This is a reply to Gene Hunn's question regarding plural forms of bird names.
A few nouns have only a plural form; hence, the singular and plural forms of
"sheep" are both "sheep." It follows that one would see 20 killdeer (although
killdeers is a growing alternative) and 17 curlews. Most bird names have a
singular form. My AMERICAN HERITAGE DICTIONARY, 2nd edition, has a relevant
section titled "Inflected Forms" on pp. 47-48. See especially the top of page
48. In matter of fact, rules follow use. When a sufficient number of us say
27 gull for a sufficient number of years, it will begin to appear in
dictionaries as the favored use.

Bob Benton