The world’s most seemingly-toxic lakes are under threat. And they are also home to one of our most familiar birds: the flamingo.
All flamingo species have evolved to live in some of the planet’s most extreme wetlands, like caustic “soda lakes”, hypersaline lagoons or high-altitude salt flats.
One species, the lesser flamingo, has taken this relationship to the limit. Most are found in super-alkaline lakes throughout Africa’s Great Rift Valley, which host immense blooms of microscopic blue-green algae (called cyanobacteria). These poisonous plants produce chemicals that, in most animals, can fatally damage cells, the nervous system, and the liver. The lesser flamingo, however, can consume enormous amounts with no ill effects (unless you count their colourful plumage, which comes from a pigment in the algae).
Birds in paradise
Two of the lesser flamingo’s preferred habitats, Lake Bogoria in Kenya and Lake Natron in Tanzania, are hypersaline and hostile to practically all other forms of life (Natron water can even strip away human skin).
For the flamingos this a bonus. Special tough skin and scales on their legs prevent burns, and they can drink water at near boiling point to collect freshwater from springs and geysers at lake edges. If no freshwater is available, flamingos can use glands in their head that remove salt, draining it out from their nasal cavity.
With few other animals able to cope in such conditions, there is minimal competition for food, and these toxic wetlands are home to massive flocks.
Gudkov Andrey / shutterstock
Million-strong gatherings provide several benefits. Mass synchronised nesting gives flamingos the best possible chance to raise the maximum number of chicks, while on choppy days a dense mass of birds swimming together also helps create the optimal feeding environment (still water) within the centre of the group. Sheer numbers also make it harder for predators like hyenas or jackals to identify individual victims.
As such, a single flamingo is not a happy flamingo. The species is happiest in huge gatherings, and these won’t occur around any old lake – the lesser flamingo specifically needs its toxic, salty paradise.
But these places are rare. Across the six flamingo species there are only 30 or so regularly used breeding sites worldwide and, while the global population of around 3.2m lesser flamingos is impressive, it is largely reliant on a few huge groups (about 75% nest at Lake Natron alone). What if something happens to one of their highly-specialised breeding sites?
Unlike many other species that can still breed in smaller populations as their habitats become damaged, these birds cannot easily survive in small groups. Having evolved in such a hostile environment with few rivals, they would have trouble adapting to a more competitive lifestyle elsewhere. With most of their eggs in one toxic basket, the lesser flamingo is unusually vulnerable for a species with millions of individuals.
Steffen Foerster / shutterstock
Indeed, the number of lesser flamingos in the wild is already decreasing each year. And humans are to blame. Wetland habitats have been polluted by agricultural chemicals and sewage, feeding and breeding grounds have been disturbed, and declining algal blooms mean some populations are starving to death.
Even a diet of toxic algae can’t save flamingos from ecological disturbances. If humans take too much water from a lake, or climate change causes excess evaporation, then salinity levels will become unstable. Populations of cyanobacteria can explode and the birds end up consuming new species which can poison them and cause mass deaths.