make possible songs which are both individually and specifically recognisable. There are instances of songs which suggest that the bird is actively seeking new auditory and vocal experience- enjoying and playing with sounds. Winter-singing birds show no suggestion of high sex activity, that is, of sex hormone production. Subsong is the vehicle of playful imitation of sounds of no im- mediate consequence, but possibly facilitating the later acquisition of full traditional song. This is a valuable scientific contribution to our knowledge of the meaning and mechanics of bird song. Much of the work was carried out with the aid of the sound spectograph, now manu- factured commercially. Dr. Thorpe describes how this instrument has provided evidence, among other recordings of bird vocalisa- tions', of a double or multiple sound-producing mechanism--so that two or more notes in which no harmonic relationship is evident are being sounded at the same instant. R.M.L. Beasts of the North Country. By HENRY TEGNER. Galley Press, Ltd., London. 1961. 25s. This is a pleasantly discursive account of the author's im- pressions of the mammals of, principally, Northumberland and Durham. He covers, in a few words, a fairly extensive but some- what random selection, from the killer whale to the pygmy shrew. He is an amateur naturalist, now well known for his anecdotal writings on nature he is also a business man and stockbroker and very pleasantly he writes. As the book does not pretend to be a scientific record or fauna of these counties, it is not for the expert. But, enhanced as it is with beautiful formal drawings by Denys Watkins-Pitchford, it is an ideal present to give to the young country-lover interested in mammals. R.M.L. Down the Long Wind. By GARTH CHRISTIAN. Newnes, London. 1961. 21s. Despite its romantic title, this is a somewhat more serious book by another capable writer and lover of nature. It deals primarily with the story of the migration of birds, with modern bird-study methods and descriptions of changes in bird habits due to modern agricultural and other human activities and factors. On homing he describes the experiments of Kramer, Matthews, and the Sauers, whose general conclusions were that birds navigate by an inherited knowledge of the sun and the stars, whereas man does so by learning the positions of the heavenly bodies. He describes the discoveries of angels on radar-the visible hosts of migrating birds, whose movements have been interpreted by David Lack. The book is excellently illustrated by maps and photographs and is eminently readable as an up-to-date account of the study of bird movements and migration. V.A.P.