If you are interested in finding a truly excellent birding guide for the Guanacaste area (and even beyond), then you should contact Carlos Luis Jimenez, who can be reached at http://www.ecoexplorercr.com.
My wife and I were at the Occidental Grand Papagayo in Guanacaste for a week in mid-March. (This all-inclusive hotel was generally ok and, all things considered, of good value.) As far as birding goes, I was fortunate to engage Carlos for a full day of birding (very early morning to very late afternoon). It was a wonderful and productive outing combing low land dry forest (Santa Rosa National Park) and rainforest (north side of Rincón de la Vieja National Park). I had been to other parts of Costa Rica in earlier trips so many of the birds that we saw I had seen before but it was a joy to see again some old favourites such as the long-tailed manakin. There were plenty of new ones to list as well, including Pacific north-west specialties such as thicket tinamou, tody motmot, banded wren, stub-tailed spadebill, and brown-crested flycatcher. Other delights included great curassow, collared forest-falcon, royal flycatcher, northern bentbill, ocellated antbird, spotted antbird, and rufus-winged tanager…and more.
Carlos was a superb guide. I have had day outings with quite a few guides in Costa Rica and as well as in Panama and I can honestly say that he ranks among the very best. He has a remarkable ear (and voice) for bird song and calls and is amazing in his ability to locate birds in the dense foliage. He blends persistence and patience in both finding birds and, the key part, making sure you get a good look at them. Carlos’ English is very strong and he is a pleasant person to spend time with. Finally, his rates are reasonable and more than fair.
My only regret is that I did not have more time to spend with him.