Why Love Matters to a Zebra Finch

When birds choose their own mates, they're better partners and parents.

Love is complicated—ask anyone who's ever been forced into an arranged marriage at the hands of mad scientists. That’s exactly what 160 Zebra Finches faced during a recent study conducted by the Max Planck Institute for Ornithology in Seewiesen, Germany—though to be fair, the scientists weren’t necessarily mad, just very curious about the role love (or "behavioral compatibility," as they like to call it) plays in successful bird reproduction.

Zebra Finches make the perfect subjects for such an investigation, because they're monogamous birds that often mate for life, sharing nesting and offspring rearing duties (though they’re also known to enjoy an occasional midnight rendezvous with a sultry neighboring finch). To find out how much love matters when it comes to reproduction, the researchers put single Zebra Finches in a sort of speed-dating chamber, and allowed them to select a partner at will.

Females, who do the mate selecting, clearly had personal preferences, even if their rationale for those choices wasn't immediately clear to the researchers (there’s no obvious beauty standard among these birds). Once the birds were coupled up, though, the scientists butted in and did a little twisted match-making of their own: Half the couples were separated and forced into new pairs, while the other half were left alone. Over the course of several months, all the birds were given time to bond with their partners (forced or chosen) before being released in a communal aviary to breed.

Tension among the arranged pairings was immediately evident. While males in both groups courted their lovers without second thought, female finches in forced pairings were much less responsive to these overtures. The arranged-partnership males, for their part, were more likely to indulge in promiscuity and neglect their parental roles.

The discord between forced partners was even more obvious when the scientists examined how the birds fared at reproduction and chick-rearing. All the female birds laid nearly the same number of eggs, but the survival rate of chicks resulting from self-selected partnerships was 37 percent higher than that of the chicks whose parents had been forced together. The lovey-dovey finches also displayed a more synchronized relationship when it came to the rearing of their young, and they remained physically closer together throughout the study.

What the researchers ultimately concluded is that female finches select mates based on how well the two birds complement each other’s behaviors. The right pairing stimulated finches to perform better as partners and parents and proved crucial to their hatchlings’ success. Dr. Malika Ihle, the study’s lead author, hopes the findings could enhance reproductive success rates in captive breeding conservation programs, especially those that focus on monogamous bird species. “To make individuals invest the most into their reproduction,” Dr. Ihle says, “we should give as many mate choices as we can.”

For example, the critically endangered Maui Parrotbill, found only within a 50-square-mile radius on the eastern side of Maui’s Haleakalā volcano, is one bird that may benefit from the study’s findings. Like Zebra Finches, Maui Parrotbills are monogamous breeders and are prone to similar compatibility setbacks, especially in captivity. Maximizing parrotbills’ mate selection may prove vital to their recovery.

While the study didn’t answer exactly how finches pick their ideal partners, one thing was clear: When it comes to love, compatibility is key.