Tobacco use kills . It is something that we all know, and that most of us have assumed. Tobacco ingredients include nicotine , which is highly addictive, and at least 70 chemical compounds associated with various types of cancer. Although many are products that are inhaled when smoking, up to 30 substances present in tobacco are still carcinogenic even if consumed in a different way, either by chewing, inhaling or vaporizing.
These chemical compounds, led by nicotine, are not only toxic to smokers; many other species are sensitive to these substances . Antimicrobial activity has been reported in tobacco extracts, inhibiting the growth of pathogenic bacteria and fungi. In some places, steeped tobacco is used as an insecticide, and its effectiveness in controlling the potato beetle has been proven. Other arthropods, such as mites, are also affected by nicotine.
And all this is very relevant for birds.
nests with nicotine
The Renaissance botanist and chemist Paracelsus is credited with concluding that everything is poison and nothing is poison, only the dose makes the poison . Today we know that the minimum dose from which a substance becomes toxic depends on the species that receives it and the weight of the individual. So the same amount of nicotine in a puff of smoke breathed by a 7-kilo baby does not affect the same amount as it does by a 70-kilo adult. In the baby, it will have a much higher toxicity.
And the same thing happens in animals. An insect weighing a few milligrams, or a mite that is in the order of micrograms, has a much lower toxic dose than a sparrow weighing 30 or 40 grams.
That is the main advantage birds get from tobacco butts. Once the cigarette has been consumed, the cellulose that makes up the filter is impregnated with nicotine. Some birds crumble the filter and intertwine its component strands with the twig weave of their nest . We don’t know why they do this — cellulose is an excellent thermal insulator, and they could do it by seeking that function — but we do know its effects.
It is a fact that the presence of cigarette filter remains significantly reduces the number of parasites in the nest , particularly insects and mites. It is most likely due to the insecticidal effect of nicotine. In arthropods, this alkaloid affects brain development and acts as a neurotransmitter disruptor, reducing the ability to control muscles and the heart, which often has a lethal outcome.
Not everything is advantages for the nest
This apparent advantage is not necessarily so. On the one hand, the use of butts by birds as raw material for their nests can have negative consequences for their health and, especially, that of their chickens . They maintain prolonged contact with everything in the nest, and through the skin they can absorb these products . In addition, they frequently deposit food in the nest that they will consume later . If there are remains of cigarette filters, nicotine and other dangerous compounds can pass into the food and enter the food chain . Only the dose makes the poison, said Paracelsus. But birds don’t usually read Paracelsus.
The apparent benefit that the absence of parasites may provide them does not compensate for the risks inherent in sleeping in a poisonous bed.
But there is another problem underlying this behavior. And it is that if many birds have the opportunity to decorate their nests with filter remains, it is because they have them within their reach.
The cigarette butt as a contaminant
Not surprisingly, these behaviors have been observed mostly in urban populations. Cigarette butts are one of the most common litter items in the world . It is estimated that each year approximately 5.5 billion cigarettes are produced in the world and the discarded butts reached some 1.2 million tons in 2020, a value that could increase up to 50% in 2025.
Since they are frequently thrown to the ground, it is normal for them to end up carried away by the wind or by water, and end up in natural environments.
Filters are typically made from non-biodegradable materials, which take years to break down naturally . In addition, the contaminants that remain in the butt after smoking the cigarette have antimicrobial capacity, thus inhibiting the growth of many organisms responsible for spoilage. They are toxic to plants, algae, fish, amphibians… Of course, their toxicity is greater the more recent the butt is, however, evidence of toxicity has been found in microalgae up to five years after the butt has been discarded.
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