Wild Romance

"Birds do it, bees do it, even educated fleas do it..." By Sam Curtis

This story is featured in Montana Outdoors
May–June 2002

I can feel the sound on my ears before I hear it in them: concussive waves of air against my skin and then the slow, resonant thumps that bump against my ear drums to become a hollow whir. It’s a ruffed grouse, a male on a log, “drumming” for the attention of a female he cannot see. He beats out a message with his wings: “Hey honey, I’m over here.” Where I live in southwestern Montana, drumming is the sound I associate with spring.

An entirely different sound ushers in fall. It’s a weird, almost comical cross between a growl-like roar and a high-pitched squeal. Someone with a sense of humor or a tin ear once dubbed it “bugling,” and the term caught on. Bull elk bugle to advertise their sexual prowess to cow elk and to either intimidate other males into skulking off or to egg them into a fight.

Drumming and bugling form some of the dramatic music of animal courtship. And animal courtship is a display to hear and behold. Would-be mates dance, strut, and fight. They show off their finery and their property. They sing and bellow and offer things to eat. They change colors. They build homes. They bully and they fawn. They leave scented notes and amorous signs. All to attract, win, and mate with a suitable partner.

The timing of courtship is anything but haphazard, particularly in regions with distinct and dramatic seasonal extremes such as those in Montana. Due to evolutionary adaptations, individual species respond to environmental changes such as decreasing daylight hours, changing moon phases, fluctuating temperatures, or precipitation increases. These external stimuli help synchronize courtship, and therefore birthing schedules, with times of the year that are favorable for the survival of both mothers and their young. In other words, animal time courtship and mating (usually in spring) so that their young are born when food is likely to be plentiful and the weather moderate—which, for most species, means summer.

Chemical attraction
On its most basic level, courtship is a single signal encoded in a chemical package, called a pheromone, sent out into the world for a potential partner to taste, smell, or absorb. And that may be all it takes to bring male and female together to mate.

Some underwater sea creatures use electrical impulses to attract a mate; others use fluorescent markings that glow in the dark depths of the sea. In the air, the initial attraction of a male to female mosquito is triggered by the slower frequency of her wing beats, which the male detects with the hairs on his antennae. (Because males beat their wings faster than females do, they aren’t drawn to each other.) But the award for communicating a lot with a little must go to lightning bugs. They can actually distinguish the species, sex, and willingness to mate of another lightning bug by the color, timing, and frequency of its illuminated message. Sound, of course, is a major attractor during the courtship of many animals. Frogs croak their amorous intentions, and biologists have found that whales and porpoises actually “talk” to each other about mating. Often, an animal conveys much more in its mating sound that just “Hey, you, here I am.” A bull elk’s bugle, for example, carries in its pitch and frequency a clue to the animal’s size and relative social rank among other bulls. A large, mature male has a deeper voice than that of a young bull, and he bugles more frequently. His bugling may inhibit the advances of younger males while advertising to females a potential mate who has physical and social dominance over other bulls. Such traits are desirable to a cow, which after mating would pass them on to her offspring to help improve their odds of surviving.

Choosing one mate over another is at the root of all the flamboyance and fanfare seen in courtship displays. It is the male, in most cases, who struts his stuff and the female who chooses to take him or try elsewhere. The widely held theory explaining this arrangement centers on the relative number of sperm and eggs that males and females produce in a lifetime, and how these ratios influence male and female courtship strategies.

The presumed biological goal of both a male and a female member of any species is to produce as many survivable offspring, with his or her genetic imprint, as possible. Because a female of any species produces far fewer eggs than a male produces sperm, she has to be far more selective in choosing a mate. In his book The Dance of Life: Courtship in the Animal Kingdom, Mark Jerome Walters notes that a female giraffe might expect to produce just a few hundred eggs in a lifetime, only ten or so of which will ever become fertilized. And a female sperm whale will produce just six baby whales in her lifetime.

Yet a single male of these and other mammal species, including humans, will produce billions of individual sperms in his lifetime, theoretically enough to fertilize billions of eggs and billions of young.

Because a male has very little invested in each sperm, he can afford to spend them lavishly in an attempt to maximize his genetic imprint by mating with any agreeable female. A female, on the other hand, has quite a bit riding on each egg. She needs to choose a mate who can contribute the kind of genetic stamina that will give her eggs the best chance of becoming healthy, long-lived offspring. The end result, the theory goes, is that males tend to be showoffs, while females tend to be choosy.

Therefore, the more information a male can put on display to indicate that he is a good choice for a female, the better his chances of being selected as a mate. The bull elk bugles to indicate his size and social standing. He displays his big antlers to show the healthy diet and good genes that went into their growth and he uses those antlers to fight with rivals to prove he has the physical stamina and survival strategy to dominate.

Equally flamboyant in their courtship displays are male sage grouse, which each spring gather at a display arena, called a “lek,” to put on a gaudy show of fanning tails, inflating breast air sacs, and making loud “popping” sounds. The generally accepted theory of this display is that males are vying for the attention of females, which visit leks to compare males and find a superior mate. The process has been compared to medieval jousting tournaments, where each knight fought to stand out among rivals before an admiring crowd.

Yet Walters notes in The Dance of Life that all this falderal could very well be a scam (or, in the words of Shakespeare, “full of sound and fury, signifying nothing.”) Writes Walters: “Some biologists…have begun to doubt the fundamental assumption that there must always be an underpinning of ‘rationality’ in the designs of nature. They suggest that the females may simply be ‘dazzled’ into choosing the male who has invented the most elaborate eye- or ear-catching performance. In other words, she is influenced by slick advertising to choose a male of good form rather than proven substance.”

This argument implies that males with nothing more to offer than sperm, and that don’t stay around to help raise the young, often are the most showy and flamboyant in their courting. Conversely, males with more subdued courtship tactics may in fact be more worthy, or at least more helpful, to the female.

Take the male common tern, for example. He shows his parental worth by catching a fish and offering it to his intended mate to prove his ability to feed the family. Other male birds present sticks, grass, or pebbles as nest-building material to show they can provide a home.

On the other hand, the male of some animal species can be downright passive in courtship, leaving the female to devise a test for evaluating his worth. Dr. Charlotte A. Hosie, in the “Courting Rituals” chapter of Animal Behavior (edited by Tim Halliday), writes that a female North American red-backed salamander will “sample a male’s feces by ‘nose-tapping’: pressing the snout repeatedly into the droppings. These salamanders prefer to eat juicy thin-skinned termites, which are a richer food source than the hard-skinned ants they may also take. Females can discern the contents of males’ diets by nose-tapping their droppings, preferrig those that have been feeding on termites.

Mood music
Once courtship rituals have helped potential mates find each other and choose partners, there is still the matter of readiness. That’s why courtship displays are also necessary to stimulate in couples a desire to mate.

A male brown trout, for example, takes little interest in a female until she begins using her tail to fan a depression in stream bottom gravel where she can deposit her eggs. This act, called “cutting,” appears to stimulate the male, which then swims alongside the female and “quivers,” an act that, in turn, stimulates her. The male trout’s quivering increases in frequency and intensity until the female, opening her mouth to a gape, releases her eggs in the gravel depression. Simultaneously, the male squirts his milt over the eggs. Thus are brown trout made.

One of the most spectacular bits of choreographed foreplay is performed by western grebes when a male and a female skitter across the water in unison—necks curved like commas, feet beating up a spray—and then dive together beneath the surface at precisely the same moment.

Many frog and toad species, on the other hand, mate using a brutally crude sexual hug called “amplexus.” And then there’s the male North American two-lined salamander, which grapples the female while secreting a sex stimulant from his chin gland onto her. He then lacerates his mate’s skin with his teeth so the secretion flows into her bloodstream.

But for the truly bizarre in animal courtship, consider the mating habits of snails, as told by Lorus and Margery Milne and Franklin Russell in The Secret Life of Animals: “Two snails circle each other for an hour or more as a prelude, apparently, to the firing of what may be called love darts. Both snails produce these tiny, sharp darts, which are about a centimeter long and are made of a carbonate of lime. The dart is fired by a propellant that is stored in a glandular chamber just behind the creature’s eyes; the snail makes a slight hissing sound as it ejects the dart. The love darts apparently have something to do with synchronizing the mating process. The first creature to fire the dart becomes temporarily passive, while the other snail continues to show its desire by circling before it, too, ejects a dart. This strange foreplay is mutually exciting and eventually leads to copulation…”

Clearly, courtship displays run the spectrum from sublime to ridiculous, but they all have a common goal: to bring together two different genetic contributions, in the form of an egg and sperm, that will continue to produce offspring that have a slightly different genetic makeup from that of their parents. And it is this very capacity for genetic change in each succeeding generation that forms the basis of evolution in all species on earth.

And who says romance is dead?Bear bullet

Sam Curtis is a freelance writer based in Bozeman