Proper writing of bird common namesTweets,

Not to change the subject or anything from issues of capital letters, but I've noticed another odd grammatical phenomenon in many birders' postings, that is, the "plural deletion rule," one might call it. Lists are presented as if all the birds were like "deer" [one deer, two deer, three deer...], e.g., three dowitcher, 376 wigeon, etc. This always strikes me as somewhat unconventional. Is there a reason for it?

Gene Hunn.