EASTERN BROWN-HEADED COWBIRD 423 



One of the possibilities is that parasitism may have arisen from the occasional 

 laying of eggs in strange nests by birds that are very sensitive to the ovarian 

 stimulus provided by the sight of a nest with eggs resembling their own. This 

 is substantiated by experimental evidence collected by Craig who found that in 

 doves ovulation could be induced by comparable stimuli. 



Otto Widmann (1907) offered the following interesting theory to 

 account for the origin of the parasitic habit: 



We know that fossil remains of horses, not much unlike ours, are found abun- 

 dantly in the deposits of the most recent geological age in many parts of America 

 from Alaska to Patagonia. 



It was probably at that period that the Cowbird acquired the habit of accom- 

 panying the grazing herds, which were wandering continually in search of good 

 pasture, water and shelter, in their seasonal migrations and movements to escape 

 their enemies. As the pastoral habit of the bird became stronger, it gave rise 

 to the parasitic habit, simply because, in following the roving animals, the bird 

 often strayed from home too far to reach its nest in time for the deposition of 

 the egg, and, being hard pressed, had to look about for another bird's nest where-in 

 to lay the egg. * * * By a combination of favorable circumstances this new 

 way of reproduction proved successful, and the parasitic offspring became more 

 and more numerous. In" the 'course of time the art of building nests was lost, 

 the desire to incubate entirely gone, paternal and conjugal affection deadened, 

 and parasitism had become a fixed habit. 



Dr. Friedmann (1929) disposes of this theory as "more interesting 

 than suggestive," and adds: "It is somewhat surprising to find a 

 naturalist of Mr. Widmann's ability advancing such a theory. Prob- 

 ably he meant it more as a suggestion to be taken for whatever it 

 might be worth than as a real attempt at an explanation." The 

 trouble with the theory is that we have no known facts on which to 

 base it, there being no record of a cowbird leaving its nest to follow 

 cattle, horses, or bison. Probably the parasitic habit was developed 

 before the cowbirds invaded North America. And we do not know 

 to what extent the primitive cowbirds, in South America, had de- 

 veloped the habit of following the wandering herds. 



Dr. Coues (1874) makes'the following suggestion: 



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

 delivery without a nest prepared, was loth to lose her offspring, and deposited 

 her burthen in an alien nest, perhaps of her own species, rather than on the 

 ground. The convenience of this process may have struck her, and induced 

 her to repeat the easy experiment. The foundlings duly hatched, throve, and 

 came to maturity, stamped with their mother's individual traits — an impress 

 deep and lasting enough to similarly affect them in turn. The adventitious 

 birds increased by natural multiplication, till they outnumbered the true-born 

 ones; what was engendered 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. 



The weakness in this theory is that such cases of adventitious laying 

 in alien nests must have been very rare at first, and the inherited 



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