Ostriches, like humans, deal with the problems of motherhood by banding together to care for their babies.
Individuals take turns incubating eggs in communal nests where groups reproduce.
However, there are consequences to cooperative breeding since there can be fierce rivalry over mating and who gets to incubate the eggs.
In cooperative animals, the optimal breeding group size varies by sex
(Photo : PRAKASH SINGH/AFP via Getty Images)
"In nature, the opposing forces of competition and collaboration are predicted to result in an ideal group size," explained lead author Julian Melgar, a postdoctoral researcher at Lund University in Sweden, as per ScienceDaily.
The most prevalent argument is that group sizes fluctuate in response to changes in environmental circumstances, however, this does not explain why groups with different compositions exist under comparable settings.
Researchers set out to investigate the costs and advantages of group size under controlled ecological settings, untangle the influence of individual variations from group qualities on reproductive success, and determine how competition and cooperation vary with group size.
Over an eight-year period, experimental groups of ostriches were created at the start of each mating season in May by putting various numbers of males and females in huge enclosures in the Klein Karoo, South Africa.
Similar to the variety of group sizes reported in the wild, groups consisted of one or three males and one, three, four, or six females.
The cooperative incubation behavior was temporarily suppressed during the mating season by removing eggs.
The influence of the number of men and females in groups, as well as collaboration during incubation, on reproductive success, was studied.
These disparities in male and female reproductive success can help explain why group sizes vary so greatly in nature.
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How Ostriches Do It
The mating methods of the various subspecies are similar, however, specifics may vary, as per Livescience.
Males will often defend their own little area from the competition, while groups of females may move around, visiting possible mates.
Men will mate with several females and females will mate with many males in a single season.
To attract a female, a male will do a little dance in which he crouches down and alternately brings his black-and-white wings forward, one after the other.
A wooed female will sit down, allowing the male to mount her from behind and inseminate her by putting his phallus (pseudo-penis) into her cloaca (waste and reproductive orifice).
Although the male will mate with the other females in the group, he will only create a life-long mating relationship with one "dominant" female.
After mating, the male digs a shallow hole in which all of the ladies lay their eggs, with the dominant female's eggs in the middle (the best spot).
Evans told LiveScience that the dominating female will incubate all of the eggs while the other females flee. They go to begin another breeding effort with another man.
Surprisingly, once the chicks hatch, the males take care of them. If a child-rearing male encounters another ostrich parent, the winner will take both pairs of chicks.
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