Love match: zebra finches make great parents if they get to choose their own mates (Image: blickwinkel/Alamy )

True love seems to make birds better parents. Birds that are allowed to choose their own partners are more diligent parents, according to a team who arranged “marriages” for zebra finches.

Zebra finches are one of many animals that pair up for life with both sharing parental duties.


Most research on how animals select their mates has focused on indicators of quality, assuming that all individuals agree what constitutes an attractive partner, with little attention paid to the reasons why individual preferences may vary. One idea is that individuals choose partners whose genes are compatible with their own. Alternatively, they may pick a mate whose behaviour is a good fit.

To test this out, researchers from the Max Planck Institute for Ornithology in Seewiesen, Germany, wondered what would happen if animals were matched with partners arbitrarily instead of being given free choice.

First, they organised a “speed-dating” event for their population of 160 aviary finches, allowing the birds to form pairs freely. They then paired up half the females with males they hadn’t chosen – essentially breaking up the earlier relationships.

Breeding success

The new pairs were put in individual cages for a few months to enable them to bond. Both the control group and the arranged pairs were left to breed for five months in cages shared by three pairs, while the team studied their breeding success.

The number of surviving chicks was 37 per cent higher in pairs who chose their own mate. In the arranged pairs, three times as many eggs were unfertilised, more eggs were buried or lost, and more chicks died after hatching. Males in these partnerships also attended the nest less diligently while the eggs were hatching, when chicks are most vulnerable.

Unsurprisingly perhaps, females were less willing to mate with males they hadn’t chosen, and the males were more likely to look for new partners.

The researchers also found that the death rate for embryos was the same across the two groups, suggesting that the lower egg survival rate was due to the quality of parenting, and not genetic incompatibility in the mismatched pairs.

If the birds were choosing mates for their genetic compatibility, you would expect that the embryo mortality rate would be lower in chosen pairs, as they would be more genetically compatible and therefore produce healthier embryos.

The lead author Malika Ihle thinks reproductive success was lower among forced pairs because “psychological constraints” prevented them from parenting to the best of their ability. “They should have worked as much as they could and raised as many chicks as they could, but they simply couldn’t,” she says.

Complex behaviour

Pair bonds involve immensely complicated behaviour, says Tamás Székely, from the University of Bath, UK. Couples function well partly because they are willing to work hard to raise offspring together, but also because they may complement each other.

“If a male, let’s say, is better at defending the nest than the female, whereas females might be better at feeding the young, a successful couple might be one that splits the roles,” Székely says. “Such behavioural complementarity can maintain pair bonds, and can be the trademark of a successful family.”

Nick Royle at the University of Exeter, UK, says it wasn’t entirely clear from the study how individuals identify behavioural compatibility in prospective partners, but personality traits, such as how bold or shy an individual is, might play a role. “The current study nicely demonstrates the importance of getting your choice of mate right first time, and that attractiveness is a relative, not absolute, concept,” he says.

Journal reference: PLOS Biology , DOI: 10.1371/journal.pbio.1002248