FLUCTUATING ALGAL FOOD POPULATIONS AND THE OCCURRENCE OF LESSER FLAMINGOS (PHOENICONAIAS MINOR) IN THREE KENYAN RIFT VALLEY LAKES¹

Abstract

The last two decades have witnessed increasing episodes of lesser flamingo die-offs in East Africa. Based on data on phytoplankton composition, biomass, and flamingo population density in three alkaline-saline lakes of Kenya (Bogoria, Nakuru, and Oloidien) in 2001-2010, this study explored the link between sudden flamingo deaths and fluctuations in algal food quantity and quality. The phytoplankton biomass ranged from 13 to 768 mg AE L )1 . Similarly, flamingo numbers varied widely from <1,000 to >500,000 individuals in the study lakes. The dominance of the cyanobacterium Arthrospira fusiformis (Woron.) Komárek et J. W. G. Lund was interrupted at irregular intervals in each lake and replaced partly by populations of different species of the nostocalean Anabaenopsis or by the picoplanktonic chlorophyte Picocystis salinarum Lewin. The populations of Anabaenopsis have the potential of blocking the flamingo food filtration system with their large and slimy colonies; moreover, they are able to produce cyanotoxins. Estimates of flamingo populations suggest that low flamingo numbers coincided with periods of low algal food quantity and ⁄ or poor quality. A food deficit can be theorized to have two effects on the flamingos: (i) it weakens them to the point of being susceptible to attacks of infective diseases, such as the ones caused by Mycobacterium avium and Pseudomonas aeruginosa, and (ii) it predisposes them to poisoning by cyanotoxins and pollutants, by reducing their capacity to handle toxic substances. This study therefore concludes that the challenges facing the flamingos are associated with changes in their environment, which affect food and water supply.

A detailed time series assessment of the diet of Lesser Flamingos: further explanation for their itinerant behaviour

“…These phytoplankton taxa are less preferred by the Lesser Flamingos, consequently the presence of very low flamingo numbers that occurred at this time. For instance, the large slimy lumps of Anabaenopsis may clog the excluders and lamellae of flamingos hence preventing food uptake, which could lead to starvation and consequently, malnutrition (Krienitz & Kotut, 2010). Moreover, single-celled cyanoprokaryotes, cryptomonads and diatoms are much too small to be held back effectively.…”

“…In L. Nakuru, reports indicated sudden mortalities from 1993 to 2003, with deaths going beyond 500 in 1998 (Ndetei & Muhandiki, 2005). Krienitz & Kotut (2010) reported the highest mortality of flamingos (*30,000) in L. Nakuru in 2006. In 2008, the same authors also recorded about 30,000 carcasses of Lesser Flamingos that had accumulated along the shoreline of L. Bogoria.…”

“…In 2008, the same authors also recorded about 30,000 carcasses of Lesser Flamingos that had accumulated along the shoreline of L. Bogoria. Among the possible causes for the sudden mortalities cited were the changes in food quantity (Sileo et al, 1979;Mlingwa & Baker, 2006) and composition (Ndetei & Muhandiki, 2005;Krienitz & Kotut, 2010). Problems with food composition are mainly associated with mucilage clogging the filters in the beaks and the production of cyanobacterial toxins by some taxa of cyanobacteria, which are ingested during feeding (Vareschi, 1978;Codd et al, 2003;Krienitz et al, 2003;Krienitz & Kotut, 2010).…”

“…However, no studies so far have addressed variations in nutritional quality of phytoplankton community in terms of lipids, carbohydrates and crude protein content over short-term intervals in the natural environment. Krienitz & Kotut (2010) related flamingo movements to changes in algal food quantity and quality in terms of toxicity on an irregular basis. To our knowledge, a detailed time series assessment of the nutritional quality of the diet for the Lesser Flamingos on a regular basis has not previously been done in African saline lakes.…”

“…In recent years, much work has been done to explain fluctuations and shifts in the phytoplankton community composition in the soda lakes of the East African Rift Valley and how they influence the abundances of Lesser Flamingos (Phoeniconaias minor Geoffrey) which inhabit these water bodies (Vareschi, 1978;Harper et al, 2003;Krienitz & Kotut, 2010). These saline-alkaline lakes are renowned for their abundant phytoplankton biomass dominated by the cyanobacterium Arthrospira fusiformis (Voronichin) Komárek & Lund (formerly called Spirulina plantensis Voronichin), which is the main food source for these birds (Vareschi, 1978;Owino et al, 2001).…”