Picked out as a medicine? A study suggests that great bustards specifically fight pathogens by ingesting medicinally effective plants. In particular, the males of the heaviest flying birds in Europe develop an appetite for two plants during the mating season, which the researchers were able to demonstrate an effect against parasites and fungi. It may be one of the few known examples of self-medication in birds, say the scientists.
Humans have been using nature as a pharmacy since time immemorial: It is well known that certain substances and especially medicinal herbs can have beneficial effects on many different health problems. However, studies have already shown that it is not only humans who make use of the pharmacological potential. Some animals also practice so-called self-medication instinctively or on the basis of positive experiences. In order to fight wounds or diseases, special substances are ingested or used, such as certain parts of plants.
Forms of this self-medication have so far been observed primarily in primates – but also in representatives of other animal groups. In the case of birds, in addition to parrots, the great bustard (Otis tarda) was already considered a possible self-treating species. With a weight of up to 16 kilograms, they are among the heaviest flying birds in the world. The great bustard is also known for the elaborate courtship behavior with which the males want to win over the much smaller females on special "dance grounds". In addition to many show elements, they also present their cloaca to the females. It is believed that in doing so they show the extent to which they are free from potentially sexually transmitted diseases, which can be reflected in fecal contamination.
Medical applications?
An earlier study already suggested that the males might improve their condition through a form of self-medication: it became apparent that they eat special beetles that contain active substances that can suppress parasitic worms, especially during the mating season. In the current study, the researchers led by Luis Bautista-Sopelana from the National Museum of Natural Sciences in Madrid have now investigated whether this pattern is also reflected in the consumption of plants. They examined the excrement of female and male Great Bustards in Spain at different times of the year. Under the microscope, they counted the amount of plant remains from the 90 plant species that are on the bustards' diet.
As the researchers report, there were striking results for two plants: corn poppy (Papaver rhoeas) and plantain viper's bugloss (Echium plantagineum) were eaten by the birds more frequently than would be expected based on their occurrence. In addition, there was a special time of high consumption and a gender-specific difference: "Great bustards select corn poppies and viper's bugloss especially during the mating season in April. And the males, who put a lot of effort into sexual display during these months, prefer them more than the females,” reports Bautista-Sopelana. Although the two plants have a nutritional value, they are usually avoided by cattle, for example. Another aspect aroused the interest of the researchers in particular: both plants are used in traditional medicine and are considered, among other things, to strengthen the immune system.
Action against parasites and fungi
They then followed this lead further: they produced extracts from the plants and examined their effect on laboratory cultures of two important bird parasites and on a fungal pathogen. These were the protozoa Trichomonas gallinae, the worm Meloidogyne javanica and the fungus Aspergillus niger. These laboratory tests showed that the extracts from both plants significantly inhibited the protozoa and worms or even killed them. The plantain bugloss also showed an effect against the fungal pathogen.
"We show that at certain times great bustards prefer to eat two types of herbs that are also used by humans in traditional medicine. In addition, our results demonstrate that both contain antiprotozoal and anthelmintic compounds, while the second type also contains antifungal agents,” summarizes co-author Azucena Gonzalez-Coloma from the Institute of Agricultural Sciences in Madrid. Theoretically, both sexes could benefit from consuming more of these medicinal plants during the mating season, when diseases become more easily transmitted. However, the effect could be particularly important for the males, who are particularly stressed during this time, and it could also lead to an increase in their attractiveness, the researcher explains.
The team now sees the results as a further indication that the great bustard actually practices a form of self-medication. However, Bautista-Sopelana emphasizes: "The definitive proof of self-medication still requires further investigations". According to the scientist, more information could be provided by an investigation into the extent to which the consumption of the plants actually leads to a lower pathogen load in the animals.
Source: Frontiers, professional article: Frontiers in Ecology and Evolution, doi: 10.3389/fevo.2022.1027201