Scientists from the University of Gothenburg analyzed the population dynamics of all the birds that have ever existed on Earth. They revealed that humans are to blame for the extinction of nearly three-quarters of non-flying birds.
The ability to fly is an extremely useful adaptation, but one that consumes a lot of energy. Not surprisingly, in the right conditions, birds don’t fly. This is most common on islands where there are no land predators or competing mammals.
Paleontological findings suggest that flightless birds were quite common during the Cenozoic era. However, the rise and spread of humans made life very difficult for them: people not only hunted birds that had lost their ability to fly, but also brought rats, cats, and other invasive species into their habitats.
A team of researchers led by Ferran Sayol from the University of Gothenburg decided to evaluate the human impact on the diversity of flightless birds.
To do this, they compiled a list of all known bird species that became extinct since the late Pleistocene that began 126,000 years ago to the present day. Then they recorded separately those who have lost their ability to fly. The authors did not analyze the specific causes of extinction for each species: they held the common view that humans are responsible for the vast majority of extinctions since the late Pleistocene.
The authors counted a total of 581 species of extinct birds, representing only about 5% of the total diversity. Some 166 species, or 29%, could not fly or did it badly. By comparison, there are 60 species of non-flying birds on Earth today. Had it not been for anthropogenic extinction, there would be at least 226 of them. Or, moreover, ornithologists say, as Paleontologists have not discovered all extinct species.
The study revealed a disproportionate number of extinct species that had lost their ability to fly. Overall, due to humans, the diversity of flightless birds has decreased by almost three-quarters.
Furthermore, in the past, flightless bird species were not only very diverse but also more widely distributed geographically.
The results clearly demonstrate the impact of humans on reducing the diversity of birds and, in particular, of flightless species. The study shows how human-induced extinctions distort ideas about the evolution of birds. Taking into account the extinct species, it turns out that birds of different classes refused to fly much more often than modern species. In other words, the small number of flightless bird species that can be observed today is not a norm, but an anomaly, the researchers conclude.
The results were published in Science Advances.