• 1The Sudan Dioch (Quelea quelea) occurs in flocks sometimes numbering more than one million. It possesses an internal sexual cycle essentially like that of temperate zone passerines but it breeds only after rainfall and irrespective of the swing of the sun in Tanganyika.
  • 2No proof is available that rainfall as such stimulates the seasonal reactivation of the gonads but these are already in an advanced state of maturation at the time of nest-building towards the end of the wet season. The males are by then in full, vivid nuptial dress.
  • 3It is possible that ovulation depends partly upon the rain-induced, seasonal appearance of the fresh green grass invariably used in nest-building and almost certainly upon the assumption of breeding plumage by the male. The male constructs a perpendicular nest-ring of fresh green grass and displays thereon to a female. Copulation occurs on or near the ring, after which the final stages of nest-building are completed. Meanwhile, ovulation occurs.
  • 4Successful reproduction partly depends firstly on the presence of vast quantities of insects (used to feed the young during the first five days of life) and next on green grass seeds with which nestlings are subsequently fed. Only after “good rains” do such conditions persist. Breeding sites are frequently abandoned after nests have been built and while the males are at the height of spermatogenesis.
  • 5In Tanganyika, an average of only 2–8 eggs per nest is laid.
  • 6Factors conducive to the prodigious reproductive success of Q. quelea may include the following:
  • (i) It is probably capable of breeding at the age of nine months, and twice in one year if environmental conditions are propitious.
  • (ii) Even if it fails to reproduce during a curtailed wet season in one area, its extreme mobility may allow it to breed elsewhere and certainly during the second season of rainfall some months later.“Stationary” xerophilous species must wait for rain to come to them: the Dioch can go to the rain.
  • (iii) Although the food requirements of the young are rigidly (and pluvially) circumscribed, adults can live on dry seeds which are more widely available. The species is sufficiently mobile to be able to reach water somewhere and so escape large-scale mortality in times of drought. The young, though of course nidicolous, can look after themselves within twenty days of hatching.
  • (iv) Predators are few. The species is rigidly colonial in nesting, roosting and even in food gathering. It is therefore at all times mutually protective.