Cm. Francis et al., EFFECT OF RESTRICTIVE HARVEST REGULATIONS ON SURVIVAL AND RECOVERY RATES OF AMERICAN BLACK DUCKS, The Journal of wildlife management, 62(4), 1998, pp. 1544-1557
Population management of waterfowl requires an understanding of the ef
fects of changes in hunting regulations on harvest and survival rates.
Mean survival and recovery rates of American black ducks (Anas rubrip
es) were estimated during 3 periods of increasingly restrictive harves
t regulations: 1950-66, 1967-82, and 1983-93. From the first to the se
cond period, direct recovery rates declined for at least 1 age class i
n 3 of 6 reference areas, with a mean decline of 14% for adult and 7%
for immature black ducks. From the second to the third period, direct
recovery rates declined in all areas, declines averaging 37% for adult
s and 27% for immatures. Estimated mean survival rates increased from
the first to the second period, consistent with a model of additivity
of hunting mortality. Limited evidence existed for increases in surviv
al rates from the second to the third period for immature males. For a
dults, however, survival increased less between these periods than wou
ld be expected if hunting mortality were additive and changes in recov
ery rates were proportional to changes in hunting mortality. Changes i
n survival and recovery rates of block ducks banded postseason were si
milar to those of adults banded preseason. Comparisons among estimates
by degree;blocks of latitude and longitude indicate that at least bet
ween 1967 and 1983, estimated survival rates of immature and adult bla
ck ducks were lower in areas with high direct recovery rates. Smaller
samples of banded birds and changes in banding locations in recent yea
rs may be limiting ability to evaluate consequences of recent changes
in harvest rates. These correlation-based studies are limited in their
ability to explain causes of observed changes in survival rates, sugg
esting the need for alternative approaches such as adaptive harvest ma
nagement to increase understanding of the effects of hunting on black
duck populations.