Waterbirds increase more rapidly in Ramsar-designated wetlands than in unprotected wetlands.
There is a general lack of information on how international conservation treaties affect biodiversity. The Ramsar convention on the protection of internationally important wetlands is such an international conservation policy. It initiated the world-wide establishment of over 2000 protected areas currently covering more than 200 million ha. The convention came into force in 1975, but to date, it remains unknown whether it actually produces biodiversity benefits. We analysed 21 years of survey data from a wide range of waterbird species in over 200 Moroccan wetlands and examined whether Ramsar designation as well as a national protected areas programme Sites d'IntérêtBiologique et Ecologique (SIBE) positively affected bird abundance. Furthermore, habitat characteristics of wetlands in protected areas and control sites were compared and bird abundance was related to habitat characteristics. After designation, waterbird species richness and abundance increased more rapidly in Ramsar wetlands than in non-designated wetlands. In SIBE sites, increases in bird abundance were intermediate. Waterbird abundance was significantly related to habitat characteristics, most importantly cover of water or bare ground. Compared to control sites, Ramsar sites had significantly higher cover of habitat types favoured by most waterbird species. It remained unclear, however, whether these differences were caused by conservation management or were already present prior to conservation designation. Surprisingly, waterbird population trends in Moroccan wetlands were markedly positive. Trends were found to be related to precipitation levels in the Sahel which may have caused changes in migratory strategies. Synthesis and applications. This study demonstrates a powerful approach to systematically evaluating biodiversity responses to major international conservation policies. The results highlight that data on management and habitat quality are critical for reaching general conclusions about the effectiveness of conservation instruments. Site managers or conservation authorities should be encouraged to collect standardized data on conservation actions to help interpret the mechanisms behind population responses and thus extrapolate findings beyond the study system. These findings represent a first small step towards unravelling the contribution of international conservation tools towards global policy objectives of halting the biodiversity decline.