Munich, Germany – In a new study, researchers aimed to find the effects that monogamy has on the reproduction and success of a species. With this in mind, they analyzed the socially monotonous bird zebra finch.

Among scientists there has been an increasing interest in the study of mate choice and the different factors or elements that make individuals attractive to others. However, in many species the individuals can vary significantly in who they find attractive. This variations are commonly labeled as “mate choices for compatibility”. The team from the Max Planck Institute for Ornithology who conducted the research aimed to quantify the benefits of the mate choice in the zebra finch.

Australian zebra finches are small colourful birds native to Australia. They have mostly grey plumage with a white underside. Credit: twycrosszoo

But, why the zebra finch?

This type of birds actually share some similarities with human behavior. First of all, like humans, zebra finches pair up socially for a lifetime. They form “marriages” which they tend to keep for their whole lives. However, like humans, this doesn’t mean they are sexually monogamous. In different degrees, both male and female zebra finches are known to look out for sex elsewhere. Additionally, the females birds seem to have a very particular taste. Every female zebra finch will choose a mate based on her own criteria, meaning that there is no a unique quality that would make a male zebra finch more attractive to all the females.

All of these behaviors from the bird species are applicable and comparable to humans, according to the authors of the research.

The Love Experiment

The study, published in the journal PLOS Biology, placed male and female zebra finches into a room and let them pair up. Malik Ihle and colleagues Bart Kempenaers and Wolfgang Forstmeier set up a “speed-dating” session for the birds, allowing 20 females to choose freely between 20 males. Then, the team separated the bird couples into two groups. Half the couples were kept intact, and other half were split up and put into arranged partners.

For the surprise of the scientists, they found that, “Zebra finch pairs that resulted from free mate choice achieved a 37% higher reproductive success than pairs that were forced to mate,” Ihle and her team wrote. As for the forced partners, they suffered from an increased failure to fertilize eggs and from increased mortality of hatched offspring.

Researchers also observed more infidelity in the artificially paired mates, even though males payed initially just as much attention to their females when they were paired randomly. In females, the experts observed a reduced disposition to copulate with the assigned partner, while males that were force paired demonstrated a reduced parental care and increased activity in searching for other females mates.

Results showed that zebra finches ultimately choose their mate based on behavioral compatibility, rather than by a genetic compatibility, which would allow female zebra finches to select a partner with whom they could minimize the rate of embryo mortality.

Source: PLOS Biology