Several male-females form communal breeding unit –  (Polygynandry)

Several females and several males form a communal breeding unit. This kind of mating system is believed to occur only in nine percent of total number of bird species.

Alpine Accentor (Prunella collaris)

Alpine Accentor  (Author - Dibyendu Ash) (CC BY-SA 3.0)

Alpine Accentor (Author – Dibyendu Ash) (CC BY-SA 3.0)

The mating system in Alpine Accentor, a small passerine bird, is of particular interest as these unrelated birds are socially polygynandrous. Among them males have a dominance hierarchy, with alpha males being usually older than subordinates. Alpine Accentor females try to mate with all the males, although the alpha male may defend her against mating with lower ranking males. In turn, males also try to mate with all the females.

DNA fingerprinting has shown that there is often mixed paternity, within broods, although the female is always the true mother of the nestlings raised within her nest. Another interesting aspect is that males provide food to chicks at several nests within the group, depending on whether they have mated with the female or not – males provide care only when they are likely to be the true fathers of the chicks.

In their social system home ranges are occupied by breeding groups, which generally include 3 or 4 males with equal number of females. Nests are built low in a bush or rock crevice and 3-5 unspotted sky-blue eggs are laid.

This robin-sized bird prefers bare mountains with some low vegetation and is found throughout the mountainous regions of southern temperate Europe, Lebanon and Asia at heights above 2000 m. It is primarily resident, but winters more widely at lower latitudes, but some birds wander as rare vagrants as far as Great Britain.

Acorn Woodpecker (Melanerpes formicivorus)

Acorn Woodpecker (male) (Author - marlin harms) (CC BY 2.0)

Acorn Woodpecker (male) (Author – marlin harms) (CC BY 2.0)

In Acorn woodpeckers group of adult birds may participate in nesting activities: breeding groups range from monogamous pairs to breeding collectives of three joint-nesting females against seven co-breeding males; however, most nests are made up of only three males and two females. Nesting groups can also contain up to ten non-breeding offspring that act as helpers. Interestingly, these breeding coalitions are typically closely related. The males are often brothers, and the females are usually sisters. Inbreeding is rare, however, meaning that co-breeders of the opposite sex are almost never related. Nestlings from a single brood have been found with multiple paternities.

This bird practices a relatively rare evolutionary feature — Cooperative breeding where more than two birds take care of nestlings. In the society of Acorn woodpeckers the system works in two ways: coalitions and family groups. Coalitions of adults nest together, localizing to storage granaries. Additionally, adult offspring often stay with their parents and help raise the next generation. It is commonly believed that limited territories force cooperative breeding behavior in birds, and in the case of this bird, this limited territory is the acorn storage granary.

In groups where breeding females are more than one, the females put their eggs into a single nest cavity. If there is any egg in the nest before she starts to lay, it is usually destroyed by the female. Once all the females start to lay, they stop removing eggs.

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