300 INFLUENCE OF ff FATHER 



Weather, in its various forms, is one of the basic influences affecting the character of organ- 

 ized life throughout the earth. During the planets formative stages. i)recii>itation and frost 

 action motivated the forces of erosion which gradually broke down the original rock of the 

 earth's crust enabling primitive plant life to gain a foothold. Rainfall, as well as melting snow 

 and ice, also gave rise to the oceans in which, under warm temperatures, the earliest forms of 

 life developed. Throughout succeeding eons of geologic time, these same forces have been 

 instrumental in establishing the vast array of rock formations and soil types which are funda- 

 mental in supporting the vegetation upon which animal life so greatly depends. 



Then, too, conditions created by weather have been directly responsible for many of the 

 major changes in life over the earth's surface. Today the distribution of plants and animals, 

 as well as the nature of many of their characteristics, rests to a large extent upon their reac- 

 tions to conditions controlled by weather. Animals inhabiting these regions, therefore, have 

 become physiologically adapted to certain conditions. When their range reaches an area where 

 the environment is excessively severe, they cease to occur. Similarly, within its normal range, 

 the abundance of a species from year to year may be affected by variations in weather. 



Despite its universal significance, however, knowledge of this factor is still quite limited. 

 The science of meteorology has advanced to the stage where short-time weather forecasts can 

 be made with fair accuracy. But prediction of the effect of such conditions upon the growth 

 and abundance of plants and animals is largely speculative. 



A major reason why existing knowledge with respect to wildlife is meager lies in the com- 

 plexity of the manner in which weather usually exerts its influence. In the first place it com- 

 prises a number of components: temperature, precipitation, sunshine and humidity, to mention 

 a few. But more important are the high variability of these forces, the rapidity with which 

 they fluctuate and the fact that their pattern is constantly changing. Furthermore, the indi- 

 rect and often delayed nature of their effect on an animal tends to obscure the actual relation- 

 ship. 



Another reason involves the applicability of existing weather data to wildlife problems. The 

 standard observations of the Federal Weather Bureau afford an excellent index to the general 

 trend of the various climatic elements. But such records, even those of the nearest individual 

 station, usually differ from the specific conditions experienced on local areas where wildlife 

 studies are being conducted. Therefore, while it is possible, in many cases, to recognize cor- 

 relations between weather trends and the behavior of animal ])opulations, it is usually much 

 more diflicult to determine the mechanism responsible*. 



Weather, with respect to grouse, has long been considered an important factor affecting its 

 abundance from year to year. Many observers have suggested cold, wet conditions during May 

 or early June as a primary cause of scarcity the following fall through in(rcasc<i nest and 

 brood losses. Likewise, "hard" winters have been thought detrimental to the adults. V^Tiile 

 these conclusions have been based largely on conjecture, they are, to some extent, corroborated 

 by findings of the Investigation. Similarly, a number of other ways in which weather affects 

 grouse have been recorded. 



Weather, of course, can be either favorable or unfavorable. Field observations, however, 

 pertain pritnarily to its effect on mortality. For this reason, the observations discussed here- 

 with deal largely with this phase of the subject. 



Apparent correlations have been observed during each of the three life periods. Undoubtedly 



* Reaparch in esperimcntal phytiology (ace Chapter U) ia beginaing to throw tome tight on theac relationahipa. 



