Birds (by location or taxonomic grouping)
eBird - a great free app for bird enthusiasts that allows you to see where specific birds have been reported, allows you to record your own sightings, connect with other birders, and much more.
Merlin - another great free app for identifying birds. You can download "bird packs" that have photos, calls, descriptions and range maps - all on your cell phone. No need to lug a heavy bird guide around with you (but always good to have one of those as a back-up reference back at camp - our recommendation for that is below).
Birds of Peru, Schulenberg et al. (2010 - Revised and updated edition). By far the best field guide for birds in Peru with consistently good illustrations, descriptions and maps. With 1,817 species covered, this book is a bit heavy and bulky to carry in the field, but you can alternatively purchase the Birds of Peru app (google it) for either iPhone or android. A Spanish version of the printed guide can be obtained through CORBIDI