108 
ZOOLOGY OF THE VOYAGE OF THE BEAGLE. 
with the usual black kind, there were generally a few dull brown coloured ones, 
(. Icterus sericeus of Liclit .) which 1 presume are the young. Azara states that 
the brown-coloured birds are smaller than the black glossy ones, and that they 
sometimes form one-tenth of the whole number in a flock. In the single specimen 
which I brought home, the size, with the exception of the length of the wing, is 
only a very little less. Sonnini, in his notes to Azara, considers the brown birds 
as the females ; I can, however, scarcely believe that so obvious a solution of the 
difficulty could have escaped so accurate an observer as Azara, These birds 
in La Plata often may be seen standing on the back of a cow or horse. While 
perched on a hedge, and pluming themselves in the sun, they sometimes attempt 
to sing or rather to hiss : the noise is very peculiar ; it resembles that of bubbles 
of air passing rapidly from a small orifice under water, so as to produce an acute 
sound. Azara states that this bird, like the cuckoo, deposits its eggs in other 
birds’ nests. I was several times told by the country people, that there was some 
bird which had this habit; and my assistant in collecting, who is a very accurate 
person, found in the nest of the Zonotrichia ruficollis (a bird which occupies in 
the ornithology of S. America the place of the common sparrow of Europe), 
one egg larger than the others, and of a different colour and shape. This 
egg is rather less than that of the missel-thrush, being -93 of an inch in 
length, and ’78 in breadth ; it is of a bulky form, thick in the middle. The 
ground colour is a pale pinkish-white, with irregular spots and blotches of a 
bright reddish-brown, and others less distinct of a greyish hue. This species is 
evidently a very close analogue of the M. pecoris of North America, from which, 
however it may at once be distinguished by the absence of the glossy brown on 
the head, neck, and upper breast, — by the metallic blueness of its plumage in 
the place of a green tinge, and by its somewhat greater size in all its proportions. 
The young or brown-coloured specimens of these Molothri resemble each other 
more closely ; that of the M. pecoris is of a lighter brown, especially under the 
throat, and the small feathers on its breast and abdomen have each an obscure 
dark central streak. The eggs of the Molothri, although having the same 
general character, differ considerably ; that of the M. pecoris being smaller 
and less swollen in the middle ; it is '85 of an inch in length, and *78 in breadth. 
Its colour cannot be better described than in the words of Dr. Richardson* — it is 
“ of a greenish white, with rather small crowded and confluent irregular spots of 
pale liver-brown, intermixed with others of subdued purplish grey.” From this 
* Fauna Borealis, Birds, p. 278. Dr. Richardson states that the egg is only seven lines and a half in length. 
I presume the measure of eight lines, instead of twelve to the inch, must in this case have been used. I am 
much indebted to the kindness of Mr. Yarrell for lending me an egg of the Molothrus pecoris, forming part of a 
collection of North American eggs in his possession. 
