The avian world gave us lovebirds, the Heart-spotted Woodpecker, bleeding-heart doves, the Rock-loving Cisticola (a clear fan of Dwayne Johnson) and the famously monogamous Wandering Albatross. The thing is, despite the existence of some monogamous species, those faithful ones are far from typical. Birds should be associated more with promiscuity and cheating than with faithfulness and monogamy.
Even though many bird species mate for life, there’s still plenty of cheating going on with a lot of them. This pattern may seem familiar to the humans among today’s readers, because the same thing is true for a lot of people. Just because members of a species are socially monogamous—in a long-lasting relationship or even a marriage—does not mean that they are sexually monogamous.
One of the earliest studies to reveal high rates of cheating involved Red-winged Blackbirds. It was well-known that males mated with more than one female because they had territories on which multiple females nested. However, scientists did not realize that the females were cheating with males from adjacent territories until a study in the 1970s. Scientists castrated a large number of males and were surprised when many of the females on their territories still had offspring. The females with sterilized mates who were closest to territories with fertile males were most likely to produce fertile clutches of eggs.
There are advantages of having an unfaithful mother. Research has shown higher fledgling success in the offspring of females who have cheated. Fewer of them are killed by predators and they are less likely to be victims of starvation, presumably because of the behavior of the off-territory males who mate with the mother. These neighboring males are more aggressive to potential predators of nests tended by the females with whom they had mated. Also, they allow only these females to enter their territory to feed.
When scientists began using genetic techniques to ask “Who’s your daddy?”, it became clear that promiscuity was more widespread among birds than was previously thought. Across a wide range of species, many of the eggs in a nest were not fathered by the male tending that nest. Often, a male in a nearby territory and the female at that nest had some explaining to do.
The Superb Fairywrens of Australia have the distinction of being the most promiscuous birds among the socially monogamous. Watching a male and female work together to feed and protect the young in their nest, it is easy to think of them as the perfect family unit, but DNA studies tell a different story. Over three-quarters of the young have a different father than the male taking care of them and over 95 percent of nests have at least one offspring from a different father.
For those hoping for at least some small sign of loyalty, one Superb Fairywren female cheated with the same male for seven consecutive breeding seasons even though she had moved to new territories twice.
On that note of fidelity, I wish everyone a Happy Valentine’s Day!