NUMBER OF EGGS LAID 



361 



A hen grouse potentially might lay many more eggs than she actually does. A single bird 

 reared at the Research Center was found to have 177 ova of various sizes in her ovaries, all 

 visible to the naked eye. More than 150 ova have similarly been counted in a wild female 

 taken just prior to the breeding season. 



A grouse might thus conceivably lay hundreds of eggs in its lifetime, whereas actually it 

 will lay but a few dozen at most. The maximum number of eggs laid in a single season 

 appears to be about 19. The normal average first clutch is 11.5, with an average of 7.5 

 for the renest, in case the first attempt is unsuccessful. 



What causes a female grouse to stop laying eggs as the season progresses is not certain. It 

 probably involves some fundamental physiological changes. As has already been mentioned* 

 temperature may have some effect. Likewise, a study of the influence of light, both as to 

 duration and intensity, on the reproductive period of grouse was carried on at the Research 

 Center during 1935 and 1936, In the winter and spring small amounts of light above normal 

 were found to stimulate reproduction: large amounts at first stimulate, then inhibit, this reac- 

 tion" '". It is entirely possible that the increasing intensity and the longer hours of daylight 

 which characterize the advance of spring at first encourage, then, within the physiological 

 limits of the birds, delimit the period of reproduction. 



Loss of weight has been considered as a possible factor in cessation of egg laying. It seems 

 logical that this drain on the bird's system might so exhaust her as to cause a condition when 

 egg laying is physically no longer possible. The available evidence fails to support 

 this concept, however. 



Most of the birds" weight-loss takes place in the late winter, during incubation and in the 

 early brood period. This rate does not ai)prcciably increase during egg laying. Furthermore, 

 at the Research Center, both the males, and the females that do not lay, also lose weight. This 

 is also typical of males in the wild^. 



The very fact that many birds, after laying a full clutch of eggs, lay another group follow- 

 ing destruction of their first clutch, is evidence enough that the bird is not limited at this time 



» See Chapter \ 1, p. 303. 

 A See Chapter II. p. 92, 



