306 The Ruffed Grouse 



July, covering a three-day period, clearly caused a large loss of young 

 grouse, and led to the highest brood mortality (77 per cent) ob- 

 served in the eleven-year study. Since these excessive losses occurred 

 following high breeding populations, it is likely that they were pre- 

 conditioned by population density relations, whatever may have 

 been the immediate decimating agencies. 



As the young grouse grow older, predation gradually becomes a 

 more important cause of losses. Along about the time the birds 

 reach eight weeks of age, the loss from predation notably rises. This 

 August increase in deaths from predators is largely attributable to 

 the accipitrine hawks, mostly shai-p-shinned hawks, as they are more 

 common. The susceptibility of the young grouse to these attacks in- 

 creases at this time for a short period. The chicks assume more inde- 

 pendence of their mother and take more excursions on their own as 

 they begin to feel their oats. Those that escape are soon educated 

 to cope with this danger and the rat6 of loss drops off again. After 

 the moult in August and September, the young birds assume adult 

 plumage and are hardly distinguishable from their elders. Their 

 losses then are considered to be a part of the adult mortality. 



Adult Mortality. As a matter of convenience, we calculate the an- 

 nual losses of adults from September to September rather than on a 

 calendar year basis, since the young grouse become adults in Sep- 

 tember. The yearly losses of adult birds on New York's Connecticut 

 Hill study area over a twelve-year period have a mean of forty-eight 

 per cent. This mean was exceeded in eight years and in four years 

 the losses were below this figure. The extremes were twenty-three 

 per cent and sixty-four per cent. In five of these years the loss was 

 between fifty-one per cent and fifty-eight per cent, and only once 

 did it exceed the top of this range. On the Adirondack area the ex- 

 tremes were similar, twenty-two per cent minimum and seventy- 

 three per cent maximum witli a mean of about forty-six per cent 

 over a ten-year period {N. Y. S. Cons. Dept. Ann. Reports). 



The spacing of losses of grouse through the year is fairly consist- 

 ent. The high mortality period is from January through April, with 

 the hunting season period added in heavily hunted regions. Summer 

 losses are ordinarily negligible, but rise considerably in September 

 as the young of the year join the ranks of the grown-ups. There is a 

 generally steady increase in rate of loss through fall and winter. 



