Travels on the Amazon

by Alfred Russel Wallace

The species of Pithecia, No. 14 of my list, is found on the west side of the Rio Negro for several hundred miles, from its mouth up to the river Curicuriarí, but never on the east side, neither is it known on the south side of the Upper Amazon, where it is replaced by an allied species, the P. irrorata (P. hirsuta, Spix), which, though abundant there, is never found on the north bank. These facts are, I think, sufficient to prove that these rivers do accurately limit the range of some species, and in the cases just mentioned, the evidence is the more satisfactory, because monkeys are animals so well known to the native hunters, they are so much sought after for food, and all their haunts are so thoroughly searched, and the localities for the separate kinds are so often the subject of communication from one hunter to another, that it is quite impossible that any well-known species can exist in a particular district, unknown to men whose lives are occupied in forming an acquaintance with the various tenants of the forests.

On the south side of the Lower Amazon, in the neighbourhood of Pará are found two monkeys, Mycetes beelzebub and Jacchus tamarin, which do not pass the river to the north. I have never heard of monkeys swimming over any river, so that this kind of boundary might be expected to be more definite in their case than in that of other quadrupeds, most of which readily take to the water.

Towards their sources, rivers do not form a boundary between distinct species; but those found there, though ranging on both sides of the stream, do not often extend down to the mouth.

Thus on the Upper Rio Negro and its branches are found the Callithrix torquatus, Nyctipithecus trivirgatus, and Jacchus (No. 21), none of which inhabit the Lower Rio Negro or Amazon; they are probably confined to the granitic districts which extend from Guiana across the sources of the Rio Negro towards the Andes.

Among birds it cannot be expected that we should find many proofs of rivers limiting their range; but there is one very remarkable instance of a genus, the three known species of which are separated by rivers, namely, the three species of genus Psophia, P. crepitans (Linn.), P. viridis (Spix), and P. leucoptera (Spix). The P. crepitans is the common trumpeter of Guiana; it extends into the interior all over the country, beyond the sources of the Rio Negro and Orinooko, towards the Andes, and down to the Amazon, both east and west of the Rio Negro, but is never found on the south side of the Amazon.

The P. viridis is found in the forests of Pará, at Villa Nova, on the south bank of the Amazon, and up to the Madeira, where it is found at Borba, on the east bank.

The P. leucoptera, a most beautiful white-backed species, is found also on the south bank of the Amazon, at São Paulo, at Ega, at Coarí, and opposite the mouth of the Rio Negro, but not east of the Madeira, where the green-backed species commences. These birds are all great favourites in the houses of the Brazilians, and all three may sometimes be seen domesticated at Barra, where they are brought by the traders from the different districts in which they are found. They are inhabitants of the dense forests, and scarcely ever fly; so that we see the reason why the rivers should so sharply divide the species, which, spreading towards each other from different directions, might otherwise become intermingled. It is not improbable that, if the two Brazilian species extend as far as the sources of the Madeira, they may be found inhabiting the same district.

Of the smaller perching-birds and insects, which doubtless would have afforded many interesting facts corroborative of those already mentioned, I have nothing to say, as my extensive collection of specimens from the Rio Negro and Upper Amazon, all ticketed for my own use, have been lost; and of course in such a question as this, the exact determination of species is everything.

The two beautiful butterflies, Callithea sapphira and C. Leprieuri, which were originally found, the former in Brazil, and the latter in Guiana, have been taken by myself on the opposite banks of the Amazon, within a few miles of each other, but neither of them on both sides of that river.

Mr. Bates has since discovered another species, named after himself, on the south side of the Amazon; and a fourth, distinct from either of them, was found by me high up in one of the north-western tributaries of the Rio Negro, so that it seems probable that distinct species of this genus inhabit the opposite shores of the Amazon.