318 



PRE DAT I ON 



Adult Period 



Considering birds of the year as adult by September 1. the fall season ushers in the last of 

 the three life periods. Most broods soon break up, the fall shuffle takes place and then winter 

 sets in. Like their parents, the young birds must now fend for themselves and "the devil take 

 the hindmost". Between this time and the following April the final culling of the breeding 

 stock takes place. 



Again data have had to come from the areas on which seasonal censuses were being con- 

 ducted. In measuring adult mortality two major milestones have been used each year, 

 namely, the breeding season (April), and the following September when the next year's 

 increment comes of age. On Connecticut Hill losses during the former |)eriiid have averaged 

 41.6 per cent, while for the full twelve months the mortality has been 50.2 per cent. On 

 the Adirondack area the figures have been 52.6 per cent and 57.9 per cent respectively. The 

 low proportion taking place during the summer has been consistent on both areas. In table 

 38 is shown the total mortality each year as well as the size of the initial fall population. 



TABLE 38. ADULT MORTALITY RECORDED ON CONNECTICUT HILL AND 

 ADIRONDACK STUDY AREAS— 1930- 19H* 



♦Year uidicated is that of the boKiiining of each September 1 to August 31 period, 

 .^Katimute made in January 1M32 und therefore somewhat below September level, 



till l'*33 oil the Adirondaek area and in 1937 on Connecticut ilill. mortalities of 52,9 per cent and 45.8 per cent respectively 

 were recorded by April hut during the ensuing summers more birds moved into the areas than wen> lost. 



The remains of a large proportion of the adult grouse lost each year have been found and 

 brought in to the laboratory for examination arcom])anied by a description of the situation in 

 which each was found. They have then been studied for evidence as to what the cause of death 

 may have been. 



Only about half of the specimens, however, have been sufficiently fresh and complete to 

 diagnose*. In fact in Uj.S per cent of those looked over it has been impossible to form any 

 conclusion at all. Of tlie balance 9L1 per cent have shown signs of predation. a proportion 

 which undoubtedly would apply to the others as well. But whether or not this was the initial 

 decimating agent can seldom be determined directly. 



One must, therefore, weigh the available evidence with respect to the other important pos- 

 sible causes of this mortality. Besides predation only two, accident and disease, warrant 

 consideration. The often suggested relation to birds crippled during the hunting season does 

 not enter here since shooting has been prohibited on these areas. 



Regarding the former a few birds have been found which had died from injuries sus- 

 tained ill flying into some obstruction. Most of these have occurred during the fall "crazy 

 flight" season. Yet the majority of the loss does not take place until after mid-winter. It is 



• See Chapter XII, p, 532. 



