Here is something useful and free.

"The app works on iPhones, iPads, and iPod Touch devices. Developed for NPCA by the folks at eNature.com, these apps focus on wildlife and ecosystems of 50 national parks. According to a release from the park advocacy group, "the guide includes bird portraits, call recordings, information about endangered and poisonous species, range maps, and wildlife. Users will also find current news about featured parks, access and reservation information, and directions to park visitor centers.""
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Verum audaces non gerunt indusia alba. - Ipsi dixit MCMLXXII