|The Chasidah [white stork]|
וְאֵת הַחֲסִידָה "The chasidah" [Shemini 11:19]
Why is its name chasidah (literally meaning "kind one") asks Rashi. "Because it does kindness with its companions with food."
According to the Ramban, said the Chiddushei HaRim (R' Yitzchak Meir Alter of Gur), the reason why the nonkosher birds are not kosher is because of their cruel nature. If so, the chasidah should have been a kosher-type bird; after all, it bestows kindness upon its companions!
The chasidah acts kindly towards its companions, answered the rebbe, but it does not act kindly toward anyone else. This is why it is considered not kosher.