1912.] NATURAL SCIENCES OF PHILADELPHIA. 323 



species of bird tested with the same stage of the same species of 

 insect, in the two sets of experiments, is Leiothrix with larvse of 

 Pieris brassicce. The result in each case was acceptance. 



A. D. Bartlett recounts an experience in rearing young water 

 ouzels which well illustrates the fundamental difference between 

 experimental and natural conditions. He says: 71 



"They had been tried with the usual food for most insect-eating 

 birds, such as scraped beef and hard-boiled eggs, ant eggs, mealworms, 

 spiders, flies, beetles, aquatic snails, shrimps, salmon spawn, and 

 many other mixtures, but all failed, until my clerk and assistant, 

 Mr. Arthur Thomson, who had taken as much interest in rearing 

 these birds as myself, hit upon the idea of scalding the mealworms, 

 and tried it. It was soon apparent that in this condition the meal- 

 worms could be digested, while in a raw or living state they (espe- 

 cially their hard skins) would pass through the birds in a hard and 

 undigested condition. From this moment I had but little trouble. 

 The birds fed greedily upon the half-boiled mealworms, and I soon 

 found them ready to leave the nest." 



Thus these birds did not thrive upon a regimen that included 

 several elements of their natural food, but did well only when the 

 staple food was partially cooked. Mr. Bartlett adds : 



"In May, 1869, I obtained my first living water ouzel. Since 

 that time I have had a great many of these birds. Some of them 

 I reared from the nest, and I fed them upon boiled mealworms, the 

 larvse of the caddis fly and other insect food; but as soon as they 

 were able to feed themselves and took to the water, they caught and 

 fed upon very small fish, especially young minnows. I found them 

 rather expensive pets, having to provide for a family of four, as they 

 caught and devoured several dozen daily, and seemed to prefer live 

 fish to all other food." 



If experimental results could be taken as a guide to natural be- 

 havior, we should conclude from this testimony that water ouzels 

 feed largely on fish. It is worthy of note, therefore, that Newstead 72 

 found no fish in the stomachs he examined. 



In the account 73 of the experiments by Dr. G. Rorig, previously 

 referred to, it is stated that all of the following insects : 



71 Wild Animals in Captivity, 1899, pp. 308-310. 

 n Suppl. Joum. Bd. Agr. Lond., XV, No. 9, December, 1908, p. 25. 

 73 Arb. Biol. Abt. f. Land. u. Forstwirtschaft . K. Gcsandheitsamte, IV, 1903, 

 Heft 1, pp. 34-50. 



