The navigation of land-birds: Over the sea the radar evidence

236

ANIMAL BEHAVIOUR, IX, 3-4

been studied at Clayesmore and since reported from other areas . It is less efficient than the spring movement and differed in that the toads fed enroute, no pairing took place except on reaching water, the sex ratio was more even, and the orientation was less accurate, males tending especially to wander . Toads are physiologically in a condition to breed by the end of September

and the accumulation of prolactin is thought likely to initiate their wandering . The movement was regarded as an abortive breeding cycle, that was interrupted by winter, and in particular by the low temperature of the water which was thought to be the explanation for no spawn having been found .

ORIENTATION IN DUCKS . By G. V . T . MATTHEWS, The Wildfowl Trust, Slinibridge .

Mallard caught at Slimbridge, Gloucestershire, and released at many points in various directions consistently fly off between North and West regardless of time of release, season of capture, sex, age, wind direction or topography of the release point . The direction is not maintained, subsequent recoveries being scattered at random . Orientation at release is stastically clear within 30 seconds and can therefore give a false impression of immediate position fixing when the home and "nonsense" directions coincide . The work on pigeons in Germany and North Carolina is open to criticism on this score . The thickness of overcast needed to prevent sun-orientation is being assessed by photometry . At night the use of small `sputnik' lights

attached to the legs of the Mallard have fully confirmed star orientation and possibly moon orientation . Mallard caught at Borough Fen, Northamptonshire, show a N .W . orientation in September, but later in the season no particular orientation is apparent . It is possible that this may be due to the influx of migrants with a different orientattion . Birds caught at St . James's Park, London, fly predominantly between East and South . The part played by learning, possibly in relation to the topography of the `home' area, is being investigated by rearing experiments . Preliminary tests with Teal have indicated a S .W . `nonsense' orientation in Britain, Holland and France .

THE NAVIGATION OF LAND-BIRDS : OVER THE SEA THE RADAR EVIDENCE. By D . LACK, Edward Gre y Institute of Field Ornithology, Oxford.

Observations by high-power radar of migrants over the sea show that l . Migrants normally maintain steady tracks, both by day and by night . 2 . They do not normally change direction with the change from daylight to dark or from dark to daylight, though presumably switching between solar and stellar navigation . 3 . Their tracks are normally the resultant between a determined heading and the wind at the time, without allowance for lateral drift by a cross wind . However, migrants do not usually set out in a strong cross-wind . 4 . Tracks were random for 6 per cent . of the periods analysed, the area of dis-orientation being local, and always associated with fog or rain . Visual observations show that low-flying

migrants may maintain orientation in full overcast . 5 . Migrants may head in at right angles on sighting the coast, and sometimes continue in a rather different direction over the land from that over the sea, or they may turn up-wind along a coast . More complex gradual changes in direction have sometimes been recorded by day in the southern North Sea . When land-birds are drifted far out over the Atlantic during the night, they may head back into the wind at daylight, in a direction nearly opposite to that in which they were previously flying . 6 . Especially in autumn, migrants normally set out with a very light wind or a more-or-less following wind . Migration in a direction opposite to that normal for the season of year sometimes occurs with a head-wind .

MIGRATION AND ORIENTATION IN PINNIPEDIA AND CETACEA . By K . M . BACKHOUSE, Charing Cross Hospital Medical School, Chandos Place, London, W.C.2 .

The Pinniedia are commonly considered to be migratory animals. Callorhinus ursinus, for instance, may travel thousands of miles through-

out the North Pacific from its northern breeding grounds . This constitutes a wide feeding dispersal with little or no tendency for maintenance