A new study has shown that the iconic lesser flamingoes could soon be extinct as a result of low food availability due to rising water levels in soda lakes.
More than three-quarters of the world’s lesser flamingos feed on the cyanobacterial blooms present in the productive soda lakes of East Africa.
The new study shows that their populations are in decline as the rising water levels are driving significant declines in soda lake productivity.
The study titled ‘Current Biology. Productivity declines threaten East African soda lakes and the iconic lesser flamingo' says the bird distribution will likely shift north and south, away from the equator.
Scientists who conducted the study are from the Department of Geography, King’s College London, National Museums of Kenya, Tanzania Wildlife Research Institute, Zoological Society of London, Regent’s Park, School of Geography, Geology and Environment, University of Leicester, Freshwater Biological Association and Natural History Museum.
They are Aidan Byrne, Emma Tebbs, Peter Njoroge, Ally Nkwabi, Michael Chadwick, Robin Freeman, David Harper and Ken Norris.
Soda lakes are some of the most productive aquatic ecosystems.
Their alkaline-saline waters sustain unique phytoplankton communities and provide vital habitats for highly specialised biodiversity, including invertebrates, endemic fish species and lesser flamingoes.
The declining population of the birds has been attributed to their highly specialised diet of cyanobacteria and dependence on a network of soda lake feeding habitats that are highly sensitive to climate fluctuations and catchment degradation.
However, changing habitat availability has not been assessed due to a lack of water quality and hydrology data.
Scientists combined satellite earth observations and lesser flamingo abundance observations to quantify spatial and temporal trends in productivity and ecosystem health in 22 soda lakes in East Africa.
They found that lesser flamingo distributions are best explained by phytoplankton biomass (algae material), an indicator of food availability.
However, time series analyses revealed significant declines in phytoplankton biomass from 1999 to 2022, most likely driven by substantial rise in lake water levels.
Declining productivity has reduced the availability of healthy soda lake ecosystems, most notably in equatorial Kenya and northern Tanzania.
“Our results highlight the increasing vulnerability of lesser flamingoes and other soda lake biodiversity in East Africa, particularly with increased rainfall predicted under climate change. Without improved lake monitoring and catchment management practices, soda lake ecosystems could be pushed beyond their environmental tolerances,” the scientists said.
The study says lesser flamingoes move nomadically between networks of the 22 soda lakes for feeding and courting.
Movements are in response to the sporadic nature of cyanobacterial bloom growth.
The researchers assessed the influence of food availability, lake surface area, season, wind speed, water temperature, rainfall and shoreline vegetation.
They found that lesser flamingo distributions were best described by food availability and lake surface area (water levels).
Of the eight fixed effects variables, only two were identified to influence flamingo abundance.
First, flamingo abundances were higher at lakes with high food availability.
Also, flamingo numbers decreased as lake surface area (water levels) increased.
Water levels have risen in many East African lakes in recent years, leading to a decline in food availability for flamingoes.
The rising water levels in East African lakes have been attributed to increased rainfall, land use change within lake catchments, lake sedimentation and tectonic activity.
However, there is no consensus as multiple drivers likely interact and contribute to increasing water volumes.
The study did not attempt to identify the drivers of rising water levels.
However, the results presented here are consistent with previous studies that have shown the sensitivity of soda lakes to climate change and El Niño events.
Due to the lack of in situ water level data and many of the study lakes lie outside of satellite altimeter data collection paths, they quantified lake surface areas using remote sensing imagery as a proxy for lake water levels.
Across the 22 soda lakes, phytoplankton biomass typically decreased as lake levels increased and vice versa.
To explore these relationships further, the researchers analysed the time series of phytoplankton biomass and lake surface areas for individual lakes using segmented regression models and breakpoint analyses.
Over the 23-year study period, they identified two main phases for changing lake conditions.
On average, water levels declined from 2000 to 2010 and increased from 2010 to 2022.
They also compared surface area changes in each period to changes in phytoplankton biomass.
Water levels declined in 14 lakes from 2000 to 2010, while chlorophyll-a concentrations increased at 14 lakes.
“From 2010 to 2022, surface areas increased in 12 lakes while chlorophyll-a concentrations decreased at 16 lakes. The largest losses in phytoplankton biomass occurred in the equatorial Kenyan lakes-Bogoria, Nakuru and Elementaita- and in northern Tanzanian lakes,” the study says,
Nakuru is one of the most important flamingo feeding lakes in East Africa, supporting about one million birds.
The lake increased in surface area by 90.7 per cent from 2009 to 2022, leading to a drop in chlorophyll-a concentrations.
The researchers said food availability for lesser flamingoes mostly increased towards the northernmost and southernmost extents of their East African range.
