than generalist guilds. Each monitoring location was scored based on the bird species detected, which can then be summed to produce a final BCI score for a suite of locations, a park or a region. I estimated and analyzed patch and landscape scale habitat variables to determine how these variables influenced the BCI score at each of the 385 avian monitoring locations across 11 National Parks, and two physiographic regions. The National Parks of the Piedmont/Coastal Plain region had greater BCI scores than the parks in the Appalachian region (P < 0.001). The National Park with the largest contiguous portion of forest (Prince William Forest Park) had a greater BCI score than any other park. BCI score was positively related to forest cover in both regions and negatively related to the proportion of impervious surface in the Piedmont/Coastal Plain. Patch scale variables were significant only in the Piedmont/Coastal Plain with the BCI score positively related to the number of samplings per ha and negatively related to the proportion of exotic cover. Concomitant with increased development is increased traffic volume and traffic noise. Urban sound environments may be disproportionately affecting some bird species by interrupting the critical tasks of territory defense, mate attraction, and other aspects of auditory communication. Traffic noise is a predominately low frequency noise and may be masking acoustic signals that overlap at that same frequency. I hypothesized that birds that sing at lower frequencies would suffer increased acoustic interference or masking and show decreased occupancy of loud habitats. To evaluate this hypothesis, I estimated occupancy of eight forest breeding birds in areas dominated by traffic noise versus quiet areas. I found that for the two species with the lowest center frequency (Yellow-billed Cuckoo Coccyzus americanus and White-breasted Nuthatch Sitta carolinensis), noise characterization was the single best model in predicting occupancy, and occupancy rates were 55% and 35% lower in noisy areas versus quiet areas. For all other species, other habitat variables were more important than noise in explaining occupancy, or no single model best described the data. Through this research in the National Parks of the mid-Atlantic, I show that the avian community is influenced by both patch and landscape scale habitat variables, and in urban areas, traffic noise.

Patch, Landscape, and Soundscape Effects on the Forest Bird Communities in the National Parks of the National Capital Region.

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