each year in visibility, in observers, in 
weather, and in a host of other factors. 
However, the winter survey data have 
great value for determining the use made 
of various wintering areas and the change 
in waterfowl distribution from year to 
year in response to changing weather and 
habitat conditions. 
All data referring to the 1964 winter 
survey are based on observed birds — 
appendix tables A-l to A-17. 
BREEDING GROUND SURVEYS 
The breeding ground surveys are co¬ 
operative. The Bureau of Sport Fisheries 
and Wildlife, the Canadian Wildlife Ser¬ 
vice, the Provincial game branches, 
Ducks Unlimited, and the State conserva¬ 
tion departments combine their equipment 
and manpower to conduct the necessary 
surveys throughout the vast extent of the 
waterfowl breeding range. 
Flyway biologists of the Bureau survey 
most of the important waterfowl breeding 
areas in Alaska, Canada, North Dakota, 
South Dakota, and Minnesota from the 
air. Statistically designed sampling tech¬ 
niques and similar methods of collecting 
and analyzing data are used throughout 
these areas. In addition, many of the 
Northern States conduct breeding ground 
surveys which may vary somewhat but 
are generally similar in methods to those 
employed in the Dakotas, Canada, and 
Alaska. 
The aerial crews count the birds on 
somewhat less than 1 percent of the total 
breeding area. This is sufficient cover¬ 
age to reduce sampling error to less than 
20 percent of the average population den¬ 
sity in most survey areas, and to much 
less than 20 percent when considering the 
breeding range as a whole. 
The results of the breeding ground 
surveys are presented as indexes. When 
conducting aerial surveys of breeding 
birds or of broods, not all birds present 
are seen by the aerial crews. Methods 
are being developed to measure the pro¬ 
portion of birds present but not visible 
from the air. These studies have not pro¬ 
gressed to the point where visibility fac¬ 
tors can be determined throughout the 
breeding range. Therefore, the indexes 
in this report are based on birds actually 
seen, and it is emphasized that they do 
not constitute estimates of the total num¬ 
bers present. 
Surveys are conducted for the purpose 
of estimating the relative size of the fall 
flight from each of the breeding areas. 
Two coverages are required to obtain 
the necessary information: during May 
and June to measure distribution and re¬ 
lative size of the breeding population, 
and during July to forecast the relative 
number of young that will be produced. 
It is necessary to make an estimate of 
the number of young that will be pro¬ 
duced, since only a part of the eggs will 
have hatched before the shooting regu¬ 
lations are established. The production 
survey, therefore, is a measure of the 
number of broods on the water at the 
time of the survey plus a measure of 
weather, water, and other conditions 
that affect or reflect production success 
following the survey period. 
Results of the May breeding popula¬ 
tion survey and of the later production 
survey, which form the basis for fore¬ 
casts of changes in the relative size of 
the fall flight, are contained in tables 
B-l to B-70. 
ALASKA 
Data supplied by Henry A. Hansen and 
James G. King, Jr., Bureau of 
Sport Fisheries and Wildlife 
Based on the past 8 years of air and 
ground surveys, the stratification of 
Alaska's waterfowl habitat for sampling 
purposes was changed in 1964 to com¬ 
prise two strata based primarily on like 
ecological characteristics. Stratum 1 
encompasses all the treeless, coastal 
2 
