“Whole families of birds devote themselves, as does the titmouse, to this patient quest for insect eggs in the crevices of tree-trunks or concealed in rolled-up leaves, for larvæ between the scales of buds and in worm-holes in wood, and for insects hidden in cracks and crannies. In this kind of hunt the bird does not have to chase its game and catch it by superior swiftness of flight; it must simply know how to find it in its lair. To this end it needs a keen eye and a slender beak; wings play but a secondary part. “But other species spend their energies in the free open-air chase: they pursue their game on the wing, hunting for gnats, moths, mosquitoes, and flying beetles. They must have a short beak, but one that opens wide and snaps up unerringly insects on the wing, despite the uncertainties of aërial flight; a beak in which the victim is caught and held without any retardation of the bird’s swift course; in short, a beak with a sticky lining which a tiny butterfly cannot so much as graze with its wing and not become entangled. Above all, an untiring and swift wing is necessary, one that does not flag in the pursuit of game desperately putting forth its utmost efforts to escape, and one that is not baffled by the tortuous course of a moth driven to bay. A beak inordinately cleft and wings of extraordinary power—such, in a word, should be the equipment of the bird whose hunting ground is the vast expanse of the open air. “These conditions are fulfilled in the highest degree in the swallow and the martin, both of which hunt flying insects, pursuing them this way and that, back and forth, ceaselessly and with a thousand subtle tricks. They catch them in their wide-open and viscous gullet, and continue their course without a moment’s pause. “The bird that lives on grain and seeds, the granivorous bird, as it is called, has a beak that is very wide at the base and adapted by its strength to the opening of the hardest seeds. In this class are the chaffinch, the greenfinch, the linnet, the goldfinch, and the swallow. The bird that lives on insects, or the insectivorous bird, has a beak that is fine and slender, in delicacy proportioned to the softness of its prey. To this number belong the nightingale, the warbler, the fallow-finch, and the wagtail. Agriculture has no better defenders against the ravages of worms than these little birds with slender beaks, voracious devourers as they are of larvæ and insects.