Why is the finest down of the eider-duck called " live" down?

Because it is found in the nest: that which is plucked from the dead bird is little esteemed.

Eider-down is imported chiefly from Iceland, and other northern countries. It is collected from the nests of birds; if the nest be deprived of its down, the female takes a fresh quantity from her breast; but, if the nest be a second time deprived of its down, she cannot supply it; the male then takes from his breast the necessary lining. - Selby.

Why have the bills of ducks a soft covering ?

Because it supplies them with a real sense of taste; this covering being supplied with exceedingly large cutaneous nerves. Accordingly, it is easy to remark the manner in which ducks probe, as it were, the puddles, in search of their food, where they cannot be guided by their sight or smell. - Blumenbach.

Why do the wedge-like forms of flocks of wild-geese so often change during their flight?

Because, it is conjectured, of the leader of the van quitting his post at the point of the angle through fatigue, and leaving his place to be filled by another, himself dropping into the rear.

Why is the pied oyster-catcher so called ?

Because it feeds on oysters and limpets, and its bill is so well adapted to force asunder the valves of the one, and of raising the other from the rock, that " the Author of nature," as Derham says, " seems to have framed it purely for that use."