Try setting your game mode to “ThirdPerson_GameMode” in the world settings, and see if the birds are still acting up. Most likely you are setting up a non standard character setup and the references to “Player Character 0” need to be swapped out in the blueprints with whatever you are using. Is this a multiplayer game you are setting up? Look at the demo level and see whats different from your level in connection to the player, from the limited info you gave me I’m guessing this is where your issue is 
The Birds behavior changes based on the distance to the player, so if the player references are not correct the Birds will just fly away to the world origin (aka-you broke their brain) .
Out of the box Birds is set up for a single player game- where the player is “Player Character 0”. If you are using a different setup (like multiplayer) then you will need to replace the references to “Player Character 0” with whatever your using for your character labels.
Here is an example of a node you need to Swap out
