This gland, which is on the rump, and contains the oil necessary for
anointing the feathers, sometimes becomes hard and inflamed, and an
abscess forms there. In this case the bird often pierces it itself, or
it may be softened by applying fresh butter without any salt; but it is
better to use an ointment made of white lead, litharge, wax, and olive
oil, which may be had at any good chemist's. The general method is to
pierce or cut the hardened gland, in order to let out the matter, but if
this operation removes the obstruction it also destroys the gland, and
the bird will die in the next moulting, for want of oil to soften the
feathers[12].
The gland is known to be obstructed when the feathers which surround it
are ruffled, the bird never ceasing to peck them, and instead of being
yellow it becomes brown. This disease is very rare among wild birds,
for, being exposed to damp, and bathing often, they make more use of the
liquor in the gland, consequently it does not accumulate sufficiently to
become corrupted, sour, or cancerous. This confirms the necessity of
giving them the means of bathing as often as instinct would induce them,
as nothing can be more favourable to their health.
Dr. Handel, after piercing the gland, recommends a little magnesia to be
mixed with the bird's drink.