Well since they're the dominant species maybe they didn't move in because they're already so prolific?
Maybe instead of our problems with Global Warming they're going through a mini-ice age. The bird-race would live higher up in the mountains but be forced down by cooling so they could still hunt as water ways would have frozen killing off various fish species and forcing the bird-race to hunt elsewhere.
The conflict could come from that, the wahnans/wawnans/weasel-things (seriously we need to pick D:) disapprove of hunting in their territory and so the bird-race harries them to try and get some for themselves. And maybe baby wahnan's just happen to taste good.
Well depends on the world, we could give the planet a severe axial tilt which would A) create less area to actually live on and B) make seasons more extreme at certain points.
If we had it at say a 90 degree tilt on an circular orbit certain points would be like here except it would experience a polar twilight (so 24 hour sun) and have freezing winters and hot summers. Actual polar living would be hard for these aliens, the summer would be hot enough to melt metal so we'll avoid that.
Now in polar twilight you still have four season, summer is hot and winter is freezing while spring and autumn are comparable to a (northern Canadian) spring and autumn, so wet and comparably mild. Note that the summer here is not a tundra-like summer unlike the autumn and spring. Tundra summers are 10 Celsius on average and can drop drastically, these summers are hot.
For more information I suggest the very helpful World Building pieces by kassyopeia planetary habitability for those interested.
Haha, fair enough. XD
So, if this planet travels around the sun in a circle and has an axis tilt (the position the planet rotates on) of 90 degrees there will be four seasons in the "twilight band" AKA the equator, while the actual poles will be too extreme to survive in.
Summer will be hothothot, winter coldcoldcold and spring and fall mild but pleasant and fairly short. They will all happen once a year. The place will have a 24 sun, so that there is never complete darkness. So no nocturnal animals in that world.
Better? I some times take for granted people know what I'm talking about, I'm the art student who's friends with a theoretical mathematician, a theoretical chemist and a metaphysics student. /neverknowswhat'sgoingonbecausemathandsiencenerdsarebadatcommunication.
edited 4th Mar '11 7:27:35 PM by AwayLaughing
Well, in the 19th century some Scandinavian scientists observed mini-ice ages in Scandinavia, Russia and Canada. They argued that this was caused by extremely slight "wobbles" in the earth's orbit. So this planet's orbit could have "wobbled" slightly away from the sun causing glaciation in the northern parts of the twilight band and therefor lowering global temperatures.

Maybe there was some sort of climate shift or natural disaster elswhere, and one tribe of birds had to migrate into the weasel's territory to survive.