Humans may have caused the end of 1,500 species of birds – 12/21/2023 – Science

Human action may have already led to the extinction of at least 1,500 species of birds since the end of the Ice Age — more than twice the number estimated to date. For now, the main victims have been typical island birds, more vulnerable to invaders, but the chances that the process will continue and worsen in other places in the world are high if the current trajectory of global environmental degradation is maintained.

The new estimate of the group’s extinctions was made by a group of scientists coordinated by Rob Cooke, from the United Kingdom’s Center for Ecology and Hydrology. If the analysis carried out by him and colleagues from other European institutions (among them the Brazilian Alexandre Antonelli, from the University of Gothenburg, in Sweden) is correct, it will mean that 12% of the world’s bird species have already been eliminated because of Homo sapiens in this year. period.

The calculation, presented by Cooke and his colleagues in the specialized journal Nature Communications, involves a series of assumptions. In addition to using available data on the most recent wave of bird extinctions, conventionally dated from the year 1500 (marking European overseas expansion, the processes of economic intensification generated by it and, centuries later, the Industrial Revolution), the team also included fossil data.

This means that in addition to extinctions documented directly by European naturalists, recorded in writing from the 16th century onwards, the group included bird disappearances that can be inferred by analyzing ancient skeletons and eggs.

Everything indicates that this process began in the initial phase of the expansion of our species across the planet, between 100 thousand years and 70 thousand years ago, leaving Africa (the cradle of Homo sapiens). However, fossil data strongly suggest that the damage intensified much later, starting 3,000 years ago, when Polynesian navigators first colonized the so-called Western Pacific (such as the Tonga and Fiji archipelagos) and, several centuries later, the Eastern Pacific (which includes Hawaii and New Zealand).

All of these island regions combined a series of factors that placed them at the top of the “risk groups” for bird extinctions. Due to their isolation and distance from the continents, they tended to have terrestrial vertebrate faunas formed, to a large extent, by these animals. Since mammals do not fly (with the exception of bats) and amphibians can almost never cross salt water, only birds and reptiles can reach such islands.

This caused the birds there to diversify greatly, occupying ecological niches (such as large herbivores, for example) that would fit other animals on the continent. At the same time, the relatively small space of the islands means that populations of these species were never very large. And finally, their isolation also left them particularly vulnerable to invasive species, as they hadn’t evolved alongside many predators and competitors.

In short, Pacific island bird species were many and fragile. When humans arrived, hunting them or bringing with them domestic animals and pests (such as pigs and rats, respectively) that could devour them or eat their eggs, the damage was quick.

Thus, for example, several species of moas, flightless birds from New Zealand that may have weighed more than 200 kg, and several species of eagles, large pigeons, crows, cockatoos and many other birds disappeared. A similar process, although on a much smaller scale, also appears to have occurred on Indian Ocean islands such as Madagascar.

The trick of the work’s methodology was to consider that, even based on the analysis of fossils and historical records, a good part of the missing diversity of birds did not reach us, since the remains of many of the species would not have been preserved. Using data on territorial size, climate, level of isolation, type of vegetation and several other factors, the researchers created a mathematical model capable of predicting the original diversity of archipelagos around the world.

As a result, they estimated that 55% of past extinctions occurred without leaving a trace. They also pointed out that the last major peak in disappearances would have occurred around the year 1300 AD, at which time the group’s extinction rates were 80 times higher than what is considered normal taking into account the fossil record as a whole.

The current wave of extinctions is, for now, more or less half the magnitude of the previous peak, and appears to have lost some strength since the second half of the 20th century. The problem, however, scientists warn, is the existence of the so-called “extinction debt” — broadly speaking, the fact that some species have already become or are close to becoming unviable from a reproductive point of view in the long term.

With this, their disappearance would be practically assured — it is as if they were zombie species. One estimate cited by the study’s authors suggests that the current “extinction debt” already affects around 700 bird species. This would mean that the current outbreak of extinctions is happening at a rate between three and four times that of the worst wave in the past.

The only way to minimize this risk is to invest in conservation actions, especially preserving the habitats of the most threatened birds and curbing hunting and the action of invasive species.