10 BIRDS OF LA PLATA 
species, he certainly does mock the notes of indivi- 
duals of his own species; for it must be borne in 
mind that no two individuals sing quite alike, and 
that the same bird constantly introduces new notes 
into his song, and never repeats his notes in the same 
order. I have often observed that when a bird while 
singing emits a few of these new notes, he seems 
surprised and delighted with them; for, after a 
silent pause, he repeats them again and again a vast 
number of times, as if to impress them on his memory. 
When he once more resumes his varied singing, for 
hours and sometimes for days the expression he has 
discovered is still a favourite one, and recurs with 
the greatest frequency. But this is not all. If the 
new note or phrase happens to be a very striking 
one, it immediately takes the fancy of all the other 
birds within hearing, and often in a small thicket 
there will be a dozen or twenty birds near together, 
each sitting perched on the summit of his own bush. 
After the new wonderful note has been sounded 
they all become silent and attentive, reminding one 
in their manner of a caged Parrot listening to a sound 
it is trying to learn. Presently they learn it, and are 
as pleased with its acquisition as if they had dis- 
covered it themselves, repeating it incessantly. I 
noticed this curious habit of the bird many times, 
and on one occasion I found that for three entire 
days all the birds in a small thicket I used to visit 
every day did nothing but repeat incessantly two or 
three singular notes they had borrowed from one of 
their number. The constant repetition of this one 
