Status of the Black Stork Ciconia nigra in Africa - Synthesis of the waterbird census data (1991-2000)
Fairly widespread in Europe, the Black Stork Ciconia nigra remains scarce in Africa, where its population estimate is 27,500 (Rose and Scott, 1997). To join its winter quarters in Africa, the Black S...
Fairly widespread in Europe, the Black Stork Ciconia nigra remains scarce in Africa, where its population estimate is 27,500 (Rose and Scott, 1997). To join its winter quarters in Africa, the Black Stork follows two main flyways: the Strait of Gibraltar for the population going to sub-Saharan Africa, and the Sinai in Egypt via Israel for the population spending the winter in East Africa. A nesting population of Black Storks is also reported in the southern part of Africa, mainly in Zimbabwe where 150 pairs were observed on the rocky cliffs. This population, estimated at 1,000 individuals, seems to be completely isolated from that of Europe (Strazds, 2001). Analysis of the African waterbird census (AfWC) data provides information on the numbers, distribution and abundance of the Black Storks wintering in Africa. Generally speaking, the species is less common in Africa, for out of a cumulative number of 327,890 storks counted from 1991 to 2000, only 756 Black Storks were observed throughout the African winter quarters, that is, 0.23% of the numbers observed. Analysis of the status of the winter sites shows that Black Storks most often establish themselves in the vicinity of major rivers, and that over 60% of the sites frequented are protected areas or cynegetic reserves. These sites hold the optimal conditions for the tranquillity of this species. The numbers of Black Storks show noticeable fluctuations in the winter quarters. They have remained fairly low between 1991 and 1994, probably following the effects of the drought and its corollaries. Besides, the intensification of large-scale irrigation schemes has partly undermined the winter quarters of the species. As from 1995, we can consider that the African population knows a positive evolution, which could be the result of a larger coverage of the follow-up sites, and of the involvement of a greater number of observers and of specialised structures. In West Africa, the Black Storks’ distribution area spreads between latitude 16° and 10°N and longitude 16°W and 4°E: in the far north west, the river Senegal delta and in the far south east, Lake Kainji on the Niger river in Nigeria (Jadoul, 2001). This west African part, characterized by a bush or wooded savannah, is comprised between isohyets 200 mm in the north and 1000 mm of rains in the south. Black Storks can use three major winter zones (map 1): a western zone comprising the south of Mauritania, Senegal and the west of Mali; a central zone comprising the inner Niger delta; an eastern zone comprising the south and east of Burkina Faso, the west and south west of Niger, the west of Nigeria, the north of Benin, the north of Togo and the north of Ghana. The western zone seems to support most of the storks. The distribution frequency shows that the total number of Black Storks undergoes a positive evolution in the West Africa winter quarters. This increase could be the result of the improvement in the region’s climatic conditions (rainfall, presence of large stretches of wetlands, food, abundance and availability, etc.) and of the extension of the counting sites as well as the counting efforts made in West African countries. Tracking of Black Storks with satellite transmitters in the 1995-2000 period has permitted to discover two buffer zones in West Africa, in which storks gather by several tens of individuals (Bobek, 2001): they are the region of Maghama, on the border between Mauritania and Senegal, and the region of Karakoro, on the border between Mauritania and Mali. Some storks remain in these areas all winter round, making only short trips; contrariwise, others use them as resting and feeding grounds before continuing their migration to other winter quarters. The individuals’ distribution frequency shows that the western zone is the main winter zone for Black Storks, with a maximum of 94% of the total number staying in West Africa. The South of Mauritania (51%) and Senegal (43%) apparently play a predominant part in providing refuge for the Palaearctic migrants, in particular Black Storks.