Annual fluctuations in population levels.=-The degree to 
which mallard populations will fluctuate is obviously a function not 
only of changes in annual mortality rates but also those yaarly 
changes involving productivity. The interrelationship of these | 
two variables is set forth in table 71. From unpublished data 
furnished by A. S. Hawkins of the U. S. Fish and Wildlife Service, 
I find that the annual productivity of mallard populations (as 
indicated by bag analyses in Arkansas) do vary within the magni- 
tudes set forth in this table. One should notice then that with 
adult mortality rates of O per cent per year, population increases 
may be anywhere from 2 to 80 per cents; the difference between these 
two is 78 per cent. On the other hand, with a-65 per cent adult 
annual mortality rate, the variation in population levels covers 
US per cent (from -l,0 to +5). From this we may conclude that 
maximum fluctuations will tend to be more associated with differences 
in productivity than with variations in adult mortality. The recent 
research emphasis on productivity analyses of waterfowl is an impor- 
tant reaction to Hawkins' results along these lines. 
Table 71.=-Annual Changes in Level of a Population of Even 
Sex Ratio 
This table illustrates the magnitude of population fluctuations 
to be expected in mallards, Thus wnen young number 0.7 per adult 
(i. e. kl per cent of the population) at the end of the hunting 
season, the population will increase 2 per cent if the adult 
mortality rate is hO per cent per year; it will decrease 6 per 
cent if this adult mortality rate is 45 per cent per year. 
Annual 
Adult Number of Young Per Adult at End of Hunting Season 
Mort. 

40 2 8 1k 20 26 32 38 kh 5O 56 62 68 7h 80 
LS -6 -1 k 10 16 21 26 #32 #38 #443 4b Sh 60 65 
50 -15 -10 -5 0O 5 10 15 20 25 30 35 hO 4S 50 
55 -2 -19 ~1) -10 ~6 -1 8 12 17 22 26 30 35 
60 =32 ~28 -24 -20 -16 -12 -8 -) OF 8 12 16 20 
65 -0 -37 =3 -30 ~26 -23 -20 -16 -12 -9 -6 -2 2 §G 
% Young 
in Rp bl Wh 7? 50 52 55 57 58 60 62 63 6h 66 67 

Summary 
A possible correlation was found between annually fluctua- 
ting mortality rates for adult mallards and variations in first- 
season recovery rates. A potential method of obtaining the percentage 
162 
