Many animals use colorful ornaments and exaggerated dances or displays to attract mates, such as birds of paradise. Some animals go even further and have colors that can change as they dance, such as in peacocks or morpho butterflies. This special type of color is called iridescence, and its appearance changes based on the angles of observation and illumination. Thus, the appearance of iridescent coloration can be easily manipulated by specific movements, postures, and orientations to potentially exhibit a lot of changes in color appearance during a particular dance—in other words iridescent coloration can produce a flashy color display.
Hummingbirds are incredibly fast-moving birds that exhibit a dazzling array of iridescent coloration. Some hummingbirds, in a group called bee hummingbirds (which includes many US species like the ruby-throated or Anna’s hummingbirds) also court females using a special dance called the shuttle display. Shuttles are characterized by a male repeatedly and rapidly flying back and forth in front of a female and erecting his colorful throat feathers to show them all to the female.
We set out to understand 1) what male broad-tailed hummingbirds (Selasphorus platycercus) look like to females as the males dance, and 2) what might drive the variation in what males look like as they dance, such as their individual dance moves or how they position themselves with regards to the sun. To answer these questions, we filmed male courtship displays using a female in a cage to elicit male dances. We then measured several characteristics of the dances, such as how the male oriented himself towards the female as he moved, the shape and width of the back-and-forth movements, and how the male display was positioned relative to the sun. Then, we captured the males we filmed and plucked some of their iridescent feathers to measure male color appearance. To quantify male color appearance, we took the male feathers and moved them as if they were that male dancing, using his specific positions and orientations, and at each position in the display, we measured the color of the feathers.
We first asked: do males orient themselves towards the sun in a specific way, for example, do males always dance facing the sun? We found that males dance oriented toward the sun in many ways—some facing the sun, some facing away from the sun, and some in between.
We then asked: how might male orientation towards the sun affect his color appearance and variation in color appearance among other males? It turns out that those males who tended to face the sun while dancing appeared brighter, more colorful, and flashier. On the other hand, those males who tended to face away from the sun appeared darker and less colorful, but maintained a consistent color appearance as they displayed. Another way to think about hummingbird dances and color appearance is to compare it to when people dance in sequin clothing. If someone were to dance in a sequin outfit while facing a bright stage light, they would appear brighter, more colorful, and flashier, while someone who danced with their back to the stage light would appear darker, less colorful, but have a consistent color appearance.
Additionally, we found that males who maintained a persistent angle of orientation towards the female while dancing appeared flashier, and males with bigger colorful throat patches exhibited little changes in color appearance throughout their displays—in other words they were consistently colored. Back to the sequin dancer analogy, if the dancer was always facing you in the same way, they would appear flashier. We believe this flashiness is because if the dancer is keeping a relatively fixed angle of orientation towards you as she/he moves, then her/his angle towards the light is constantly changing.
While we do not currently know if females prefer flashier colored males or more consistently colored males, recent work by Dakin and colleagues has shown in peacocks that the flashier males had higher reproductive success. It is also possible that some broad-tailed females prefer flashier males, while others prefer more consistent males. Flashy coloration might be better at demonstrating a male’s dance moves, while consistent coloration might be better for showing off how big a male’s color patch is. Future work is needed to test these ideas; however, our study begs the question: would you rather be flashy or consistent?
Featured image credit: Hummingbird landing on pink flower with green stem by Andrea Reiman. Public domain via Unsplash.