iii. RADAR (Radio Detection And Ranging).

During the Second World War, RADAR was invented to identify military aircraft in foreign airspace. However, from time to time strange echoes showed on the screens which mystified operators. They did not correspond to aircraft, and were thus nicknamed angels5. Most of these echoes were later identified as flocks of migrating birds; radar had provided the night-vision to see this phenomenon for the first time.

The use of radar has since helped reveal the main migratory directions, ground speed, scale and altitude of migrating flocks. However, most birds cannot be identified to species by radar alone, as wing-beat frequencies are the only possible method of identification, and these are indistinguishable for most species.

iv. Radio telemetry and satellite tracking

Transmitters can now be attached to birds that enable us to follow their movements to within 150m, providing an amazing new level of detail about migratory routes. The two main types of tracking device use electromagnetic impulses (radio telemetry) or satellite signals (satellite tracking) to track the bird, and are now so light in weight (<1g) that they wont interfere with the flight of larger birds. The passage of some tagged birds can be followed online: click here to see the paths of honey buzzards migrating south in 2003 http://www.roydennis.org/migration%20maps%202003.htm or raptors migrating over the Strait of Gibraltar http://www.gibnet.gi/~gonhs/raptor_satellite_tracking.htm

Have The Ultimate Flutter and bet on an albatross migrating to S. Africa this spring www.ladbrokes.com (and follow the big bird race link).