470 R. T. YOUNG 



Experiment 4- Same as Experiment 3. The hawks remained on 

 their perch for five minutes, taking no notice of the mice. I then 

 drove one of the hawks from its perch. It flew across the cage and 

 retm'ned, dropping to the gromid near the perch. It then immediately 

 ran across the cage and took the mouse from the hme. After eating 

 this, it took the mouse from the earth. 



Experiment 5. Figures 1 and 3. One Mus on lime and one on 

 earth over which were scattered a few scraps of leaves. A hawk left 

 its perch almost immediately after I left the cage and dropped to the 

 ground below. A few seconds later it walked across the cage and 

 took the mouse from the lime. 



Experime7it 6. The same species of prey and the same backgrounds 

 were employed in this experiment as in Experiment 5. Two hawks 

 left the perch in succession and dropped to the ground, one of them 

 within 0.6 m. of the mice and somewhat nearer the mouse on the 

 earth background. The latter hawk took the mouse from the lime. 



Experiment 7. In this experiment the same species of mice and 

 the same backgrounds were employed, but the backgrounds were 

 reversed in position. Two hawks left the perch together and flew 

 to the ground, one of them taking the mouse first from the earth back- 

 ground, and then from the lime. 



Experiment 8. The prey and the background arrangement were 

 the same in this experiment as in Experiment 7. One hawk soon left 

 the perch and flew to the ground near the backgrounds, but apparently 

 did not see the mice as it retreated a short distance and remained for 

 several seconds with its attention apparently fixed on something out- 

 side of the cage. Then it appeared suddenly to see the mouse on 

 the lime and quickly seized it. The hawk was possibly 6 or 7 cm. 

 nearer the mouse on the lime than that on the earth when it espied 

 the former. 



Experiment 9. The same prey and the same backgrounds were 

 employed in this experiment as in the preceding, except that the earth 

 background was moved a few centimeters nearer the perch than the 

 lime background. Three minutes after starting the experiment, a 

 hawk left its perch and dropped to the ground about midway between 

 the perch and the backgrounds. It remained there for a few seconds 

 without apparently seeing the mice. Then it suddenly ran to the lime 

 background from which it took a mouse. 



Experiment 10. Figure 10. In this experiment the same prey 

 was employed as in the last experiment, but the position of the mice 

 was reversed, they })eing placed with the venter uppermost, one on 

 a background of earth and the other on one of dry leaves of corn (Zea), 

 the latter background replacing in position that of lime in the last 

 experiment. In this experiment the contrast between the mice and 

 earth was greater than that between the mice and the corn leaves. 

 After four minutes, one hawk flew directly from the perch to the earth 

 background and took the mouse from it. 



Experiment 11. Figure 4- In this experiment the same prey was 

 employed as in the last experiment. The prey was placed venter 



