XXIII ANIMAL MIGRATIONS 379 
the grey of the evening and morning, is one of the 
first things that strikes the attention of the voyager 
on the Amazon. 
The periodical appearance of certain birds in a 
district has been supposed by the inhabitants to 
have some mysterious connection with the Christian 
festivals. Thus there are two beautiful little birds 
in Maynas, apparently belonging to different genera, 
for one of them is a Seven -coloured Tanager 
(Pajaro de siete colores), and the other (which I 
have not seen) is said to be of a bright blue colour 
and differently shaped ; but both are called by the 
Indians Huata-pisco (Bird of the Year), because 
they make their appearance together, in large 
flocks, about the end of the year (people will tell 
you, precisely on Christmas Day), and remain 
throughout January, when they are seen no more 
until the same epoch comes round again. Mr. 
Bates has given a capital account of the movements 
of these hunting-parties of frugivorous and insec- 
tivorous birds, and of the superstition of the Papa- 
uira or Patriarch Bird, who is supposed to head 
them (vol. ii. p. 333 et seq.). I suspect that this is 
something more than mere superstition, and that 
the Patriarch leaders are not one but several to 
each predatory band. 
Distribution of Pishes 
The abundance of fish in rivers of white water, 
and their scarcity in black-water rivers, may easily 
be shown to depend chiefly on the luxuriant littoral 
vegetation of the former and its scarcity or utter 
absence in the latter ; for on the Rio Negro there 
