HOW TO USE FIELD GUIDES Using an Audubon Fieldguide to identify a Pine-gopher Snake, Pituophis melanoleucus

At the left, the Audubon Field Guide North American Reptiles and Amphibians is used to identify a snake found in a garden. It's the Pacific Gopher Snake, Pituophis melanoleucus ssp. catenifer. Here you see how field guides function, though seldom do you have such cooperative species to work with.

In this particular 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 gopher snake was "patterned," and it took only about 30 seconds to thumb through the "patterned pages" to find a match. In the picture, the matching illustration appears on the page's right side, just above the hand's two middle fingers.

scales on snake head

Once a good match was made, the identification was confirmed by referring to notes in the accompanying text where, among other things, descriptions of the various scales on the snake's head were provided. At the left, on the head of a Freminville's Scorpion-hunter, Stenorrhina freminvillii, you can see that on snakes each head scale has a name, a definite shape, and a definite relationship with surrounding scales.

HOW FIELD GUIDES ARE ORGANIZED

Field guides are organized so that we can skip most pages when looking for a matching illustration. They're organized in three main ways:

Fox Sparrow, Passerella iliaca, Copyrighted photo by Dan Sudia Song Sparrow, Melospiza melodia, copyrighted photo by Dan Sudia
photos courtesy of Dan Sudia
Trogon tails

Often differences between species are so subtle that general photos of each species are inadequate. In such cases many field guides provide aids such as shown at the left. The bird in the drawing is one of several species of Mexican trogons. It happens that several trogon species are so similar that to distinguish them it's helpful to see the "bar coding" on the undersides of their tails. In such cases, drawings can be more helpful than photos.

This is an important point to keep in mind because certain field guides are photography based, while others are hand illustrated.