Effects of Vegetation Modification due to High Deer Density on Breeding Bird Communities in Oku-Nikko, Japan

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We aimed to assess the effects of vegetation modification caused by deer on birds. We examined the effects of deer density on vegetation modification and the relationship between the species composition of bird communities and the vegetation structure in 3 areas (8 plots/area) with different deer densities in Oku-Nikko, central Japan. The number of living trees, number of tree species, and basal area of living trees decreased significantly with an increase in deer density, suggesting that deer density contributes to vegetation modification. Using TWINSPAN, the 24 plots were divided into groups A (high deer-density) and B (low deer-density) and 32 bird species were divided into groups 1∼4. Bird species with a preference for open habitats tended to belong to group 1 and were observed primarily in group A plots. Bird species with a preference for foraging in shrubs tended to belong to group 4 and were observed primarily in group B plots. Tree-hole nesting birds tended to belong to group 2 or group 3 and were observed equally in group A and group B plots. Discriminant analysis indicated that the plot classification by TWINSPAN could be interpreted according to the number of shrub trees, sub-canopy trees, and shrub species. These results indicate that vegetation modification because of high deer density may contribute to changes in the species composition of bird communities.