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).
SHOVELER.