food, usually peculiar to the East; lemmings, by the snow-owl; and in former wars of great severity, the armies by wolves, hawks, and ravens; and I have been told by eye-witnesses that the relics of the Grand Army were pursued in their disastrous retreat from Russia by thousands of ravens. Many birds owe their specific diffusion to their eeking out men, the products of their civilization, or their domestic animals, to live upon them; and many formerly strange species no doubt find their way into new countries after the introduction of grain and fruit-raising.
The relation of subsistence to the propagation of birds is of the highest importance; upon it largely depend the time of breeding and the number of the eggs and of the brood. We are accustomed, without sufficient grounds, to assign the reason of our putting fowls to sit in the spring, as well as the migrations of birds, directly to climatic influences. "We speak of the awakening of Nature, and it seems self-evident to us that the bird's nest with its tender chicks is a necessary part of it. Yet the time of year has hardly anything to do immediately with the propagation of birds, which is rather determined by the presence of a sufficiency of proper food.
In warm countries, such as Egypt, Ceylon, or Brazil, birds hardly observe a fixed period in their nesting, but each pair sets about the business whenever it finds itself in the most favorable conditions of subsistence, so that we can find nests and eggs of the same species in every month. The Falco eleonoræ of Southern Greece breeds at the unusual season (for a bird of prey) of August, and has its young in September. Quails are plentiful in the country at that season, having come down fat from the north, and in their multitude and helplessness fall a ready prey to the young falcons, and a much richer support than the birds can find in the spring, when, according to Erhardt's observations, no quails are ever taken in Greece. The Bombicilia Carolinensis of North America breeds as far north as 40° in June; it feeds its young on berries and cherries. The cross-bill never asks about the season or the temperature. It fixes its household indifferently in winter amid ice and snow, and in the height of summer, provided only sufficient nourishment for its children is present. The barn-owl likewise breeds irregularly. Its eggs and young have been found in October and November, but always in those years and places in which field-mice are unusually prevalent.
These few examples may suffice to show how, with birds, nearly everything turns upon subsistence; how the fact holds good not only for individuals and species, but that it is a matter of fundamental importance in their structure, their spread, and their habits, and how we may, with perfect right, apply to birds the maxim, "Tell me what you eat, and I will tell you who you are."—Translated for the Popular Science Monthly from "Unsere Zeit."
