Coots in Łódź, whose colonisation of the city began much later, show behaviour somewhere between the long-established Warsaw population and birds living outside urban areas. The findings suggest that adaptation to city life progresses from generation to generation.

‘The coot is a secretive bird by nature. Outside the city, it usually nests in dense rushes, and when disturbed by the presence of humans, it leaves the nest and hides. Meanwhile, some coots living in Warsaw do not leave the nest even when touched by hand’, Professor Piotr Minias from the Faculty of Biology and Environmental Protection of the University of Lodz tells PAP.

For several years, the scientist has been researching how wild birds colonise cities and how their behaviour changes in new conditions. The coot (Fulica atra) is particularly interesting in this respect because its entry into the cities of Central Europe can be observed almost on an ongoing basis.

The Warsaw population was established in the mid-20th century and was among the first urban populations of the species in Poland. In Łódź, colonisation began in the late 1990s and continued over the following two decades.

Minias and his team used this difference to investigate whether the length of time a population had lived in a city was related to changes in bird behaviour. The study results were published in the journal Behavioral Ecology and Sociobiology.

The authors compared three populations of coots: from Warsaw, Łódź and non-urban areas, with the latter living on fish ponds in central Poland, far from large agglomerations.

They conducted two experiments involving birds incubating eggs. In the first, a researcher approached the nest directly, stood half a metre away for one minute and then moved away. For the next 15 minutes, he watched from a hiding place to see whether the coot returned to the nest and resumed incubating its eggs, and how long it took to do so.

In the second experiment, the researchers introduced an additional obstacle: an object completely unfamiliar to the birds was attached to the entrance of the nest – a strip of green fabric. It was designed to test neophobia, or fear of something unfamiliar.

‘We wanted to check whether the birds would overcome their fear of a new object and return to the nest’, Minias says.

In the first experiment, coots from all three populations returned to their nests relatively often, but they did so after very different periods. Warsaw birds took an average of about three minutes to approach the nest again, compared with about 7.5 minutes for birds from outside cities. They resumed incubating their eggs after 3.3 and 9.3 minutes, respectively.

Coots from Łódź were in between: they took an average of about five minutes to return to the nest and just over six minutes to resume incubation.

The experiment with the unfamiliar object revealed even more pronounced differences. Within 15 minutes, approximately 57 percent of Warsaw coots and only about 21 percent of coots from outside cities returned to the nest. Approximately 53 percent and 9 percent, respectively, resumed incubating their eggs.

Again, the results from Łódź were intermediate: approximately 43 percent of birds returned to the nest, while approximately 30 percent resumed incubation.

‘These are very interesting results because they show that changes in bird behaviour intensify with the time the population lives in the city. Those who have lived there for a long time are the least cautious, those from outside the cities are the most skittish. The reactions of birds from recently established urban populations are somewhere in between’, Minias says.

He says moving to a city means a radical change of environment for coots. Outside urbanised areas, they most often build nests in dense rushes. Urban parks often lack such vegetation, so coots breed in more exposed places and have much more frequent contact with people. To function effectively in these conditions, they must reduce their natural skittishness.

Frequently reacting to people, cars or other unfamiliar stimuli by running away is costly. Birds that tolerate human presence spend less time and energy avoiding threats. Less fear of unfamiliar objects, in turn, makes it easier for them to use resources that they do not encounter in their natural environment, ranging from food provided by humans to artificial objects used to build nests.

Although the study did not analyse the mechanism behind the changes in coots' behaviour, Minias says two processes may be important.

One is the plasticity of individual behaviour. The same bird may react differently depending on the environment in which it finds itself. When it enters a city, it has to gradually get used to people and new stimuli, which most often do not pose a real threat.

The second mechanism concerns changes occurring across the population over successive generations. Individuals that are less skittish may function better in new conditions and produce more offspring, gradually changing the population.

According to Minias, both hypotheses also explain why the Łódź birds showed behaviour between that of Warsaw coots and those from non-urban areas.

‘The observed changes do not stem solely from behavioural plasticity; over time, genetic changes also come into play’, he says.

According to the researcher, the differences observed between the populations were substantial.

‘In Warsaw, there were instances during the experiment where we were simply unable to flush the bird from its nest. It would not flee even when touched by hand. Compared to the natural secretive and skittish nature of coots, this represents a 180-degree shift’, he says.

Katarzyna Czechowicz (PAP)

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