Take a boat ride to the north of the island at sunset and watch the fruit bats as they fly over to the mainland to feed. This is a really spectacular sight - the bats are absolutely HUGE! Some unscrupulous locals offer tours through the forest to visit the bats during the day, but avoid doing this - it disturbs their natural sleeping habits.
The number of bats is declining every year, from over 2,000 two years ago to just over 1,000 now, due to a (so-called) eco-resort being built on their nesting site. Go and see them as soon as possible, as they are about to begin building a Shangri-La hotel on top of them too, which will no doubt wipe them out completely.
It is a great shame that the local authorities in Boracay seem to care so little about preserving the island's endangered wildlife, such as monkeys, birds, and fruit bats.
In a year or two, there may be none left.