The more difficult species of the endemics, or the ones which required the most effort to see would be the Elfin Woods Warbler (unless you get lucky like some have), PR Lizard- Cuckoo, PR Screech-Owl, and PR Nightjar (all these are easy to hear, can be hard as heck to see).
(the ones; required; the most effort to see) (The more difficult species of the endemics, or the ones; would be; the Elfin Woods Warbler) (PR Lizard- Cuckoo, PR Screech-Owl, and PR Nightjar; can be; hard) (you; get; lucky) (heck; to see; ) (some; have; )
the ones The more difficult species of the endemics, or the ones PR Lizard- Cuckoo, PR Screech-Owl, and PR Nightjar you heck some
required would be can be get to see have
the most effort to see
the Elfin Woods Warbler
hard
lucky