Mr. Waterton doubts ("Mag. of Nat. History," vol. v. p. 413) if
the small nipple on the rump of birds is an oil-gland, or that
birds ever oil their feathers with matter obtained from it; and he
asks if any naturalist will say that he has ever witnessed this
process, and if so how it is that the bird contrives to take this
oil in its bill and how it manages to oil its head and neck? I
will therefore state what I think I have witnessed, and trust to
Mr. Waterton's forbearance if I am in error; yet I cannot help
suspecting that Mr. Waterton's queries are (like those of Charles
the Second to the Royal Society) more for the purpose of laughing
at our ignorance than from any wish he has to obtain information,
for I can scarcely suppose that so acute an observer can have
failed to perceive everything perceptible on the point at issue.
I have just watched a Muscovy Duck go through the operation of
preening and dressing its feathers, and it certainly appears
obvious enough to me that this bird uses the gland on the rump for
the purpose for which birds are generally supposed to use it. The
bird erected the feathers on the rump so as to exhibit the gland
very distinctly, and then, after pressing it with the bill, rubbed
the under mandible and chin down to the throat upon it, and then,
after drawing some of the feathers through the bill, rubbed the
lower mandible and chin upon the back and scapulars, apparently to
apply the oil which adhered to them, and then, turning its head
back, it rubbed the crown and sides of the head and neck upon
those parts which it had previously rubbed with the chin and under
mandible. By this rubbing of the head and neck it is easy to
perceive how birds can oil these parts if it be allowed that birds
oil themselves at all.
I cannot see how we can explain this action of birds in relation
to any other object. It certainly does not seem calculated to
expel or disturb any vermin lodged there, and I remarked that it
never occurred except when the bird had been applying its bill to
the gland as above mentioned. However, Mr. Waterton, and anyone
who doubts this oiling, may readily judge for themselves. Let them
take a common duck, and shut it up for two or three days, so that
it can have no access to water except for drinking, and at the end
of that time let them turn it out, and allow it to go to a brook
or pond; it will give itself a thorough ablution--ducking, diving,
and splashing with its wings--and on coming out, will begin to
dress and arrange its feathers, very frequently applying its bill
to the gland on its rump. If this application is not for the
purpose of procuring a supply of oil, perhaps Mr. Waterton will
have the goodness to inform us what it is for, and what end this
gland answers in the economy of the feathered tribes if not that
which has hitherto been supposed. (June 30, 1832.)
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