°i8^6 in J Chadbourne on Individual Dichromatism. ?2I 



EVIDENCE SUGGESTIVE OF THE OCCURRENCE OF 



'INDIVIDUAL DICHROMATISM' IN 



MEGA SCO PS AS/O. 



BY ARTHUR P. CHADBOURNE, M. D. 1 



The common Screech Owl and some of its varieties are typical 

 examples of dichromatism, which may be defined as the occurrence 

 of two distinct phases of color in different individuals of the same 

 species, entirely independent of age, sex, or season. It is evident 

 that "the occurrence of two distinct phases of color " in the same 

 individual, if " independent of age, sex, or season," must consti- 

 tute an individual, as distinct from the specific form of dichroma- 

 tism. The following account of a pair of Screech Owls shows 

 that ' individual dichromatism ' probably occurs in this species, 

 though it is doubtless infrequent, and possibly found only under 

 artificial or even diseased conditions. 



Two Screech Owls (Megascops asio), said to have been taken 

 from the same brood late in the spring of 1894, were sent to me 

 about Nov. 1, 1894. Both birds were in typical gray plumage, 

 but a minute examination of the feathers was not made at the 

 time, as the possibility of a change in phase had not been thought 

 of, though, as an intermediate between the red and the gray 

 plumage was wanted, it is safe to say that any reddish tint would 

 have been noticed if present. The two Owls were in full 

 autumn dress except for a few downy feathers near the so-called 

 ears. 



The Owls were put in a large box cage, with the front of wire 

 netting ; and a hole at one side opened into a second box, thus 

 making a dark retiring place, that was never used. Six times 

 each week they were given all the raw beef or sheep's liver that 

 they wanted ; but the seventh day they fasted. Fresh water for 

 drinking and bathing, and also gravel were put in the cage daily ; 

 while in addition dead guinea pigs, and occasionally live mice, 

 were to be had in the ' animal room ' at the Medical School, where 



1 Read at the meeting of the Nuttall Ornithological Club, March 4, 1S95. 



