known that when using the aerial method in particular that a portion of the birds 
are missed. Even though the "index!! figures are not a measure of total . 
populations, it is believed that they are representative of relative population 
levels to the extent that year to year changes can be detected: ‘Although a. 
measure of total population would have certain advantages, a determination 
of relative changes seems adequate for the purpose of practical management. 
Needless to say, the breeding ground surveys are cooperative in nature. 
The Fish and Wildlife. Service, the Canadian Wildlife Service, the Provincial 
Game Branches, and Ducks Unlimited combine their manpower and equipment 
to cover all of the important waterfowl breeding areas in Canada. Service 
Biologists cover the important areas in Alaska, while the State Conservation 
Agencies, with some help from the Service, carry on surveys in about 25 States. 
