We would recommend watching this with headphones.
During our time staying in the Rio Claro Reserve, we explored the Guacharos Cave, named after its avian inhabitants. The pitch-black of the cave is home to two flocks of nocturnal Oilbirds.
At night, they fly out to search for palm seeds to eat, but in the day, they take refuge in caves like this. They use a clicking sound as a means of navigating the caverns (similar to bats), weaving their way through incredibly tight spaces. Although we could only vaguely make out their silhouettes as we made our way through cavern after cavern, we were still impressed by the agility with which they managed to avoid the cavern walls. Sometimes one would flap in the wrong direction, towards the light of the cave entrance and have to make a last minute turn almost instantly.