May: Bat flight season begins as hundreds of thousands of Brazilian free-tailed bats spiral out of the cave at dusk. It runs roughly late May through October.
Permits and reservations
To enter Carlsbad Cavern you need a timed-entry reservation (it only picks your entry time). You still buy the entrance ticket at the visitor center, and it is good for three days. The rest of the park needs no reservation.
Timed entry to Carlsbad Cavern: A timed-entry reservation is required to enter the cavern (the reservation only picks your time; pay the entrance fee on arrival). Guided cave tours also need reservations.
Backcountry use permit: A free backcountry permit is required, picked up at the visitor center on the day you arrive. Advance reservations are not issued.
Ranger-guided cave tours: Reservations are highly recommended for all ranger-guided tours. Cancelling costs $3 per ticket.