Extracting bird migration information from C-band Doppler weather radars

Although radar has been used in studies of bird migration for 60 years, there is still no network for continuous monitoring of bird migration. Europe has a dense network of military air surveillance radars but most systems are not directly suitable for reliable bird monitoring. Since the early 90’s, Doppler radars and wind profilers were introduced in meteorology to measure wind. These wind measurements are known to be contaminated with insect and bird echoes. The aim of the present research is to assess to what extent bird migration information can be deduced from meteorological Doppler radar output. We compare the observations on migrating birds by a dedicated X-band bird radar with those of a C-band Doppler weather radar. The observations were collected in the Netherlands, from 1 March to 22 May 2003. In this period, the bird radar shows that birds are present in 20% of all measurements, 86% of which are correctly recognised by the weather radar. Reliable density profiles of birds can not be obtained from the weather radar. However, when integrated over altitude, weather radar reflection does correspond with bird radar density. Moreover, for bird speed both radars give the same results in 78% of the cases, and for flight direction in 73% of the cases. The usefulness of the existing network of weather radars for deducing information on bird migration offers a great opportunity for a European wide monitoring network of bird migration.