The most unique birds on Earth also tend to be the most at risk of extinction, according to a new study that has looked at 99% of all known bird species on the planet. Lead author Jarome Ali explains why.

J Ali

Profile: Jarome Ali

Jarome Ali is an evolutionary biologist and ecologist. He is interested in why the natural world has so many diverse forms of life. He has studied guppy behaviour, catfish speciation, and bird morphology.

In his current research at Princeton, he studies the evolution of the diverse colours of parrots. Formerly of Imperial College London, he is currently a PhD candidate at the Stoddard Lab at Princeton University.

Top image: Blyth’s kingfisher (Alcedo Hercules) grows to around 22-23cm in length and it is found throughout south and southeast Asia. © Henry Koh (CC BY 2.0)

A new study has found that bird species with extreme or uncommon combinations of traits, face the highest risk of extinc­tion. Led by researchers at Imperial College London, the study suggests the most unique birds on the planet are also the most threatened.

Losing these species and the unique roles they play in the environment, such as seed dispersal, pollination and predation, could have severe consequences on the functioning of ecosystems.

The study analysed the extinction risk and physical attributes (such as beak shape and wing length) of 99% of all living bird species, making it the most comprehensive study of its kind to date.

Aether spoke to lead author Jarome Ali to find out more about this startling, and worrying, research.


Aether: Why are the most unique bird species most likely to become extinct?


JA: This is actually a very hard question, and it’s one that we weren’t able to answer in the paper. But what we did find was an association between unique shape or morphology and the risk of extinction. One explanation for this association is that birds with unique morphologies have a very specialised role in the ecosystem.

Take for example the Long-tailed Woodnymph (Thalurania watertonii). Like other hummingbirds, it has a very long and thin bill, compared to its body. Research has shown that traits such as bill length and shape relate to what birds do in the ecosystem. A bird with very specialised morphology might have a very specialised relationship with other elements of the ecosystem. In the case of the hummingbird, their extreme bill shape might mean they are very tightly related to specific plant species in terms of where they get nectar.

As you have habitat destruction and loss, those very tight relationships are more easily untangled. Also, species with unique morphology and specialised roles might have smaller habitats. We know that the Long-tailed Woodnymph is suffering population decrease related to habitat fragmentation. These and other factors could combine to make unique species more at risk.

We don’t have all the answers right now. It’s very important that future research investigates the underlying reason for the link between unique traits and risk of extinction.


Aether: Do these more unique species tend not to be wide­spread in either number or range?


JA: As is often the case in biology, the relationship is complicated. There are species that aren’t that unique, but that are themselves quite endangered. This might be because they’re found on a small island and nowhere else and have a very small population size. Species can be at risk of extinction just by virtue of having a small population size.

What we do find is that there’s an elevated risk of extinction for unique species. However, not all unique species are highly endangered. In fact, there are unique species that are very widespread.

If we take cattle egrets as an example, they have a quite unique morphology. They’re very odd looking if you compare them to sparrows, which is an example of a more common morphology. But cattle egrets are found all over the world and they’re very common where they’re found. So, it’s not always the case that unique birds are restricted in terms of pop­ulation size or range. It’s complicated.


Aether: To what extent can you attribute the effect of Man in terms of some of these most at risk unique species?


JA: The impact of humans on animals is undeniable. We are increasingly putting pressure on animals in terms of the pollution and habitat destruction. Not to mention the threat of climate change.

One way we categorise extinction risk is by using trends in population size. As habitats are destroyed, populations decline. Look at the Amazon Forest, for example. Almost 20% of the Amazon has been lost already and the habitat destruction and degradation are only increasing. That’s all human activity.

Agami heron

Considered ‘vulnerable’ on the IUCN Red List, the agami heron (Agamia agami) is found in Central and South America. © Chris Jimenez (CC BY-SA 2.0)

Aether: Can you give some examples of unique birds that fall into this bracket and explain why they specifically are more at risk than other birds within the same area?

JA: In our analysis, hummingbirds were among the birds that were both unique and at high risk of extinction. As I said earlier, some hummingbirds have very tight relationships with a limited number of plant species that they’re good at getting nectar out of. As we degrade and destroy their habitats, they might be less able to cope than species that have less specialised diets.


Aether: What examples can you provide of the loss of unique species having an impact on ‘seed dispersal, pollination and predation’?

JA: Previous work has shown that the measurements we use (beak, wings, tail, legs) reflect what roles birds have in the ecosystem. For example, you can use these traits to predict whether a bird is a scavenger or carnivore and so on. In our analysis, we separated birds into herbivores, omnivores, carnivores and scavengers and we found that extinction would cause a huge decrease in the diversity of bird shapes in all these categories. If we lose all that diver­sity, we also lose the roles these animals play.


Aether: Scavengers and carnivores tend to be larger and tend therefore have smaller populations, are they therefore at greater risk of extinction?

JA: Small populations are definitely a risk factor when it comes to extinction. Regarding body size, there is a well-established link between large body size and high extinction risk—lots of studies have found this. It is certainly true in mammals, it’s true in reptiles, and it’s true in birds. Just look at the loss of megafauna in mammals, for example, to see that species that are very large tend to go extinct.

There is a range of reasons why that might be, but in our analysis, we did our very best to remove body size from the equation. We used statistical methods to remove body size, in effect what we were really looking at was shape.

That is the novelty of our results; finding that birds with extreme traits are highly threatened is not new, but finding that birds with extreme shape are highly threatened is quite new.

Bristle-thighed curlew

The bristle-thighed curlew (Numenius tahitiensis) migrates between tropical islands in the south Pacific to the Alaskan tundra where its breeding grounds are found. © Public Domain.


Aether: Is there an element of evolution at play if a species struggles to adapt to its circumstances?


JA: Evolution and extinction are con­stantly ongoing processes. The problem we have now is that many species might be unable to adapt at the rate that humans are changing the environment. We are causing unusually high extinction rates. That’s the problem.

It’s not that species aren’t evolving because everything is evolving all the time. The problem is it might be that species can’t adapt at the rate they need in order to keep up with our influence on the environment, whether it be climate change or whatever else.

But species can respond in a few ways. One of the ways that species can respond to changing environments is called phenotypic plasticity. This is where morphology, physiology and/ or behaviour change in response to the environment. This occurs because the genes can interact with different environments to produce different phenotypes or traits.

Another thing that we might expect, and there’s a lot of really interesting work on this, is that as the climate warms, the habitable area for certain species will change. Take a mountain as an example. Species will have certain elevations and temperature ranges along the mountain where they’re very happy. As warming happens, we expect that species might move up the mountain to track their ideal habitat. That is a crucial question because we don’t know that all species will be able to adapt or move fast enough.

Another interesting possibility is that where species are found currently, might not fully represent the range of places that the species could inhabit. A species at a particular elevation and temperature might just be where it prefers to be, but as that habitat warms, it’s possible that it could still survive there. We don’t know yet, which is why continuing research into animals’ preferred habitats, their natural history, is really important.

There is also intriguing evidence that birds are evolving in response to human impact; a study in Nebraska found that some birds are evolving shorter wings. Birds with shorter wings have higher manoeuvrability and might have higher survival in areas where they need to escape from heavy highway traffic.


Aether: Is there a case to be made for the translocation of those species in very localised areas as part of a conservation effort?

JA: The ideas are intriguing, but it’s very hard to predict whether a trans­location will work. This is a matter for practicing conservation biologists but I’ll give answering this a shot.

There is a trend for in situ conserva­tion to be the priority. For example, breeding programmes that happen at the locations where these animals are found, in addition to habitat conservation and restoration.

There is evidence that as you restore habitats, species come back. So, one way of preserving a species’ future is habitat restoration, and that is an area we’ll probably see more and more focus on.

Another example comes from nesting seabirds. In countries where there are regulatory frameworks and the resources to implement them, seabird habitats are tightly protected and restricted, especially during the nesting season.

A temporary restriction of an area is one example where we can aid in conser­vation and reduce the human impact. There are beaches in Long Island, for instance, that they simply close off during the nesting season of the Piping Plover. It might not always be popular with beachgoers, but it is necessary and it is really important for this species.

Cattle egret

A cattle egret close to a bloat of hippos in the Okavango Delta, Botswana. The cattle egret is an example of a widely distributed and common bird with a quite unique morphology.

Aether: Going back to your research, what was the most satisfying aspect of it for you?


JA: What is really incredible about what we were able to do with this paper is that we were able to do an analysis for pretty much every bird species on the planet, and that data set is now available to the public. The response to the research that I’ve seen online is at first alarm but also increased motivation to take action to protect threatened species. Encouraging people to care more about the planet’s birds is very rewarding.

That being said, I want to highlight the work of museums and field biologists.

Collecting data for several specimens for almost 10,000 species is an incredible amount of work. This dataset represents the fruits of the labour of work out there everywhere from deserts to rainforests, mist netting birds, measuring birds, often going out very early and spending long days in the field. It also represents an incredible effort by people working in museum collections.

A lot of what a museum has in its collections is not on display to the public. But researchers have access to these specimens. That is a huge part of how it was possible to collect this dataset. And it was a global effort. I measured some of the specimens myself in Philadelphia, but lots of measurements were taken, for example, at the large ornithological collection at Tring in the UK.

I have to mention my masters advisor, Dr Joseph Tobias, who had this dream of a global database of measurement for all birds and spearheaded the effort to collect the data.

Incredibly valuable research is being done in museum collections. These collections are a real resource for humanity because we are able to use them to do research, we are able to use them to engage the public. Museums hold secrets and mysteries that we are yet to even know that we don’t know. For example, we can get DNA from specimens, and have been doing this for a while, but these collections existed long before we even knew what DNA was.

Museums are a real treasure trove for scientists, for the public and for the good of the planet.


Jarome Ali

Stoddard Lab/ Department of Ecology and Evolutionary Biology

Princeton University