Appendix S1. In order to evaluate the influence of the transition from 10 to 5 min on our abundance estimates, we used a network of 20 count points in 2002. All skylarks and corn buntings contacted were localized each minute to obtain cumulative curves of recorded birds. This protocol was repeated five times during the breeding season.

Appendix S2. Plot of the relationship estimated using a logistic GAM, between total skylarks observed and the proportion of skylarks singing.

Appendix S3. Differences in wheat and grassland proportion, between before-after the designation of the SPA (2004), inside versus outside, and differences in wheat and grassland proportion between inside and outside the SPA, before versus after 2004. Significant results are in bold characters.

Appendix S4. Model selection procedure with the inclusion of habitats (% Wheat and % Grassland) and AES (% arable AES and % of perennial AES) covariate to SPA model on corn buntings and skylarks on presence (binomial error) and abundance (Poisson error). AICc values, Akaike weights (w) for the models are presented.

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