Data from: Malar stripe size and prominence in peregrine falcons vary positively with solar radiation: Support for the solar glare hypothesis

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.