East Africa's Lake Nakuru almost doubled in size in 13 years — and that's bad news for flamingos

Huge pink flocks of millions of flamingos — flamboyances of flamingos — are one of nature's great spectacles. But colleagues and I have uncovered worrying trends in the salty and highly-alkaline "soda lakes" of east Africa where most of these birds live.

Lesser flamingos are the most numerous of the six species of flamingo found across the world, and more than three quarters are found in the soda lakes of Kenya, Tanzania and Ethiopia. Despite their numbers, with estimates ranging between 2 million and 3 million birds, the species is in decline and officially classified as "near threatened".

The causes of the population decline have been difficult to identify due to the remoteness of many soda lakes and the nomadic nature of the birds. They often fly at night between the soda lakes in search of new feeding sites, in response to the boom and bust nature of the cyanobacteria they feed on, commonly known as blue-green algae.

However, rising water levels at many of the feeding lakes are decimating the cyanobacteria the birds have evolved to eat. In research now published in the journal Current Biology, my colleagues and I found that only half of the lakes that provided high-quality feeding habitat in 2000 were still suitable feeding lakes in 2022.

Lesser flamingos feed by turning their heads upside down, pumping water through fine hair-like structures called lamellae in their beaks and catching only cyanobacteria of a certain size. This highly specialised tactic means the birds are heavily dependent on certain cyanobacteria species such as spirulina.

This is the same vitamin-rich spirulina you might have seen in smoothies or supplements. In nature, the species that flamingos feed on only grows in highly salty and alkine conditions, and in soda lakes it grows in such numbers that these lakes are some of the most productive ecosystems on the planet.

But these lakes are especially sensitive to change because they often have no outflowing rivers. And as their waters rise they are diluted, reducing their salinity and alkalinity and limiting the growth of the cyanobacteria the flamingos depend on.

More water, less food

To assess the threats facing lesser flamingos, we used satellites to monitor 22 key feeding lakes across Ethiopia, Kenya and Tanzania between 1999 and 2022. This is the first time the whole east African range of lesser flamingos has been monitored at this scale.

Water levels have risen the most in recent years in Kenya and Tanzania, particularly at historically important flamingo lakes Bogoria and Nakuru, which supported more than 1 million birds in the recent past.

However Nakuru almost doubled in size between 2009 and 2022, while its mean concentration of chlorophyll a — a photosynthetic pigment measured by satellites that can be used as an estimate of cyanobacteria presence — halved. The number of birds has noticeably declined in response to the losses in their food source.

Lake Natron in Tanzania is also worth highlighting as it is the only regular breeding site for lesser flamingos in east Africa. The rising water levels and declining food sources at Natron therefore threaten not only current populations but the birds' ability to breed in the region, possibly leading to drastic declines in the future.

Rising water levels are likely caused by a combination of increased rainfall in recent decades and deforestation which causes the rainfall to run off directly into the lakes. Rainfall is predicted to increase in east Africa with climate change, driving further lake level rises in the future.

It's not entirely bad news, for the flamingos at least. Six of the 22 lakes provided more suitable flamingo habitats in 2022 compared to 2000. The birds will likely find new feeding lakes in shallow salt pans and seasonal lakes. However, without a history of flamingos living there, many of these lakes do not have the same international protections.

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It's not only the flamingos that are at risk. Soda lakes contain plants and animals found nowhere else on earth including fish species, invertebrates and phytoplankton. Declines in their most charismatic birds provide an insight into what could be happening beneath the surface.

These lakes can act as early beacons of how climate change can impact inland waters across the world. If we want to protect these highly fragile ecosystems and their iconic pink birds, we'll have to take action to mitigate the increasing rainfall in the region.

We need to know what's happening on the ground and where the flamingos are going, so more regular water quality monitoring and bird counts are required across the soda lakes. We also need to protect forests near the lakes most susceptible to change and restore lake catchments that are already degraded. This will reduce the amount of rain running straight into the lakes and will give the cyanobacteria a fighting chance.

With the right help, spectacular flamboyances of flamingos will continue to grace east African lakes in the future.

This edited article is republished from The Conversation under a Creative Commons license. Read the original article.