Weather Conditions in Relation to Grouse 185 



compare Weather Bureau records of sunshine with grouse egg-laying 

 dates, we conclude that the greater the number of hours of sun- 

 shine in March and early April the earlier egg-laying will begin. 

 There seems to be no correlation with precipitation and only a slight 

 one with temperature. The latter is probably a by-product of the ef- 

 fect of day length and the involved sunniness on temperatures. 



The part played by sunlight (or light) in determining the time 

 of egg-laying is corroborated by laboratory experiments which 

 show that grouse, as well as other game birds, poultry, trout, etc., 

 can be stimulated to egg production months ahead of the normal 

 time by the use of artificial light. 



Egg Losses Little Affected by Cold or Rain. A bird's egg has re- 

 markable ability to resist the hazards of changeable spring weather. 

 With eggs in the nest and before incubation has begun, tempera- 

 tures as low as twenty-one degrees Fahrenheit have been observed 

 and in no case has any adverse effect been noted. After incubation 

 the temperature is kept constant most of the time by the mother's 

 body, but even then the eggs can withstand surprisingly adverse 

 conditions. Temperatures well below freezing far into May, storms 

 that leave snow on the ground for as long as four days, and many 

 gully-washer rains, occur many times with no discernible effect on 

 the eggs. Eggs taken from a nest two days after the mother had 

 been killed, when temperatures had been below forty degrees, 

 hatched in an incubator a few days later. 



Evidently the eggs can stand considerable hardship without 

 themselves being destroved. How much weakening of the young 

 is caused by such adversity, with resulting delayed mortality, is un- 

 known. It is reasonable to assume that chicks from eggs that have 

 been seriously exposed will be somewhat weaker than normal and 

 may, therefore, have a higher subsequent mortality. However, we 

 have not been able to correlate egg losses with variations in weather 

 conditions. 



Leopold (1933) referred to the drowning of nests or young in 

 heavy rain or floods as due to accident. We have observed only one 

 nest destroyed by water and believe that such losses are ordinarily 

 of no particular significance. 



Brood Mortality Affected by Weather. One of the most baffling 

 problems in the life history of the grouse is the high mortality of 



