I settled on this title yesterday, and an elemental plot: a patron sends the players to capture an exotic beast in the middle of the Fifth Frontier War.
Now I need to prepare it for the convention. So I'm posting this to elicit suggestions or opinions.
Since you specifically include the Fifth Frontier War, I assume that this is taking place in the Spinward Marches. That sort of limits the planets that you can consider, along with the chance of being nailed by a Zhodani or Sword World raider. You also have the possibility of becoming a "friendly fire casualty". How close to the major zone of combat are you thinking of sending your clay pigeons?
Vanejen is not too close to the combat area, and already has some background. It does have a Chirper population, but I assume that is not what you are thinking of. It is not that well populated, and with a Tech Level of 5, a ship can get in and out without being detected fairly easily. The northern continent has been pretty much left to the Chirpers, so may have some interesting critters, along with the small north-south running continent, based on the Wiki Map, and some of the larger islands. Given the interesting fauna of Madagascar, the Indonesian archipelago, New Guinea, Australia, and New Zealand, you could make up something quite interesting for Vanejen. A Giant Moa equivalent would be good, as would something like the Terror Bird Phorusrhacos. With the northern climate, a polar bear equivalent might be possible, or for that matter, a collector with a predilection for sea mammals like the white whale. The Komodo Dragon, one of the varieties of the Bird of Paradise, a Tasmanian Wolf or oversized Tasmanian Devil give some ideas. Or you could be really nasty and send them after a Jabberwock.
If you use Vanejen, your party could also get all sorts of credit from the Droyne for letting them know about the large Chirper colony, which the local government would be very unhappy about. Helps to keep the party on their toes is the local government decides that they need to be thoroughly educated regarding the Chirpers. I just came across online a really good report on Soviet disciplinary battalions by a member just prior to the German invasion of 1941 to give you some good ideas on the education process.