Data and R-code from: Migration, habitat and hunting style do not affect the malar stripe of different falcon species

The solar glare hypothesis suggests that malar stripe of a falcon
decreases the sun’s glare in the eye, possibly increasing their hunting
success. The amount of sunlight an individual experiences could be
affected by its migratory strategy, hunting strategy, or main habitat.
However, it is not known if these environmental variables impact the size
and intensity of the malar stripe. Therefore, this study aimed to analyse
differences in size and intensity of malar stripes between individuals of
twelve falcon species with different migratory strategies, habitats, and
hunting styles distributed worldwide. The malar stripes of twelve falcon
species were measured and scored using more than 6000 photos from citizen
science repositories. The measurements of the malar stripes were first
reduced with a principal component analysis (PCA) and then analysed using
a linear mixed model that included migratory strategy, habitat, and
hunting style as fixed factors and several posture variables as random
factors. The relationships between the measurements of the malar stripe
and solar radiation of the individual’s location were also analysed using
linear mixed models. Overall, we found no differences in malar stripe size
and intensity between species with differing migratory strategies, habitat
and hunting styles. The relationships between various characteristics of
the malar stripe and solar radiation did depend on the species and the
habitat the individual occupied. Therefore, migratory strategy, habitat,
and hunting style do not markedly influence the size and intensity of
malar stripes across falcon species, suggesting that other mechanisms,
such as thermoregulation or camouflage, also play a role.