“The most important thing in communication is to hear what isn’t being said.” — Peter Drucker

By CAMERON BARROWS

Birds sing using a specialized organ called the syrinx. The syrinx is similar to our larynx, but while our larynx consists of a single air passage, a bird’s syrinx branches into two tubes like an upside-down Y. Air flowing over vibrating tissues near the intersection of these tubes generates sounds. With a syrinx, birds can simultaneously sing different notes with each syrinx tube, increasing their song’s complexity beyond what our ears can detect – but birds almost certainly can. When male birds sing they are simultaneously communicating two distinct messages: first, to other males, “This territory is taken; go elsewhere!” and second, to females, “This territory is occupied by a male with a particularly beautiful song; come check me out.”

How those listening males or females respond when hearing a territory-holder’s vocal stylings can depend on the complexity and volume of the song. Louder, more complex songs can be interpreted both as more threatening (to interloping males) and more alluring (to potential mates). At the same time, singing tells potential predators exactly where you are, so singing puts the males at some risk, apparently a risk they are willing to take to find mates and pass their genes on to the next generation.

Charles Darwin identified two ways that organisms might change over time. Natural selection was a term he coined for the incremental genetic changes that provide an individual with an enhanced ability to survive and reproduce despite the rigors of life in nature – longer claws, smarter, better ways to conserve water, etc. Sexual selection was another term he came up with for describing genetic changes that made one more alluring to a potential mate, even if those changes increased the risk of becoming someone else’s dinner. Sexual selection explains structures such as a peacock’s enormous, gaudy tail feathers which almost certainly would make it more vulnerable to predators. It turns out that peahens prefer peacock tails that are as big and gaudy as possible, and it is that preference that incrementally led to the peacock tail we see today – sexual selection. If she could analyze why she had such a preference, a peahen might surmise that if the peacock could survive despite having the handicap of such a ginormous tail, his genes must be worth considering. Peahens likely don’t make that sort of calculation, but over generations, if a preference for a bigger tail yielded more healthy peachicks surviving to maturity, then a preference for big tails would dominate those future generations. Sexual selection is also responsible for the complex bird songs we hear each spring – female birds are apparently smitten by song complexity and those musical genes then pass on to her offspring.

Lizards need to communicate the very same messages that birds do. However, lizards lack a syrinx. Like mammals (including we humans) and amphibians, they do have a larynx, but in the case of lizards they lack vocal cords. As such they are mostly mute other than hisses, although some tropical geckos are capable of a few guttural monosyllabic chirps. Territory holding lizards need to influence interlopers to “move-on” or risk a fight that could lead to injury or attract the attention of a predator. They also need to advertise their willingness to entertain the attention of a potential mate, without an inordinate amount of chasing and subduing of that potential mate, all such activity that would again attract predators. So, without a voice how do lizards communicate? They do head-bobs and/or push-ups.

To appreciate the communication versatility of a lizard’s push-up, one needs get close to the ground and view those up and down movements from a lizard’s perspective. Many lizards have species-specific and gender-specific patches of colors on their necks and bellies. Like a peacock’s tail, the size and color intensity of those patches are then displayed to other lizards by those up and down actions, immediately letting the lizard watching the push-ups know what species and what gender they are dealing with. Push-ups also allow lizards facing each other to assess the other’s size and health. Belly patch color intensity could also be an indication of health and age. Size is a strong determinant of who would ultimately win a wrestling match; unless the two lizards are evenly matched in size, the smaller one will usually bow to the larger one’s prowess and inevitable success, and back away from any confrontation. If the interloper remains unconvinced of the inevitable outcome, a territory holder can arch his back and expand his throat (referred to as a gular region), making it appear even larger. If the “interloper” is a female, and if she is adequately impressed by the male’s size and animated behavior, she might raise her tail, signaling to the male a willingness to take their meeting to the next level, and at the same time diffusing his aggression. If not impressed she can simply move on. Drawn-out chasing and wrestling inevitably will attract predators and result in one or both lizards becoming dead ends on their genetic tree. Survival depends on effective communication of each lizard’s intentions and the ability to weigh the probable outcomes of pursing further interaction.

Some male lizards appear to have taken a page from the peacocks’ playbook. Not content to only show off their ventral belly colors, some males have developed bright dorsal colors as well. Chameleons are noted for their bright breeding colors, colors that they can turn on and off by opening or closing chromatophore cells in their skin. That trick is not limited to chameleons; granite and desert spiny lizards do the same. Granite spiny lizard males are typically a dull black color, but during the mating season and in response to the presence of a female, they can open chromatophores that turn their scales bright turquoise. The brighter colors communicate the male’s health and dominant status to potentially interested females. In turn, females that are gravid (carrying eggs or embryos within their body) can also develop bright colors, colors that make it clear to the males that they have no interest in taking their interactions “to the next level.”

Curiously, there are some lizards who do not engage in push-up communication or changing colors. Horned lizards don’t. Nor do they have any species-specific color patches on their neck or belly. They also do not actively defend territories. These lizards have reached a pinnacle of camouflaged color and behavior, so much so that they will often allow us to approach them within just a couple feet or less, “knowing” that any movement will immediately put them at risk of being detected and then suffering whatever consequences result. Head bobbing and push-ups would be antithetical to staying undetected. So, what do they use to communicate? It turns out they sample each other’s pheromones using tongue-flicking and then make decisions regarding what to do next based on smell or taste. Why didn’t horned lizards follow their cousin’s communication style? My guess is that on a scale of which desert lizards are most vulnerable to becoming someone else’s meal, horned lizards are close to the top. Their cryptic camouflage is their best defense. Anything that makes them less camouflaged, be it movement or colors, may tip the scale in favor of that lizard never passing along its genes.

Communication is critical for survival and reproduction (and a happy marriage). We use words, but there are many alternatives in nature that appear to work just as well.

Nullius in verba

Go outside, tip your hat to a chuckwalla (and a cactus), think like a mountain, and be safe