Date of Award
8-2022
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Forestry and Environmental Conservation
Committee Chair/Advisor
Dr. Greg Yarrow
Committee Member
Dr. Kyle Barrett
Committee Member
Dr. Jim Anderson
Committee Member
Dr. Richard M. Kaminski
Abstract
The wood duck (Aix sponsa) has experienced one of the most significant declines and recoveries among species of North American waterfowl (Anatidae). With enactment of the Migratory Bird Treaty Act (1918) and installation of hundreds of thousands of artificial nest structures for this cavity-nesting species in North America, wood duck populations have recovered and remain a sustainable harvested resource. However, long-term research on box-nesting wood ducks conducted at the Savannah River Ecology Laboratory, Aiken, South Carolina, has revealed uncertainty as to whether recruitment rates of yearling females from natal box-nesting populations are self-sustaining without immigration of hens from other complexes of boxes and natural cavities.
North Carolina and South Carolina have intensive wood duck nest box programs on public and private lands, numbering in the tens of thousands of boxes. Therefore, I conducted a study in 2020 and 2021 at Lake Moultrie in South Carolina and in North Carolina at Mattamuskeet and Roanoke River National Wildlife Refuges (NWR) and Heron Bay, a private property adjoining Mattamuskeet NWR. I monitored nearly 400 boxes examining wood duck reproductive and recruitment data and evaluating strategies to deter rat snakes (Pantherophis alleghaniensis) and woodpeckers, both major predators of wood duck eggs at my study sites. I also calculated cost indexes of yearling female recruits over an assumed 20-year longevity of nest boxes.
Box use was high at all sites and both years but was greater at Lake Moultrie (98%) than the pooled average for North Carolina sites (86%). Across all sites and years, nest success was 54.6%, and frequencies of successful and unsuccessful nests did not differ between sites in 2020 but did in 2021. The difference between years can be attributed to increased snake predation (9%) from 2020 to 2021. An average of 2.31 more ducklings exited successful nests in boxes at Lake Moultrie than from the North Carolina sites in 2020, but the 1.84 more ducklings exited North Carolina boxes in 2021. Despite the between-year differences, no difference in number of ducklings exiting boxes occurred between sites when yearly data were pooled (i.e., 11.3 ducklings/successful nest). I calculated an index of the cost of wood duck box construction and maintenance over 20 years in relation yearling female recruits, using a published recruitment rate and the average recruitment rate from Lake Moultrie from 2020–2021. The average cost per recruit was 1–4 times less than the cost of the box and its management over 20 years, suggesting cost-efficiency based on this approach.
To deter rat snakes from entering nest boxes, I attached a black cotton sock containing one cup of Snake-A-Way®pellets on nest boxes above the predator guard at boxes with previously recorded or current snake predation of wood duck eggs. An empty black sock was deployed likewise as a control in this experiment. In addition, I tagged snakes with a passive integrated transponder (PIT tag) and took morphometric measurements of each rat snake captured in nest boxes. Using a Lincoln-Petersen estimator, I estimated 138 (SE = 25) rat snakes using nest boxes at Lake Moultrie, where snake depredation of eggs was greatest. I PIT tagged 106 snakes among all North Carolina sites and Lake Moultrie. Average total length of male and female snakes combined was 143.1 (SE = 2.01) cm, with captured males being larger than females at all sites. A total of 456 eggs were consumed by captured snakes, with peak snake predation occurring in April. Snake pellets were deployed 39 times across field sites where snakes were encountered; there were 14 snake encounters after pellets were deployed compared to no encounters after the other 25 pellets deployments. However, I did not detect a significant difference in the number of snakes accessing boxes treated or not treated with pellets. I deployed trail cameras in each state to determine how snakes were circumventing functional predator guards. Snakes wrap their body around the post and use predator guards to leverage their ascent upward to access the box entrance.
To deter woodpeckers from entering nest boxes, I attached a Bird-B-Gone® plastic hawk decoy to boxes with previously recorded woodpecker depredations of wood duck eggs. Decoys were deployed after 12 twelve days of incubation to discourage hen abandonment of nests from the hawk effigy. Across both years and all sites, woodpeckers were responsible for 65.6% of nest depredations. A total of 26 woodpecker encounters were recorded for nest boxes with and without the hawk decoy. There was a significant difference in the number of successful nests in boxes containing the hawk decoy in 2021. My study indicated there is a need for continued recruitment data and sensitivity analysis to determine if rat snakes, woodpeckers, and other agents of nest loss are decreasing recruitment rates from boxes in my study sites, in our regional study across the Southeast, and throughout the range of North American wood ducks.
Recommended Citation
Miller, Emily, "Recruitment, Cost Indexes, and Management of Box-Nesting Wood Ducks in South Carolina and North Carolina" (2022). All Theses. 3885.
https://open.clemson.edu/all_theses/3885