182 MOLOTHRUS PECORIS, COW-BIRD. 



only Avould the connection between the habits of the Cow-bird and 

 Cnckoo be plain, bnt we should discern how such peculiar modifi- 

 cations of its instinct were effected. The production of the traits in 

 question is a theme fruitful of speculation, if not of solid information. 

 Ages ago, it might be surmised, a female Cow-bird, in imminent danger 

 of delivery without a nest ])repared, was loth to lose her olispriug, and 

 deposited her burthen in an alien nest, perhai)S of her own species, 

 rather than on the ground. The convenience of tliis process may have 

 struck her, and induced her to repeat the easy experiment. The found- 

 lings duly hatched, throve, and came to maturity, stamped with their 

 mother's individual traits — an impress deep and lasting enough to simi- 

 larly affect them in turn. The adventitious birds increased by natural 

 nuiltiplication, till they outnumbered the true-born ones ; what was en- 

 gendered of necessity was perpetuated by unconscious volition, and 

 finally became a fixed habit — the law of reproduction for the species. 

 Much current reasoning on similar subjects is no better nor worse than 

 this, and it all goes for what it is worth. 



There are several species of the genus Molothrits in the warmer parts 

 of America; their habits, so far as we know, are like those of our repre- 

 sentative. The position of the genus is a little uncertain ; it has strong 

 affinity with the Blackbirds {Icteridw), yet it is difficult to see in what 

 respects it differs from certain Iringilline birds. But in any event, there 

 is nothing whatever in the structure of the birds to give a hint of their 

 peculiar habits. Attending the central fact of reproductive parasitism 

 are numerous circunhstances worthy of attention, since they all tend to 

 insure the perpetuation of these species under anomalous conditions, 

 and react against the multiplication of the various birds which are 

 selected as foster-parents. It is mysterious, indeed ; the inHiction is 

 certainly an unmitigated evil to the birds who are drawn into the cou=- 

 nection, and yet we cannot rationally conceive of the existence of such 

 thing, except as a means of some greater good. Can it not be possible 

 that this special check upon the increase of certain kinds of birds pre- 

 serves the delicate balance of some of Nature's forces f 



I do not feel at all sure that the small relative size of the Cow-bird's 

 egg should be accounted a circumstance favorable to the bird, as some 

 have believed, reasoning that a larger egg could not be adequately in- 

 cubated by the small species usually selected as nurses. No a, 2yriori 

 reason ai)pears why the Qgg should not have been of ordinary dimen- 

 sions, and a different series of birds been called upon to incubate it 5 

 while, as the facts stand, it is clear that the bigness of the egg, in com- 

 parison with those among ^hich it is usuall}' deposited, and not its 

 smallness relative to the Cow- bird's bulk, is the favoring element. For 

 the larger egg must mechanically obstruct the incubation of the smaller 

 ones, and so receive the greater share of warmth from the bud's body. 

 But perhaps both the circumstances may be brought into reasonable 

 connection. Were the Cow-bird's egg of ordinary dimensions relative 

 to the bulk of the species, it might be susceptible of successful incuba- 

 tion only by other birds large enough to remove or destroy it, as would 

 certainly be done when practicable ; it is therefore unusually small, in 

 order that it may be committed to the charge of birds able to hatch it, 

 yet too weak to eject it ; and now its superiority in size to the eggs of 

 such birds becomes a favorable circumstance. 



It is stated that the Cow-bird's egg hatches sooner than that of most 

 birds, the period of incubation being not over ten days. But I am not 

 aware that the evidence in this case is either sufficient, explicit, or pre- 

 cise ; it would be well to have it checked by many additional observa- 



