Pink spots across the blue-green water; the low grunting sound of thousands of feeding flamingos in the distance –Lake Bogoria’s alkaline water creates a haven for almost a quarter of the world’s Lesser Flamingos after their breeding season in Tanzania’s Lake Natron.
This year, however, as one nears the shore the scene changes – dozens of flamingo carcasses dangle from the branches of dense Prosopis juliflora thickets that blanket the lake’s shores. Some flamingo seem to have lost the fight after struggling to disentangle from the sharp thorns of the low trees.
“It is worrying,” says James Kimaru, the Kenya Wildlife Service (KWS) senior warden at Lake Bogoria National Reserve. “Tens of flamingos are dying from being trapped by Prosopis bushes while attempting to either land or take off,”
Prosopis juliflora, a kind of mesquite, is an aggressive invader that replaces native vegetation, especially in dry areas where there is seasonal flooding.. It is ranked among top 100 invasive species globally, ravaging other arid and semi-arid areas of Ethiopia, Sudan, Egypt, West Africa, Australia, and other countries.
The plant was introduced in Kenya in the 1970s to rehabilitate the Arid and Semi-Arid Areas (ASALs), due to its resilience, fast growth rate and edible pods. Here it became known as ‘Mathenge’.
Prosopis does not normally grow on the shores of strongly alkaline or saline lakes, and flamingos can use the muddy shores dusted with white soda ash for takeoff and landing. In the past decade of heavy rain and catchment degradation, however, many alkaline lakes have flooded and become fresher. Prosopis became established in the shallow, relatively fresh water along the edges of the lakes.
“Flamingos prefers shallow water near the shores, which unfortunately has been taken over by Prosopis. This becomes a challenge whenever the birds are landing or taking off,” Richard Kipng’eno, Birding and Membership officer at Nature Kenya says.
Lake Bogoria has expanded by 7 square kilometre from its original size. The rising water levels have submerged administration offices and the gate of the \national reserve.
“Prosopis has also created navigational challenges in some parts of Lake Baringo,” Kipng’eno adds. “During the recent waterbird counts at Lake Baringo, we experienced some difficulties in manoeuvring boats through the Prosopis thickets.”
Large concentrations of Prosopis are to be found in Tana River, Turkana and Baringo counties. The invasive Prosopis has also colonised parts of Taita Taveta, Malindi, Samburu, Isiolo, Mandera, Marsabit, Wajir, Kajiado and Migori counties.
The plant has also been documented to have invaded some of Kenya’s important wetlands including River Tana Delta in Tana River County, Lorian Swamp (Isiolo/Garissa Counties) Lengurruahanga swamp (Kajiado) among others.
Prosopis charcoal is highly rated, but it is very difficult to cut the hard wood of the spreading, thorny trees.