Do conservation designations provide positive benefits for bird species and communities?

There have been recent renewed commitments to increase the extent of protected areas to combat the growing biodiversity crisis, but yet the underpinning evidence for their effectiveness is mixed with causal connections rarely evaluated. We use data gathered by four large-scale citizen science programmes in the UK to provide the most comprehensive assessment to date of whether national (SSSI) and European (SPA/SAC) designated areas are associated with improved state (occurrence, abundance), change (rates of colonisation, persistence, and trend in abundance), community structure and, uniquely, demography (productivity) on a national avifauna, while controlling for differences in landcover, elevation and climate. Positive associations of with state suggest these areas are well-targeted, while positive associations with change tended to be restricted to rare and declining species and habitat specialists suggesting their benefit is greatest for the most conservation-dependent species. Associations with productivity suggest a plausible a demographic mechanism for positive effects of designation.