THE BREEDING BEHAVIOUR OF THE LESSER FLAMINGO PHOENICONAIAS MINOR

This paper summarizes what has been learned about the breeding behaviour of the Lesser Flamingo Phoeniconaias minor from 1954 to 1969, especially at Lake Magadi, Kenya, in 1962. The only known regular breeding site is on soda mudflats at Lake Natron, Tanzania. Lake Magadi, used in 1962 when Lake Natron was full of water, may only have been used once this century. Breeding has been sporadically reported from other lakes, but reports are usually inadequate and in many cases successful breeding was not proven. At Lake Natron the breeding site is in the middle of the lake which is 70 km long by 24 km wide. Breeding conditions are extremely harsh, mid-day temperatures regularly exceeding 50^oC and reaching 70–75^oC. The advantage of the site lies in its complete freedom from predatory mammals. Details of known breeding, obtained by aerial surveys, are given. Lesser Flamingos do not breed annually, and tend to start in the last quarter, October to December, of any year in which they breed. There is no obvious relation between food supply and this breeding date. The last quarter of the year at Lake Natron tends to be rainy and warm. No really large-scale breeding has been observed since 1962. The methods used for estimating adults and young are given. They have shown good correlation with ground counts at Lake Magadi in 1962. The total population is of the order of three to four million, and the largest known breeding colonies were of 1,100,000 pairs at Lake Magadi in 1962 and 570,000 pairs in 1957 at Lake Natron. From 1953 to 1962 inclusive about 275,000 pairs (1/5 to 1 /6 of the population) bred annually on average, but since 1962 the average number breeding per year has been less, reducing the overall average to perhaps 180,000 pairs. At this rate a pair takes 22–24 years to replace itself. The nuptial display of the Lesser Flamingo resembles in many respects that of the Greater Flamingo Phoenicopterus ruber. When displaying, Lesser Flamingos congregate in a tightly-packed flock, rapidly moving, in which various ritual movements are performed. Display normally takes place in certain sites far from known breeding grounds, and may be stimulated by conditions of very dense population. Lesser Flamingos build mud-mound nests similar to but smaller than those of the Greater Flamingo. Measurements, weights, and other details are given. The huge 1962 Magadi colony involved the excavation of some 20,000 metric tons of soda mud. One egg is normally laid. Large numbers of birds tend to lay synchronously in particular parts of the colony. The threshold numbers for breeding may be of the order of 5,000 pairs. Both sexes incubate, for about 28–29 days. Incubating birds are liable to desert en masse when disturbed, e.g. by hyenas. 70–90% of eggs hatch, usually about 85%. Larger colonies are more successful than smaller, and birds that lay out of phase with others tend to desert without hatching. The development of the young resembles that of the Greater Flamingo, but the two are distinguishable at an early age by bill structure. At Lake Natron the fledging period is about 70 days, but at Lake Magadi it was about 90 days, probably because the parents had to fly to Lake Natron for food. Adults attend the chicks closely for the first week of life, but thereafter leave them increasingly. Chicks more than one week old gather in herds, which eventually aggregate to huge numbers, 300,000 or more. Both at Lake Natron and Lake Magadi the chicks moved en masse out of the breeding area to gathering grounds in shallow water, where they remained till able to feed themselves and fly. Both sexes feed the young with regurgigated liquid matter, delivered bill to bill with parent and young both facing forward, as in the Greater Flamingo. Feeding details were not closely observed at Lake Magadi as most feeding took place after dark. Breeding success has varied from 5 to 75%, averaging 41 to 43% of eggs laid. The 1962 Magadi colony had 33 to 38% breeding success. Mass moult to flightlessness is described. It may occur before, during, or after the breeding season, or without breeding, and normally only at Lake Natron. It lasts six to eight weeks, perhaps three weeks for an individual, and may be controllable in that it did not occur at Lake Magadi in 1962 when its effects would have been fatal for the colony. Predation by large mammals (from lions to jackals) and birds, especially Egyptian and other Vultures, is described and roughly quantified. Predation from all causes may have resulted in 5% loss at the Magadi colony, but at Lake Natron is probably less. Eight thousand young Lesser Flamingos and 80 Greater Flamingos were ringed at Lake Magadi in 1962. Ringing methods are described. Recoveries have been meagre, the most distant being from the Awash Valley, Ethiopia. No rings have been observed among the adult population in recent years. The most probable explanation of the poor results is ring loss through chemical action of the water.