We had expected to find a craft of some kind awaiting us so that we might immediately pursue our journey down the river, but in this we were disappointed, although, as it later developed, a boat was then on its way to us, sent by order of Colonel Rondon. There were only two small dugouts available, which were entirely inadequate for our purpose, so the men were put to work cutting down a tree of large size and hollowing out a canoe which would hold the party and the necessary luggage. This work we estimated would take some weeks, so in the meantime we busied ourselves exploring the country in the vicinity of Barão de Melgaço.
A short reconnoissance through the forest revealed a veritable zoological wonderland. I was consequently very glad that we were delayed, as this gave me an opportunity to study the fauna of a zoologically unknown region, and to work on some of the problems of nature with which we are constantly confronted, but of which so little is known. One of the facts that no field-naturalist can fail to have thrust upon his notice is the exact precision and nicety with which the balance in nature is preserved. Take the familiar example of the oyster. In its early stages of development it is subject to the raids of such a host of enemies and adverse conditions that out of a million eggs only a few bivalves reach maturity; to offset this wholesale destruction nature has provided that a single oyster may lay several millions of eggs, and thus the race is preserved. Birds, to a less extent, are subject to this same thoughtful provision; therefore we find that the species which are subject to many dangers during the nesting-period or which undertake long, perilous seasonal migrations, lay comparatively large sets of eggs; this is best evidenced by ducks and quail. Species which are subject to the natural dangers of migration only and are protected during the nesting-season, comparatively speaking, rear small broods of young; warblers, thrushes, and a number of our own native birds would come in this category; to further offset the loss, some of these latter may even rear two broods in a season. When we reach the tropics a marked change is noticeable; the extremes in climatic conditions are usually represented by the wet and dry seasons; there are few enemies and food is abundant, consequently the loss of life is comparatively small. If reproduction proceeded there at the same rate as in the northern lands, it must be obvious that the country would soon be overstocked; but again it has been decreed that the equity should be preserved, and the great majority of tropical birds nest but once a year, and then the full complement of eggs is but two. Of course there are a number of exceptions on each side, and on such matters it is difficult to generalize, but in the majority of cases this will be found to be true.