Abstract
The degradation of permanent grasslands and the associated decline in biodiversity are critical issues in France. In order to monitor changes in the ecological status of grasslands, the Observatoire National de l'Ecosystème Prairie de Fauche (ONEPF) was set up in 2001, focusing on the monitoring of bird populations associated with these environments. However, it was put on hold in 2021 to redefine its objectives and explore the possibility of synergy with other national schemes. The aim of this study is to compare ONEPF with the Temporal Monitoring of Common Birds (STOC) in order to assess their complementarity in terms of monitoring trends in grassland bird abundance. The two protocols adopt a relatively similar field methodology. To carry out this work, three aspects were analysed: the spatio-temporal coverage of the stations, the landscape composition of the stations studied and the comparison of abundance trends modelled using data from the two systems. The analysis includes a total of 944 ONEPF stations and 5186 STOC stations, covering the period from 2003 to 2021.Comparative analyses highlight that the objectives of the STOC and ONEPF monitoring systems differ fundamentally, leading to major disparities in the landscapes and geographical areas monitored. There is very little spatial overlap between the two systems. The overlap in ecological contexts is also limited: a comparison of the landscapes monitored by the two systems shows that STOC mainly monitors fragmented grasslands, with little representation of hay meadows, whereas ONEPF focuses on larger expanses of hay meadows on a local and landscape scale.A comparison of the abundances and species richness captured by each system reveals that the averages for the target species are significantly higher at the ONEPF stations than at the STOC stations. This can be explained by the fact that ONEPF targets very specific species, which are often under-represented in STOC data, due to their affinity with particular habitats such as large hay meadows. The results show that by concentrating on these specific environments, ONEPF provides more robust estimates of abundance trends for most of the observatory's target species, accompanied by narrower confidence intervals. On the other hand, the STOC provides less accurate estimates for species that depend on grassland environments.