How do Field Guides Work?

Using an Audubon Fieldguide to identify a Pine-gopher Snake, Pituophis melanoleucus

The picture at the right is worth a thousand words on the topic of "How do Field Guides Work?" In the picture I'm using the Audubon Field Guide called North American Reptiles and Amphibians to identify the snake in my hand -- one found sunning itself in a neighbor's garden. It's the Pacific Gopher Snake, Pituophis melanoleucus ssp. catenifer.

In this Audubon Field Guide pictures of snakes are separated into groups based on color patterns -- plain, two-toned, striped, patterned -- except that the venomous pit-vipers have their own section. The snake in my hand was "patterned," and it took only about 30 seconds to thumb through the "patterned pages" to find a match. As you can see, my snake matched very well the middle illustration on the page on the right, just above my two middle fingers.

Once I had a good match I needed to confirm the identification so I went to the text in the back of the book where there were two full pages of information about gopher snakes. Here I confirmed such details as the fact that this species has a somewhat pointed snout, an "enlarged rostral scale extending upward between internasal scales," and that usually there are four prefrontal scales. The scales are keeled, in 27-37 rows, and the anal plate is single. Also, the distribution map of the species confirmed that the species existed in that part of the country where I was at that time -- the foothills of the Sierra Nevada Mountains in California.

HOW FIELD GUIDES ARE ORGANIZED

As we saw above, finding an unknown item's name in a field guide does not require that each time you want to identify something you must begin at the front and slog through every page until you find your unknown thing's illustration. Field guides are organized in ways that enable us to do a lot of skipping. In fact, field guides are organized in three main ways:

According to physical traits of the things being identified. For instance, a field guide to the trees might group its species according to whether leaves are attached to twigs singly, in pairs, or in threes. Within these groups, further subdivisions might take into account whether the leaves are composed of single blades or divided into leaflets. You might want to take a look at our page contrasting the field marks of a Fox Sparrow and a Song Sparrow.

According to what's related to what -- by "taxonomic relationships." For example, bird field guides nearly always group together birds belonging to the same order (the duck order, the owl order, the perching-bird order...), and then within each order all birds belonging to the same family are placed together (within the perching-bird order, there's the nuthatch family, the wren family, the warbler family...).

According to both the above criteria. A field guide to wildflowers might first group its species according to flower color, then within each of these groups, according to plant family. Thus all red- flowered members of the Sunflower Family may be in one place, then next to them all red-flowered members of the Milkweed Family.

You'll just have to decide which approach is more appealing to you and choose your guides accordingly. In general, beginners tend to prefer field guides based mostly on obvious physical traits but experienced field workers find they can work faster and with greater accuracy using guides based on taxonomic relationships.

Trogon tails Often differences between species are so subtle that general photos of the type seen in the guide above are inadequate. In such cases many field guides provide aids such as shown at the right. The bird in the drawing is one of several species of Mexican trogons. It happens that to distinguish certain trogons from look-alike relatives you have to look at the "bar coding" on the undersides of the tails. Thus a guide might just show what a typical trogon looks like, and then provide special descriptions of each species' tails, as shown here.

FIELD GUIDES AT AMAZON.COM

If you have a special interest, such as birds, wildflowers, or even something like clouds you might want to use the special form below which enables you to search at Amazon.com for special books, recordings, software, etc. dealing with your topic. Try it. Just type your topic of interest in the "Keywords" blank, click on "GO!" and you'll be amazed at what's out there. Nowadays anyone can identify almost anything likely to be spotted in backyards by using field guides and other resources!

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Conrad, Jim. Last updated . Page title: . Retrieved from The Backyard Nature Website at .