Ok, so I'm running Melan's Terror on Tridentfish Island. Set on the tiny island "west" of New Pictland and "north" of the Skarag Coast archipelago, basically the last thing before you hit the River Okeanos.

They are exploring the palace. It is night time and they decide to explore the roof. They have a bullseye lantern.

There are 4 winged, carnivorous apes that "nest" there at night.

They are sneaky bastards. Initially dropping stuff on folks.

I gave the party a chance to "see" them while the apes attack, mostly if the party wins initiative but a smaller chance if they don't.

I partly did this because the apes would be smart enough to "stay out of range" of the light but they still have to be close enough to easily target them.

Any thoughts on how to handle this better?

I think it's mostly the "at night" that is the main modifier to this thing