548 MR. HUDSON ON THE BIRDS OF BUENOS AYRES. [June 23, 
(No. VI.) 
“ Buenos Ayres, April 11, 1870. 
“My pear Sir,—The Blackbirds, Pajaro negro (Molothrus 
bonariensis), with characteristic irregularity, often leaving us at the 
end of March, apparently for good, have again appeared this year in 
great numbers. When summer is over these birds congregate in vast 
flocks, and are then seen for many days flying north ; but it is not pro- 
bable that they migrate to any very great distance. They pass with 
a rapid, low, undulating flight, one flock behind the other, their 
wings producing a soft and agreeable sound. ‘The Blackbirds feed 
on the ground, following the plough in spring to pick up the worms, 
and are fond of keeping round cattle in the pasture, frequently 
alighting on their backs. The song of the male is, when wooing, 
accompanied by strange gestures and actions. Swelling and ruffling 
his feathers like a turkey-cock, and frequently suddenly taking wing 
and flying directly away from the female, and performing a wide 
circuit round her in the air, he sings all the time. The song begins 
with remarkable hollow, internal notes, ending with others loud and 
clear. The female is homely in appearance in her dull mouse- 
coloured suit, and has no song but a low chattering, not often ut- 
tered, and always appears very indifferent to the advances of her 
beautiful glossy partner. In the evening, when they settle on the 
trees to roost, they sing until itis quite dark. From their great num- 
bers, their singing at such times often sounds like the rushing of a 
strong wind among the trees. When disturbed on their roost at 
night the males repeat their song as they take wing; they also settle 
on the trees on rainy days to sing, continuing their concert for hours. 
One of our marsh-Blackbirds, the Chrysomus frontalis, possesses 
this habit of singing while it is raining; its song begins with a low 
mourning note, to which succeeds a long, soft, plaintive whistle; this 
is followed by others, short and in rapid succession as they rise, 
growing longer as they sink again, until they die away. This song 
heard in wet and gloomy weather has an indescribably sweet and 
melancholy effect. But to return to the common Blackbird; the 
most remarkable thing about this bird is its manner of reproduction ; 
and this would be a very interesting subject of study to the philo- 
sophie naturalist. It is well known that, like the European Cuckoo, 
it deposits its eggs in the nests of other birds. But the Cuckoo lays but 
one egg ina nest, and its peculiar habit possesses one thing in common 
with the instincts of other animals; it is regular and definite, ensures 
the safety of the young, and, for all that has yet been established to 
the contrary, is unchangeable as are the laws of matter and force. 
The instinct of the Blackbird is, on the contrary, unsettled and inde- 
finite and truly a ‘monstrosity.’ It is as if the true instinct had 
been partially eradicated or disfigured, so that its traces appear in 
various modes and degrees of intensity in different individuals—strong 
enough, though deformed, in some to secure the safety of the young, 
in others so dim and uncertain as to make reproduction impossible. 
Had Darwin been well acquainted with the habits of this bird he 
