Updated: Mar 9
When animals engage in courtship displays they tend to transform their bodies or perform actions which minimize psychotermal combinations and maximize thermoaesthetic mixtures from the point of view of a potential mate. The animal sexual world, like that of human idiom, probably has examples of every possible visual mixture of the basic, more exciting perceptual qualities juxtaposed to opposites, except for mixtures involving hot and coldness, which are not visible. Visual courtship behavior should evolve to exploit universal sensory biases favoring mixtures such as dynamic—down, up—static, fluid—down, up—solid, up—round, down—spiky, dynamic—in, out—static, bright—down and up—dark.
Bald Eagles, Haliaeetus leucocephalus, hold each other by the feet and fall nearly to the ground while spinning chaotically in courtship. The activity, in detail, is very unlikely to be understood as either adaptive in a survival sense or as any kind of signal that can be interpreted by a potential mate as indicating superior health or genes. There are many different ways that an eagle can demonstrate its prowess without engaging in a wild dive-bombing dance, and many, much simpler approaches to determining how healthy, fast, mite-free, successful or generally fit a potential mate is. Clearly the birds enjoy the dance. The fact that it’s part of the process of choosing a partner suggests as much, assuming they have feelings like us, which is reasonable, and should probably be the null hypothesis for all animals. This is especially true given the extreme similarities between what we like and what other animals like, which itself is abundantly evident in universal animal preferences for song, dance, flowers, color mixtures, dorsoventral color gradients with a darker upper surface, disruptions of roundness, exciting things in containers, projections, flowing features and/or brightness around bodily entrances and other things. Eagle dive spiral dancing is deliberately both downward and disorderly at the same time. If the behavior is informative, it probably evolved to be so as a consequence of the behavior itself rather than being the ultimate explanation. They could fall without spinning but they choose to spin. They could sit on the ground and touch each other on the feet but they choose to mix touching with disorder and falling. Pairs fail to release their grip and hit the ground commonly enough to be discovered regularly, so if they do it for information both of them take a huge risk, and the odds are against the behavior evolving at all, let alone being excessive and elaborate. Humans do the same thing sometimes for fun and some of them get married on the way. It's similar in very simple ways to other things humans appreciate such as dresses, water slides, break dancing, moon walking, Olympic diving, throwing dice, downhill races, "London Bridge is Falling Down," "Ring a Ring o’ Roses," "Jack and Jill" and the inexplicably popular expressions go down swinging, falling in love, crack down, break down, break it down, downward spiral, drop kick, drop a bombshell, come crashing down, down and dirty, free falling, the rundown, swing low, turn it down, running low, down play, play it down, race to the bottom, winding down, and fell swoop. The idioms indicate that we see disorder, motion and speed as opposite to downwardness and that we appreciate contradictory mixtures made of them; otherwise the idioms wouldn't be so popular and diverse. Humans reflexively add fluidity, disorder, dynamism and other exciting things to ideas and expressions of downwardness. Various perceptual opposites should be relevant to a bird, including up and down, in and out, and dynamic and static, and this only assumes that birds are aware of their distance from the ground, proximity to each other and whether they’re spinning. The dance could be depicted in the form of the perceptual qualities involved as in—down—fast—dynamic. They experience first inwardness as they move close to grab claws, then downwardness as they begin to fall, then chaotic spinning and speed for as long as they can before splitting up and, presumably, doing it again in a complex perceptual cycle which they clearly enjoy.
To some extent high-pitched sound influences the brain the same way as the perception of disorder and dynamic motion, since we relate them in a mental category, based on idiomatic and other evidence. It tends to appear in idioms mixed with the same less exciting things, and thus it's predictable that animals appreciate in general the mixture of high-pitch with downwardness like they do a mix of dynamism, chaos, or brightness with downwardness. Costa's hummingbird Calypte costae performs a dance for the female in which he ascends in the distance high above the female's position, as she watches from a branch. He dives in her direction at high speed along a curve which brings him back up to her level, emitting a high-pitched whistle-like sound with his feathers near the bottom of the curve, a dramatic example of the mixture high-pitch—down under aesthetic election in an nonhuman animal. Like with spin-diving eagles there's little chance of understanding hummingbird sexual preferences and mating behavior in the absence of a strong hummingbird preference for the complex mixture of down—high-pitch, similar to the eagle preference for down—disorder. There's almost no chance of hummingbird courtship details being more adaptive or telling to female onlookers than diving with no sound, making a sound without diving or proving yourself as a sufficiently sexy hummingbird in a far more conservative, reasonable, meaningful, less effortful and less complicated expression of admiration, such as racing other males of bringing her a worm. A female should not be surprised by the ability of a fellow hummingbird to fly and make a high-pitched sound. Male Parotia birds of paradise demonstrate how animals like downward dynamism and fluidity in that the males have evolved to wear skirts that they shake and spin to impress the females. Downward brightness, length and fluid motion are mixed in the long tail ribbons of the Ribbon-tailed Astrapia Astrapia mayeri. Bright-down bias is likely responsible for phrases such as "the fire down below" and "sitting on a gold mine." The Grebes offer examples of the fluid—down effect involving actual water. In Western Grebes, Aechmophorus occidentalis, pairs will dance together by running on the surface of the water and holding the upper portions of their bodies as still as possible. The stasis of their bodies, necks, and heads contrasts with their motion and the water splashing up and outward around them as they dance. It's analogous to twirling a dress in human dance, moonwalking, dunk tanks, splashing in puddles and doing cannonballs in a pool for fun, or the expressions teardrop, blow me down, rain down, trickle down, watered down, what it boils down to, breathing down my neck, melt down, low blow, under the weather and sink or swim. The Red-Capped Manakin Ceratopipra mentalis performs a moonwalk dance in which he keeps his upper body still and rapidly moves his legs to scuttle along a branch. Downward dynamism and upward stasis are both apparent, as well as down—bright in the way the bird lower his bright red cap down to near his feet during the dance so that his yellow legs and red cap are displayed to an onlooker below the level of his black body.
Further examples of downward disorder and dynamism in the world of dancing include the Sharptail shuffle of the Sharptail grouse Tympanuchus phasianellus, the Somali Ostrich (Struthio molybdophanes) dance, the dance of the American Woodcock Scolopax minor, and that of the Flame Bowerbird (Sericulus ardensd), who makes chaotic and fast movements and disordered sounds in its dance when it moves its body downward and careful, regular and slow movements as it move its body up.