35 LIFE-HISTORIES OF BIRDS 



eggs are subjected. Now the egg of the Cow- 

 bird being perceptibly larger than the 'others, 

 would receive more heat from the body of the 

 foster-mother than the latter's own, for the obvious 

 reason that it would be in closer proximity to the 

 source of heat. This in our judgment will satis- 

 factorily explain its much shorter period of incuba- 

 tion. Were the eggs hatched by their rightful 

 mother, it is probable that the period would vary 

 but a trifle, if any, from that of the rusty blackbird. 

 Like the Cuckoos of Europe, this species never 

 builds a nest, and never hatches or attempts to 

 rear her own offspring; but, as before remarked, 

 practises imposition upon other species, which, 

 either unconscious of the fraud, or unable to rid 

 themselves of the foreigner, are constrained to 

 hatch the alien at the peril of their own offspring. 

 The egg of the Cowbird hatching sooner, the 

 stronger has increased somewhat in size, when 

 the others are hatched, and having an insatiable 

 appetite, and continually clamoring for food, it 

 grows at the expense of its foster-companions 

 which either stifle or die from starvation, and are 

 carried away by their parents \ to some distance 

 from the nestT It is well-known that some species 

 are not slow in detecting the intrusion, which, 

 when they have done so, they do not hesitate to 

 get rid of immediately. Mr. J. A. Allen, says Dr. 

 Brewer, saw a female Hyporhynchus rufus feeding 

 a Cowbird in Western Iowa, which had nearly at- 

 tained maturity. This is the only recorded proof 



