Estimating flight height and flight speed of breeding Piping Plovers

Collisions with wind turbines are an increasing conservation concern for migratory birds that already face many threats. Existing collision-risk models take into account parameters of wind turbines and bird flight behavior to estimate collision probability and mortality rates. Two behavioral characteristics these models require are the proportion of birds flying at the height of the rotor swept-zone and the flight speed of birds passing through the rotor swept-zone. In recent studies, investigators have measured flight height and flight speed of migrating birds using fixed-beam radar and thermal imaging. These techniques work well for fixed areas where migrants commonly pass over, but they cannot readily provide species-specific information. We measured flight heights of a nesting shorebird, the federally threatened Piping Plover (Charadrius melodus), using optical range finding and measured flight speed using videography. Several single-turbine wind projects have been proposed for the Atlantic coast of the United States where they may pose a potential threat to these plovers. We studied Piping Plovers in New Jersey and Massachusetts during the breeding seasons of 2012 and 2013. Measured flight heights ranged from 0.7 to 10.5 m with a mean of 2.6 m (N = 19). Concurrent visually estimated flight heights were all within 2 m of measured heights and most within 1 m. In separate surveys, average visually estimated flight height was 2.6 m (N = 1674) and ranged from 0.25 m to 40 m. Average calculated flight speed was 9.30 m/s (N = 17). Optical range finding was challenging, but provided a useful way to calibrate visual estimates where frames of reference were lacking in the environment. Our techniques provide comparatively inexpensive, replicable procedures for estimating turbine collision-risk parameters where the focus is on discrete nesting areas of specific species where birds follow predictable flight paths.