EXPERIMENTS ON PROTECTIVE COLORATION 473 



one of the two birds, which flew part way across the cage alighting a 

 trifle nearer the earth than the ash background and remained there 

 for another half hour. At the end of this time, one of the birds (which 

 is uncertain, as I was not looking at the moment) took the mouse from 

 the earth and almost immediately afterwards the mouse on the ash 

 background was taken (probably by the same hawk). 



Experiment 2. Figure 3. In this experiment two Mus were em- 

 ployed, one being placed on moist earth mixed with dead leaves and the 

 other on ashes. Viewed from a point approximately one meter beyond 

 the hawks' perch, the former mouse was invisible to me in the growing 

 dusk, while the latter was plainly seen. In about two minutes, one 

 hawk left its perch, flew directly to the ground about 0.3 m. distant 

 from the mice, paused for a second and then took the mouse from the 

 ashes. 



Experiment 3. This was a repetition of Experiment 2, except that 

 the position of the backgrounds was reversed. In about ten minutes 

 a hawk flew directly from its perch to the ash background and took 

 the mouse from it. 



Experiment 4- Figures 4 (md 8. Two Mus were placed (venter 

 uppermost), one on ashes and one on moist earth. In this experiment 

 the greater contrast was presented by the latter combination, but the 

 resemblance between the mouse and the ashes was not very close, as 

 I observed it from the opposite end of the cage. Furthermore, in the 

 dusk (6.12 p.m., Sept. 27) objects on ashes are much more conspicuous 

 than those on earth. In one minute a hawk dropped to the ground 

 near its perch, paused for a few moments, and then ran to seize the 

 mouse on the ashes. 



Experiment 5. Figures 3 and 15. One Mus was placed on light 

 clay and one on dark earth covered with scattered bits of dead leaves. 

 For thirty-eight minutes the mice were not disturbed. During this 

 time one of the hawks three times left its perch, flew part way across 

 the cage and returned to its perch, while the other one left its perch, 

 flew over the backgrounds and returned. Then the latter left its perch 

 a second time, dropped to the ground and ran almost directly to the 

 clay background from which it took the mouse. The contrast in this 

 experiment was greater between the mouse and the clay than between 

 the mouse and the earth. 



Experiment 6. Figure I4. Two Mus were placed venter upper- 

 most, one on light clay and one on dark earth. Both were partly 

 embedded in the l^ackground so as to bring the ventral surface flush, 

 with it, thus eliminating shadow effects and the contrast between the 

 darker sides of the mouse and the light clay. For one hour and twenty- 

 two minutes the mice were apparently unnoticed by the birds, although 

 during this time both birds left their perches and flew to the ground, 

 and one of them flew over the backgrounds and alighted near them. 

 At the end of this time the other flew over the mice and lit close to them, 

 taking the mouse from the clay. In this experiment the mouse-earth 

 was the combination showing greater contrast. 



THE JOURNAL OF EXPERIMENTAL ZOOLOGV, VOL. 20, NO. 4 



