A new study estimates that humanity could drive another 1,300 species to extinction in the next 200 years, jeopardizing their vital roles in ecosystems.
The ongoing disappearance of many scavenger species is beginning to cause environmental and public health problems due to the lack of animals that remove carrion. In the image, a griffon vulture in a Thai reserve.
The ongoing disappearance of many scavenger species is beginning to cause environmental and public health problems due to the lack of animals that remove carrion. In the image, a griffon vulture in a Thai reserve.
Among the victims of humanity’s successful expansion across the planet are the other members of the animal kingdom. But the case of birds is one of the most dramatic: around 600 species have gone extinct in the last 130,000 years, according to a new study published today, Thursday, in Science. This research goes beyond the numbers, highlighting that with each bird species lost, the ecological function it performed in nature also disappears. Key roles like pollination, insect control, or carrion removal are compromised. The situation is set to worsen. The authors of the study fear that more than 1,300 bird species could vanish in the next 200 years.
Beyond cataclysms (meteorites, supernovae, or megavolcanoes) that have caused past mass extinctions, species extinction used to be rare. For birds, it is estimated that the natural loss rate was no higher than 0.1 per million species per year. However, shortly after humans began their global expansion, the number tripled. The new study, based on a review of archaeological records and major taxonomic collections from large museums, estimates that since the late Pleistocene, about 130,000 years ago, at least 610 bird species have disappeared. Nearly all of them (562) went extinct due to anthropogenic causes such as hunting, habitat destruction, or the introduction of invasive species, especially domesticated or assimilated ones, like cats and rats. For the remaining 48 species, researchers are unsure what happened, so they cannot rule out human factors.
One aspect confirmed by this new work is the acceleration of the extinction rate. Since 1500, the era of great Western explorations, the extinction rate has multiplied by 28. Other studies suggest that humans have increased the natural extinction rate by 100 times. These data are the basis for many scientists’ claims that we are witnessing the sixth mass extinction, the first caused by a single species, and within a very short time frame. Even the meteorite impact that wiped out the dinosaurs took thousands of years to claim its last victim. According to this study, if we add the potential 1,300 extinctions in the next 200 years to the species already lost, nearly 20% of the 10,000 bird species that existed on the planet before human expansion could be gone.
Nearly all frugivorous bird species in Hawaii have disappeared, leaving many trees without a means to disperse their seeds, triggering new extinctions among plants. Of the Hawaiian mamo birds, only taxidermied specimens remain.
Nearly all frugivorous bird species in Hawaii have disappeared, leaving many trees without a means to disperse their seeds, triggering new extinctions among plants. Of the Hawaiian mamo birds, only taxidermied specimens remain.
In the present day, the situation is compounded by new factors. “Climate change, invasive species that arrive more easily due to increased human mobility, and habitat loss are some of the problems species face, and the scenario becomes more complex when several of these impacts are combined,” explains Ferrán Sayol Sanyol, a researcher at the Center for Ecological Research and Forest Applications (CREAF) and co-author of the study.
“It’s not just about the number of species that have been lost or could be lost,” the researcher adds. “Each one might have had an important role. What’s new here is that we tried to quantify what the loss of that number of species means for the ecosystem.” He provides an example: “We’ve observed a tendency for species with unique functions in the ecosystem to go extinct. Among them, the iconic dodo dispersed large fruit seeds in Mauritius, and few birds have replaced that function.” A similar thing likely happened with the extinction of the moa. “They were giant birds living in New Zealand that grazed. They were like the large herbivores of the region because there were no terrestrial mammals,” Sayol continues.
The extinction of moas, dodos, and so-called elephant birds allows us to identify some of the traits that made these birds particularly vulnerable: all three were large, flightless, and lived on islands. In fact, island living is behind up to 80% of past extinctions. Raised and evolved in the absence of humans and everything that came with colonization, they disappeared soon after humans arrived, mainly due to hunting and the introduction of invasive species. It might seem that these circumstances happened in prehistory. But no, most extinctions have occurred in relatively recent times, dating back to the 15th and 16th centuries, the era of great explorations. As Jorge Orueta, a researcher and expert on species at SEO BirdLife, puts it: “These extinctions were not so much caused by humans in general, but specifically by Western humans.”
The authors of the study have quantified the loss of functional diversity, the decline in ecological functions that extinct birds performed, at 20%. This figure could rise to 27% if the rate of species extinction estimated by scientists continues over the next 200 years. In some ecosystems and for certain roles, extinctions have compromised the entire system. For instance, on some of the Hawaiian Islands, the removal of many frugivorous species is facilitating deforestation: without fruit-eating birds, there’s no one to disperse the seeds. Human pressure and fires fueled by climate change complete a bleak future for the archipelago.
Thomas J. Matthews, the study’s lead author from the University of Birmingham (UK), cites examples from Mauritius and Hawaii, where all or almost all native frugivores are gone. “Frugivory is an important function because birds that eat fruit and then move around help disperse the seeds of the plants from which the fruit came,” he explains. One consequence is secondary extinctions, as illustrated by Mauritius. “For example, Mauritius has a large number of endangered tree species.”
The British scientist adds another, more recent example, one that is only now beginning to emerge: “The loss of scavengers (such as vultures), which eat and recycle dead animals, has led to an increase in the amount of animal carcasses left in the environment, and consequently, an increase in the prevalence of certain diseases among human populations living there.” Orueta, the SEO BirdLife expert who did not participate in the study, highlights that when it comes to scavengers, they don’t need to go completely extinct to lose their function. “In South Asia, in India or Bangladesh, vultures still exist, but their population decline has caused their ecological functions to disappear, even though the birds themselves are not extinct.” In fact, rabies cases among humans are rising in the region because there are no longer birds to remove carrion. Scientists fear that if bird extinctions double over the next two centuries, there will be a multiplication of cases where ecological functions lack any species to perform them.