Science | July 23, 2024

How Will Climate Change Hurt Lesser Flamingos?

Their food supply in East African lakes could collapse as rains increase

A lesser flamingo feeds at Lake Bogoria, in Kenya. David Harper

Contributing Writer

Zoologist Aidan Byrne heard the sound of the lesser flamingos of Lake Bogoria before he laid eyes on the birds. He was taking water samples of the soda lakes of East Africa in July 2022 when he heard a powerful noise, like a distant waterfall, and then the sky turned pink as thousands of the birds took flight.

“It was a very beautiful sight,” says Byrne, a PhD candidate in zoology at the Natural History Museum and King’s College London.

In the 20 years prior to that moment, Byrne’s colleagues had been studying the way that increasing water levels are changing the delicate chemical composition of the soda lakes of East Africa. The water in many of these roughly two dozen lakes is very salty and alkaline, creating a unique aquatic habitat for a host of species endemic to the area. Many parts of these lakes are very shallow, and fragile ecological conditions in them allows for the growth of cyanobacteria—food for the flamingos.

While Byrne had been studying the flamingos since joining the project in 2020, most of his work had been remote. In 2022, Byrne had been taking water samples in Kenyan lakes when he made a detour to see the flamingos. Watching them fill the sky produced a feeling of awe.

Now his work reveals that changing conditions in the lakes are likely reducing the food available to lesser flamingos. At a time when the species is already in decline due to a host of other factors like pollution and habitat loss, the find reveals another potential cause for conservation concern—one that could affect other creatures as well.

“Flamingos act as a good indicator of what’s happening in the wider ecosystem,” Byrne says. If these increases in water level affect the iconic pink birds, it’s likely only the tip of the iceberg, since a whole host of endemic animals also depend on very specific conditions.

What are the soda lakes?

Flock of Lesser Flamingos — A flock of lesser flamingos covers Lake Bogoria. Aidan Byrne

Lesser flamingos are one of six flamingo species found around the world. They are classified as “near threatened” by the International Union for Conservation of Nature, and their numbers are thought to be declining, Byrne says. But researchers haven’t always been clear on why.

Several populations of lesser flamingos inhabit Africa and India—researchers estimate between two million to three million lesser flamingos exist in the world. But most of them live around the soda lakes in Ethiopia, Kenya and Tanzania. These lakes, which vary in size from less than a square mile to more than 385 square miles according to Byrne, are so-called due to their high levels of salinity. They also have very high alkaline levels—or a pH of more than seven that is the opposite of extreme acidity. Many freshwater species couldn’t survive in this kind of harsh environment, but the ones that do are highly adapted to this chemical composition. Endemic species include cichlid fish, invertebrates and microbes.

“These have all adapted to these extreme conditions,” Byrne says.

Many of these lakes are known for being quite shallow, which allows for the growth of the cyanobacteria that the flamingos feed on. The carotenoid pigments in this alga gives flamingos their pinkish hue.

How are the lakes changing?

Flamingo Feathers and Cyanobacteria — Flamingo feathers can be seen amid a dense cyanobacteria bloom at Lake Bogoria. Aidan Byrne

Byrne and colleagues had noticed that heavier rainfall was causing increases in water levels in many of the soda lakes. So they decided to track whether this was affecting the production of cyanobacteria, and therefore the food source of lesser flamingos.

The researchers wanted to see if they could determine the amount of cyanobacteria in the lakes, and how it changed over time. They gathered satellite images taken of 22 of the lakes from 1999 to 2022. Previously, researchers had compared satellite images of lake chlorophyll with the amount of cyanobacteria taken from water samples. They examined the level of lake reflection in the photos to get accurate numbers of the flamingos’ food source. Byrne and his colleagues used this calculation to determine the concentration of the cyanobacteria for the images in their 23-year study period.

Analysis revealed that the water levels of the lakes had increased over the study period due to higher rainfall driven by climate change. At the same time, the biomass of phytoplankton like cyanobacteria decreased significantly. As the water level increases, the salinity and alkalinity levels change, making it less suitable for cyanobacteria.

“The cyanobacteria can no longer grow, because that’s what it’s adapted to,” Byrne says, referring to higher salinity and alkaline levels.

The team also looked at flamingo abundance taken from the International Waterbird Census. The surveys revealed that as the food density decreased, the flamingos went with it.

“They were moving away from lakes with increasing surface water levels,” Byrne says.

The researchers published their results this past April in Current Biology.

Alex Jahn, a research scientist at the Indiana University Bloomington who studies South American flamingos but was not involved in Byrne’s research, says these findings are “worrying” since climate change has such a stark effect on lesser flamingo food supply.

“Across birds generally, food drives a lot of their behavior and even survival,” he says. His research has shown that climate change is also affecting the population of Andean flamingos in South America, though in that case, a decline in surface water is reducing the birds’ foraging grounds. “A common species can become rare pretty quickly if it gets hit hard enough.”

What is next for the flamingos?

Lesser flamingos are nomadic, but they don’t follow a seasonal trajectory like many birds, flying south for the winter and north for the summer. Most of them nest on Lake Natron, which straddles the border of Kenya and Tanzania. They only breed when the conditions are just right—usually every five to eight years, when the water levels are high enough from the rain to isolate islands on the lake from predators. The rain also can’t be so high that the islands are flooded, since the birds need to build their mud nests there.

In other periods, they seem to fly around from lake to lake, harvesting cyanobacteria as they go. They adapt to lower food levels in some lakes by moving to others. As rainfall increases, some salt shallows and other seasonal lakes see an increase in cyanobacteria. The data showed that six lakes had more suitable flamingo foraging habitat in 2022 compared to 2010. But they are losing more than they are gaining, Byrne says—16 of the lakes declined in phytoplankton.

These decreases in food availability have likely happened in the past. Byrne says that tens of thousands of years ago, research shows the soda lakes had much higher water levels.

“Being nomads has, in the past, protected them against an unsuitable environment,” says Paul Rose, a lecturer at the University of Exeter in England who studies flamingos but was not involved in the recent study.

The concern is the speed of the current shift, many researchers agree, which may be driven by climate change.

“They might find it hard to adapt in such a short space of time,” Byrne says.

Another problem lies in the local protection afforded to the lakes. Lakes Bogoria and Nakuru in Kenya have various conservation protection laws and have historically provided some of the best foraging habitats. But these lakes saw some of the biggest declines in food. If flamingos move away from these more protected lakes, they will likely face problems caused by human disturbance. Sewage and other types of pollution in other places can degrade the water and throw the chemical composition out of whack. Meanwhile, more infrastructure and humans stress populations and scare birds away.

“Lesser flamingos are impacted by climatic change, disturbance from humans, novel disease and a lack of quality nesting and feeding sites,” Rose says. He worries that alternative sites won’t open up as formerly good foraging habitat disappears.

Both Rose and Jahn hope that their recent study will increase awareness and prompt conservation measures. Rose says that steps could be taken to artificially boost the natural alkaline and salinity levels in some parts of the lakes, for example, which could increase food supplies. New areas could also be protected, to buffer them from pollution and other human problems. While millions of lesser flamingos inhabit the world, they are in decline and are vulnerable to the impacts of climate change. “Issues that affect a population now may not be noticeable until decades into the future,” Rose says. “This research is a warning signal to act now to bolster and support habitat quality to prevent future flamingo population crashes.”