I saw a documentary on Rat Island once upon a time, and those rats are VICIOUS, man. It's almost surreal to see how they 'take down' a bird with coordinated strikes, and start ripping it to pieces. Even more bizarre, is that we've discovered 'stockpiles', or 'caches' of dead birds - organized as you can see below.
Here is a picture of one of the caches, as discovered:
One might be tempted to think that given enough millions of years, these rats could start to actually form patterns of what we might call 'society', or 'intelligent life', 'politics', 'war', 'leadership', 'construction', etc.
They might even build 'vessels' and colonize the rest of the Aleutians. It's d@mned scary, man. That's why we MUST act now. Mammals & evolution are not to be underestimated, afterall.