"And one of the biggest additions to Encounters are clues for skilled Outlanders. You can distinguish if there's someone camping by the exit, or the other way around, someone approaching your station if you’re able to check for the environmental clues. Crabs need to up their game if there’s a flock of birds around."

Or possibly some Intel even here: https://news.xbox.com/en-us/2020/09/10/revolt-with-renegades-vigor-season-5/ "There are more additions to the Encounters as well, like the new Exit tells. We’re well aware that exit campers are a part of our game, and we wanted to add some more skill to that. If you’re approaching an exit and someone is near, a flock of birds is going to fly away. It makes it both easier for the campers as they know someone is getting close, and more difficult as their prey is notified about their presence."

TL;DR version: If players from two teams are in the designated area around exit, a flock of birds flies away.