Great bustards are pretty hard to miss, being one of the heaviest flying birds in the world and armed with an unforgettable lek performance to boot, but it seems they’ve got another trick up their feathered sleeves. New research has found that they may be self-medicating out in the wild, as it was discovered that these birds seek out two weeds known to contain compounds that tackle pathogens and parasites.

Proving animals are self-medicating isn’t easy, but a good place to start is looking for plants that they’re eating more often than their abundance in the environment would predict. This could be evidence that the animal in question – in this instance, the great bustard (Otis tarda) – is seeking it out, a behavior they’ve adapted because the plant affords them some kind of benefit.

Studying the great bustards revealed that they dine on corn poppies (Papaver rhoeas) and purple viper’s bugloss (Echium plantagineum) more than you’d expect. And it appears they’ve developed seasonal tastes.

“Great bustards select corn poppies and purple viper’s bugloss mainly in the mating season, in April, when their energy expenditure is greatest,” said first author Dr Luis M Bautista-Sopelana, a staff scientist at the National Museum of Natural Sciences in Madrid, in a statement.

“And males, who during these months spend much of their time and energy budgets on sexual display, prefer them more than females.”

Corn poppies have long been used as a painkiller and sedative, and are thought to have benefits for our immune function. They’re also rich in fatty acids, whereas purple viper’s bugloss has lots of edible oils, and it was these compounds the researchers used to look at the species’ constituent lipids, volatile essential oils and alkaloids.

Breaking them down into their molecular fractions revealed that both plant species were highly effective at inhibiting and killing the protozoan Trichomonas gallinae, and the parasitic nematode Meloidogyne javanica, both of which commonly affect birds. Viper’s bugloss was also reasonably good at hampering the growth of Aspergillus niger, a type of fungus.

It seems clear, then, that if the great bustards are indeed self-medicating, it would be a pretty handy adaptive behavior.

“In theory, both sexes of great bustards might benefit from seeking out medicinal plants in the mating season when sexually transmitted diseases are common – while males that use plants with compounds active against diseases might appear more healthy, vigorous, and attractive to females,” said co-author Dr Azucena Gonzalez-Coloma, a researcher at the Institute of Agricultural Sciences in Madrid.

However, it’s important to note that the compounds’ antiparasitic and antifungal effects were studied in vitro (in a culture dish), which is part of the reason the study authors urge caution in jumping to conclusions just yet over whether or not great bustards are self-medicating.

“The ultimate proof of self-medication requires experimental protocols developed in the biomedical, veterinary, and pharmacological sciences,” Bautista-Sopelana said.

“Until then, we continue with our fieldwork. For example, quantifying the prevalence of remains of corn poppies and purple viper’s bugloss and pathogens in fecal droppings across different populations of great bustards could falsify our hypothesis of self-medication in this species.”

The study was published in Frontiers in Ecology and Evolution.