HOMING OF SEA-SWALLOWS 5 



and out past Tortugas through the Straits of Flor- 

 ida. The current differs in color from the surround- 

 ing water and from the return current which runs 

 nearer the coast-line. But the color 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? (3) It has been sug- 

 gested that the birds get their bearings visually 

 by ascending to a great height. But, in the first 

 place, they never seem to rise very high; in the 

 second place, they would require at a distance of 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 observers 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 sup- 

 posed susceptibility. Care was also taken to test 



