WASHINGTON : The Dodo, the famous flightless bird that inhabited the Indian Ocean island of Mauritius, is a case study in extinction caused by humans. The Dodo, finely adapted to its isolated ecosystem but unprepared for the arrival of people, was first encountered by Dutch sailors in 1598. Hunting, habitat destruction and the introduction of non-native species doomed it in under 80 years.
It is hardly alone. New research has documented the extinction of 610 bird species over the past 130,000 years, coinciding with the global spread of our species Homo sapiens, an avian crisis that has only accelerated in recent years and decades. For instance, the Kauaʻi ʻōʻō, a Hawaiian songbird, was declared extinct just last year.
The researchers also revealed the ecological consequences, as the disappearance of avian species erases functions they serve in innumerable ecosystems.
“Birds undertake a number of really important ecosystem functions, many of which we depend on, such as the dispersal of seeds, the consumption of insects, the recycling of dead material – for example, vultures – and pollination. If we lose species, then we lose these functions,” said ecologist Tom Matthews of the University of Birmingham in England, lead author of the study published this week in the journal Science.
“A good example of this is on the islands of Mauritius and Hawaii, where all or almost all the native frugivores – birds that eat fruit – have gone extinct,” Matthews said.
The Dodo and Kauaʻi ʻōʻō, believed to have had fruit as part of their diets, were among those.
“Frugivory is an important function, as in eating the fruits and then moving around, birds will disperse the seeds of the plants the fruits belong to,” Matthews said.
This can precipitate “secondary knock-on extinctions,” Matthews said, with Mauritius now having many threatened tree species.
Most of the documented extinctions occurred on islands. Habitat loss can have huge effects given the isolation and reduced area involved, while the introduction of animals such as rats, cats and mice can have substantial impacts given the evolution of flightlessness among many island-endemic birds that left them unable to escape new predators, Matthews said.
Human hunting was a big extinction driver in the past and remains problematic in certain regions. Capturing birds for the songbird trade is a big issue, particularly in Southeast Asia, Matthews said.
Certain regions and species had more specific factors involved. For example, avian malaria, introduced by people, has triggered large numbers of extinctions in Hawaii – particularly among the endemic Hawaiian honeycreepers – where the birds possessed no natural immunity.
“The big unknown going forward is the role of anthropogenic climate change as a driver,” Matthews said.
Some wondrous birds have been lost.
The large flightless elephant birds endemic to Madagascar vanished after people arrived, including Aepyornis maximus, possibly the largest bird that ever existed, about 10 feet (3 meters) tall. The flightless moa birds endemic to New Zealand, including the South Island giant moa that rivaled the elephant birds in size, similarly disappeared after humans colonized the islands.
North America’s migratory passenger pigeon numbered in the billions, but was hunted into oblivion.
The 610 species combined represented 3 billion years of unique evolutionary history, the researchers said, with each lost species like chopping off a branch from the tree of life.
The number 610 is “likely a large underestimate” of avian extinctions, Matthews said, because of a paucity of data from some locales and the fact some lost species may not have left behind skeletal remains to be found. Regardless of the true number, Matthews said, “the vast majority of extinctions over the last 50,000 years are attributable to human actions.”
About 11,000 bird species now exist, occupying a dizzying array of ecological niches. The researchers projected future extinctions of more than 1,000 species over the next two centuries.
“So even if you don’t care about the moral and ethical concerns regarding the loss of species, these extinctions are important for other reasons, such as the loss of species that helped the environment to function effectively,” Matthews added.
