94 H. BOYD 



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DISCUSSION 



H. Klomp: How were the mortalities between hatching and fledging 

 determined ? 



H. Boyd: The method varied with the species. For mallard, for example, 

 a direct census method was used. The most pubHcized method in the litera- 

 ture is to follow the changes in brood size, but this is complicated by a 

 tendency of broods to aggregate in some species. In many cases it is only 

 possible to measure the output of eggs, and the ultimate output of young, 

 but not the progress of mortahty in the intermediate stages. 



H. Klomp : Many of the species you have discussed breed in the very 

 far north, where data must be hard to gather. How many actual counts 

 have been done for such species? 



H. Boyd: Some of these Arctic breeders have been studied fairly well. 

 The snow geese of northern Canada have been studied extensively, and 



