Nesting success of colonial tree-nesting waterbirds on selected wetlands in northeast South Dakota

The northern Great Plains of North America provides the primary breeding habitat for numerous species of waterbirds. Reproductive status and population parameters of colonial tree-nesting waterbirds are largely unknown within the prairie pothole region. Objectives of this study were to: (1) evaluate nesting and fledging success of colonial tree-nesting waterbirds on selected wetlands in northeast South Dakota, (2) assess overall colony nesting and fledging success of colonial tree-nesting waterbirds breeding on selected wetlands in northeast South Dakota, and (3) identify important local and landscape habitat characteristics necessary for colonial tree-nesting waterbird populations on wetlands of northeast South Dakota. During the 2008 and 2009 breeding seasons I monitored nesting success of black-crowned night heron (Nycticorax nycticorax), great blue heron (Ardea herodias), cattle egret (Bubulcus ibis), great egret (A. alba ), snowy egret (Egretta thula), and double-crested cormorant (Phalacrocorax auritus) on wetlands in northeast South Dakota.;I monitored 28 colonies in 2008 and 25 in 2009, 14 of which were monitored in both years. Colonies were visited once every 6 -- 8 days throughout the 2008 and 2009 breeding seasons. I monitored a total of 1,174 and 1,376 individual nests with a 20-60x82 spotting scope at a distance of 100 -- 150 m to mitigate observer disturbance from 15 April -- 15 August in 2008 and 2009, respectively. I evaluated the apparent nest and fledge success for all 6 study species. Overall, nest and fledge success were, black-crowned night heron (52.1%, 47.9%), great blue heron (58.2%, 35.9%), cattle egret (73.1%, 69.2%), great egret (61.5%, 50.7%), snowy egret (83.6%, 81.7%), and double-crested cormorant (70.4%, 54.2%), respectively. Colony nesting success was significantly different (p<0.05) between years in 6 of the 14 colonies, while colony fledging success was significantly different (p<0.05) between years in 4 colonies.;Nest abandonment was the leading cause of nest failure and ranged from 34.7% of total failures in black-crowned night heron to 64.3% in cattle egret, with a mean of 47.6% for all species combined. Nest structure was the second highest leading cause of nest failure, which accounted for a mean of 30.4% for all species. Great blue herons had the highest rate of nest takeover, 37.3%, solely attributed to double-crested cormorants. There were 1,234 (48.4%) of the monitored nests that did not fledge any young while successful nests had a fledging rate of 77.2%. The highest sources of fledge failure were primarily attributed to nest structure failure and young dying within the nest.;I surveyed local vegetation characteristics at 27 of the 39 active colonies monitored when all nesting was completed. I also surveyed 32 non-nesting sites within the study area that were deemed to contain suitable nesting habitat. I measured land use characteristics in 5 concentric rings expanding from the center of each colony and non-nesting site to assess how landscape attributes affect colony site selection, and nest and fledge success. Buffer distances used were 400 m, 800 m, 1600 m, 3200m, and 6400 m. Land cover was obtained by using the 2001 National Land Cover Database.;Colony site locations of black-crowned night heron, cattle egret, great egret, and snowy egret were almost exclusively located on islands. These locations were positively associated with bare ground and water surrounding colonies, and negatively associated with herbaceous vegetation within colonies. Great blue herons selected sites that contained green ash trees (Fraxinus pennsylvanica) and were surrounded by a high percentage of herbaceous wetland area. Double-crested cormorant colony locations were positively associated with bare ground on island colonies, open water, and total wetland area. The best colony site predictive models for all species contained both local and landscape variables, while nest success models were variable. However, nesting success for all species was positively influenced by increased bare ground occurring within colonies and the amount of open water and wetland area surrounding colonies.;According to my findings, the low reproductive success of black-crowned night herons and great blue herons suggests that these breeding populations in northeast South Dakota are declining. Cattle egret, great egret, snowy egret, and double-crested cormorant reproductive success is relatively high in northeast South Dakota, but other than the double-crested cormorant their breeding numbers are relatively low. Predictive colony site and nest success models created for all species indicate that management practices should be conducted at both the local and landscape levels.