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Bird ID guides come in several forms, from books and laminated cards for field use to online searchable databases. In between are printable, often single-page, illustrations of particular groups of birds to aid in discriminating between species. Some are quite basic, others more sophisticated, a number of them designed originally as posters. Most described in this article are free.
The Warbler Guide, by Tom Stephenson and Scott Whittle, published by Princeton University Press in 2014, presented a "ground-breaking" system for identifying the vast numbers of New World warblers which can be found in the United States. A particularly engaging and useful part of that book is the set of illustrated guides to many features of these often hard to distinguish species. Amazingly, those have now been released as free downloads from the publisher, and can be viewed on any device and even printed for field use.
Less specific, but equally comprehensive, is the Cornell FeederWatch "mini poster" with excellent drawings of common backyard birds. Intended for printing, it is a useful aid to beginning birders, and in two colorful pages it covers a lot of avian territory. Even if your backyard has Chestnut-backed rather than Black-capped Chickadees, you'd quickly learn to tell them from the Finches or the Cardinals.
An astonishingly innovative and inventive series of "BirdFaces", created by Richard Edden, presents simple, icon-style, images of the distinctive markings on the heads of many bird species. Originally intended to be part of an iPhone app, the entire enormous collection of ID pages is now available, free, on his BirdFace Facebook account. Several of these surprisingly endearing images can also be purchased as decorations on coffee mugs and T-shirts from Zazzle. (a Favorite)
Similar in style to the FeederWatch poster, the full-sized (24"x36"), art-paper offerings from Windsor Nature Discovery with collections of Birds of the Garden, Raptors, State Birds, etc., appear accurate and are likely worth the purchase price, perhaps as a present. For the true hard-core birder on your gift list, however, nothing can beat the definitive Empidonax Flycatcher chart, done in the BirdFaces style of Richard Edden, but without attribution. Its provenance is unknown, but it is hosted on this website as a free public service.