152 Trans. Acad. Sci. of St. Louis. 



females have arrived in force by the middle of April the species 

 becomes for nearly two months one of the most conspicuous, 

 especially in the morning hours, when its call note is in the air 

 everywhere, its song is coming from the treetops, and restless 

 troops of excited males and females follow or chase each 

 other, the males usually in the majority. The Cowbird is one 

 of the most social birds and even during the period of mating 

 and oviposition troops of from 20 to 30 are seen in the evening 

 going to the common roost in the river bottom. These troops 

 are joined by the young ones as soon as they can dispense with 

 the care of their foster-parents. Together they visit pastures 

 and stubble fields, roaming more and more as the season advances, 

 until, in September, migration begins and many of their summer 

 haunts are deserted. The willow thickets covering the shores 

 and islands of the Mississippi and Missouri Rivers offer safe 

 retreats to migrants of all kinds and thither large flocks of 

 wandering Cowbirds repair in the evening to spend the night in 

 company with Grackles, Martins and others. In October they 

 join the different kinds of blackbirds in the marshes, where the 

 thickly tangled weeds and grasses offer warmer quarters than 

 the willows along the rivers. Not many Cowbirds are with us 

 after the first of November, but as in early spring, a few stay with 

 the Redwings until real winter drives them farther south. Much 

 has been written about the damage done by the Cowbird's 

 parasitic habit, but no hypothesis has ever been offered as to the 

 origin of this peculiar habit. Ten years ago the author published 

 the following conjecture in ''Science," new series, vol. 5, no. 

 109, on the " Origin of Parasitism in the Cowbird." "Repro- 

 ductive parasitism, as we find it in the Cowbird, is such a rare 

 exception to the rule among higher animals, where parental 

 affection is highly developed, that it never ceases to be an object 

 of speculation as to its origin. There are two peculiarities 

 for which our Cowbird is renowned: the one which gives him 

 his scientific name Molothrus, a parasite; the other which causes 

 him to be called Cowbird, his strong attachment to grazing 

 animals especially horses and cattle. Now, should there not be 

 a connection between these two traits? Nobody would think 

 that the habit of following horses and cattle has been formed 

 since the introduction of these animals by the white man. 

 Its Indian name Buffalo-bird was certainly no misnomer and it 

 can hardly be questioned that for ages the buffalo, or American 

 bison, was the animal which, in the economy of our Cowbird, 



