EFFECT OF AGE ON BREEDING 359 



In general there seems to be no hesitation on the part of either sex in accepting a different 

 mate, provided each is in the mating phase of the breeding cycle. If males do occasionally 

 fail to mate, it does not, ordinarily, very seriously affect the number of eggs fertilized. 



Females 



Perfect mating is much more important with the females than with males. Every failure 

 means infertile eggs. A small decline in the number of successful grouse nests in some favorite 

 covert may well mean the difference between good and poor hunting the following fall. 



Also some females apparently do not attempt to nest and lay eggs. An accurate evaluation 

 of this factor in the field is difficult, even where the population of females is known, due to 

 the difficulty of locating all of the nests on an area as well as the impossibility of recognizing 

 all instances of renesting. However, a fair estimate of the proportion of females nesting is 

 possible through interpretation of known figures. 



The number of unlocated successful nests has been determined by subtracting the number 

 of located nests from the number of broods found in the summer. By assuming that the 

 number of unlocated nests that were broken up is in the same proportion to the number of 

 located broken-up nests as the corresponding figures for successful nests, the number 

 of unlocated nests that were destroyed may be estimated. The total number of nesting 

 females may then be computed by adding the number of successful and unsuccessful nests, 

 after adjustment for the number of renests. Finally, comparison with the known female pop- 

 ulation gives an estimate of the proportion failing to nest. 



The degree of non-nesting obtained by this method has varied from zero to over 25 per 

 cent of all the females on the Connecticut Hill study area in different years, the figures for 

 1933. 193Sand 1936 being especially high. That this is usually a minor factor, however, is 

 evident from the fact that during most of the other ten years studied all known females were 

 accounted for as attempting to nest. 



What may have been responsible for a high incidence of breeding failure when it did occur 

 could not be determined. In a broad way it may be said that such females are probably 

 physiologically upset and unable to breed properly. At least there is no observation to the 

 contrary. But what the underlying causes of such variations may be remains an enigma. It 

 has been suggested that, on the study areas, human disturbance of the breeding birds may 

 have been involved, but this influence has not varied greatly from year to year. 



Thus, while losses resulting from failure of females to breed may now and then significantly 

 reduce productivity, they are usually one of the host of minor influences on the grouse crop 

 which, by themselves, are relatively unimportant but, which when added together, may 

 measurably affect the hunting season population. 



EFFECT OF AGE ON BREEDING 



The ruffed grouse is sexually mature early in the first spring following birth. In captivity 

 at the Research Center, they have usually bred during the first year, a conclusion likewise 

 confirmed for wild birds by observation. In some years, every female known to reside on 

 certain areas studied has at least started a nest. Since the whole population would inevitably 

 include some female birds born the preceding year, these cases support the conclusion. 



One wild female was known to continue nesting attempts at least through five years. This 

 bird was nest-trapped and leg-banded in 1936. That year she laid ten eggs. The next year 



