A key is a short cut used to approximate identification without
reading a great number of descriptions. The keys given here differ in
no essential particular from those to be found in other systematic
works on ornithology, but for the benefit of the beginner their use
may be briefly explained.
Having in hand an unknown bird begin with the key to the Orders
(p. 7), reading first the line beginning a1; if the specimen has
the characters given after a1 then the bird belongs to the Order
Pelecaniformes and another key is to be used which will be found
under that order, (p. 200). If the characters on the line after
a1 are not found in the specimen, then those given on the line a2
are to be examined and these the specimen must have, if no mistake
has been made. The next choice is between b1 and b2 and so on until
characters are found which agree with those of the specimen and at
the same time lead to a word at the right printed in heavy face type;
this is the name of the order to which the specimen belongs.
Having determined the order turn to the page where the order begins
and use the key there which leads to the suborders or to the families,
then find and use the keys to genera and species.
To illustrate the use of keys with a concrete example, suppose that we
have a specimen of the common spoon-billed duck or shoveler, but know
nothing of its affinities. Beginning with the key to orders we find:
"a1. Hind toe connected by a web to the inner toe." As this does not
agree with our specimen we try:
"a2. Hind toe not connected by a web to the inner toe." Yes.
"b1. Nostrils tubular." No.
"b2. Nostrils not tubular." Yes.
"c1. Cutting edges of bill more or less distinctly fringed or
serrated, tip of bill rounded ... Anseriformes."
Yes, and our bird belongs in the order Anseriformes. By a similar
procedure we find that our duck belongs in the subfamily Anatinæ
(p. 185) and in the key to genera (p. 187) we find:
"a1. Bill not spatulate."
"a2. Bill flattened, and spatulate ... Spatula."
As our duck has a flattened, spatulate bill we turn to the genus
Spatula (p. 196) and as there is but one Philippine species in this
genus we know that our bird is--
Spatula clypeata (Linnæus).