I was at a reserve a few weeks back (wont name names just in case the individuals are online) and when i arrived there Birds such as Pintail, Water rail, Bearded tits, other Wildfowl, etc and even Red deer (oh well maybe i've given it away now).
It was just me in the hide, and all the Birds were close in and numerous, giving great views! And then a big gang of Birdwatchers, 5ish all came in, with all their belongings (Scopes, Bins, FOOD, Bags, etc) and they all came in as noisily as they could. Plus they spoke as if they had to shout, the Water rail in front of me flew away, so too did the Bearded tits, and most other Birds scampered. After c15 minutes of waiting for any more Birds to come back, i left as they had still not quietened down.
Sometimes i think people think Hides are sound proof and anything outside can't here you (they may well be) but Birds aren't stupid and when they here noise they aren't gonna wait all day for you are they?
Also maybe if people were more quiet and payed more attention to the areas outside the hide, rather than just using it as a social gathering then they might actually pick something up. Just a thought.
Cheers.