10,385 and 9,615 and were assigned to 1955 and 1956, respectively. 
The values about a mean of 8,700 that reflected a 38-percent increase 
were 7,310 for 1963 and 10,090 for 1964. 
These hypothetical population values, created for trend infor¬ 
mation only, are compared with winter and breeding ground survey 
statistics in table 3. Graphic presentation in figure 6 shows 
directional agreement in trends for the group-characteristics 
procedure and the winter survey for the Atlantic Flyway. Winter 
survey data are shown as flyway totals and also as totals for States 
north of Maryland. The group-characteristics procedure results 
show closer agreement with the winter survey for the States north 
of Maryland than with the winter survey for the whole flyway. 
The breeding population survey index differs markedly from the 
others, particularly in 1963. Referring back to table 1, we note 
that the number of black ducks per segment in the northern zone in 
1963 was about double the figure for any of the other 3 years. The 
group-characteristics in the North in 1963 showed highest values 
of any year for paired birds, single birds, and flocked (five or 
more) birds. This pattern could mean that at the time of the 1963 
survey nesting was in an early stage, but at the same time there 
was an influx of postbreeding males from the South. 
Discussion 
The group-characteristic method of computing annual changes in 
black duck breeding populations seems to improve the reliability of 
the data. This is evidenced by its directional agreement with the 
population trend shown by the winter inventory data. There is con¬ 
siderable variation in the degree of trend between the two 
independent sources of data, and the reliability of the annual 
percentage changes in the new method may be quite low. Since it 
appears that the cost in time and money necessary to develop a 
statistically reliable quantitative measure of a sparse population 
of ducks scattered over a large area would be prohibitive at the 
present time, the group-characteristic procedure, which indicates 
trend only, may be, despite its shortcomings, the best possible alter¬ 
native. The bias in selecting certain zone and year combinations as 
representative of the total population may be less misleading than 
accepting the total annual sample each year with no regard for 
evidence of phenological disparity. 
At present, the group-characteristic procedure is considered 
exploratory and tentative. The approach, as outlined in this report, 
should be considered preliminary. Modification may be indicated 
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