A number of Pixar's shorts give the impression that showcasing a new animation technique was a higher priority than telling a story (this is nothing new - ever see that Disney short, The Old Mill?), and For the Birds is good example of this. The centerpieces on offer here are the CGI feathers; the rest of the birds' anatomy may be purely cartoony, but their feathers ruffle and spread in a really convincing way.
The plot is extremely light, but the intrinsically funny designs of the birds make up for this. The way they squabble in squeaker-toy arguments is beautiful.
In the end it's not particularly memorable or remarkable, and probably won't be remembered as one of Pixar's finest hours. But hey, it makes for an entertaining three-and-a-half minutes, and that's really all it was meant to do.