Why would the presenseof carrion birds suggest that a battle is amminent?

Answer 1

Carrion birds feed on dead flesh. At the scene of a battle, they are ubiquitous as they would descend on the battle field after the fighting had ceased to feast on those left behind.

It may have been a bit of poetic license to say that the birds gathered before the battle, however. It is logical to think that the noise of several thousand men, dwarves, elves, and whatnot would have been enough to frighten away most wildlife.

Answer 2

Carrion birds eat the meat of the dead. The birds might fly over battles to eat the dead when the battle is over.

Answer 3

Carrion birds eat dead things. Battles produce lots and lots of dead things.

Answer 4

Carrion birds feed on dead flesh. They would follow an army to feast on the dead after battle.