THE COWBIRDS 607 



as to drop an egg with others that have already been sat on, unless 

 incubation be very far advanced, it still has a chance of being hatched 

 before or contemporaneously with the others; but even if the others 

 hatch first, the extreme hardiness of the embryo serves to keep it alive 

 with the modicum of heat it receives. 



4. Whenever the Molothrus is hatched together with the young of 

 its foster parents, if these are smaller than the xJarasite, as usually is 

 the case, soon after exclusion from the shell they disappear, and the 

 young Cowbird remains sole occupant of the nest. How it succeeds in 

 expelling or destroying them, if it indeed does destroy them, I have not 

 been able to learn. 



5. To all these circumstances favorable to the Molothrus may be added 

 another of equal or even greater importance. It is never engaged with 

 the dilatory and exhaustive process of rearing its own young, an.d for 

 this reason continues in better condition than other species; and, more- 

 over, l^eing gregarious and practising promiscuously sexual intercourse, 

 must lay a much greater number of eggs than other species. In our 

 domestic fowls we see that hens that never become broody lay a great 

 deal more than others. Some of our small birds rear two, others only 

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

 taking up much time, so that they areusually from two to three months 

 and a half employed. But the Cowbird is like the fowl that never incu- 

 bates, 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 4, 16 eggs. I^o doubt the Cowbird lays a 

 much larger number than that; my belief is that every female lays from 

 60 to 100 eggs every season, though I have nothing but the extraordi- 

 nary nuTuber 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 attenti(m should be given to another circumstance, viz, the new 

 conditions introduced by land cultivation and their effect on the spe- 

 cies. The altered conditions have in various ways served to remove 

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

 birds inu]ti]tly the more irregular and disordered does the instinct 

 necessarily become. In wild districts where it was formed, and where 

 birds building accessible nests are proportionately fewer, the instinct 

 seems different from what it 1i"oes in cultivated districts. Parasitical 

 eggs are not common in the desert, and even the most exposed nests 

 there are probably 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, opeu-foliaged trees 

 planted by man. 



