The effect of white-tailed deer density on breeding songbirds in Delaware
Date
2010
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Publisher
University of Delaware
Abstract
Currently, population goals for white-tailed deer (Odocoileus virginianus) are based solely on deer data with little consideration given to other parts of the ecosystem. A wider ecological approach is needed to provide managers with a more justifiable target deer density. I investigated the use of breeding birds to determine an ecologically based carrying capacity for deer management by studying the relationship between the forest breeding bird community and deer density in Delaware. Using Breeding Bird Survey (BBS) data from 2005-2009, my own point count data from 2008-2009, and Delaware Division of Fish and Wildlife deer density data from the same time periods, I compared avian species richness and relative abundance to deer density. I divided deer densities into low (≤10 deer/km2), moderate (11-19 deer/km2) and high (≥20 deer/km2) categories. I placed birds into 7 deer-sensitive guilds: interior obligates, ground nesters, shrub nesters, ground gleaners, low canopy foragers, and neo-tropical migrants. The abundance or richness of most guilds and most individual species did not differ by deer density. Of those guilds that did, shrub nesters (P = 0.074), interior forest obligates (P = 0.050), low canopy foragers (P < 0.001), and neo-tropical migrants (P = 0.023) had the greatest species richness and/or relative abundance at low or moderate deer densities. Chipping Sparrows (P = 0.021), Red-eyed Vireos (P = 0.023), Great Crested Flycatchers (P = 0.044), Acadian Flycatchers (P < 0.001), and Ovenbirds (P = 0.028) had the greatest abundances at low or moderate deer densities. Our results suggest that areas in Delaware with deer densities of <20 deer/km2 have the greatest avian richness and abundance. Thus, management efforts should focus on this level as an ecological threshold that will maintain the quality of the ecosystem as a whole.