The effect of white-tailed deer density on forest songbirds

Graduate Research Assistant: Elizabeth L. Tymkiw

Collaborators: McIntire-Stennis research funds and the University of Delaware

White-tailed deer (Odocoileus virginianus) abundance in North America, particularly in the Mid-Atlantic and Northeast, is well above historical levels. Deer have been shown to have an impact on the populations of herbaceous and woody plants, insects, and birds. My primary objective in this study is to determine if deer are having an impact on bird abundance and species richness. My secondary objective, if deer are having an effect, is to find a threshold density for management at which deer have a minimal effect on the abundance and diversity of vulnerable breeding songbirds in Delaware. I will use 2 sources of data to reach these objectives. First, the Breeding Bird Survey (BBS) will provide 4 years of existing breeding bird data. Second, my own point counts will narrow the focus to forested habitats within areas where the deer density is known. I will also conduct vegetation surveys. I will count and identify every mid-story stem within 0.01 acre and visually estimate the percent ground cover within 0.001 acre. I will estimate the percent mid-story cover using a Nudds board. I will also record the basal area of the forest at each point using Basal Area Factor (BAF) 5 and BAF 10 prisms. By comparing this information with the deer density for each point I can determine what sort of impact deer are having on bird populations and vegetation.

The effect of deer browsing on bearded and unbearded wheat yield

Graduate Research Assistant: Matthew T. Springer

Collaborators: McIntire-Stennis research funds and the University of Delaware

Wheat is an important agronomic crop that is a common winter food source for white-tailed deer (Odocoileus virginianus) in agricultural landscapes. Two types of wheat are grown, unbearded and bearded. Farmers believe bearded wheat deters deer browsing because of the long awns. In 2007, I investigated spatial and temporal browsing on the 2 types of wheat in Little Creek, Delaware in fields bordered on one side by a forest. I placed 240, 4.6 m2 plots in the middle of 10 m distance classes starting from the forested edge out to 60 m. I systematically assigned 1 of 2 treatments (no protection, protected at planting) to the plots. Plots were protected using a 1.4 m welded-wire fence. After head emergence, I conducted weekly browse surveys on all unprotected plots to determine temporal browse rates. I collected weekly biomass samples to estimate the amount of wheat being removed by browse. In July, I harvested a 1 m2 area in the middle of each plot to determine the impact on yield. Bearded wheat had a greater yield than unbearded wheat (bearded 4187 ± 91.4 kg/ha, unbearded 3664 ± 113.2 kg/ha). Deer browsing increased yield (unprotected 4068.3 ± 105.0 kg/ha, full protection 3783.5 ± 104.7kg/ha). Browsing increased in intensity as head development progressed and most browsing occurred on the unbearded wheat. In 2008, I added a third treatment to my design, protected prior to heading, to better understand the effects of the awns on browsing, and I increased my sample size to 720 plots. My research demonstrated the positive impact of deer browsing on wheat yield but more research is needed to better elucidate the effect of awns on deer browse and the subsequent effect on wheat yield.

A Spatial Explicit Model of the White-tailed Deer Population in Delaware

Graduate Research Assistant: Brian R. Jennings

Collaborators: The University of Delaware

The Efficacy of Controlled Hunts for Managing White-tailed Deer in an Exurban Landscape

Graduate Research Assistant: Regina L. Misiewicz and Craig L. Rhoads

Collaborators: The Maryland Department of Natural Resources Wildlife & Heritage Service, The Jack H. Berryman Institute, the MacIntire-Stennis Forestry Research Program, the University of Delaware Research Foundation, and the University of Delaware

The effects of long piers on birds using tidal wetlands in Worcester County, Maryland

Graduate Research Assistant: Alison E. Banning

Collaborators: Maryland Department of the Environment, Worcester County, and the University of Delaware

Tidal wetlands are an essential part of coastal systems and provide breeding and foraging habitat for many marsh birds. As human development continues in coastal areas, shoreline properties adjacent to expansive marsh are increasingly used. To gain access to coastal waterways, homeowners must now construct long piers over marsh habitat. To date, no published research has investigated the effect of long piers over tidal marshes on marsh birds. My objectives were to determine the effect of long piers over vegetated tidal marshes on the relative abundance and species richness of marsh birds, and to determine what landscape variables could be used to predict the relative abundance and species richness of marsh birds. I completed 72 surveys (i.e., combined passive and callback) in tidal marsh at 22 sites with long piers and 24 without piers, May-July 2005-2006. The presence of long piers negatively affected obligate marsh bird relative abundance and species richness (P ≤ 0.06), positively affected gulls and terns (P ≤ 0.07) and herons and egrets (P ≤ 0.03) but had no affect on facultative marsh birds (P ≥ 0.213). Long pier density was negatively related to obligate marsh bird relative abundance and species richness (P ≤ 0.06), but was positively related to the relative abundance and species richness of gulls and terns (P ≤ 0.021). Herons and egrets were not related to long pier density (P ≥ 0.069). Facultative marsh bird relative abundance was not affected by pier density (P>0.696), but species richness was negatively related (P = 0.054). Obligate marsh birds revealed a strong, positive relationship with marsh area (P ≤ 0.001), whereas facultative marsh bird relative abundance was positively related to agriculture (P ≤ 0.003). Herons and egrets showed a negative trend with agriculture and marsh (P ≤ 0.07), whereas gulls and terns were not related to either marsh or agriculture. To reduce negative effects and promote biological integrity of tidal marsh habitat, management should reduce or eliminate long piers over tidal marshes and conserve marsh area.

Seasonal food availability for wintering and migrating dabbling ducks and its implications for management at the Hackensack Meadowlands of New Jersey

Graduate Research Assistant: Matthew T. DiBona

Collaborators: Ducks Unlimited and the University of Delaware

Wetland loss and degradation in the Northeast has been especially severe and the ability of remaining wetland resources, heavily impacted by human populations, to support wintering and migrating waterfowl needs to be assessed. I conducted a food availability study in the Hackensack Meadowlands, New Jersey, to estimate available food biomass and duck use-days for dabbling ducks in tidally-influenced (tidal) and tidally-restricted (restricted) wetlands. I sampled invertebrates, seeds, roots and tubers, and vegetation in waterfowl-focused microhabitats during fall, winter, and spring in 2005-2006. Food availability was greater in tidal sites than restricted sites for all seasons (P<0.05). Food availability ranged from 82±14 kg/ha (spring) to 300±56 kg/ha (fall) at restricted sites and from 392±147 kg/ha (spring) to 586±121 kg/ha (fall) at tidal sites. I also conducted scan-sampling behavioral surveys in winter and spring 2006 to determine the extent of waterfowl foraging in the Meadowlands during my sampling periods. Duck use-days/ha (DUDs/ha) did not differ between tidal (1084±165 DUDs/ha) and restricted (774±136 DUDs/ha) sites in fall (P=0.166). In winter, more DUDs/ha were available in tidal sites (1123±259 DUDs/ha) compared to restricted sites (534±144 DUDs/ha; P=0.034). Spring estimates of carrying capacity were greater in tidal sites (853±246 DUDs/ha) than in restricted sites (173±41 DUDs/ha; P≤0.001). I modeled the potential to sustain the energetic requirements of current and target waterfowl populations expected to use the Meadowlands as wintering and migration habitat. Under all modeling scenarios, a surplus of DUDs remained, which indicates the Meadowlands was capable of supporting additional wintering and migrating waterfowl. The results of my research suggest that carrying capacity is greater in tidal habitat than in restricted habitat during waterfowl spring migration and wintering periods. Restoration activities in the Meadowlands should focus on restoring tidal hydrology and native saltmarsh vegetation to restricted and phragmites-dominated wetlands to maximize energetic carrying capacity for wintering and migrating dabbling ducks.

Evaluating the effect of amendments and landscape position on the biotic community of constructed depressional wetlands

Graduate Research Assistant: Amy J. Alsfeld

Collaborators: Delaware Department of Natural Resources and Environmental Control, Watershed Assessment Section and the University of Delaware

To increase wetland area and biodiversity, agencies constructed >220 depressional wetlands throughout Delaware. During wetland construction, they included amendments thought to increase wetland diversity [coarse woody debris (CWD), microtopography, and organic matter]. Because the efficacy of amendments is unknown, I investigated their effects on anuran, avian, macroinvertebrate, and vegetative communities. I also investigated the effects of landscape variables within 1,000 m and 5,000 m of wetlands on each community. I selected 20 standardized wetlands in which 5 contained CWD and microtopography amendments, 5 had neither, 5 had CWD but no microtopography, and 5 had microtopography but no CWD. Additionally, 12 wetlands received organic matter amendments. CWD increased insect biomass (P = 0.046), total plant richness (P = 0.038), and obligate wetland plant richness (P = 0.015). Microtopography increased total (P = 0.035) and facultative wetland (P = 0.034) plant richness, and bird richness (P = 0.023). Although organic matter amendments did not result in greater percent soil organic matter, they increased insect richness (P = 0.020) and diversity (P = 0.033), and macroinvertebrate biomass (P = 0.024). Additionally, bird abundance (P = 0.045; r2 = 0.10), insect richness (P = 0.010; r2 = 0.16), and insect (P = 0.023; r2 = 0.13), Ephemeroptera (P = 0.027; r2 = 0.12), and Odonata biomass (P = 0.046; r2 = 0.10) increased with CWD volume. Green frog (Rana clamitans) relative abundance increased with microtopographic variation (P = 0.001; r2 = 0.26). Green frog abundance (P = 0.029; r2 = 0.12), bird richness (P ≤ 0.001; r2 = 0.34), bird abundance (P = 0.008; r2 = 0.17), and total (P = 0.027; r2 = 0.12), native (P = 0.036; r2 = 0.11), and FACW (P = 0.001; r2 = 0.24) plant richness increased with percent soil organic matter. I detected negative relationships with distance to nearest forest and anuran richness (P =0.025), bird richness (P = 0.004), bird diversity (P ≤ 0.001), total plant richness (P = 0.003), facultative wetland plant cover (P = 0.038), and native (P = 0.008; P= 0.023), exotic (P=0.043; P=0.022), and obligate wetland (P= 0.001; P= 0.024) plant richness and cover. Furthermore, bird richness (P = 0.029) and diversity (P = 0.001) increased with forest area within 1,000 m and bird diversity increased with forest area within 5,000 m (P = 0.001). To optimize wetland biodiversity, future constructed wetlands in Delaware should contain CWD, microtopography, and organic matter amendments and should be located near forests.

The Ecology of the Eastern Box Turtle in a Fragmented Landscape

Graduate Research Assistant: Rebecca L. Kipp and Nathan H. Nazdrowicz

Collaborators: MacIntire Stennis and the University of Delaware