ARGENTINE COW-BIRD 73 
where they are feeding seems carpeted with black, 
and the trees when they alight appear to have a black 
foliage. At such times one wonders that many small 
species on which they are parasites do not become 
extinct by means of their pernicious habit. In 
Buenos Ayres, where they are most numerous, they 
have a migration, which is only partial however. It 
is noticeable chiefly in the autumn, and varies greatly 
in different years. In some seasons it is very marked, 
when for many days in February and March the 
birds are seen travelling northwards, flock succeeding 
flock all day long, passing by with a swift, low, un- 
dulating flight, their wings producing a soft musical 
sound; and this humming flight of the migrating 
Cow-birds is as familiar to everyone acquainted with 
nature in Buenos Ayres as the whistling of the wind 
or the distant lowing of cattle. 
The procreant instinct of this Molothrus has always 
seemed so important to me for many reasons that I 
have paid a great deal of attention to it; and the 
facts, or at all events the most salient of them, which 
I have collected during several years of observation, 
I propose to append here, classified under different 
headings so as to avoid confusion and to make it 
easy for other observers to see at a glance just how 
much I have learnt. 
Though I have been familiar with this species from 
childhood, when I used to hunt every day for their 
wasted eggs on the broad, clean walks of the planta- 
tion, and removed them in pity from the nests of 
little birds where I found them, I have never ceased 
