Expansion et régression: deux mots clés de la dynamique des populations du martin pêcheur (Alcedo atthis)

Annual censuses of nest kingfishers are performed since 1973 in the valley of the river Lesse, a tributary of the river Meuse (Belgium). The authors document sharp population fluctuations. It appears that these are mainly due to the weather conditions prevailing at key-periods. Hard winters reduce the numbers, sometimes to a low level, whereas heavy late-spring or early- summer rains involve a bad reproduiction rate (namely through clutch losses following flooding). Hence, the recovery of the nesting population is weakened. In comparison, other factors such as predation, seem to have only a limitid effect. In other respects, the noxious consequences of permanent disturbances are illistrated in the that part of river Lesse where kayak is practised on a large commercial scale.