The adaptive value of polygyny in marsh-nesting red-winged blackbirds; renesting, territory tenacity, and mate fidelity of females

Abstract

Some female red-winged blackbird individuals laid as many as four or five clutches in a single breeding season. Renesting attempts followed nesting failures and high renesting rates were characteristic of unsuccessful females. Most renesting female redwings exhibited a strong territory tenacity. However, some females renested in a different territory and I tried to determine why these individuals moved. Since certain birds always moved more between their renesting attempts than others, the female tendency to move is probably intrinsically determined. Extrinsic factors such as the density of nest predators, male age, and harem size did not influence female movements.The strong site tenacity of female redwings has probably been favoured by (1) advantages of familiarity with the habitat, and (2) strong selection on females for mate and harem fidelity which can be achieved most efficiently when males and females return to their original territories. Renesting with the same male and females from the same harem should increase female's reproductive success because cooperation in nest defense is more efficient between familiar birds. The strong tendency of females to renest in the same area in consecutive years significantly influences mating success of males because new males "inherit" harems of previous territory holders.