By Paul Donovan
If there’s one thing I loath more than anything else, it’s shopping. Trudging around shops is something I could well do without, but unfortunately it has to be done. The only consolation I get from this loathsome activity, is watching a colony of Rainbow skinks Trachylepis (Mabuya) margaritifer which have taken up residence in a planted rockery in the carpark of one of the shopping malls I have to frequent.
Most people must think I’m crazy (those who don’t think, know I am), because I’ll spend 40 minutes or an hour just watching these skinks. People assume I’m just staring at a heap of rocks, and don’t even realise there are lizards there. And if they do, their interest in them will never extend into understanding the dynamics of social behaviour. When someone asks me “what are you looking at?”, and I tell them “a group of skinks”, then off they wonder.
Interaction is complex
The way in which lizards interact with one another, whether it’s males protecting their territory, their harem of females, recognising one another, or females asserting their standing over lower ranking individuals, can be a very complex behaviour. And if those individuals live in a social colony, communication is fundamental to keeping order within that colony. Communication within lizards, follows three lines of approach; visual, audible and chemical. Let’s look at these in a bit more detail.
Visual communication
Communication is a behaviour in which one animal communicates its intention to another. Obviously, with humans this is through vocalisation. But what is the process in lizards? There are various cues which lizards rely on for interacting with one another, be this male-male or male-female. Some can even go as far as trying to communicate with us. A good example of this, is if you have kept a Green iguana, Iguana iguana. It is not uncommon for them to head-bob, or even to extend their dewlap when they see you.
In one collection I was responsible for, we had a large iguana donated to us, which I named Charlie. He was such a character, as most iguanas are. As soon as I turned the lights on and he saw me, he’d begin head-bobbing. And when I opened the door of his enclosure, he would leap out and sit on my shoulder. He could, at times, do the same head-bobbing to other members of staff, but interact in an entirely different manner. He would tail whip them, scratch, and even attempt to bite.
The head-bobbing and extending the dewlap that Charlie was displaying, is visual social communication. It is a behaviour witnessed in several other lizard species as well, notably Anoles. With Anoles this form of communication is highly complex, not to say species specific, and can follow three lines of display;
Simple: the dewlap is uniform in color and accompanied by head-bobbing.
Compound: the base color of the dewlap is broken by a big red spot in the middle, again being linked with head-bobbing.
Complex: the dewlap is intricately patterned with contrasting colors, accompanied by lines radiating out from the base to the edge. Head-bobbing may also be evident, but color changes and head-bobbing may be carried out independently.
Given that the displays are complex, and are performed by all males, some degree of variation in the display between the males must take place, certainly to allow females to choose between a strong displaying male and a weaker individual. Through some observations, females seem to prefer “normal” head bobbing displays and will avoid males which exhibit any slightest deviation in the bob. In addition, bright colors are preferred by females over marginally drab ones.
Visual communication is a highly complex behaviour serving many functions, which can be expressed in numerous ways. I have talked about head bobbing, and dewlap displays, but lizards will also express themselves by doing push-ups, raising their limbs, flattening the body against the ground, puffing up the gular region, and even raising the tail.
This last behaviour is rather interesting, because it only occurs in a few species, so it is not widespread. It is very common, for example in the aptly named Zebra -Tailed lizard, Callisaurus. In this species, and those which display the behaviour, the underside of the tail is striped; the stripes do not extend all the way around the tail. The fact that the lizards display these stripes to one another is a sure sign of social communication, and is widely seen in female’s tail lifting to males, though male-male tail lifting is also common. The exact meaning of the display, however, is still a bit of a mystery.
Audible communication
In the amphibian world, auditory communication is widespread; frogs and toads can be extremely vocal, but in the reptile world it is limited to all but a few lizard species. Although relatively widespread within those species in which it occurs, auditory communication in lizards has, surprisingly, not been well studied. In those in which it has, it can be linked with male-male territorial reinforcement, courtship, and even defence.
Possibly the most vocal of all the lizards are the geckos. If you have ever kept a Tokay gecko Gekko gecko, and tried to pick it up, you may very well have dropped it the first time you did so, as it ‘barks’ when handled. This is a defensive mechanism causing the predator to drop it, from which the gecko can then make its escape. But the same bark can be used to communicate with other individuals. As the sun sets and relinquishes duty to the moon, these geckos can be extremely vocal. If you have ever visited regions where this gecko occurs, you will know what I mean.
By and large, auditory communication is carried out on a one to one basis, but in some species, such as the Common Barking gecko, Ptenopus garrulus, the males sit at their burrows entrance and call in unison during the evening, emitting an ear-piercing clicking sound. This can often be confused with reed frogs calling. While I have camped in areas populated by reed frogs and easily drift into sleep under their warbling choruses, the same cannot be said for the nightly renditions given by Ptenopus; I had to wear earplugs to get to sleep.
One lizard which uses both visual and auditory communication is the Tuatara Sphenodon punctatus, an extremely rare lizard found in New Zealand. Territorial disputes are solved by approaching one another, and ‘puffing’ themselves up to appear larger than they really are. This is accompanied by erecting the dorsal spines, and increasing the darkness of the skin. The owner of the territory will then begin shaking its head. This is usually enough to see off the intruder, but if his will is strong, they will approach one another head on and begin snapping their mouths shut. The standoff then sees them chasing one another while at the same time croaking. The dominant individual will bite and tail-whip the intruder. This is usually enough to see it seek sanctuary elsewhere.
Chemical communication
We can see visual communication between lizards, and hear audible communication, but another mode of communication we cannot detect is that of chemicals. Some of the better known chemical producers are the Scincidae and Lacertidae. Chemical cues are the most sophisticated of all forms of communication. Although generally used by the female to attract a mate during the breeding season, chemical cues can also be used to recognise one another.
There is some evidence to suggest that females of certain skinks can identify members of a colony, and non-colony members based on their odour. In addition, females of certain species can identify their offspring from those of other females. However, once the two are separated, the ability of the mother to recognise her offspring is lost. It is unsure how the mother can identify her young, but there is some evidence pointing to the presence of pheromones in the skin, from the femoral pores, and even odour in the faecal matter. Faecal matter has also been shown to play an important role in juvenile green iguana recognising their siblings.
The presence of chemicals contribute to how a social group of lizards maintain their colony, how they recognise one another, and each individual knows its place within it. In those species where adults may cannibalise their young, or are aggressive towards them, chemicals within the faecal matter allow the young to detect adults, and so avoid a potentially harmful situation.
The use of chemical communication is also important when it comes to mating. A female will give off chemical signals to indicate that she is ready to be mated, but can determine the health of a male by the pheromones he releases, and surrender or rebuff his advances. No matter how good some sexual displays are by the male, if he is not giving out the correct chemical cues to attest to his strength, he will have little chance of mating. This is why the strongest males maintain a harem, and weak nomadic males try and take their chance with someone else’s female when their back is turned.
Femoral pores
Many lizards possess structures on the ventral surface of the thigh called femoral pores which exude a waxy secretion, and are usually larger in males. These pores, and their waxy secretions have been found to play an important role in communication. Not only do they contain secretions which align to mating but, may be important in scent marking territories. Males with higher levels of a chemical called hexadecanol in the waxy secretions can signal their dominance to other males, and their state of health by the trail of hexadecanol left on the ground.
Tail-end
The social dynamics of a group of lizards, is a fascinating behaviour to watch. As I have mentioned, I could sit and watch the colony of skinks at the shopping mall for hours; if it wasn’t for the fear of getting carted off to the local asylum, or earning the reputation around town ‘as the man who stares at rocks’. A male has established a territory which he protects from other males. Within this territory, he lives with a group of females again, which he has to protect from rival males. And within this group of females is a basic hierarchy. He also knows when a female is sexually receptive, and can distinguish kin. All of these behaviours are based on visual, auditory (sometimes), and chemical communication. And who said reptiles were simply uninteresting?
