In the course of Backyard Bullies, the birds attempt to count coup on the humans. Doing terrible things to humans is a feather in their cap. The players take on the role of birds while the GM takes on the role of humans and other groundlings as well as any environmental hazards which might exist. The GM also sets targets for things the birds might do and then adjudicates their success.
The birds have enemies of course like squirrels, cats, and of course people. There are also environmental hazards ranging from difficulty finding food to fermented berries and plate glass. The birds have to overcome these hazards while they try to punish the humans for their transgressions.