For thousands of years, the crows of the Japanese city of Sendai faced a tough test in eating one of their favourite foods, walnuts.

Because the nuts are very hard to crack, the birds would carry them high up and drop them from the sky.

In 1970 a local scientist noticed that the birds had changed their tactics. They began dropping the walnuts in the middle of the road where vehicles would drive over them, cracking the hard shells and exposing the nut inside. The birds were using cars as nutcrackers.

The crows of Sendai became a unique case study in how urbanisation changes animal behaviour and speeds up their ability to adapt, something that takes others millions of years.

According to a 2018 United Nations assessment, more people now live in cities than ever before: 55 per cent of the world's population, up 34 per cent since 1960. By 2050 nearly 70 per cent of us are expected to live in cities.

This growth is having a negative impact on wildlife and biodiversity because their habitats have shrunk. But it has also triggered change in a number of species that have quickly learned how to survive in the city.

As Dutch biologist Menno Schilthuizen puts it, "Understanding the relationship between urbanisation and wildlife is very important."

Source: BBC Bangla. First published in Bengali on The Agro News.