The full name of this one is Gray-headed Chachalaca (Ortalis cinereiceps) with the only other one named “Plain Chachalaca” and it’s found only in Guanacaste (dryer NW Costa Rica). This one is a regular “chicken-sized” bird living in my neighborhood, though like other birds, I’ve been seeing fewer for a while. They always come in groups or families and “chatter” a lot, thus Ticos sometimes jokingly call a person who talks a lot “a Chachalaca!” :-)
Here’s three shots of them moving between my trees and you can see more photos in my Gray-headed Chachalaca GALLERY. I see them in many parts of Costa Rica and they are indigenous to Central America.