HI Barry:
The Garrigues and Dean guide is now considered the standard bird guide to
Costa Rica. Other titles might be of interest to you:

The Mammals of Costa Rica by Wainwright
Tropical Plants of Costa Rica by Zuchowski
The Wildlife of Costa Rica: A Field Guide by Reid et al.
Butterflies, Moths, and Other Invertebrates of Costa Rica: A Field Guide
by Henderson.

As for when field guides need to be updated. That really depends on the
topic and region. The Birds of Peru by Schulenberg et al. was published in
2007 and updated in 2010. For regions that are frequently visited by
birders I would say guides should be updated every 5 years. But the cost
of publishing a book will probably preclude this!

sincerely
--

Ian Paulsen
Bainbridge Island, WA, USA
Visit my BIRDBOOKER REPORT blog here:
http://birdbookerreport.blogspot.com/