A disease which may be called the _pairing fever_ must not be forgotten here. House birds are usually attacked with it in May, a time when the inclination to pair is greatest. They cease to sing, become sorrowful and thin, ruffle their feathers, and die. This fever generally first seizes those which are confined in cages: it appears to arise from their way of life, which is too uniform and wearying. I cured several by merely placing them in the window, where they are soon so much refreshed that they forget their grief, their desire for liberty or for pairing, and resume their liveliness and song.
I have observed that a single female in the room is sufficient to cause this disease to all the males of the same family, though of different species. Removing the female will cure them directly. The males and females at this season must be separated, so that they cannot see or hear one another. This perhaps is the reason that a male, when put in the window, is soon cured.
The length of a bird's life very much depends on the care which is taken of it. There are some parrots which have lived more than a century; and nightingales, chaffinches, and goldfinches have been known to live more than twenty-four years in a cage. The age of house birds is so much the more interesting, as it is only by observing it that we can know with any degree of certainty the length of birds' lives in general. Thus house birds are of importance to the naturalist, as giving him information which he could not otherwise acquire. It is worthy of remark, that the quick growth of birds does not prevent their living much longer than quadrupeds. The length of life with these is estimated to be six or seven times longer than the time which they take to grow: while birds live fifteen, twenty, and even thirty times longer.
This length of life is sometimes attributed to the substance of which the bones are composed being much more loose and light, and consequently remaining porous longer than those of quadrupeds. Some swans have lived three hundred years.
We are furnished with house birds by the bird catchers and bird sellers; the latter procure foreign birds, and teach them, the former the indigenous ones. A good bird catcher ought to know not only the different modes of taking birds, but also all the calls for attracting the different species and sexes: the call notes vary very much among house birds, according to their passions and wants; thus the common chaffinch, when calling its companions, often repeats _iack_, _iack_; when expressing joy, _fink_, _fink_, which it also does when angry, though louder and more quickly; whilst its cry of sorrow is _treef_, _treef_.