Tag Archives: Adaptation

Did you know that birds use cigarette butts to fight parasites?

Male house sparrow

Recently I took part in a cleaning action in my village. It was actually already rather clean, and we found little rubbish on the streets and sidewalks. However, about two out of three pieces of garbage were cigarette butts. This reminded me that some birds living in cities use those remains of smoked cigarettes to line their nests. Why do they do that?

More cigarettes – less parasites

Research conducted in Mexico City on house sparrows and house finches shows that there were fewer parasites in nests that contained more cigarette material. Adult birds and chicks are vulnerable to attacks by parasites such as ticks, mites and fleas, which not only suck blood but also spread disease.  The filters of smoked cigarettes are saturated with nicotine, which tobacco plants produce to fight small herbivores. Nicotine and other toxic substances in cigarettes repel or even kill parasites. Nests with more cigarette material had better hatching success and chick growth and survival rate.

Cigarette treatment

However, do the birds use butts specifically for their medicinal purposes, or simply for insulation, and their anti-parasitic effect is just a bonus? To test this, scientists replaced the original nest lining of house finches with an artificial one – either without parasites or with added live or dead ticks. The birds that got live ticks added more cigarette butts to their nest than birds from other groups. This show that birds use cigarette butts in response to parasites as a way of self-medication.

There is no such a thing as a free cigarette

However, we know that cigarettes are harmful to human health. They contain nicotine and other toxic substances. Are they not harmful to the birds? Unfortunately, it seems they are. Birds with more cigarette material in the nest have more DNA damage, which can lead to cancer (although a direct link between cigarette use and cancer in birds was not investigated). More DNA damage occurs in both the chicks and their parents – especially the ones that spend more time building the nest or incubating the eggs.


Adding cigarette butts to nests seems to be birds’ adaptation to city life – the use of human waste for self-medication. However, we still do not know if the short-term benefits outweigh the long-term costs. Therefore, smokers have no excuse to throw their cigarette butts on the street.


Photo: JrPol, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=40108812


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Did you know that wild mice that live near people are better at solving problems?

House mouse

Human activity is transforming the environment so much that many animal species are losing their place to live. But there are also a minority of species that can adapt to the new reality to some extent, or even prosper in it. Although life in the city means noise, pollution and less vegetation, there are also positive sides: an additional source of food all year round (in the form of leftovers from our tables) and fewer natural enemies (although cats are a big threat for many birds).

Living around people has an impact on animal behavior – for example, many birds in cities sing at higher frequencies to distinguish themselves from traffic. Research on birds also indicates that those living in urban areas are better problem solvers.

Coping with new problems seems to be one of the most important cognitive skills needed in the rapidly changing and unnatural environment created by humans. Recently, scientists have shown that mice that live close to humans are better problem solvers and, in at least one species, this is an innate ability that is a result of evolution, instead of something they learned during life.

Urban versus rural mice

In the first experiment, scientists caught striped field mice in the city and in rural areas. After treating all mice the same for a year in the laboratory, the tests began.

The mice were given various problem-solving set-ups (including a LEGO house – I’m not the only one who comes up with such ideas) which when opened – by pulling, pushing or moving various elements – gave them access to food.

Mice that were caught in the city were more likely to solve these problems. This couldn’t be explained by a fear of strange objects in the rural mice, because they actually approached the set-ups sooner and interacted with them longer.

As I wrote above, this experiment was carried out on mice that were born and grew up in the wild and it is possible that they could develop their cognitive abilities then – differently in rural and urban areas.

Long-term coexistence with humans

To find out the importance of long-term coexistence with humans, the same scientists conducted research on another species of mice – the house mouse. It is a synanthropic species that occurs almost exclusively near humans (this species also includes laboratory mice and various breeds of domestic pets).

There are several subspecies of domestic mice that have been associated with humans for different lengths of time: the Western European house mouse (Mus musculus domesticus) – about 11-13 thousand years, the Eastern European house mouse (Mus musculus musculus) – about 8,000 years, and the southeastern Asian house mouse (Mus musculus castaneus) – between 7,600 and 3,800 years. Thus, each of these subspecies had more or less time to adapt, through evolution, to humans’ changes to the environment (even if the living environment of people also changed a lot over these thousands of years). To eliminate the influence of individual mice’s life experience on the research, scientists did not study wild mice caught in the field, but studied their descendants, after several generations in the laboratory under constant conditions.

Adapting to life with humans

The descendants of the wild house mice were subjected to the same problem-solving tests as the field mice in the previous experiment. It turned out that the longer a mouse subspecies was associated with humans, the more likely it was to solve the problems. And this couldn’t be explained by the differences between subspecies in the time they took to approach the set-ups, or the differences in fear of a new environment.

Since all these experimental animals had lived under the same conditions throughout their lives, these studies show that different subspecies differ in their innate ability to deal with new problems. It seems that over the course of generations, coexistence with humans influenced the evolution of cognitive skills in wild animals.


Photo based on 4028mdk09, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=11056096


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