Jr. Freeland et al., EXTRA-PAIR PATERNITY IN WILLOW PTARMIGAN BROODS - MEASURING COSTS OF POLYGYNY TO MALES, Behavioral ecology and sociobiology, 36(5), 1995, pp. 349-355
Willow ptarmigan are one of only three monogamous grouse species in No
rth America. However, in some populations between 5 and 20% of individ
uals pair polygynously. It has been suggested that monogamy may be mai
ntained by the high cost of polygyny to males. We have used DNA finger
printing to assess the actual reproductive success of both monogamous
and polygynous adults. We determined whether or not the putative paren
ts were the biological parents of the chicks from 38 broods. Of these
clutches 30 were from monogamous matings, and 8 were from bigamous mat
ings. Of the 207 chicks from monogamous matings 96% were within-pair o
ffspring, compared to 67% of the 49 chicks from bigamous matings. All
extra-pair offspring chicks resulted from extra-pair fertilizations (E
PFs), and there were no instances of intraspecific nest parasitism. Ma
te guarding by monogamous males seems to be a highly effective method
for maintaining genetic monogamy, as the only cases in which EPFs occu
rred were when the resident female left the territory for a few days o
r when a second female visited the territory. Our results support the
notion that certainty of parentage may be one factor constraining will
ow ptarmigan males to be monogamous.