Still a Mystery

New Zealand Herald, Volume LXXV, Issue 22991, 19 March 1938, Page 10 (Supplement)

Still a Mystery

The Homing Sense in Birds

SOMEWHERE about the time of the first full moon in March the main body of our Arctic bird migrants take their final departure from New Zealand. The flocks of godwit, knot and others that have spent the southern summer on the estuaries and shallow lagoons of the coast have been moving northward for weeks and no doubt there has been the usual concentration of auch birds on the tidal harbours of Manukau, Kaipara and Parengarenga. Their vital energy has shown itself in restlessness jand erratic flighting until Borne circumstance ordains the final departure and they head off ovor the Pacific, Not Explained On other occasions in this column the problem of migration has been discussed and various theories reviewed. It is comparatively easy to understand how migratory habits are of advantage to birds, and that tho dangers involved in long flights are actually less than tho difficulties of surviving throughout the year in 0110 placo. Tho mechanical

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difficulties ot long (lights .arc not groat for most birds. The question of when to fly is solved for them by physiological changes within their bodies at the appropriate season. It is rather the sense of direction, the answer to the question "How do they find their way P" that is not yet explained fully by either observation or experiment. Experiments on "homing" or the sense of orientation are gradually indicating how common a feature of bird I life this is. Because it had been recognised and trained in carrier pigeons tlieso birds were once thought to possess it as a peculiarity. The study of wild birds lias now shown it to bo moro general and sometimes better developed in them than in carrier pigeons. The preliminary experiments that have become classic were those of Watson and Lashlcy, working with sooty terns at an island in the Gulf of Mexico. Sooty Terns The terns chosen for this experiment are sea-birds nesting in tens of thousands on low islands and deriving their food supply from tho surrounding sen. Cortnin birds and their nests wore marked, and tho bird itself transported from the island on a ship to some selected distant point. The results showed a fair percentage of safe returns from varying distances in several directions. Four returned to Bird Key, the nesting island, from Havana, a distance of 108 miles, in one day. Of five taken to Cape Hatteras, a distance of 850 miles, three returned in a few days. 11l this case the following of a coastline could have led them back, bi;t it

Specially Written for the New Zealand Herald by R. A. FALLA, M.A.

must be taken into account that several other marked birds returned from Galvoston over ail open sea course of 800 miles. Independent of Sight It is necessary to take into consideration the possibility that birds may make use of sight and other senses in some of their homing flights. Often they do so, but experiments tend to show that homing may be independent of sight and familiarity with surroundings. A Polish investigator in 1933 showed that swallows have more sense of orientation and are better able to find their homes than even carrier pigeons. According to a German investigator, swallows, starlings, and wrynecks can find their homes from distances as great as 1100 miles. White Storks Last year tljren Polish enthusiasts collaborated in experiments on white storks. 11l one series of tests the birds were transported by tho ueroplanes of Polish Airways from Butynv to Bucharest, and to Lydda in Palestine, distances of 400 miles and 1350 miles respectively. The birds were specially marked so that it was comparatively easy to recognise them after their return to their nests and young. The results confirmed that 75 per cent of the birds tested camo home safely. It was also found that the average speed of

their journey was one-third slower than the speed of swallows ovpr small distances, although it equalled the speed of swallows in distances over 1000 miles. Preparing for Flight The behaviour of the birds, when given freedom, was much tho same and characteristic as a rule. They all took their time in cleaning and putting their feathers in good order, preparing thus for flight. Having taken wing, they circled above the place where they had been set free for a time, which varied practically with every bird, after which each took a proper direction for home. The conclusion reached by these Polish investigators is that some species of birds possess a special sense of orientation which enables them to find their homes from great distances without the help of kinesthetical factors.. Further, they do not doubt that similar results would be obtained ovci longer distances than those tested. Course Not Known The actual course taken by migrants from New Zealand to Siberia and Alaska is not known, nor is the longest non-stop stage of the flight known. The total distance from feeding grounds to breeding grounds, however, is not less than eight thousand milos. The godwit and smaller related waders leave about tho middle of March. They are on the nesting grounds from mid-May till midAugust, and they begin to appear in New Zealand again in October. Our other departing migrants, the cuckoos, nre in different enso. They have just finished their annual breeding season and are leaving on a comparatively short flight of one thousand miles or so to tho Solomons and other Pacific islands on this side of tho equator.