Natalité et mortalité dans une population naturelle d’un passereau tropical, le Lagonosticta senegala

The breeding cycle, clutch size and frequency, mor tality rate of eggs, nestlings and adults, and general productivity of a wild population of the Senegal fire- finch Lagonosticta senegala, banded at the Ornithologi cal Station of Richard-Toll, Sénégal, were studied during the period 1954 to 1964. The breeding season lasts for 9 months, from the first half of July to the beginning of April. During the season a single individual adult male has been shown by banding to be capable of breeding four times in succession. Despite the fact that they have been hatched in different months of the breeding season, the young all reach matu rity simultaneously, about the beginning of August, and are then ready to breed in their turn. Both the number of eggs and the number of fled glings produced per pair of breeding adults each year are very high, off-setting the high mortality rate of the population. Only 45 % of the eggs laid are hatched, and only 28 % of them result in fledged young. The adult death rate has been estimated in two different ways ; by the use of the « composite life table », as defined by Hickey, in the case of males, and by calculating the percentage of banded individuals breeding for the first time out of the total breeding population. Both methods give an average annual adult mortality rate of 70 to 75 %. Des pite the fact that a very small percentage of individuals in the population survived to an old age (7 years), the expectation of life of the newly-hatched Senegal Fire- finch is low and the population turnover rapid. At the nest stage the parasitic weaver Hypochera chalybeata is one of the most important mortality factors among nestlings. Although clutch-size is the same in normal and parasitized nests (3.5 and 3.3) , and although the percentage of eggs hatching is the same in both cases, the mortality among nestlings is twice as high (53 %) in parasitized nests as in normal nests (25 %)