Fruit flies -- the tiny insects that swarm our kitchens over the summer months -- exhibit rational decision making when selecting mates, according to research published today in Nature Communications.

Researchers observed different combinations of fruit flies mate about 2,700 times, and were surprised to discover that male flies almost always pick the female mate that would produce the most offspring.

"The cognitive process of making rational choices is something we often think of as uniquely human," said University of British Columbia zoologist Devin Arbuthnott.

"While it is largely unknown whether animals are capable of making rational choices, this study provides the first evidence that fruit flies can, and do."

In the experiment, conducted by Arbuthnott and colleagues at the University of Washington, single male fruit flies where given the choice between two potential mates.

The researchers could tell the fruit flies were making consistent choices because flies would select mates based on a linear hierarchy. The top choice, A, would be picked over the second-best option, B, 70 to 100 per cent of the time.

When given the choice between second-best mate option B and third-best C, males would still follow the hierarchy. That trend continued down the line of ten different females.

Ten genetically different strains of females were paired in all 45 possible combinations in the trials, and each combination was preformed 12 to 20 times.

While it's unclear what female characteristics are driving the choices, chemical signals, and female receptivity (speed from courtship to matting) appear to be factors.

When the researchers impaired either the male flies' sight or sense of smell, the flies where still able to constantly select preferred female mates. When both sight and sense of smell where impaired, the mating rate dropped dramatically.

Arbuthnott wants to investigate variation in females and what genes are associated with attractive traits. The research was funded by the National Institutes of Health.