Abstract: PERMISSION has now been obtained to publish the fact that birds can reflect radio waves with sufficient strength to be detected by radar sets. Evidence of this was given to us in the summer of 1941 by Dr. E. S. Shire, then developing centimetric radar equipment at the Air Defence Research and Development, Establishment, Ministry of Supply. Confirmation was obtained by G. C. Varley in September 1941, when echoes observed on an operational centimetric set at Dover were established by visual checks to come from gannets (Sula bassana) flying singly above the sea. The facts were published in a secret report of the Army Operational Research Group, Ministry of Supply, in April 1942. Much fuller details, with numerous further records, were published in a secret report dated February 1945.