The importance of spatial scales in long-term monitoring of colonial charadriiformes in southern France

Most bird monitoring programs aim at detecting changes in numbers in order to estimate the health of populations, to identify the causes of fluctuations, or to measure the success of management. These objectives may be difficult to attain for colonial waterbirds. Large scale movements, unpredictable dispersion and demographic factors related to long lived birds tend to limit the indicative value of bird numbers, particularly at the local scale. In the Camargue region of France, 9 species of colonial Charadriiformes have been monitored since 1956. For 5 species, regional breeding population fluctuations did not indicate actual conservation problems. For at least 3 species, numbers increased as a result of immigration and the Camargue is apparently a sink. Breeding success may be a more powerful indicator of population health. A comparative analysis of numbers at different spatial scales seems necessary to identify species-specific causes of changes in numbers, and to prioritize conservation strategies.