Why have birds that live on seeds, a crop?

Because they swallow the grains unbroken, and the crop, abounding with glands, softens the seeds, which are thence gradually propelled into the stomach. The latter is in birds extremely muscular, and so powerful, that, according to the remarkable experiments of Reaumur and others, it is able to break nuts and olive kernels, and to wear the impressions on pieces of money as smooth as paper. - Blumenbach.

Why do voracious birds, when devouring their quarry, swallow bones and feathers, and all matters indiscriminately?

Because the bones, feathers, etc. assist to promote digestion.

Why do birds swallow little pebbles?

Because they assist in the division and subsequent digestion of their food. Physiologists have differed as to the object and use for which stones are thus swallowed. Many have even supposed that it proceeds from stupidity. According to my own investigation, it is an indispensable measure of assistance to digestion, by depriving the seeds swallowed of their vitality, without which they would not yield to the digestive powers. - JBlumenbach.

Why have most nocturnal birds large eyes and ears?

Because large eyes are necessary to collect every ray of light, and large concave ears to command the smallest degree of sound or noise.

Why are aquatic nocturnal birds, as cranes, wild-ducks, etc. very noisy and loquacious?

Because their perpetual clamour prevents them from dispersing, and losing their companions.

Why are certain birds called "waders"?

Because they usually frequent marshy grounds, and the margin of rivers, and wade among the mud or water. All of them are qualified for flying, by the size of their wings, and for running, by the length of their legs.

Why do some birds stand for a great length of time on one foot only, without much exertion?

Because of the length of the toes, and the manner in which they are disposed, joined to the disposition of the body with regard to its centre of gravity. Thus, in the stork," the surface of the femur, (or thigh-bone,) that articulates (or joins) with the tibia, (or the largest leg bone) has, in its middle, a depression which receives a projection of the latter bones. In bending the leg, this process is lifted out of the depression, and removed to its posterior edge. By this motion the ligaments are necessarily more stretched than during the extension of the leg, in which the process remains in its socket. These ligaments, therefore, preserve the leg extended in the manner of some springs, without receiving any assistance from the muscles." - Cuvier.

Why have many genuine land birds the middle toe concerted by a web with the outer toe, as far as the first joint?

Because the sole of the foot is thus increased, and better adopted for standing or walking on the ground.

Why have some birds a claw cut like a saw or short-toothed comb?

Because they may comb out or rid their plumage of its vermin.