| Summary: | Many falcons ( Falco spp.) exhibit a distinct dark plumage patch below the eye, termed the malar stripe. This stripe is hypothesised to reduce the amount of solar glare reflected into the eyes while foraging, thereby increasing hunting efficiency in bright conditions. Here, we use a novel, global-scale correlative approach to test this "solar glare hypothesis" in peregrine falcons ( Falco peregrinus ), the most widespread falcon species, using web-sourced photographs from across the species' global range. We found that the size and prominence of the malar stripe were positively associated with average annual solar radiation, but not with other environmental variables, such as temperature and rainfall. Our results provide the first published evidence for the hypothesis that this plumage feature functions to reduce the amount of solar glare reflected into the falcon's eyes, thereby improving the ability to pinpoint and target agile prey in bright conditions. See the ReadMe file for descriptions of the variables used in this dataset and package installation requirements. For detail regarding the malar stripe and head position scores and how these were calculated, see the supplementary material of the associated publication. All statistical analysis for this study was performed using R version 4.0.3. Instructions for running the code and descriptions of outputs are provided in the descriptive text within the R code file, and in the associated publication. A list of all photographs analysed in this study is included as a set of appendices accompanying the associated publication. Funding provided by: National Research Foundation Crossref Funder Registry ID: http://dx.doi.org/10.13039/501100001321 Award Number: 40470
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