SCOPE

In the chapters to follow, dealing with the three hundred and fifty-five kinds of terrestrial vertebrate animals in the Yosemite section, general uniformity of treatment has been one aim. For each species there is given, first, the accepted or approved vernacular name; then the scientific name, chosen with regard to the best technical usage. The order in which the chapters follow one another is essentially that in which the species are classified in the standard lists of North American vertebrates; namely, for mammals, Miller's List of North American Land Mammals in the United States National Museum, 1911; for birds, the American Ornithologists' Union Check-list of North American Birds, edition 3, 1910; and for reptiles and amphibians, Stejneger and Barbour's Check List of North American Amphibians and Reptiles, 1917. Departures from these authorities, either in sequence or in names employed, have been made occasionally by us, but only when justified by special study.

The present volume is not a systematic treatise in the sense of relating primarily to descriptive zoology or to classification. Hence, technicalities along these lines are reduced to a minimum, being mentioned briefly, or restricted to small-type footnotes. The theme of the present book is natural history—that which relates to the living animal.

The "field characters" are intended to include the chief features by which each species may be recognized out of doors. They do not have to do with the scientific 'specimen,' such as constitutes the basis of the usual descriptive account. Ideally, our "field characters" are such as are discernible in the living animal at the ordinary eye-range into which a person can approach the animal under normal conditions. The great majority of these characterizations have been derived from our own observations in the Yosemite region, as recorded in our notebooks. Exceptionally, we have drawn upon our experience elsewhere; or, in the few cases where experience was lacking altogether, we have drawn upon specimens for characters inferred to be useful in the field.

In small mammals and in reptiles and amphibians, the field characterization has been amplified to cover their appearance and proportions when in hand; for opportunity to capture these animals often presents itself to an out-of-doors observer. Even in these cases, however, it is exclusively the external, macroscopic features of the animal that are set forth in the paragraph on "field characters."

Field characters may consist in relative size, in proportions of parts, in general color tone, in pattern of contrasted markings, in peculiarities of movement (flight, gait, mannerisms), in voice, and, with many mammals, in 'sign' (foot-prints, tooth-marks, droppings). Measurements are given, more especially with mammals, and are stated as a rule in both inches and millimeters. Otherwise size is indicated by comparison with some animal commonly familiar. Since size impressions in the field are likely to associate themselves in memory with the best known animals, comparisons among birds are most often made with the robin; among mammals, with the house mouse, house rat, or house cat.

Our paragraph on "occurrence" relates explicitly to the Yosemite section. The status we give of each species is as based on actual findings in the Yosemite section, not upon inference from conditions in the surrounding territory. It must not be supposed to apply to the Sierras generally or to any larger area. "Occurrence" is intended to cover concisely the concepts: season, relative abundance, and distribution by geography, life zones, and vegetational tracts.

In the general, large-type account next following, there will often be found one or more paragraphs discussing some or all of the field characters, especially in comparison with similar species with which confusion in the field might occur. In some cases, characters are discussed with relation to the distinctive habits of the species in question; in other words, correlation of structure and function may be dealt with.

But, let it be emphasized by repetition that, save for only occasional general statements, each account is limited to what was found out by us in the Yosemite region. This will explain the very uneven magnitude of the accounts. Their relative degree of comprehensiveness merely reflects our own varying opportunities of observation. A number of well-known species of the Sierras at large are given but meager attention here because opportunity did not present itself for studying them adequately in the Yosemite 'section.'

Each general account, where the facts have been fully available, has been drawn up, with regard to its subject-matter, on a more or less definite plan of presentation. An introductory paragraph gives local names, other than the accepted vernacular, and an epitome of the leading facts about the species. Comparisons with related species are then made. There follows a discussion of its distribution in the Yosemite region and the special nature of its habitat preferences. Then comes a description of the animal's behavior; its voice; nests, or dens; eggs, or young; care of young; and its feeding habits. We give as much as we have learned with respect to the food of the species, and its relation to plant life in general; also, its relation to other animals, as predator or victim. And, finally, though not appearing at any definite point in the account, we attempt to point out where general biological principles are illustrated.

The facts observed have been gathered together in orderly sequence, and every effort has been made to secure accuracy of expression. Where these facts, thus assembled, point toward some generalization, we have felt free to set it forth. At the same time, we have tried to refrain from idle speculation.

The study of natural history should develop the power of insight—keenness, not only in seeing what animals do, but in determining why those things are done. The interrelations existing between any animal and its environment are exceedingly manifold and vital. To understand these, even in some small degree, brings into play a superior type of intellectual activity, and, we believe, leads to enhanced powers of perceiving and solving human problems. We therefore recommend to the reader that he take advantage of his opportunities to observe and infer without limit beyond whatever we may have set forth herein, to the end that he find both pleasure and profit.