(Original post by DH-Biker)
Unless they have found tyranical leaders with intelligence, I don't think we should worry about that.
Its very, very rare that any animal will willingly sacrifice itself. It has been known to happen, Lemmings will kill themselves to equate population in an area, some sick animals have been known to lead alligators (or Crocs, I forget which is which) towards them so the main bulk of a herd can move on unhindered.
However, there is a key sub-concious imprint within pretty much every living creature and that is to survive. Especially within humans, but also within other animals. It is very rare that a society will openly subject themselves to suicide. There have been times within the last few years when most North Koreans would blindly charge the DMZ if asked, and its happened before throughout human history too. Specifically the term "Beserker" often targets blood-thirsty warriors with absolutely no regard for their own well being. If you want to call this suicide, people would be hard pressed to argue.
I sincerly doubt, however, birds would willingly throw themselves into engines. It is rare for a bird strike on planes as it is, cases that have been recorded are typically in one of two locations:
1) An area of heavy cloud cover. The plane or flock of birds has come out of a cloud straight into the other.
2) At airports, an aircarft generates a significantly higher sound when taking off, this will scare birds up from trees or the ground and in the confusion they are sucked into the engines.
It is also worth noting that whilst there have been somewhere under a dozen cases of birdstrikes actually bringing a plane down, as far as I know no one has yet died from a bird strike.
A documentary about Luton airport showed what can happen with a birdstrike and this plane, when it crashed, looked unrecognisable and yet no one was hurt.
Regardless, I doubt its much of an issue. Firstly they wouldn't have the mental processes capable, secondly it would take a significant amount to destory an aircraft and finally, they have to fly either faster then the aircraft or just hope to be in the right place at the right time.