Wa. Searcy et K. Yasukawa, THE REPRODUCTIVE SUCCESS OF SECONDARY FEMALES RELATIVE TO THAT OF MONOGAMOUS AND PRIMARY FEMALES IN RED-WINGED BLACKBIRDS, Journal of avian biology, 27(3), 1996, pp. 225-230
We use two approaches to compare the reproductive success of secondary
(S) females to the reproductive success of monogamous and primary (M/
P) females in two populations of the polygynous Red-winged Blackbird A
gelaius phoeniceus. One approach is to calculate x, the mean reproduct
ive success of all S females divided by the mean reproductive success
of all M/P females. Estimates of x are corrected for seasonal declines
in reproductive success of MIP females when necessary. Considering al
l nests, the mean x is 0.98 for two years in a Washington population a
nd is also 0.98 for four years in an Indiana population. Considering o
nly successful nests, and pooling data over years, x is 0.98 for Washi
ngton and 0.96 for Indiana. A second approach is to perform pair-wise
comparisons of the reproductive success of each S female to the reprod
uctive success of those MIP females that choose unmated males availabl
e to, but not chosen by, the S female. In both redwing populations, in
dividuals more often than not have higher success breeding as S female
s than they would have breeding as M/P females with available unmated
males. The implications of these results for polygyny models are discu
ssed.