You cherish your partner and love spending time with them, but it’s obvious you two have different ideas of what’s fun; you think staying in is an ideal way to connect with your significant other, but they keep insisting on hiking trips? You’d rather order takeout but they want to try out a new restaurant every time you go on a date?
Turns out humans are not the only species that overlooks differences in personality traits when choosing a partner! Thinking like an animal, choosing a good mate is an important evolutionary trait, because it can determine the future of your offspring. Animals who do this typically choose their mates based on the visible, physical traits such as feather color or antler size. But we can argue that a heritable personality trait of a parent can very well affect the life of an offspring. For example, an exploratory personality comes in handy when it’s time to look for food or find a nesting spot. Wang et al. (2022) examined mate choices in female Lonchura oryzivora (Java Sparrows) to see what is the preferred male personality type, and if a female’s own personality affects her choice.

 First thing Wang and colleagues had to do was separate all birds based on their levels of exploration. They did this by putting each bird in a chamber that contained five feeding trays, four in the corners and one in the center. They let the birds accommodate for three minutes and then left them in the chamber for ten minutes. One of the researchers measured how long it took the birds to visit all the feeding trays in the corners, and graded the birds on a 0-10 point scale (where 10 is the least time taken – under 1 minute). The second test was done in two rounds; in each round, the birds were introduced to an object they’ve never seen before, a penlight battery and a plush carrot doll, which were placed on a random perch in the chamber. Wang et al. measured how the birds responded to a new object; if they stayed as far away as possible or they interacted with it. They were graded on a 0-5 point scale after each round (where 0 means they stayed as far away as possible, and 5 that they hopped on a perch with the new object). They summed up the scores of the three trials to build personality scores, meaning the maximum amount points was 20, and separated the birds by their exhibition of exploratory behavior.
As mentioned earlier, a male’s physical appearance can affect the female choice. This means Wang et al. had to make sure that the males they use have similar physical characteristics. Once they accounted for that, they paired males who had similar physical, but different personality traits. 

To test if females show preference for more exploratory males, they used a three-compartment chamber with one-way glass baffles separating the compartments. They placed one female in the center, and two males (with different personalities) on the outer sides in a way that the female could see the males through one-way glass. This way the female could observe the males without them knowing, and could determine their exploration levels. The baffles were removed after ten minutes and the birds were left to interact for twelve minutes, which was recorded. At the end of twelve minutes, the positions of the males were switched and the baffles were removed which started the second twelve-minute recording. The researchers were able to determine the percentage of time a female spent close to each male. A female was considered biased when it spent more than 80 % of the total time with one of the males. 

Wang et al. assumed that females would choose a mate that matches their own exploration levels. However, the results of their tests showed that females chose high-exploratory males significantly more than low-exploratory males, no matter their own exploration leves. This indicates that high exploration trait might be evolutionarily favorable for reasons that would make them better parents than low-exploratory males. 

This study demonstrates Java Sparrows’ ability to perceive more than easily detectable physical cues; they are able to recognize behavior patterns and differentiate distinct personality traits. Moreover, they are able to determine which personality traits are more advantageous.  However, this study doesn’t tell us how much personality affects mate choice. Presumably it’s easier to notice physical traits, and figuring out a personality takes more time and energy, which may push personality traits in the background. More comprehensive studies need to be conducted to know this for certain.

References:

Wang, Jiayu, Daiping Wang, Qiuyang Chen, Juan Zhang, Paul Racey, Yiting Jiang, Dongmei Wan, and Jiangxia Yin. “Female Java Sparrows Prefer High Exploratory Males without Assortative Mating.” Behavioural Processes 200 (2022): 104671.

Image credits:

Java Sparrow” by Angeleses is licensed under Pixabay license
Gallatin River” downloaded from https://www.visitbigsky.com/ 
“Birdhouse” ⓒ Jada Fitch
Paddle” is licensed under CC BY-NC 4.0
Sunglasses Frames” is licensed under CC BY-NC 4.0
Java Sparrow” ⓒ Lucas Bobay
Java Sparrow” by 70154 is licensed under Pixabay License

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