The world’s heaviest bird may be self-medicating on plants used in traditional medicine, which kill parasites in vitro
If you see a great bustard (Otis tarda) in the wild, you’re unlikely to forget it. Massive, colourful, and impossible to mistake, they are the heaviest birds living today capable of flight, with the greatest size difference between the sexes. They are also ‘lek breeders’, where males gather at chosen sites to put on an audio-visual show for the visiting females, who choose a mate based on his appearance and the quality of his ‘showbirdship’.
But now, a new study suggests that great bustards have another claim to our interest; they actively seek out two plants with compounds that can kill pathogens. They may thus be a rare example of a bird that uses plants against disease – that is, self-medication.
Study first author Dr Luis M Bautista-Sopelana, a staff scientist at the National Museum of Natural Sciences in Madrid, said: “Here we show that great bustards prefer to eat plants with chemical compounds with antiparasitic effects in vitro.”
Co-author Dr Azucena Gonzalez-Coloma, a researcher at the Institute of Agricultural Sciences in Madrid, said: “Great bustards seek out two species of weeds that are also used by humans in traditional medicine. We show that both contain antiprotozoal and nematocidal (i.e., worm-killing) compounds, while the second also contains antifungal agents.”
Self-medication in animals is suspected to occur, with a lesser or greater degree of confidence, in animals as diverse as primates, bears, deer, elk, macaws, honeybees, and fruit flies. But it’s tricky to prove beyond doubt in wild animals.
Bautista-Sopelana warned: “We can’t compare between control and experimental treatments. And double-blind trials or dose-effect studies, obligatory steps in human or veterinary medicine, are obviously impossible in wild animals.”
Great bustards, classified as vulnerable on the International Union for Conservation of Nature’s Red List of Threatened Species, breed on grasslands from western Europe and northwest Africa to central and eastern Asia. Approximately 70% of the world’s population live in the Iberian peninsula.
Gonzalez-Coloma said: “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.”
Some members of the present research team have studied great bustards since the early 1980s, mainly in the regions of Madrid and Castille-Leon, Spain. They collected a total of 623 droppings from female and male great bustards, including 178 during the mating season in April. Under a microscope, they counted the abundance of recognisable remains (tissue from stems, leaves, and flowers) of 90 plant species that grow locally and are known to be on the bustards’ menu.
The results showed that two species are eaten by great bustards more often than expected from their abundance: corn poppies, Papaver rhoeas and purple viper’s bugloss, Echium plantagineum.
prime candidate birds
Bautista-Sopelana said: “Great bustards select corn poppies and purple viper’s bugloss mainly in the mating season, in April, when their energy expenditure is greatest. And males, who during these months spend much of their time and energy budgets on sexual display, prefer them more than females.”
Of these two species, the first is avoided by cattle and is used in traditional medicine as a pain reliever, sedative, and immune booster. The second is toxic for humans and cattle if eaten in great quantities. They also have nutritional value: fatty acids abound in corn poppy seeds, while the seeds of purple viper’s bugloss are rich in edible oils.
The researchers discovered that extracts from both plants are highly effective at inhibiting or killing protozoa and nematodes in vitro, while purple viper’s bugloss is also moderately active against fungi.
The authors conclude that great bustards are prime candidates for birds that seek out specific plants to self-medicate. But more research is needed, they caution.
Bautista-Sopelana concluded: “The ultimate proof of self-medication requires experimental protocols developed in the biomedical, veterinary, and pharmacological sciences. 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 faecal droppings across different populations of great bustards could falsify our hypothesis of self-medication in this species.”
The study is published in Frontiers in Ecology and Evolution.
Image: A male great bustard, (Otis tarda). © Carlos Palacín.