Dunnock - Mating Systems

Mating Systems

Multiple mating combinations exist within dunnock populations, including monogamy (strict pairs), polyandry (two or three males with one female), polygyny (one male with two females), and polygynandry (two or three males with two to four females). Male dunnocks have the largest amount of reproductive success with polygyny and the least in a cooperative polyandrous relationship. Contrarily, the opposite holds true for female dunnocks, who have more success with cooperative polyandry than with polygyny. As a result, these opposite spectrums of reproductive success leads to observed conflicts in the behaviors of female versus male dunnocks as each aim to pursue their interests in a competing range of mating systems. The resulting variable mating system is therefore reflective of the different possible outcomes stemming from sexual conflict between males and females. In cooperative polyandry, females have a gain at the expense of males, while monogamy and polygynandry are mating systems where neither sex is able to have an advantage at the expense of the other.

In terms of territories, female ranges are always exclusive. If two or three males shared one or more females, the males’ ranges overlapped and they would cooperate in order to defend the territory. Among the males is a dominance hierarchy: older birds tend to be the alpha male and first year birds are usually the beta males. Studies have not found cases of close male relatives being involved in any mating combinations. It is possible that the different mating combinations form a continuum as a result of a male’s ability to monopolize his access to females, which can vary from unpaired, to shared access to a female, to sole access to one female, to shared access to multiple females, and lastly, to sole access to multiple females. The male’s ability to control his access to females generally depends on female range size, which is affected by the distribution of food. When there are dense patches of resources, female ranges tend to be small, so the males more easily monopolized them. This led to mating combinations with high male mating success, such as polygyny and polygynandry. If food patches are scarcer, female rangers were larger and more difficult for a single male to monopolize, leading to mating combinations that have lower male mating success (polyandry). In a study, extra food was provided to certain territories, causing female ranges to become smaller. In turn, the mating system shifted towards greater male mating success, such as from polyandry to monogamy and polygynandry.

In regard to parental care and mating behavior, a study found that males tend to not discriminate between their own young and those of another male in polyandrous or polygynandrous systems. However, they increase their own reproductive success through feeding the offspring in relation to their own access to the female throughout the mating period, which is generally a good predictor of paternity.