THE COWBIED. 439 



Mr. Cowbird emerged from his prison walls, large and vigorous. A day later a 

 little sparrow came forth from his delicate shell, but much smaller, and exhibiting 

 less strength than his foster brother. The other egg failed to hatch. 



"The daily increase in size of the Cowbird was something immense, while 

 his younger companion seemed to diminish rather than enlarge, until finally, at 

 the end of three days, he died, evidently for want of food, as the Cowbird, being 

 larger, greedily devoured everything that came in contact with his capacious 

 mouth. The untimely end of the rightful heir was but gain to this usurper, as 

 he now received the whole attention of the parent birds. Nature having now, 

 at the early age of seven days, provided him with a respectable dress, he was 

 no longer contented to remain within the soaall compass of the nest, and he took 

 to the branches of the tree in which the nest had been placed. But soon this 

 area became too limited for his ambitious spirit, for at the end of his second 

 week he was flitting from bush to bush, exploring the fields and hedges, his 

 foster parents providing for him all the while. Two weeks more and he was a 

 full-fledged bird. About July 20 I saw him for the last time."^ 



Such seems to be the fate of nearly all the young which have the misfor- 

 tune to be hatched with a Cowbird for a companion. I have yet to see a nest 

 containing young birds of both species more than a few days old; by that time 

 the rightful offspring are either smothered or crowded out of the nest by their 

 stronger foster brother, or they are starved, and he then absorbs the entire atten- 

 tion of the parents. Only in cases where the true offspring is as large or larger 

 than the imposter is there any likelihood of exception to this rule. It can readily 

 be seen what an immense amount of harm a Cowbird causes in the economy of 

 nature, granting that only a single one of its eggs is hatched in a season. A 

 brood of insectivorous and useful birds is almost invariably sacrificed for every 

 Cowbird raised, and they are certainly not diminishing in numbers. 



While a few of the selected foster parents resent the addition of a parasitic 

 egg in their nest, either by abandoning it entirely or by building a new one over 

 it, and occasionally even a third one, the majority do not appear to be much 

 disturbed by such an event, and after a short time go on as if nothing had 

 happened. A few species, like the Indigo Bunting for instance, will sometimes 

 abandon their own eggs should the stranger egg be removed, but apparently do 

 not mind the loss of one or two of their own, and continue incubating just the 

 same. 



.Almost invariably the nest in which one or more of these parasitic eggs 

 have been deposited contains an incomplete set of the eggs of its rightful owners. 

 Where the Cowbird drops an egg in the nest of a species considerably smaller 

 than itself, as the Glnatcatcher, etc., its much larger size seems to be a positive 

 advantage to the more rapid development of the embryo, as the egg must 

 necessarily receive more animal heat than the smaller ones, which can scarcely 

 come much in contact with the body of the. sitting bird, and the development of 

 the embryos in these must be more or less retarded thereby. 



'The Oologist, Vol. X, Aug., 1893, pp. 230, 231. 



