Lake Elmenteita Research Articles

Orthophosphate turnover in East African lakes.

Turnover rates of 32P-PO4 and concentrations of orthophosphate as soluble reactive phosphorus (SRP) were measured in five East African waters. Rapid incorporation of 32P-PO4 by the seston and orthophosphate concentrations below the limit of detectibility were found in Lakes Elmenteita, Naivasha, and Naivasha Crater Lake. Turnover was slow and orthophosphate concentration high in both Lake Nakuru and the Crescent Island Crater basin of Lake Naivasha. Further experiments in Lake Nakuru indicated that colloidal binding of orthophosphate was limited and that particles retained by an 8.0 μ filter incorporated 66% as much tracer as particles retained by a 0.1 μ filter. These experiments strengthen our conclusion that a large quantity of orthophosphate is available for algal use in Lake Nakuru.

THE BREEDING OF THE GREATER FLAMINGO AND GREAT WHITE PELICAN IN EAST AFRICA

SummaryThis paper brings together observations on the breeding of the Greater Flamingo Phoenicopterus ruber and Great White Pelican Pelecanus onocrotalus, mainly at Lake Elmenteita, Kenya, 1951–1971.The Greater Flamingo bred at Lakes Elmenteita and Nakuru in 11/21 observed years and at Lakes Natron and Magadi in 5/12 observed years. On average, it breeds about every second year, but a succession of breeding years is followed by several years in which no breeding occurs.A history of 21 years' breeding at Lakes Nakuru and Elmenteita is given. At Elmenteita three sites have been used, the main site in every breeding year, the others less often. The number of pairs breeding in any year has varied from 500–9,250, but in 1968 flamingos bred three times, involving perhaps 8,500 pairs which made about 15,700 nests, some pairs perhaps laying twice or even thrice in a year.Losses of eggs (38.2% overall) were caused by rising water (16.2%), competition for nest space with Great White Pelicans (6.9%, after 1968 only), human interference (3.5%), Marabou Stork predation (1.8%) and other natural causes (9.8%).Losses among chicks totalled 68.3% overall and were mainly due to Marabou Storks (36.5%), undiagnosed disease (8.6%), and rising water (6.6%). Disease caused serious loss only in 1966, and after 1968 losses from Marabous rose from 2.7% to 76.5%, resulting in an increase in overall mortality from 48.7 to 92%. This was perhaps associated with the establishment of a fish factory at Lake Naivasha.When attacking flamingo colonies Marabous did not actually eat many eggs or chicks, but simply caused wholesale desertion by alarming the flamingos. In 1968 total desertion of a colony of 4,500 pairs was caused between 18 and 26 March by a maximum of 17 Marabous, and similar wholesale desertion was caused in later years.The overall breeding success among Greater Flamingos at Elmenteita was about 19% of eggs laid, but without the excessive post‐1968 Marabou predation would have been about 30%. At such a rate Greater Flamingos require at least 24 years of adult life to replace themselves, but if the mortality caused by Marabous since 1968 continues they will require about 58 years, and the population will inevitably decline. Breeding success at Lakes Magadi and Natron has been higher, about 44% of eggs laid; but figures available are much more approximate than at Elmenteita.Some new data on display, nest‐site selection, laying dates, clutch‐size, hatching and creche behaviour are given for the Greater Flamingo.The Great White Pelican bred at Lake Elmenteita from 1968 to 1971 without a break, some birds laying in every month, but with reduced laying November–December. They bred on the same islands as, and in association with the Greater Flamingo, and caused heavy losses among the latter, not through aggressiveness, but simply because of their superior size and weight.Although food supply must ultimately have controlled the pelican's ability to breed, an adequate food supply was available for 6 years before they did and continued after they had ceased. Their breeding was finally triggered by the Greater Flamingo colonies, with which the pelicans associated. When a flamingo colony was deserted because of Marabou Storks the pelicans, unafraid themselves of the Marabous, also deserted. They also associated with, and wiped out, a colony of Sacred Ibis.From July 1968 to June 1969 about 2,600 pairs of pelicans bred at Elmenteita, rearing about 2,200 young to the flying stage. The breeding colony apparently comprised most of the adults from Lake Nakuru and Lake Naivasha, the main feeding areas.From July 1968 to January 1971 certainly 7,200 and probably 8,000 pairs of pelicans bred at Elmenteita. Some pairs may have bred twice or thrice in this period. Breeding ceased suddenly in January 1971, eggs, and small and large young being alike abandoned for no established reason, although food supply was certainly still plentiful.Additional information on pair formation, incubation and fledging periods, nest‐relief, etc. is given. The best available record of the incubation period is 35–36 days. Nest relief takes place on average about once every 48 hrs, and is dependent on thermal activity enabling the pelicans to soar.At Elmenteita large young ate quantities of putrefying matter, including the corpses of other young pelicans. They also ate living young hatching from eggs, and up to 14 days old. Touch probably plays an important part in helping them to locate possible food in opaque water.

THE BREEDING OF THE GREATER FLAMINGO PHOENICOPTERUS RUBER AT LAKE ELMENTETTA, KENYA COLONY

SummaryThe first authentic breeding record of the Greater Flamingo Phoenicopterus ruber in East Africa is described, and a general history of their colonies on Lake Elmenteita is given.Estimates of numbers are given and possible food supplies are discussed.The breeding cycle is described with notes on display, nests, eggs, young and behaviour of adults.Factors affecting mortality are mentioned, and a description of predation is given, with special reference to the disturbing effect of Marabou Storks Leptoptilos crumeniferus.Breeding success is estimated at from 21% to 74% in different colonies. Possible reasons for the lower success in the colonies are discussed.

Note on Damage to Grazing by Grasshoppers in Kenya

A development of grasshoppers to minor plague proportions over a limited area of the Rift Valley near Lake Elmenteita occurred in 1950. The two chief species concerned were Gastrimargus brevipes Sj. and Caloptenopsis glaucopsis meruensis Sj. but many other genera and species were present and are listed. The distribution of rain with appreciable falls followed several times by dry spells may have been a factor contributing to the increase. An unusual increase of the Coccinellid, Epilachna hirta (Thnb.) also occurred in the area a month or two before.

Cambridge Expedition to the East African Lakes

THE expedition, which is being financed by scientific societies and the University, left England in October and is at work on the rift valley lakes of Kenya. The object of the expedition is twofold: First, to continue studies on the ecology of the East African lakes which were started by the Government fishing surveys of Lakes Victoria, Albert, and Kioga in 1927–28, and at the same time to make thorough collections of the faunas of Lakes Rudolf, Baringo, and Edward, which have previously received only a cursory scientific examination; secondly, by studying the old lake beaches and deposits, to continue farther north the investigations made around Lakes Nakuru, Elmenteita, and Naivasha by Mr. L. S. B. Leakey and the biologists of the East African Archaeological Expedition. It is hoped to link up evidence from lake beaches, the distribution of the present lake faunas, and the chemical constitution of the waters into a unified whole, and so to work out, so far as possible, the previous distribution of land and water during the pluvial periods.