Blinds are certainly useful. I don't own my own portable blind, but I've often used permanent blinds at parks and wildlife reserves. Look at the L.L. Rue website for some portable blinds that usually get good reviews.
For birds though, even with a blind and good technique, a long lens will give you more chances to get good photographs, because many birds are not approachable even with a blind (unless you are also building a scaffold for birds that avoid the ground or are willing to make floating blinds for water birds that avoid the shore, presuming that such things are permitted and possible in the location where you are shooting). Another reason to use a long lens is to prevent wildlife from becoming too accustomed to human presence.