The Warbler Guideby Tom Stephenson and Scott WhittlePrinceton University Press, 2013Egrets stalk in a stately manner; red-tailed hawks circle with lordly indifference; robins run in businesslike straight lines; English sparrows conduct the whole of their brawling lives in full view; blue jays practically taunt. But wood warblers are different: they flit, they flicker, they vanish in a momentary snap. A trill and a flash of color, and they’re gone.They’re tiny little things, these perching birds (Passeriformes) of the subfamily Parulinae of the family Emberizidae, although they’re cheeringly hardy: many of the 56 wood warbler species found in the United States and Canada undertake epic migrations every, some of them departing in late spring in order to make the seven hundred mile nonstop flight through the winds and storms of the Gulf of Mexico. Their numbers have been decimated in the last few decades not by the obstacles of nature but, predictably enough, by the obstacles of man: all along the birds’ migration routes, glass-walled skyscrapers (virtually invisible at night, when most of the flying takes place) have wiped out tens of thousands of migrating birds of all types, including wood warblers.There are still plenty of birds to occupy avid bird watchers, thankfully, and this type of bird – so lovely and so engagingly elusive – has always been a favorite. The 20th century American bird spotter Charles Johnson Maynard was not alone in contending, “Throughout the world we find no finer group of birds, thus they may well be considered the pride of the American ornithologist.” The great Roger Tory Peterson put it more elegantly when he referred to wood warblers as “the butterflies of the bird world.” And Hal Harrison, in his delightful 1984 classic Wood Warbler’s World, was full of praise for the whole family, although he rather ungallantly pointed out that most American warblers don’t, in fact, warble: “The males all sing, but not always well. They lisp, buzz, hiss, chip, rollick, or zip; and one, the Yellow-breasted Chat, may chuckle, hoot, whistle, caw, and screech.” It doesn’t sound appealing, but if you hear a bit of that hooting and cawing and screeching on a gorgeous spring day in a bustling wood, you’ll think it’s just about the most perfect appoggiatura you ever heard.Ah, but birders want to do more than hear! They want to see and see accurately, informatively, and that’s notoriously tricky with a will-o’-the-wisp thing like a wood warbler.Princeton University Press has enlisted veteran bird experts Tom Stephenson and Scott Whittle to produce the ultimate aid to knowing wood warblers in the wild. The Warbler Guide is the result: a heavy field-green brick of a book with plastic covers and laminated pages designed to shrug off dirt and rain and stand up to repeated (and perhaps hurried?) thumbing. The guide is perhaps a bit heavier than is ideal for a backpack, but that’s the price readers pay for that ‘informatively’ part, because this is easily the most informative book on wood warblers – in all their stunning variety – that has ever been published for a popular audience. For each one of those 56 species, there are dozens of full-color photos showing every conceivable gradation of their seasonal colorations, every stage of their lives from chick to mature adult, every possible angle at which a lucky glance might reveal them to a startled onlooker. The Warbler Guide’s clear goal is to provide its readers with enough information to identify with confidence pretty much any glance they get of any warbler that so much as twitches in their general vicinity. The approach itself is a tacit acknowledgement of how shy these birds can be. Nobody would make a guide like this for crows.And even the shyness has been addressed, quite cleverly. The fact that birders are far more likely to hear a wood warbler than to see one has led our authors to provide an ear-guide as well as an eye-guide. The book uses sonograms to illustrate for its readers what each warbler sounds like when they’re making all those saws and buzzes and caws. This innovation can produce some grimly forbidding initial instructions:

You may have had a physics class in high school that explained the harmonics of pitched sound. When you pluck a string, there is one fundamental (or primary) pitch created by the vibration of the length of the whole string. At the same time, the string can create a "harmonic" that is twice as high as the fundamental pitch and lower in volume. There can also be additional, softer harmonics at various other multiples of the fundamental. The more harmonics in a sound, the richer it sounds to our ear, as long as the harmonics are multiples of the fundamental.

But using the system quickly becomes more or less comfortable – a little study of harmonics now, in the library, can yield more ‘ah ha!’ moments in the field and forest than a reader might at first expect, and the whole concept is a hell of a lot more impartial than the often hilarious call-approximations that fill older bird guides and had whole generations of neophyte birders listening carefully for ‘she-SAID-it, she-SAID-it’ or ‘EASY-does-it, EASY-does-it.’Bird guides have it rough these days, since birdwatching apps have progressed so amazingly that they can provide actual calls rather than sonograms, actual video clips rather than photos, actual tracking data rather than the birder’s careful notebook. It’s possible, then, that Princeton’s Warbler Guide might be the last of its kind for everyday use. That would be shame, but even so: what a splendid exit, if so.