Date of Award
Restricted Access Thesis
Master of Science in Biology
Department of Biological Sciences
Increasing installations of wind turbines at high-elevations sites in New England have caused concern for potential impacts on sensitive species that inhabit these unique areas. The Bicknell’s Thrush (Catharus bicknelli), a rare, Nearctic-Neotropic migrant, breeds exclusively in high elevation spruce-fir forests in the Northeastern US, and parts of Quebec and the Maritimes in Canada and mountaintop development within the breeding range is a possible threat to the persistence of the vulnerable global population. No study to date addresses the impacts of wind development on the species; therefore we initiated a 3 year, before and after study in 2010 to assess the Bicknell’s Thrush population and general avian community response to the development and operation of a wind park in Northern New Hampshire. The total number of birds detected and species richness remained stable from 2010 to 2012 with 870, 942, 920 individuals and 43, 50, and 49 species, respectively across the three years. There was no significant difference between the number of birds recorded among years on Kelsey peak (F= 0.13, df= 2, p= 0.08) or Dixville Peak (F= 0.25, df= 2, p= 0.77). However, when only turbine stations were included in analysis, we found a significant reduction in total individuals detected and species richness in 2012while the turbines were operational (Kelsey individual/ species total 2011 vs. 2012 (t= 5.34, df= 7, p < 0.001, t= 2.05, df= 7, p < 0.04). Model estimates for Bicknell’s Thrush abundances over the three years (47, 57, 33) reflect actual detections (21, 21, 13) showing a decline in 2012, although higher detections recorded at stations 70 m away from turbines (23) suggest the decline is due to detection probability or avoidance of cleared areas. Estimates of Blackpoll warbler (Dendroica striata) abundance (108, 181, 117) were robust and also reflect actual detections (98, 157, 154). The direct loss of forest within the study area likely has greater impacts for old forest habitat specialists and trends indicate the newly created edge habitat is causing a shift in the avian community along the ridge top. Biotic interactions such as interspecific competition, food availability, and changes in site fidelity will likely continue for several more years. Full implications of this shift remain unknown with only one year of data following treatment, therefore long-term monitoring with use of point counts should continue to detect future trends.
Male Bicknell’s Thrush exhibited a large variation in home range size with a mean of 6.29 ha ± 5.52 (S.E.), which did not differ between years, habitat, or distance from turbine but increased with turbine noise suggesting that noise altered movement behaviors. Bicknell’s Thrush did not demonstrate avoidance of turbines and occupied areas immediately adjacent to turbine pads if preferred habitat structure was present, although site fidelity may be at least partly responsible for this lack of avoidance. Vegetation was similar between core home ranges within naturally disturbed habitats and regenerating spruce-fir stands harvested approximately 17 years earlier, which were the most selected habitat type on the landscape. This suggests the possibility of a management strategy involving patch harvests over multi-decade periods. Approaches including nest monitoring, testing cortisol level for stress, and capture-recapture should be employed to determine reproductive success and site fidelity which would be more effective methods to determine individual survival and effects on the local population. Greater resolution of forest structure (e.g., through LIDAR) will allow preferred habitats to be more accurately described to better gauge long-term impacts caused by the reduction in forest cover due to the windpark.
Establishing partnerships with industry to design experiments testing impact of development on wildlife populations will not only guide management decisions in the future but may also be a cost effective approach if mitigation measures prevent species imperilment and prevent the need to list this species as part of the Endangered Species Act. Mitigation monies may be more effective in meeting long-term global population objectives if allocated through The Bicknell’s Thrush Habitat Protection Fund so resources can be applied to highest conservation priorities for the species.
Parrish, Clinton R., "Impacts of Wind Development on the Abundance and Distribution of High-elevation Birds in Northern New Hampshire, with a Focus on Bicknell's Thrush (Catharus bicknelli)" (2013). Theses & Dissertations. 6.