The effect of white-tailed deer density on breeding songbirds in Delaware

Abstract

Most population goals for white-tailed deer (Odocoileus virginianus) are based solely on deer data, with little consideration for other parts of the ecosystem. A wider ecological approach is needed for more justifiable target deer densities. We investigated the use of birds as coarse-scale indicators to determine an ecological carrying capacity for deer management by studying the relationship between the forest bird community and deer density in Delaware, USA. Using Breeding Bird Survey data from 2005 to 2009, targeted point-count data from 2008 to 2009 and Division of Fish and Wildlife deer-density data from the same time periods, we compared avian species richness and relative abundance with deer density. We divided deer densities into low ( 10 deer/km 2 ), moderate (11-19 deer/km 2 ), and high (!20 deer/km 2 ) categories. We placed birds into 6 deer-sensitive guilds: interior forest obligates, ground nesters, shrub nesters, ground gleaners, low-canopy foragers, and Neotropical migrants, as well as 1 "guild" that consisted of species found to be sensitive to deer density in past literature. The abundance or richness of most guilds and species did not differ by deer density. However, there were 1.08 more shrub nesters and 0.55 more species of shrub nesting birds in low-deer-density areas than in high-deer-density areas. Areas of moderate and low deer densities had !0.35 more species of low-canopy foragers than did areas of high deer densities. Low-deer-density areas had !0.59 more individual Neotropical migrants compared with moderate-or high-deer-density areas. Similarly, areas of low deer densities had !0.49 more migrant species than did areas of higher densities. Low-deerdensity areas had !0.17 more ovenbirds compared with high-and moderate-deer-density areas. Great crested flycatchers (Myiarchus crinitus) had 3 times greater odds of being found in low-deer-density areas than in high-deer-density areas. Chipping sparrows (Spizella passerina), Acadian flycatchers (Empidonax virescens), and red-eyed vireos (Vireo olivaceus) all had 2 times greater odds of being found in low-deer-density areas than high-deer-density areas. Our results suggest that areas in Delaware with densities of <20 deer/km 2 have the greatest avian richness and abundance. These findings are the first step toward determining an ecological carrying capacity for white-tailed deer. Ó 2013 The Wildlife Society.

Discordant response of spider communities to forests disturbed by deer herbivory and changes in prey availability

“…), as well as vertebrates that rely on understory structure browsed by deer, such as forest‐obligate birds and small mammals (Byman , Tymkiw et al. ). Beyond the physical structure of forest vegetation that may affect spider habitat, browsing from dense deer populations also reduces the density of native tree seedlings and other understory plants, ultimately altering entire forest plant communities (Rooney , Eschtruth and Battles ).…”

Overabundant ungulates in French Sologne? Increasing red deer and wild boar pressure may not threaten woodland birds in mature forest stands

“…Most of the ground-nesting bird species we considered, such as P. sibilatrix and A. trivialis, are known to prefer open forests with little understory vegetation and to be more abundant in heavily grazed forest stands (Mitchell & Kirby 1990;Fuller 2001). Working outside of Europe, DeCalesta (1994) and Tymkiw et al (2013), did not find any effect of varying deer densities on either species richness or abundance of ground-nesting birds.…”

“…One possible explanation for this contradiction is that high ungulate densities may not be detrimental to all birds in all woodlands. For instance, DeCalesta (1994) and Tymkiw et al (2013) observed that the abundance and richness of most woodland guilds were not significantly different under highly variable ungulate population densities and stand types.…”

“…Groundnesting and ground-foraging bird species may also suffer higher predation risk in patches with higher vegetation layers (Low, Arlt, Eggers, & Pärt 2010). Understory-dependent bird species may thus respond in very different ways to increasing deer (Tymkiw, Bowman, & Shriver 2013) and wild boar (Barrios-Garcia & Ballari 2012) population densities.…”

“…As an experimental tool, fencing has been used either to exclude ungulates from fenced study sites (Holt et al 2011(Holt et al , 2014, or to vary ungulate population densities inside fenced lots DeCalesta (1994). However, artificially high deer browsing intensities are likely to occur when the experimental enclosures are smaller than estimated deer home ranges (Tymkiw et al 2013). To overcome such limitations, we studied how the actually encountered ungulate population densities may affect forest bird communities in nine fenced and ten unfenced forests in the French Sologne region.…”