155 



1874.] MOLOTHRI OF BUENOS AYRRS. 



habits of the bird gives its own egg the best chance of being pre- 

 served ; for though the Molothrus never distinguishes its own e-s 

 of which indeed it destroys many, those with soft shells have°the 

 poorest chance of being preserved whenever several in the nest are 

 indiscriminately broken. 



2 The vitality or tenacity of life appears greater in the embryo 

 M. bonariensis than m other species ; this circumstance also, in 

 its relation to the egg-breaking habit and to the habit of laving many 

 eggs ma nest, gives it a further advantage. I have examined nests 

 ol the Sassor-tail containing a large number of eggs, after incu- 

 bation had began, and have been surprised at finding all the eggs 

 of the Scissor-tail addled, even when they were placed most advan- 

 tageously in the nest for receiving the heat of the sitting bird ; whilst 

 those ot the M. bonanensis contained living embryos, even when 

 under all the other eggs, and, as frequently happens, glued im- 

 movably to the nest by the matter of broken eggs spilt over them 

 before incubation had commenced. 



3. The comparatively short time the embryo takes to hatch gives 

 it another and a great advantage ; for, whereas the eggs of other 

 sniaU birds require to be sat on from fourteen to sixteen days, that 

 of Jf. bonanensis hatches m eleven days and a half from the moment 

 incubation commences; so that when the female M. bonariensis 

 makes so great a mistake as to lay an egg with others that have 

 already been sat on it incubation is not far advanced, her e<™ 



Irirh'ti \£ 1° bdn ^ } , latched before or contemporaneously 

 with the others ; but even if the others hatch before it, [he extreme 

 hardiness of the embryo serves to keep it alive with the modicum 

 ot heat which it still receives from the foster-bird 



4. Whenever the M. bonariensis is hatched together with the 

 young of its foster-parents, if these are smaller than the parasite 



K £ m °r ° aSeS they , T SmalIer >' S00n after exclusion from the 

 shell they disappear and the young M. bonariensis remains sole occu- 

 pant of the nest. How the latter succeeds in expelling or destroying 

 them, if he indeed does destroy them, I have not been able to learn 

 loall these circumstances favourable to the M. bonariensis may 

 be added another of equal or greater importance. The M. bonarien- 

 sis never being engaged with the dilatory and exhaustive process of 

 rearing its own young, and for this reason continuing in better con- 

 dition than other birds, and moreover being gregarious and practising 

 promiscuous sexual intercourse, must lay a vastly greater number of 

 eggs than other species. In our domestic fowls we see that hens 

 hat never become broody frequently lay many dozens of eggs more 

 in a season than others. Some of our small birds rear two! oth 

 but one brood in a season-building, incubation, and tending the 

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

 months and a half employed. But the M. bonariensis is like thefow! 



andaS in p^ an |. d C °^ inues dro PP in S eggs over four months 

 tip ™l beginning of September till the end of January 



the males are seen incessantly wooing the females ; and during molt 

 ot this time the eggs are found. I find that small birds wSf ifde! 



11* 



