From the NS archive: The homing of sea-swallows

28 August 1915: The success of the homing depends partly on the vigour of the birds, and partly on the smiles of fortune, as expressed, for instance, in fine weather and no hawks.

By J Arthur Thomson

Swallows fly to and from their mud nests on 17 April 2009 near Firebaugh, California. (Photo by David McNew/Getty Images)

Naturalist J Arthur Thomson writes about the homing experiments by Professor JB Watson and Dr KS Lashley where swallows were tracked off the Tortugas islands in the Caribbean. In this series of investigations from 1915, birds were captured, marked and liberated from aboard a ship to see if “these terns are able to return from Galveston, more than 800 miles away, over a body of water which apparently does not offer any basis for controlling flight direction”. Despite birds having “been used by man for more than 2,000 years”, there was very little understanding in how birds, particularly untrained birds, can navigate such large distances. While these experiments may not have offered a conclusive theory to understanding distant orientation in birds, Thomson wrote, the authors “have made a distinct step in proving that untrained birds can return successfully across the apparently trackless sea from a distance of 800-1,000 miles”.

Homing pigeons have been used by man for more than 2,000 years, and still we have no secure theory of their return from great distances to their cots. Still less can we explain the well-authenticated fact that a swallow may return from its wintering in the south to the farm-steading where it was born the year before. The problem of homing bristles with difficulties, and it is therefore with eagerness that we turn to a record of the experiments which have been recently made on the sea-swallows at the Tortugas by Professor JB Watson and Dr KS Lashley. The birds were the noddy tern and the sooty tern, which breed in tens of thousands upon Bird Key. That island was surely predestined for the experiments in question, for it is the northern limit of the migration of these two tropical terns, so that if the birds are taken anywhere to the north they will find themselves in all probability in a region which they never before visited. Furthermore, as Bird Key is the last piece of land between the coast of Florida and the coast of Texas, the birds can be sent out to sea for hundreds of miles beyond sight of all landmarks. Between Bird Key and Galveston, for instance, there is open water for 855 statute miles, obviously a fine route for homing experiments.

The technique of the experiments is as follows: A bold, vigorous tern is caught, it is marked characteristically with oil-paint on the head and neck; two tags (small and large, but otherwise duplicate) are prepared recording the date, the place, and the kind of marking; the small tag is tied round the bird’s neck; the large tag is fixed to a foot-long stake pushed down to the sand near the nest if the bird is a sooty, or tied to a convenient twig if the bird is a noddy; the bird is put into a large hooded cage and transported to a distance on board ship; it is kept in good health with minnows from the refrigerator; it is liberated at a chosen point; and then its return to the nest is watched for. The most important general result is that these terns are able to return from Galveston, more than 800 miles away, over a body of water which apparently does not offer any basis for controlling flight direction. Some returned in about six days, some took nearly 12, some did not return at all. Many of the return journeys from distances greater than 500 miles did not require more than three to five days, but sometimes as long a time was required to come from Key West to Bird Key, which is only about 65 miles. It goes without saying that the time required has nothing to do with the rate of flight, for three sooties returned from Key West in three hours 45 minutes, and probably spent part of that time on the feeding ground before reporting themselves at the nests. The success of the homing depends partly on the vigour of the birds, and partly on the smiles of fortune, as expressed, for instance, in fine weather and no hawks.

It is instructive to give particulars in regard to some of the experiments. Two noddies and two sooties were taken in the stateroom of a steamer to Havana, and liberated in the harbour there early in the morning of 11 July. They returned to Bird Key (108 miles off) next day, having probably spent most of the time recuperating around the shores of Cuba. Of five birds liberated off Cape Hatteras at least three returned in a few days, having accomplished a journey of 850 miles as the crow flies, and of much more if the alongshore route was followed. Four noddies and four sooties were taken in a hooded cage on a Galveston steamer to about 461 statute miles from Bird Key and liberated where no shore line was visible. “On release all birds with one exception started east. That one headed west and continued for about 200 yards, then turned suddenly and started east.” They had a strong head wind against them throughout the first day, but two of the noddies returned in safety to Bird Key. On 4 June 11 birds were liberated in Galveston Harbour; on 9 June one of the observers, returning to Bird Key on the steamer, saw one of his charges (a red-marked sooty) resting upon a piece of driftwood in the open sea about 409 statute miles east of Galveston. A heavy storm unfortunately removed all chance of its successful return.

The authors are not prepared to offer any solution of the problem of distant orientation in birds, but they have made a distinct step in proving that untrained birds can return successfully across the apparently trackless sea from a distance of 800-1,000 miles. Dr Lashley has shown that for short distances on the island itself the terns adjust themselves to nest and mate and young on a basis largely of visual experience, helped a little by memory of movements, and sometimes by sounds.

There is no whit of evidence of any unusual sensitiveness nor of the functioning of any hypothetical sense-organ. But what can be said in regard to distant orientation? Firstly, it has been suggested that the Hatteras birds followed the coast-line in the direction of greater warmth. This is possible enough, but it does not bear at all upon the flight from Galveston to Bird Key across the Gulf of Mexico. Secondly, it has been suggested that the Galveston birds follow a well-marked water-current which sweeps around the coast of Texas, Louisiana, Alabama, Florida, and out past Tortugas through the Straits of Florida. The current differs in colour from the surrounding water and from the return current which runs nearer the coastline. But the colour difference is only noticeable when the sun is in a certain position in relation to the observer; many of the successful birds were liberated at night, and all were out for several nights; they had to win their way home through rain, haze, and cloudy weather; they homed equally well, no matter at what point between Galveston and the Tortugas they were put down. And besides why should they not follow the current in the opposite direction? Thirdly, it has been suggested that the birds get their bearings visually by ascending to a great height. But, in the first place, they do not appear to do this; in the second place, they would require at a distance of a 100 miles to ascend almost a mile to see the Loggerhead Key lighthouse; and, in the third place, even if they ascended they would not see much because of the continuous haze.

The authors are not inclined to assume any new and mysterious “sense of direction” until they have made many more experiments, and a good beginning has been made. Thus, to meet Duchatel’s hypothesis that the retina of the bird is specially sensitive to infra-luminous rays, especially infra-red, Professor Watson made a special investigation of spectral sensibility in the chick and the homing pigeon, and found no evidence at all of the supposed susceptibility. Care was also taken to test Cyon’s theory that birds (notoriously deficient in the sense of smell of the ordinary kind) nose their way home through the air, feeling the direction, strength, and temperature of the wind as it plays on the olfactory mucous membrane. The nasal chambers of two noddy terns were filled with warm wax and varnished over, and the birds were sent to Key West, 65 miles distant, where they were released at two o’clock in the afternoon. At daybreak next morning both birds were on their nests just as usual. Thus it may be inferred that there is not in the nasal cavity of terns any special tactile or olfactory sensitiveness which functions in the homing. The observers propose to inquire whether there may be on other parts of the body-such as eyelids, ear-covering, mouth cavity-any tactile or thermal nerve endings which may assist the birds in reacting to slight differences in pressure, temperature, and humidity which they may encounter on their flight.

So the matter stands at present – the remarkable fact of untrained birds successfully reaching from a great distance a known but invisible goal surrounded by apparently trackless sea. It goes without saying that there are speculative theories galore, but what Professor Watson and Dr Lashley are working towards is a scientific interpretation. Naturalists have appealed to magnetic sense, topographical memory, registration of movements, telepathy, and so on – at least nine theories have been advanced – but the solution of the riddle is still in the future. It is a familiar step in scientific method to try to bring an obscure fact into line with others of an approximately similar kind, and this must be done in the case of the homing terns. In this connection it is unfortunate that the data in regard to homing dogs and cats and other mammals are not in a form suitable for scientific purposes, and that crucial experiments to show what untrained homing pigeons can do are lacking. Exceedingly careful experimental work has been done with ants and bees, which find their way home successfully within a limited radius, and the balance of evidence inclines to the conclusion that most of the phenomena can be explained by the gradual registration of various sets of stimuli-olfactory, tactile, visual, and kinaesthetic. Here also, however, there are residual phenomena at present as inexplicable as the homing of the terns from Galveston to the Tortugas.

Professor Watson holds the chair of Experimental and Comparative Psychology at the Johns Hopkins University, and his experimental study of the homing terns is marked by a greater psychological subtlety than is usually to be found in the adventures of zoologists in similar fields. Thus it is interesting to notice his careful observations on the duration of the nesting impulse when the normal activities have been interrupted. He finds that it remains strong for two or three weeks, and this should be borne in mind, for it gives an illuminating significance to the homing of the sea-swallows. They are returning to activities in which their life reaches its climax, to the continuance of which they are urged by a deep organic impulse, by an irresistible will which is not baulked by any waste of seas.

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