I have a 5.5 month old Grt Pyr. He is in the house right now but does bird chores with me. I don't let him play, run or rough house when we are in the birds area. He is more interested in their feed and their poop than in them.
There are many varying opinions on using LGDs to guard birds. Many people have great experiences, many don't. A lot of the problems that I have read occur when people leave the pup unsupervised with it's charges before it is old enough. Chickens are basically moving squeak toys and can be easily killed, even accidentally by an exuberant pup. I don't plan on leaving my guy out unsupervised until he is at least 1.5 yrs old, possibly older. I know someone that didn't have their first LGD outside unsupervised until he was 3. He has since assisted in the training of 2 other dogs on a farm that raises a number of breeds of waterfowl, poultry and goats.
Here are 2 sites I've found helpful. The first is BYCs sister site
http://www.backyardherds.com/forum/viewforum.php?id=71
http://www.lgd.org/ You can click on the "library" link for alot of articles on different aspects of LGDs.