Evidence from band recoveries indicates that the black ducks 
using the survey area provide most of the population that winters 
in the northern part of the Atlantic Flyway. Many black ducks 
wintering in the southern part of the Atlantic Flyway originate in 
the surveyed area also, but here they are mixed with black ducks 
which originate west of the surveyed area. The effect of this 
western component may be insignificant, but our knowledge of its 
influence is very inadequate at this time. Because of this, the 
winter survey data are shown for both the total Atlantic Flyway and 
that portion of the flyway north of Maryland. 
Breeding population survey figures were based upon matched 
transect segments in 1955 and 1956, and in 1963 and 1964, but were 
not matched between 1955-56 and 1963-64. Also, in 1955 and 1956, 
the area surrounding Knob Lake and Goose Bay was intensively sampled. 
In 1963 and 1964, only a small sample was drawn. To avoid a possible 
bias from uneven sampling intensities, the Knob Lake - Goose Bay area 
data were omitted from all 4 years. Inclusion of these data would 
have increased the upward trend from 1955 to 1956, for the change in 
that area was more marked than the overall change, as shown in the 
following table: 
Segments 
Black 
ducks 
Ducks per 
segment 
Area 
1955 
1956 
1955 
1956 
1955 
1956 
Knob Lake - Goose Bay 
95 
95 
104 
151 
1.09 
1.59 
Other 
227 
227 
300 
324 
1.32 
1.43 
Total 
322 
322 
404 
475 
1.25 
1.48 
To determine population trends from the group-characteristics 
procedure, it was necessary to assign hypothetical population sizes 
to demonstrate the percentage changes. In assigning these values, 
the change between the 1955-56 and 1963-64 sets of data was considered 
primary. An arbitrary mean value of 10,000 was given to the 1955-56 
population of black ducks. The group-characteristic procedure indicated 
that there was an average 13-percent decrease between the 1955-56 and 
the 1963-64 periods (southern zone, 8 percent; central zone, 21 percent; 
northern zone, 10 percent). Hence, the mean value assigned to the 
1963-64 period was 8,700, or 13 percent less than the value for the 
1955-56 period. 
The group-characteristic procedure suggested an 8-percent decrease 
between 1955 and 1956 and a 38-percent increase between 1963 and 1964. 
Values about a mean of 10,000 that showed an 8-percent decrease were 
9 
