Effects of Avian Wings Color Patterns on Their Flight Performance: Experimental and Computational Studies

How the monarch got its spots: Long-distance migration selects for larger white spots on monarch butterfly wings

“…This hypothesis is based on recent experimental work from that lab that has investigated effects of pigmentation on flight of other flying animals (birds). Specifically, wind-tunnel studies of fixed wings with embedded heating elements revealed that heating the air immediately above the trailing edge of a wing created micro-vortices of air which reduced drag by as much as 20% [ 33 ]. In fact, this exact position (trailing edge) provided the most efficient means of improving flight performance compared to other heating locations on a model wing.…”

“…In theory, this black margin would provide a localized zone of heated (rising) air because of how black color absorbs solar radiation, and this could act to reduce drag in the same manner. In addition, the same study of birds also revealed how alternating black-and-white color patterns on wings can improve aerodynamics [ 33 ]. The cause of this improvement was not investigated specifically, but it is noteworthy that the majority of white spots in monarch wings are positioned along the black margin of the fore- and hindwings, thereby creating micro-zones of alternating black and white pigment.…”

“…Despite all the research into the factors that contribute to the migration success of monarchs, and even the aforementioned studies of pigmentation, few have questioned if the primary wing colors themselves (black, orange or white) have any aerodynamic function, or otherwise have an impact on the migration success [but see 29]. Meanwhile, a growing body of (aerospace engineering) literature is showing how certain wing colors can influence aerial performance of other flying animals [ 33 , 34 ], essentially by affecting the amount of air resistance or drag. Specifically, a darkly-colored wing surface more readily absorbs solar energy, and this heats up the boundary layer of air immediately above it (more so than a light-colored wing), thereby creating a pocket of warm air which the wing can pass through more readily (warm air has less resistance).…”

“…Specifically, a darkly-colored wing surface more readily absorbs solar energy, and this heats up the boundary layer of air immediately above it (more so than a light-colored wing), thereby creating a pocket of warm air which the wing can pass through more readily (warm air has less resistance). As such, dark colors on wings can substantially improve aerodynamic efficiency of flying animals because of their reduced drag [ 33 , 35 ]. This finding appears to be a widespread phenomenon, as even dark colors on aquatic animals reduce drag during swimming, by the same principle [ 36 ].…”

“…Given the above considerations, and our prior work showing the impact of wing color on animal flight [ 33 , 35 ], we reasoned that monarchs would likewise have traits that take advantage of solar exposure, for improving aerodynamic performance. In fact, consider that migrating monarchs are exposed to high levels of solar exposure during their fall migrations, especially given that a large proportion of their time in the air is spent soaring (with wings spread, as in Fig 1B ), and at high altitudes [ 42 – 44 ].…”