Relations écologiques des avifaunes sédentaire et migratrice dans une savane sahélienne du bas Sénégal

Abstract

Monthly censuses were made of an area of 25 hec¬ tares (±62 acres) in the sahelian savannah of the lower Senegal valley, from February 1960 to May 1962. All the birds seen were counted, palearctic and african migrants as well as breeding pairs and nomadic individuals, to estimate the monthly biomasses of the avian consumers. The average adult weigt, the migratory status, the staple food, the layer at which the birds ordinarily live, and the seasons of reproduction of the 97 species recorded (66 sedentary species and 31 palearctic migrants) are given in table 1. Among the sedentary species, only very few live all the year round in the actual census area, most of them being nomadic. Table 2 gives, month by month for the three consecutive years, the number of individuals counted, the number of species and the biomasses in grams, both for sedentary birds and for migrants. Tables 3 to 5 give the same data for the three main trophic categories of our avian population : vegetarian, polyphagous and insectivorous. Eight months out of twelve, palearctic migrants were present in this area ; for most of that period they form an appreciable part of the total population. The highest densities and the greatest biomasses occur at the same time of the year in african species and in migrants. The maximum population density of african birds reached 4,2 birds per hectare in September 1960 and 8,2 birds