WAYS OF ANIMALS

Evening Post, Volume CXX, Issue 135, 4 December 1935, Page 6

WAYS OF ANIMALS

HABITS IN MIGRATION

MODERN KNOWLEDGE

A comprehensive discussion which covered the movements of most of the migratory groups of animals and much recent information about migration and theories concerning it took place at the recent science congress of the British Association at Norwich (says "Nature"). The discussion was' opened by Professor James Ritchie, of the University of Aberdeen, who dealt with the migrations of mammals, and directed attention to two problems—the cause of migration and the way in, which migratory routes were determined. He described briefly the well- ■ known large-scale movements of such as the lemmings in Scandinavia, the brown rats which invaded1 Europe from the Caspian region in 1727,. the grey squirrels and martens in North America before 1866. These, due to lack of food following undue multiplication, were casual, rather sporadic, one-way movements—overflow movements, and not migration proper, and' they aimed at no definite goal. The great seasonal migrations, impressive in extent as well as in the mass of animals taking part in them, were formerly represented by the movements of the wild horses of the steppes of Asia, of the countless antelopes of Africa, the bison, reindeer, and musk-oxen of America. They were determined mainly by scarcity of food, though other "hungers,"' for water or for salt, also induced regu-' lar migrations; and their route often followed regular tracks or roads surveyed and made by far distant ancestors after trial and error towards a definite goal. Road-making is characteristic of the daily activities of mammals, and migratory tracks formed a heritable property handed down from generation to generation. • MIGRATIONS OF WHALES. Dr. N. A. Mackintosh described the migrations of whales from the Antarctic region, where they are most abundant during the summer, gorging upon the crustacean Euphausia superba. In winter they move northwards to temperate waters for the breeding season, and although actual migrations have not been often traced, the circumstantial evidence is strong. For example, in the Antarctic, whales fatten enormously as the summer advances, and then off South Africa whales very fat in body and yet with empty stomachs are found, clearly immigrants from the Antarctic feeding grounds. Again in winter off the' African coast whales bearing fresh scars were found, but when whales were caught in the Antarctic the scars I were healed—they had been contracted in warmer waters during the northern .migration. How the migrating whales are guided in their movements is not clear; except in coastal waters landmarks seem to be out pi the question, but perhaps the temperature of the water controls the movements, since the regular presence of whales seen from the Discovery in the Antarctic shows that they frequent tongues of warm water and are obviously sensitive to temperature.: , ,' ~ . ' Recent discoveries "regarding;-; the | migrations of birds were described by Dr. A. Landsborough Thomson, who pointed out that the old idea of narrow migration routes along coast lines and riveivvalieys'had been abandoned in favour of the idea of migratory movements,..uponj a broad/ front. The extraordinary' complexity- and variety of migration in different species, sometimes- closely related, were' illustrated by a series of well-chosen examples, some selected from the recently investigated movements of birds confined te tropical areas; but it was pointed • out that overriding all trie complexities a regularity of time and place and route characterises migratory movements as a whole. The outstanding problem still to be solved is that of route-finding, and although there are many indications that vision plays an important part (for example,- fog is one. of the serious. disturbances of a migration) yet the orientation of a migration-journey must still be looked upon as something of a mystery. MOVEMENTS OF FISHES. Some interesting results of marking experiments were described by Dr. E. S. Russell in discussing the migrations of fishes, where knowledge of migration is of great economic importance since' the movements of concentrated shoals of food fishes regulate the fisheries. In fish-marking experiments, hundreds of thousands of individuals have been marked, and a high;return of'3o-40 per cent, gave a clear indication of the major .movements,':-.-.which was supplemented :.by: the analysis of fishery statistics.-. 'Generally-speaking, the migrations of fishes consist of three movements—of mature fish to the' spawning grounds, generally upstream, a dispersion after, spawning, generally downstream, and local seasonal migrations. . ' . The series of general, papers on migration concluded by an account of the migrations of insects by Dr. C. B. Williams. In this case, migration does hot necessarily include a return flight, though in the last five years evidence has accumulated that some Lepidoptera do make a return journey. Migration is widespread in the insect world, many instances being known from, the groups of Lepidoptera, locusts, dragon flies, and beetlesA One of the most remarkable cases is that of the American monarch butterfly, which spends the summer as far north as Alaska, and winters in the southern States and Mexico, returning to a state of semihibernation in the same groups of trees year after year, although one or two' generations have passed since the former occupants had traversed the migration route. The extraordinary movements of the world-wide : painted lady butterfly were described, '_ and it was shown' that insect migration takes place in definite directions, - and is independent of the direction of the wind. The understanding of msect1 migration is complicated by the short life of insects, which makes impossible any learning of the route from direct ancestral experience. ;

Platelayers on the Southern Railway line, England, between Ewell Road bridge and Surbiton Station, found a live hand-grenade on the embankment l-ecently.