fish, and recreational considerations, as well as agriculture, range management, 

 and forestry, and certain phases of such important enterprises as soil and 

 water conservation, fish and game administration, and farm and ranch management. 

 Life-history studies, together with investigations of classification and dis- 

 tribution, cojastitute an important part of the foundation for work in this 

 important new field. 



METHODS 



The importance of methods of study of mammalian life histories, and indeed 

 of mammals in general and their other animal and plant associates, can scarcely 

 be exaggerated. Viith proper and adequate methods the end result is sure. But 

 standardization of methods is not only undesirable, it is impossible. Each 

 species of mammal — or other animal or plant, for that matter — constitutes an 

 individual species problem. Moreover, within a species there is much variation 

 in response to surroundings, depending on age of the individual, geographical 

 location, or other factors. For every species, every year, every time of year, 

 and in every locality, different methods of study may be required. For each 

 problem Involving complicated organisms, as mammals in their environment, a 

 unique set of methods may be required. Solution of the problem is likely to 

 depend on invention or application of appropriate procedures. At best, manuals 

 of ecological methods are only a point of departure in the development of ways 

 and means for working out a given problem. Methods may well be studied and be 

 standardized, but there will always remain a point beyond which standardization 

 cannot go. The resourcefulness of the investigator will doubtless remain for 

 all time to come his most important piece of equipment. 



Relation of Field and Laboratory Methods 



In the study of mammalian life histories, the use of both field and labora- 

 tory methods is abundantly justified. The possibility of a complete control of 

 certain environmental factors under laboratory conditions sometimes leads to 

 undue enthusiasm for this type of research. The value of laboratory Investiga-. 

 tions, however, may often be lessened by a loss of the normal response of the 

 mammal* 



With some mammals, which are of such size, number, and ten^jerament that 

 laboratory work with them is possible, studies like that of Yerkes (1907) with 

 the dancing mouse may be counted on to yield results of the highest Importance 

 in respect to such problems as sense development and discrimination, habit for- 

 mation, learning ability, and modlf lability of behavior. The work of Sumner 

 (1915), although largely concerned with problems of evolution and genetics, has 

 afforded much information of value in studies of life history. Many mammals, 

 however, cannot be so easily brought into the laboratory or successfully kept 

 in captivity. The ideal method is for the life history student working in the 

 open to carry his investigations into the laboratory whenever possible. The 

 two fields are so vast and specialized, however,, that this Is rarely practicable. 

 If adequate conclusions concerning behavior under actual living conditions are 

 to be reached, it is necessary to associate work in the laboratory with direct 

 observations of the animal in the natural state; and many of the most important 

 details of animal life histories can never be learned in the laboratory. 



