Zebra Finches

Humans go through an awful lot to choose a mate. Before settling down and having children there tends to be a lengthy process that involves nervous flirting, set-ups by friends, online dating, humiliating rejections and the occasional lucky hit. At the end of it all the hope is to fall in love and live happily ever after. In evolutionary terms it all seems to be a big waste of time and energy when we could simply go forth and multiply. So what is the evolutionary point of it all?

To do an analysis of the benefits of love in humans is challenging and there are some ethical limitations on doing experiments.

But a new study published in PLOS Biology describes an experiment conducted by researchers from the Max Planck Institute of Ornithology that may give some answers to question of love.

Malika Ihle, Bart Kempenaers, and Wolfgang Forstmeier, the authors of the study. took advantage of the fact that zebra finches share many characteristics with humans including mating monogamously for life and sharing the burden of parenting.

Female zebra finches also choose mates in a way that is specific to the individual with little consensus among females as to who is the fittest mate.

The authors took a population of 160 birds and left 20 females to choose freely between 20 males. Once the birds had paired off half of the couples were allowed to remain together, while the other half were split up and forcibly paired off with other individuals.

The couples were then left to breed in aviaries and the researchers assessed the behaviour and the number and paternity of dead embryos, dead chicks and surviving offspring.

For birds that had chosen pairs the final number of surviving chicks was 37% higher than for birds who had not chosen their mates. The nests of non-chosen pairs had almost three times as many unfertilized eggs as the chosen pairs, a greater number of eggs were either buried or lost and more chicks died after hatching. Most deaths occurred within the chicks’ first 48 hours which is a critical period for parental care and in which non-chosen fathers were less diligent in their nurturing duties.

The couples’ courtships also showed some noticeable differences. Although, non-chosen males paid the same amount of attention to their mates as the chosen males did, the non-chosen females were far less receptive of their advances and tended to copulate less often.

There was also a higher level of infidelity in birds from the non-chosen pairs; the straying of male birds increased as time went by while the females roamed less.

The researchers concluded that individual birds vary in their tastes and choose mates because they find them stimulating in some way that isn’t necessarily obvious to an outside observer. This stimulation turns females on and increases the likelihood of successful breeding and encourages paternal commitment during the essential time required to raise young.

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