Measuring Habitat Quality for Least Bitterns in a Created Wetland with Use of a Small Unmanned Aircraft

Created wetlands play an important role in the conservation of Least Bitterns (Ixobrychus exilis) by compensating for the loss of natural wetlands. In 2011, we studied habitat relationships of a major population breeding in a 128-ha cattail- and bur-reed-dominated impoundment in Quebec. We surveyed for bitterns and recorded habitat parameters at 30 points, making novel use of a small unmanned aircraft system (UAS) to obtain fine-scale land cover data. A model-selection approach based on Akaike's information criterion (AIC) determined that breeding density was best predicted by cattail cover in combination with water-vegetation edge density (Akaike weight = 0.88). Breeding density was unrelated to water depth, contrary to a previous study at the site after a dyke breach significantly lowered water levels, suggesting that above a certain depth threshold other habitat preferences take precedence. We recommend that management of created wetlands for Least Bitterns focus on maintaining stable water levels of at least 25 cm on average during the breeding season and manipulating them as required later on in order to promote hemi-marsh conditions. UAS can enhance wetland habitat research and monitoring by improving the precision and efficiency of data collection in the field while reducing disturbance compared to ground-based surveys.