Table 3.-"Black duck population trends from several indexes 
_ Index and percent difference from 4-year mean _ 
Source_1955_1956_1963 1964 
Winter Survey - 
Atlantic Flyway 
(thousands) 582.5 (+37) 
Winter Survey - 
Atlantic Flyway 
north of Maryland 
(thousands), 224.9 (+18) 
Breeding Population 
Survey - segments 
matched in 1955-56 
and in 1963-64 (ducks 
per segment) 1.32 (0) 
Group Characteristic 
Procedure (reference 
numbers).!/ 10,385 (+11) 
424.8 (0) 
179.7 (-6) 
1.43 (+8) 
9,615 (+3) 
325.2 (-23) 
157.0 (-18) 
1.49 (+12) 
7,310 (-22) 
366.3 (-14) 
201.6 (+ 6 ) 
1.06 (-20) 
10,090 (+8) 
These values were created, for computation purposes only, from percentage changes. See text 
for details. 
