A new study has revealed what many people possibly already suspect – males are more honest when displaying their “quality” to a partner than to an unfamiliar female.

These findings, from a study of a socially monogamous bird, are likely to apply to any animal that forms long-term partnerships, including humans.

What do we mean by “quality” here? Well, in evolutionary terms, “quality” refers to the variation in an individual’s health, strength, size, and ability to provide resources.

In socially monogamous animals it makes sense for females to try and identify all the qualities of a male that will help her to produce lots of offspring. Males often hold territories, and provide food to the offspring, as well as providing sperm that help to create the offspring in the first place.

The long haul

Because of the prolonged association between partners, it is very difficult for a male to keep deceiving a partner about his quality in the long term. Why? It’s all about the cost.

In birds, singing is costly to males in terms of:

• the energy required to produce song
• the time invested in singing at the expense of other activities (such as foraging), and
• the cost of exposing oneself to predators.

As a result, only males in good condition can maintain high levels of singing for an extended period.

When initially encountering an unknown female for the first time, it makes sense for all males to “display” at a similarly high rate, in an attempt to attract a female’s attention and make a good first impression.

For displays that are energetically expensive, such as singing, even lower-quality males are able to perform at a similar level to their rivals for that important but short first encounter. After a short period, lower-quality males are unable to sustain the effort, but if the female has already moved on it doesn’t matter.

Speed-dating

In their new study, Morgan David and colleagues at the University of Bergundy in France placed male zebra finches in a cage with an unknown female for either five minutes or one hour. The researchers found that all males took the opportunity to court the female with their song.

In these “speed-dating” trials, the amount of song produced by different males was unrelated to the underlying quality of those males.

(In this study quality was measured by looking at individual body mass. High quality birds typically carry a little more weight than those in lower condition, and this measure of condition is a great predictor of long-term survival and how many offspring a male produces over its life.)

By contrast, when the researchers examined song rates in males that had already established partnerships, and that were singing to a “steady” female partner, they found that call rate was a very reliable predictor of underlying quality.

That is, only males in the best condition produced song at a high rate.

This is probably because males of lower quality were unable to sustain this costly activity for as long, or may have depleted their reserves more quickly and had to break off from their displaying to feed, or rest and recover.

The long game

In the short-term, low quality males can potentially bluff and perhaps dig deeper into their reserves. But when there is a true cost to a signal, it is increasingly difficult to maintain such bluff over the long-term, and it might cause long-term damage (if the male chooses singing over foraging, for example).

A good reason for the honesty with which an individual signals its quality to a partner is the nature of the partnership itself. Given partnerships are ultimately about reproduction (in animals at least), socially monogamous partners have a shared interest in being honest with one another about their quality.

It makes sense for a male to signal to his partner about his condition and qualities, because that information is useful to a female in deciding when, and how many offspring to produce. As mentioned above, it may be detrimental to a male to falsely signal his quality to his partner.

If the female tailors her reproduction to his signal, and the number of young she believes he is capable of feeding, then they may end up with too many offspring, none of which will get enough food to ensure healthy development. The male and the female will therefore both lose out in the long-run.

Not just birds

While this study was conducted on small birds native to the harsh conditions of the Australian outback, there are lessons about ourselves that can be taken from such studies.

An individual’s evolutionary interests change over time and vary with their status in the mating game. Single, young-blooded males are prone to displays of wealth, status and prowess, the reliability of which is not necessarily easy for a potential partner to assess. Having one good suit or hiring a Porsche for the weekend are good examples of ways individuals can create a false impression of status.

But having a wardrobe full of Italian suits and owning a Porsche outright is more difficult to achieve, and it’s a more honest signal of underlying wealth.

The obvious implication here is to be wary of first impressions – they can be deceptive. The secret to getting an honest appraisal of an individual is through long-term acquaintance. In that sense, a second date is probably far more useful than the first date!

The stronger a bond becomes between a couple and the more intimate they become the better they know and understand the quality and current condition of their partner.

This makes sense because, they are now working as a team and looking out for each other and trying to plan for the future accordingly.

Decisions about where to live, when and if and how many children to have are all very important and are best optimised with a good understanding of each other’s position.

The nice thing about this recent work is that it demonstrates the complexity with which animal signals are used and abused. As well as listening to the song, we need to also consider who is singing, and what his agenda is likely to be.