Fig. 4

Number of wintering locations in Morocco, Spain and Portugal over the last two decades a and spring numbers of Yellow-browed Warbler (Phylloscopus inornatus) in several European countries: France b, the Netherlands c, Helgoland, Germany d and Sweden e. In a, numbers correspond to wintering locations noted in Morocco, Spain and Portugal, extracted from GBIF [130] for the months of December, January and February over the last two decades and thinned for each year for a distance of 5 kms. Numbers must be interpreted with caution due to change in observer effort over the last decades and reporting bias in citizen-science databases. For spring numbers, left panels indicate the number of spring records per year per country over the last two decades and right panels indicate the cumulated date records over the same years with the mean date of the passage. A density curve, estimated with the density function in R, highlights the phenology of the passage. For spring numbers, data were collected from citizen-science database by the authors (for France: https://www.faune-france.org/; the Netherlands: www.waarneming.nl; Helgoland: Jochen Dierschke; Sweden: https://www.artportalen.se/)