The Ecology of Lake Nakuru (Kenya). I. Abundance and Feeding of the Lesser Flamingo

• Published in: Oecologia 1978-01, Vol.32 (1), p.11-35
• Main Author: Vareschi, Ekkehard
• Format: Article
• Language: English
• Subjects: Algae; Birds; Breeding; Food; Fresh water; Lakes; Lakeshores; Pumping; Rift valleys; Waterfowl
• ISSN: 0029-8549; 1432-1939
• DOI: 10.1007/BF00344687

The shallow, alkaline pan of Lake Nakuru (conductivity 15,000-25,000 μmho/cm, 20°C) usually maintains an exceptionally high standing crop of the cyanophyte Spirulina platensis (150-200 mg DW/1; DW = dry weight), the main food of a large population of the lesser flamingo (Phoeniconaias minor). The abundance and feeding of the lesser flamingo were studied in an attempt to quantify the lake's energy flow. Some data on other rift valley lakes with similar chemical and biological conditions are included, since they are inhabited by flamingos as well. The spatial distribution and total population of the flamingos were monitored on a monthly basis. The birds were counted automatically from aerial photographs by a particle counter. The mean was 915,000 in 1972 and 1973, and in 1974 the population dropped to a mean of 113,000. The population also showed pronounced short time fluctuations that are correlated with algal densities. Other possible causes for flamingo migrations are discussed. Flamingos feed by filtering planktonic organisms from the water with their bill. Feeding experiments with caged birds gave a clearing rate of 31.8±1.3 1/h (SE; SE=standard error) for an adult flamingo, a pumping rate of 17.5 strokes/s and a feeding rate of 5.6 g DW/h at the mean algal concentration of 180 mg DW/1 in 1972/73. The mean feeding time in that period was 12.5 h/d, which gave a daily feeding rate of 72±6.5 g DW for an adult bird and 66±6 g DW for the average bird (juveniles included). Therefore the whole flamingo population extracted per day ∼60 t DW of algae (0.7 g$\text{DW}/\text{m}^{3}/\text{d}$or 3$\text{kcal}/\text{m}^{3}/\text{d}$) from the lake. This is 50-94% of the daily primary production or 0.4 to 0.6% of the algal biomass and two to three times the amount all other primary consumers are feeding. About 0.75$\text{kcal}/\text{m}^{3}/\text{d}$are returned by fecal and urinary wastes. These feeding rates are slightly lower than calculations based on basic metabolic rates of birds. In 1974 the feeding rate decreased with decreasing algal concentrations. Feeding-rate experiments on rotifers (650 mg DW/h at a concentration of 19 mg DW/1) showed that a high rotifer population can partly substitute Spirulina as the main food of the lesser flamingo. Feeding behavior and other possible food sources are discussed.