490 R. T. YOUNG 



Summary 



In this series the combination showing the greater contrast 

 was chosen in seven out of twelve cases or 58 per cent and the 

 one showing the less contrast in four or 42 per cent. It is note- 

 worthy that in this series, as well as in series II and III, the birds 

 usually approached their prey slowly, giving them opportunity 

 to carefully inspect the backgrounds at close range before mak- 

 ing their choice. 



Two experiments were also performed with the prairie chicken 

 (Tympanuchus americanus) and the grasshopper (Melanoplus), 

 one background of lime and one of earth and straw being em- 

 ployed (figs. 31 and 47). Results similar to those of the last 

 series were obtained, the bird in each case walking to the back- 

 grounds and taking the insects from that one which it first ap- 

 proached, in one case the lime, in the other the earth — straw 

 background. 



All of the experiments recorded above are open to the objec- 

 tion that they were performed with caged birds (most of them 

 young individuals) which as a result of confinement may not 

 have acquired the normal keenness of vision. So far as I am 

 aware, most of the experiments on protective coloration (in- 

 cluding mimicry, warning coloration, etc.) which have been 

 recorded thus far have been performed with caged animals, 

 but it is quite possible that confinement does in many instances 

 render less acute an animal's senses. While none of the birds 

 experimented with became very tame,^^ some of them, notably 

 the hawks, Buteo borealis krideri, behaved very differently from 

 wild birds. One of these, when removed from the cage, instead 

 of flying off, remained on the ground as long as observed, and 

 when I approached attempted to defend itself by fight, rather 

 than flight. While this condition militates against the value 

 of my experiments, I believe it is far offset in the other direction 



-" A short time after removal from the nest the martins (Progne subis) be- 

 came so tame that they would climb up my leg in order to obtain food, while 

 the young kingbirds occasionally fed from forceps held in my hand. As the 

 birds grew older they soon lost this tameness however, and would not permit 

 me to approach them closely when possible to avoid it. 



