Hi Carol,
we have had a couple of birdwatchers staying in Atmosphere Resorts in Dauin before, so I have some ideas about the nice birdwatching sites here (although the marine life is more my specialty...). Negros is said to have a quite unique bird diversity and you can spot interesting endemic species and explore the stunning nature for example in Lake Balanan, Twin Lakes Natural Park, Mt. Talinis and Casaroro Falls. Our resort has day trips available to all those places, as well as probably most of the other resorts in Dauin (maybe best to double-check while booking though), so your top side interests should be nicely catered here. From our previous guests I remember that the other interesting birding area in Philippines is at least the Northern Mindanao, where they also have many rare species.
As the others have already told, our coastal diving in Dauin is mostly macro (but a pretty nice one - for example right now we have blue ringed octopus with eggs on the area along with other photographers' dreams!) but we also have the beautiful coral reefs of Apo Island (only 25 minutes by boat from us) and Siquijor (a bit further away) nearby. A nice balance so to speak. And if you plan to do Dauin and Malapascua, you can easily go to see the whalesharks in Oslob on the way (or during your stay in Dauin).
May is a great time to visit, since the seas are very calm and the sun is shining from the blue sky. Happy holiday planning Carol!