There's a lot of birds that can be seen in Costa Rica. There's a small handful (I can think of 3) that can only be seen there (excluding the ~25 birds that are endemics to the Chiriqui highlands shared with Panama). One is the Coppery-headed Emerald, a small hummingbird particular to a narrow elevation band mostly (I think) on the Pacific slope. It's one of the highlights of the aforementioned Cocoro Hummingbird garden.
Head-on Emeralds are stupendously green.
The white tail flash is a pretty good marker for these short-billed birds as well.
A couple better looks at the female.