72 BULLETIN 621, tJ. S. DEPARTMENT OF AGRICULTURE. 



The attacking and driving away of crows by smaller species is a 

 matter of common knowledge. This is especially true of the king- 

 bird, which appears to maintain a sworn vengeance against its much 

 larger relative. Its antipathy is most marked during the nesting 

 season, when a pair or two of kingbirds are frequently an effective 

 means of protecting poultry and crops in the immediate vicinity of 

 their nests. In this connection, Maj. Allan Brooks, of Okanogan 

 Landing, B. C, remarks, in a letter to the Biological Survey, that 

 " the crows are generally kept away from the immediate neighbor- 

 hood of houses and poultry yards by the number of kingbirds (two 

 species) present." Though other small birds vigorously attack crows 

 when the young or eggs are in jeopardy, none appears to possess to 

 the same marked degree the unceasing animosity of the kingbird. 



Probably the most important natural agency in the reduction of 

 the number of crows is a disease popularly referred to as " roup." 

 Though no exhaustive study of this malady has been made, a few 

 points regarding its nature have been established. Technically it 

 may be termed an ulcerative keratitis, in which there also appears an 

 inflammation of the mucous membranes, accompanied by exuda- 

 tions from the eyes and nostrils. In severe cases the secretion about 

 the eyes covers the cornea and blindness follows. Experiment has 

 proved that the disease is contagious among crows, and also that it 

 is specifically different from the roup of poultry. 1 



Heavy inroads have at times been made by this malady on the 

 numbers of crows at their winter roosts. Becoming partially or 

 totally blind in the advanced stages of the disease, the disabled birds 

 suffer from lack of food and soon succumb under the combined at- 

 tacks of disease, hunger, and cold, or fall easy prey to the preda- 

 tory mammals and birds which take advantage of their helplessness. 

 In one instance the writer witnessed a barred owl, closely pursued 

 by a large flock of frenzied crows, making away with a sick indi- 

 vidual too weak to resist. 



Prof. E. H. Eaton, describing an outbreak of this kind, states : 2 



About the middle of December, 1901, a malady broke out among the crows 

 (Cortnis americanus) of Ontario County, N. Y., which, ere spring, had deci- 

 mated the ranks of the local " roost." As soon as winter had fairly begun 

 reports commenced to come in of crows which had been " blinded by freezing 

 of their eyes," as the farmers expressed it. * * *. 



All the sick birds were suffering from an acute inflammation of the pharynx 

 and the anterior portion of the head, including the nostrils and eyes. Often 

 there was a mucous discharge from the nostrils. The eyes were usually blinded 

 by a membrane forming over the exterior of the cornea. Sometimes only one 

 eye was seriously affected, and this was usually the left one, as far as I 

 noticed. If this membrane was rubbed off the eye looked quite clear again 



1 Information supplied by the Bureau of Animal Industry. 



2 The Auk, XX, pp. 57-58, 1903. 



