It looks like they vary greatly in value. The best way to determine approx value is to sign up for an ebay account (it’s free), then check completed auctons and sold items check boxes. This way you can see what they are currently selling for. It looks like a woodpecker sold for around $160, but some aren’t even worth $10. Looks like the Ivory billed woodpecker, the Cardinal from 1987, and the parrot are some of the ones that break the $100 mark.
here are some examples of recently sold listings
http://www.ebay.com/itm/Lot-of-7-Lenox-Bird-Figurines-Dated-1992-1993-2-2002-2-2001-/290931419172?pt=LH_DefaultDomain_0&hash=item43bcdd2824
http://www.ebay.com/sch/Animals-/1335/i.html?_sop=16&_from=R40&LH_Complete=1%7C1%7C1&_nkw=lenox+bird&LH_Complete=1&LH_Sold=1&rt=nc