STUDIES ON SPECTRAL SENSITIVITY OF BIRDS. 



99 



LIMITS OF SPECTRAL SENSITIVITY IN THE HOMING PIGEON. 



At the time of completing the foregoing experiments upon the chick no hom- 

 ing pigeons of suitable age and stock could be found. In the fall of 1914 work 

 was begun upon 4 young homing pigeons whose parents had " flight diplomas," 

 but only one of them proved suitable for work. All were purchased when 3 

 weeks of age and were immediately given the preliminary exercises in the 

 box shown on page 89. We experienced great difficulty in getting any of the 

 pigeons to form the habit of passing completely around to the food. One 

 pigeon, after several months of preliminary practice, during which tests were 

 given daily, began to work steadily. By January 10, 1915, controlled ex- 

 periments were begun. This bird was trained on yellow and green. It was 

 found that while the pigeon was positive to light, it was not so automatic in 

 its responses as the chick. After sufficient training, however, this pigeon became 

 as invariable in its reactions to the light as the chicks. In the following 

 account the tests on the intermediate parts of the spectrum are only sum- 

 marized. As we approach the limits at the two ends the tests are given in detail. 



LIMITS AT THE VIOLET END. 



January 10. Eight tests on X =5500 were made. Only 1 error appeared.* 



January 12. Eight tests on X =5060 were given, with no errors. 



January 15. At wave-length X =4780: with slit in collimator open to 1 mm. and slit in 

 objective open to 1.5 mm., the following tests were given, without previously dark-adapting 

 the pigeon or allowing a period of adaptation after light was turned out (for method see p. 90). 

 This test was made to get rapid orientation as to sensitivity of pigeon to light rays of short 

 wave-length. The results were: 



(1) Light on left side, wrong response. 



(2) Light on left side, wrong response. 



(3) Light on right side, right response. 



(4) Light on left side, wrong response. 



(5) Light on left side, wrong response. 



Since a right position habit developed, I broke off the tests. It is evident 

 that under the given conditions the light no longer controls the response. 

 From this it would seem clear that there is no extreme sensitivity to violet rays. 



January 16. Wave-length decreased to X =4680. Animal was dark-adapted for 15 

 minutes, and 30 seconds adaptation attoived before light ivas exposed. Complete record as 

 follows, with a result of 77+ per cent correct: 



(1) Light on left, wrong response. 



(2) Light on left, right response. 



(3) Light on right, right response. 



(4) Light on right, right response. 



(5) Light on left, right response. 



(6) Light 011 left, right response. 



(7) Light on right, right response. 



(8) Light on right, right response. 



(9) Light on left, wrong response. 



Under conditions of the above test it is evident that although the limit is 

 not yet reached, the light has very low stimulating value. 



January 17. Wave-length changed to X =4580; 15 minutes adaptation and 30 seconds 

 adaptation before admitting light. 88+ per cent correct. 



(1) Light on right, response right. 



(2) Light on left, response right. 

 ('.') Light on left, response right. 



(4) Light on left, response right. 



(5) Light on left, response right. 



(6) Light on right, response wrong. 



(7) Light on right, response right. 



(8) Light on left, response right. 



(9) Light on right, response right. 



*In all of the tests recorded here the purified spectrum of Helmholtz was used (p. 88) . Unless 

 otherwise noted, a Nernst glower burning at a constant amperage was used as a source. For 

 general illumination (during feeding, etc.) a 40-watt tungsten was substituted for the tantalum 

 light of the previous paper. 



