BIRDS OF 



resorted to which shows a higher degree of intelhgence than 

 what we are accustomed to call ordinarj' instinct. Finding that 

 their newly finished cradle has been invaded, the birds build a 

 floor over the obnoxious egg, leaving it to rot while their own 

 are hatched on the new floor in the usual way. 



Should the owners of the nest have one or more eggs 

 deposited before that of the Cowbird appears, the intrusion 

 causes them much anxiety for an hour or two, but in the 

 majority of cases the situation is accepted, and the young Cow- 

 bird bemg first hatched the others do not come to maturity. 

 The foster parents are most attentive in supplying the wants of 

 the youngster till he is fit to shift for liimself, w-hen he leaves 

 them, apparently without thanks, and seeks the society of his own 

 kindred, though how he recognizes them as such is something w'e 

 have yet to learn. 



Much speculation is indulged in regarding tlie cause of this 

 apparent irregularity in the habits of the Cowbird, and different 

 opinions are still held regarding it, but whatever other purpose 

 it may serve in the economy of nature, it must cause a very 

 large reduction in the number of the different species of birds 

 on which it entails the care of its young. Some idea ma}' be 

 formed of the extent of this reduction by looking at the vast 

 flocks of Cowbirds swarming ui their favorite haunts in the fall, 

 and considering that fou each bird in these flocks from three to 

 four of a different species have been prevented from coming to 

 maturity. 



The number of species imposed upon by the Cowbird is 

 large, including Warblers, Vireos, Sparrows, Thrushes, Blue- 

 birds, etc., but the one they most frequently select in this locality 

 is the Summer Yellowbird. On the prairies where the Cow- 

 birds are numerous and the number of foster parents limited, 

 it is said that in the month of June nearly every available nest 

 contains an egg of the Cowbird. 



In Southern Ontario they disappear during July and August, 

 but usually return in vast flocks in September, when they 

 frequent the stubble fields and patches of wild rice by the edge 

 of the marshes. 



194 



