Introduced bird species fail to replace extinct bird roles


AZoCleantech speaks with Ferran Sayol of University College London who has studied the effects of humans on bird biodiversity. Sayol details his recent study on how introduced bird species fail to replace the roles of extinct birds.

How did you start your research on extinct bird species of human origin?

This research was part of a project funded by the Swedish Research Agency (Skatteverket) in Søren Faurby, aimed at understanding how human impacts can skew our understanding of biodiversity patterns. I started as a post-doctoral fellow in this project in 2018 and started collecting information on human-induced bird extinctions.

What is the current extent of bird species extinction?

We have compiled records of more than 600 bird species that have potentially gone extinct because of humans. Currently, there are about 10,000 extant birds, but around 14% of them are threatened with extinction.

What are the main causes of extinction in birds?

The main causes are habitat destruction, direct persecution (i.e., hunting) and invasive species such as cats or rats. This later threat is especially important on island birds, as they have evolved in an ecosystem lacking mammal predators.

What direct consequences occur due to bird extinctions?

One consequence of bird extinctions is the loss of some ecological functions. For instance, the extinction of nectarivores might then cause the extinction of flowers that were pollinated by birds. Other examples of functions that have been lost are the extinction of giant flightless birds such as the moas of New Zealand and the elephant birds of Madagascar that were probably acting like large terrestrial herbivores, as ungulates do in the continents.

How successful have bird introductions been throughout the world?

Introduced species are always related to human activities but can be intentional or accidental. For instance, “Acclimatization societies” encouraged the introduction of non-native species during the 19th and 20th centuries. The purpose of these associations, born when Europeans were establishing many colonies around the world, was to make some regions more familiar to Europeans, by releasing animals and plants from Europe elsewhere. The success of introductions can depend on different factors related to the introduction event, such as how many birds have been released, but also on the species’ characteristics. Some traits can make species more prone to establish when introduced, such as having a relatively larger brain or reproducing multiple times each year.

Your study found that introduced species are not replacing the roles of extinct species. Can you please explain this further?

Some of the extinct species had a role in the ecosystem that have not been replaced by other birds. For example, some giant flightless species, like the moas of New Zealand and the elephant birds of Madagascar, were probably acting like large terrestrial herbivores, as ungulates do in the continents, but unfortunately were driven extinct by humans.

Why is it the case that larger birds and flightless birds are more likely to go extinct and what ecological effect does this have on the world?

Flightless birds are more prone to extinction as they have generally evolved in ecosystems with no predation. Therefore, when humans or invasive species arrive, they are not adapted to escape. In the case of body size, larger species are more prone to extinction for several reasons: First, they are easier to find, and they would be a rewarded target for hunting. In addition, they reproduce more slowly, taking longer to recover from population declines.

What do you feel must be done to reduce the number of birds being driven to extinction worldwide?

We should try to reduce habitat destruction (i.e., deforestation) in many tropical areas, where we have biodiversity hotspots. We also need to stop the introduction of invasive species in ecosystems, as they are also a main cause of extinction.

Do you have any further research that you are able to discuss?

In a previous study, we found that flightless species have been particularly prone to human-caused extinctions. Among extant species, only 0.5% of them are flightless (including iconic species such as ostriches and penguins). However, among extinct birds, almost 30% were flightless, including the famous Dodo from Mauritius, but also many other strange creatures such as flightless ducks in Hawaii or flightless owls in Cuba.

Where can readers find more information?

Current study (Functional loss):

Previous study (Flightless birds):

Video/Interview about flightless birds:


About Ferran Sayol

My research aims to understand how biodiversity has been originated and how it can be lost by anthropogenic impacts. I use a macroevolutionary approach, mainly using birds as a study model.

I did my Ph.D. in Barcelona (UAB, 2018), where I focused on the evolution of brain size in birds. Then, I conducted a postdoc at the University of Gothenburg, where I developed a project on global patterns of bird extinctions, aiming to understand how trait distributions are affected by non-random extinctions. Currently, I am a Marie-Curie Postdoc fellow at University College London, now focusing on the evolution of ecological niches and functional roles of birds.

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