Characteristics of the Nostrils
The nostrils are generally separated from each other by a complete wall,
or septum; they are, therefore, imperforate. A few groups of birds,
such as the vultures, have nostrils without a medial septum; they communicate
with each other and are, therefore, perforate. Nostrils show other
characters:
| Tubular: the nostrils are in the ends of short prolongations of the base of the upper mandible, as in an albatross, a shearwater, or a Leach's Storm Petrel. |
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| Operculate: nostril openings are partly covered by an operculum - membranous, as in the Barn Swallow, fleshy, as in the pigeon. |  |
Linear, oval, or circular: the nostril openings are thus shaped, as in a gull, an accipitrid hawk (e.g., Cooper's Hawk), and a falcon (e.g, American Kestrel):
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