ANIMALS AND BIRDS AS SELF-MEDICATION USERS
Self-Medication– “Not all pharmacists are human.” So begins a 1993 review article on the use of medicinal plants by animals. Reading on, we learn that pharmacists can be chimpanzees, Kodiak bears, starlings and grackles. As we learn more about how animals use plants to prevent and treat ailments, this list has only continued to grow. It now even includes caterpillars.
The above image is a colourful mix of blue, yellow, white and green makes the blue tit one of our most attractive and most recognisable garden visitors. In winter, family flocks join up with other tits as they search for food. A garden with four or five blue tits at a feeder at any one time may be feeding 20 or more. Blue tits are common in woodland, hedgerows, parks and gardens. They’re widespread and found across the whole of the UK with the exception of some Scottish islands
When a substance is deliberately sought out that prevents or cures a condition and its use results in increase survival and reproduction.
For example, if you get an infection, you take antibiotics that cure the infection which might otherwise kill you.
A non-human example concerns starlings. These birds deliberately choose specific plants (that they find with their sense of smell) to include in their nests. The aromatic compounds emitted by these plants boost immune systems of chicks and reduce their bacterial loads.
Yarrow (Achillea millefolium) is one of the plants use by starlings, along with goutweed (Aegopodium podagaria), hogweed (Heracleum sphondylium), elder (Sambucus niger), cow parsley (Anthriscus sylvestris) and white willow (Salix alba).
A subsequent experiment added yarrow to the nests of tree swallows, which don’t normally use medicinal plants. The result: the abundance of blood-sucking fleas is reduce in nests containing the plant.
Corsican blue tits also add plant material to their nests. They use lavender (Lavandula stoechas), mint (Mentha suaveolens) and an aster (Helichrysum italicum).
These birds add fresh plant fragments throughout the nesting period. When researchers experimentally removed these aromatic plants from their nests, the birds quickly replaced them.
For good reason, it seems – chicks in nests with aromatic herbs had higher body and feather growth rates. The herbs also reduce the amount of and diversity of bacteria living on chicks.
Eagles and wood storks choose nesting material from trees and shrubs containing insect-repellent resins. Bonelli’s eagles preferentially use pine boughs for nest construction. Nests with a greater pine composition have lower parasite levels and fledge more young eagles.
House finches in Mexico City have made a recent innovation, achieving better living through chemistry. They have begun using cigarette butts as nesting material. Research demonstrated that cigarette butts reduce the parasites in nests.
The twist is that, as we’ve learned ourselves, synthetic chemicals can have unintended consequences. In the case of house finches, chicks from nests full of cigarette butts have increased chromosomal abnormalities.
Remarkably, every single plant mentioned above has a long history of medicinal uses by humans.
In some of the literature, there is a notion that self-medication, particularly in primates, is the result of observation, learning and conscious decision-making that is then passed on by example. A chimpanzee might learn by association that chewing the bitter pith of the Vernonia plant helps cure an intestinal parasite. It then continues to use the behaviour when appropriate and others around it follow the example. This can’t be the whole story though, and it doesn’t do much to explain how a simpler creature would know when and how to self-medicate.
In the early 20th century a Tanzanian medicine man noticed that a pet porcupine with dysentery was eating the root of a plant that people regarded as poisonous. He began treating people with the root with great success and its use as a remedy for dysentery became widespread.
This example suggests that great discoveries are possible by continuing to study the use of medicinal plants by animals. While the European plants used by starlings and blue tits are well known to us, there may be a much greater amount of undiscovered medicinal compounds being used by animals of all sorts around the world. And some of these could be beneficial to humans. It is clear that we have only just begun documenting the phenomenon.