image: Xenicus longipes longipes. Illustration: John Gerrard Keulemans
Bird species that have lost the ability to fly through evolution have become extinct more often than birds that have retained their ability to fly, according to new research from the University of Gothenburg.
Today, we know that human influence on the environment has caused large numbers of plants and animals to die out. Human impact has fundamentally changed ecosystems and, globally, has driven hundreds of animal species to extinction.
One of the consequences of this is that biological pattens have become distorted. This, in turn, means that researchers have a harder time interpreting current data on species diversity, i.e. variations of species within an ecosystem or area.
"Studying human-caused species extinction can influence our understanding of evolution and help us to better understand the loss of species not caused by chance," says Søren Faurby, senior author behind the new study and a researcher at the University of Gothenburg.
Together with his research colleagues, he has studied a larger evolutionary transition: the development of flightlessness among birds. For the first time, a study of this transition includes data from all known flightless species driven to extinction by humans.
"We have found that, in many cases, the extinctions have had anthropogenic origins, which are effects that can be traced back to human activities.
Flightless birds are more common than the researchers believed
Birds that have lost their ability to fly are a more common phenomenon than research has assumed up until now, according to the study. These species have then been impacted by human activities.
"Many bird species can develop flightlessness in environments without large predators, such as on islands, but they also become easier prey for both humans and animals, such as rats and cats," says Ferran Sayol, the lead author behind this study and previously a post-doctoral researcher at the University of Gothenburg.
The researchers have compiled a list of 581 bird species from 85 different families that have gone extinct during the past 126,000 years.
"Based on morphological descriptions, we have determined that 166 of these species lacked the ability to fly. This is equivalent to 29 per cent of the extinct bird species. Currently, there are only 60 living flightless bird species. If we add the 166 species that have gone extinct, this totals 226 both existing and extinct flightless bird species."
The study shows that by adding these extinct birds to the global picture of bird diversity, it becomes clear that flightlessness developed at least four times as often as if the researchers only looked at living species.
"We show that the development of flightlessness in birds is a widespread phenomenon. If humans had not caused some of these extinctions, we would still share the planet with more than 150 independently developed flightless groups of birds. Unfortunately, only 60[Accent1] of these remain," says Ferran Sayol.