BNA Online provides comprehensive life histories for each of the 716+ species of birds breeding in the USA (including Hawaii) and Canada.
Here is a sample article about the Belted Kingfisher.
Encyclopedia of Life Sciences (1997+)
The Encyclopedia of Life Sciences (ELS) features more than 4,000 specially commissioned and peer-reviewed articles on a broad range of biology related topics. This is an encyclopedia with in-depth, scholarly coverage of major concepts in the life sciences.
Here is a sample entry from the ELS written by EEB professor Peter R. Grant (go to the entry and open the PDF). In each ELS article, you will find the "References" and "Further Reading" sections helpful for developing your knowledge of the article topic.
Beacham’s guide to the endangered species of North America
This guide presents extensive data on the habitats and ecosystems of more than 1,200 species identified as endangered or threatened by the U.S. Fish and Wildlife service. Arranged taxonomically, entries include introductory information with an image of the species; a summary section detailing information on each species; a concluding summary of recovery efforts; and a bibliography of contacts for further information.