Animal Diversity Web - From University of Michigan. Several color photos, signed accounts, classification, range, habitat, description, reproduction, lifespan, behavior, communication, food, predation, economic importance, conservation status, references.

Christmas Bird Count - From Audubon. Obtain historical results by species of the current year or past years back to the first count in 1900.

Encyclopedia of Life - A work in progress. Several color photos, some brief summaries (description, clutch size, IUCN threat status, distribution maps), some reviews by curators.

Cornell Laboratory of Ornithology - All About Birds (online bird guide), photos, sounds, size, common name, Latin names, color, behavior, habitat, distribution map, sounds and voice recordings, size, photos, bird cams.

Birds of North and Middle America Checklist - From the American Ornithologists' Union.Official source on the taxonomy of birds of these regions.

Global Raptor Information Network (GRIN) - From The Peregrine Fund. Includes species accounts and a searchable bibliography.

A Classification of the Bird Species of South America  - From the American Ornithologists' Union.

Dan Tallman's Ornithology Course - Lecture notes from a retired ornithology professor. 

Louis Agassiz Fuertes Illustration Collection - from Cornell University Library's Division of Rare and Manuscript Collections