Volunteer-based surveys offer enhanced opportunities for biodiversity monitoring across broad spatial extent

International audienceThe growing public interest in biodiversity projects provides great opportunities to monitor biodiversity acrossbroad geographic areas at low cost. Such volunteer-based surveys should however need careful considerationduring statistical analysis since the presence of residual spatial autocorrelation and over-heterogeneity canlead to misguided inference. The recent development of new statistical tools allows accounting for these problemsin all steps of the statistical analysis. Especially, the spatial leave-one-outmethod allows accounting for spatialautocorrelation in the variable selection step while the R-INLA tool box provides a useful way to estimatecomplex spatial hierarchical models in aminimumcomputation time.Weapplied such tools on a dataset collectedby volunteers between 2000 and 2013 giving the relative abundance of 12 raptors breeding in France.Wethenestimated their spatial distribution, population sizes and trendswith a particular emphasis in quantifying the uncertaintyof our estimations. Our results suggest that broad-scale volunteer-based surveys offer enhanced opportunitiesfor monitoring widespread species but may fail in giving accurate information for less common species,especially when sampling is too scattered. Providing uncertainty of estimations helps in identifying species andareas from which estimations are the more reliable and thus gives more powerful information for conservationpractitioners