78 ICTERIDjE. 



only one brood in the season building, incubation, and tending the 

 young takyig up much time, so that they are usually from two to 

 three months and a half employed. But the Cow-bird is like the fowl 

 that never incubates, and continues dropping eggs during four months 

 and a half. From the beginning of September until the end of January 

 the males are seen incessantly wooing the females, and during most of 

 this time eggs are found. I find that small birds will, if deprived 

 repeatedly of their nests, lay and even hatch four times in the season, 

 thus laying, if the full complement be four, sixteen eggs. No doubt 

 the Cow-bird lays a much larger number than that ; my belief is that 

 every female lays from sixty to a hundred eggs every season, though I 

 have nothing but the extraordinary number of wasted eggs one finds to 

 judge from. 



Before dismissing the subject of the advantages the Molothrus pos- 

 sesses over its dupes, and of the real or apparent defects of its instinct, 

 some attention should be given to another circumstance, viz., the new 

 conditions introduced by land-cultivation and their effect on the species. 

 The altered conditions have, in various ways, served to remove many 

 extraneous checks on the parasitical instinct, and the more the birds 

 multiply, the more irregular and disordered does the instinct necessarily 

 become. In wild districts where it was formed, and where birds build- 

 ing accessible nests are proportionately fewer, the instinct seems different 

 from what it does in cultivated districts. Parasitical eggs are not 

 common in the desert, and even the most exposed nests there are pro- 

 bably never overburdened with them. But in cultivated places, where 

 their food abounds, the birds congregate in the orchards and plantations 

 in great numbers, and avail themselves of all the nests, ill- concealed as 

 they must always be in the clean, open-foliaged trees planted by man. 



Diversity in Colour of Eggs. 



There is an extraordinary diversity in the colour, form, and disposi- 

 tion of markings &c. of the eggs of M. bonariensis ; and I doubt 

 whether any other species exists laying eggs so varied. About half the 

 eggs one finds, or nearly half, are pure unspotted white, like the eggs 

 of birds that breed in dark holes. Others are sparsely sprinkled with 

 such exceedingly minute specks of pale pink or grey, as to appear quite 

 spotless until closely examined. After the pure white, the most common 

 variety is an egg with a white ground, densely and uniformly spotted 

 or blotched with red. Another not uncommon variety has a very pale, 

 flesh-coloured ground, uniformly marked with fine characters, that look 

 as if inscribed on the shell with a pen. A much rarer variety has a 

 pure white shell with a few large or variously sized chocolate spots. 



