Why is it that less than 5 per cent of mammal species are monogamous, compared with about 90 per cent of bird species? (continued)
Herman D’Hondt
Sydney, New South Wales, Australia
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One thing that previous answers overlooked is that there is a difference between social and sexual monogamy.
Most birds are socially monogamous. This means that a pair will work together to raise the offspring. That pairing may last for a year or for a lifetime. The reason for this is that most bird species are born helpless and require a lot of care from both parents. That makes it evolutionarily beneficial for the parents to stay together.
But the vast majority of birds are sexually polygamous. In other words, both males and females have sex with multiple partners, all while building a nest with their social partner. The eggs they sit on can have multiple fathers.
While this had been noticed in a few bird species several decades ago, those were considered to be aberrations. It is only with modern DNA testing that the full extent has become obvious, and we now know that some .
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