Looks like it is nectaring on some species of mist flower.
We had a couple of clearwing as new US records a few years ago in south Texas.
One was a Thick Tipped Greta (Greta morgane)
and the other a Broad-tipped Clearwing (Pteronymia cotytto)
They are supposed to use species of cestrum native to Costa Rica as a larval host. Perhaps you'll come across some larva on your walks through the jungle areas.