Evaluating an avian radar system in South Texas

Recent bird migration studies utilize radar technology, however the limits of these avian radar systems remain relatively unknown. Radar systems are potentially useful in counting birds migrating at night and at high altitudes, but its reliability in distinguishing targets requires evaluation. My study tested the tracking capabilities of DeTect, Inc.’s Merlin™ Avian Radar System using two performance evaluation methods: wild bird surveys and tracking released birds of known size. I used a logistic model to differentiate between single and flock targets detected by the radar system based on radar output variables. My logistic model consisting of radar variables determined with 79.5% accuracy that flocks constituted 14-25% of bird target detections, thus demonstrating the potentially conservative nature of radar studies that quantify passage rates. I also attempted to find which of the radar variables best described bird target size using an assortment of correlations between size measurements and radar output variables. I was unable to find a consistent relationship between size metrics and radar output variables. I aimed to estimate detection probabilities of the avian radar system used to quantify passage rates of migrating birds from 2007 to 2010 along the South Texas coast. I used Program DISTANCE to model detection curves for data collected by the radar units and determined the percent of targets the radar system tracked out of the total number of targets estimated to be passing through the radar’s coverage based on these curves. Avian radar studies that do not use methods to discriminate between insects and birds may overestimate passages rates, while studies that count bird targets as single birds may underestimate passage rates. Either way, inappropriate radar operations could lead to inaccurate results for environmental impact assessments that utilize radar systems to estimate the number of birds impacted by human development. Avian radar systems serve as a valuable tool to quantify and describe bird migration when accompanied by procedures that account for radar performance