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Bird extinctions have a greater impact than we think
Human activities are rapidly driving more bird species to extinction.
But to assess the true impact of past extinctions, we need to look beyond the loss of individual species to the wider role these animals play within an ecosystem.
Over the past 130,000 years, significant global change has driven numerous species to extinction.
Some of these losses have been the result of natural climate fluctuations. But our impacts on the environment have increased extinction rates beyond normal background levels.
Since the Late Pleistocene, there have been over 610 known bird extinctions with humans contributing to at least 92% of these losses. Scientists want to fully understand the true impacts these past extinctions have had on the wider ecosystem and the evolutionary history of these animals. But when a species goes extinct, it also impacts other species that rely on its function within the ecosystem. Birds play a range of essential roles, including pollination, seed dispersal, and keeping prey numbers in check.
Some species also occupy unique branches on the tree of life, so their loss could erase millions of years of evolutionary history. Scientists want to fully understand the true impacts these past extinctions have had on the wider ecosystem and the evolutionary history of these animals.
A recent study, published in the journal Science looked in more detail at these wider impacts. They found that over the past 130,000 years, bird extinctions have caused a loss of around three billion years of evolutionary history and have had a disproportionate effect on the functioning of ecosystems. Islands were found to have been particularly affected over the past 500 years.
Dr Julian Hume, an avian palaeontologist at the Natural History Museum and coauthor of the study says, “It’s not just a bird extinction that is involved here, it’s how that fits into the whole jigsaw. There is a knock-on effect for every loss.”
“We often focus on the number of extinctions that have taken place, but an extinction is a much bigger loss than we might first realise.”
A great example of this is the dodo, which used to live on the island of Mauritius in the Indian Ocean. Within a hundred years of the first record of a dodo, the birds were extinct and with them a host of other species.
“During the excavation of fossil sites on the island, we not only uncovered dodo bones but a whole suite of animals that were associated with them,” explains Julian. “This included six dung beetle species that specialised in tortoise and bird dung. These are all extinct too.”
“With the loss of the dodo, we lost this group of insects that went with it. So when you take into account how other species may be affected by extinction, it really hits home just how much biodiversity has been lost.”
Birds perform important roles within ecosystems, such as seed dispersal. The seeds of guava are often spread by birds, such as this toucan. © Paul S. Wolf/ Shutterstock
Why is island biodiversity more heavily impacted?
Species losses have been particularly extreme on islands over the last few hundred years.
Since 1500, around 75% of extinctions documented by the International Union for Conservation of Nature have taken place on islands, despite islands making up only 7% of the earth’s land area.
This is because islands hold a number of unique species whose population ranges and sizes are often small. Many have also developed traits that make them more at risk of extinction, such as the loss of flight, which arose due to a lack of ground predators.
As these habitats have evolved in isolation from the rest of the world, most island species fulfil essential roles within their habitats. This means that when they disappear it has a bigger knock-on effect on the rest of the ecosystem.
“Before the 1500s most animal extinctions took place on continents, but then a shift happened,” says Julian. “Since then, islands have been hit much worse.”
As Europeans began to explore and colonise the globe in the fifteenth century, they had a detrimental impact on many ecosystems as they destroyed habitats and hunted new species. But they also brought with them non-native plants and animals which quickly outcompeted or destroyed the native plants and animals.
“Humans have been getting to islands for thousands of years, but after the 1500s, island systems started to rapidly break down,” explains Julian. “As humans brought with them invasive pigs, rats and cats, there was a huge loss in fauna as they ate birds which had not evolved with these predators, and so had no adaptions for protecting themselves.”
The extinction of the dodo on Mauritius impacted other species that had evolved to depend on it. © Julian Hume
What does the future look like for birds?
As humans continue to impact the planet through habitat destruction, hunting and the introduction of non-native species, these extinctions are likely to increase.
Researchers predict that around 1,305 bird species could go extinct over the next 200 years. Islands are still expected to be more heavily impacted, but we may see this loss in ecosystem function occurring more rapidly on continents.
“As habitats on continents are becoming increasingly lost and more fragmented, these areas are now essentially becoming small islands within the continent,” says Julian. “So they are reacting the same as if they were islands in an oceanic environment. And that is why extinction rates are going up.”
Given the wide range of roles that birds play in an environment, these losses will likely have far-reaching implications for ecosystem functioning and resilience. Without birds, many habitats may experience reduced flower pollination, seed dispersal, insect population control, and an increase in disease risk as there are no birds to help consume dead animals.
“As conservationists, we can’t just pour all our resources into protecting one species,” says Julian. “We have to think of environments as a complex unit of species that all need protection. This is vital if we are going to reverse the current extinction crisis.”
