The Weather Radar as a Tool for Collecting Quantitative Data on Migrating Birds

Radar observations have an important role in surveying bird migrations and the multifaceted links they have with human activities and environmental changes. Indeed, radars can detect birds at distances much beyond the visual range and at heights that cover the flight altitudes of most migrating birds. However, turning a radar sensor into a tool for quantitative measurements of birds in flight requires calibration, ad-hoc data sampling strategies, models of birds as radar targets and methods for extracting data from the raw radar echoes. This paper summarizes our experience in the observation of the seasonal migrations of birds in Northern Italy with an S-band weather radar. We present, as original results, an automatic procedure for extracting the features of individual bird echoes (e.g., the wingbeat frequency) from fixed-beam scans, as well as an electromagnetic bird model based on the observed echo signatures, which reproduces a full wingbeat cycle. Even though the standard products of operational weather radar networks are today much used for surveying bird movements over large spatial scales, specialized radars remain a unique tool for extracting high-quality data on the local habits of the avian fauna.