Language Instincts: Do animals lie?

Liar

From November 11, 2006

In my last few posts you may have noticed a theme: signals that are used to advertise sex in the animal world are generally thought to be honest ones. In fact, animal communication in general is pretty truthful. There may be different reasons for this: some signals may be impossible to fake (for instance, toad calls may contain honest information about the caller’s size simply because bigger bodies produce lower-frequency sounds). But even when a signal could be faked, the evolution of dishonest signaling is very unlikely. There is a simple reason for this: in the long run it would not benefit receivers to respond to a signal that could be cheated.

This is something that we might find surprising given the amount of deception that goes on in human interactions. Is deception really so rare in animal communication systems? Are there any animals liars?

We have some examples of deceptive communication between different species: for example, ground-nesting birds will fake an injury to draw a predator away from their nest, and some birds in mixed-species flocks will give false alarm calls to increase their own foraging success. Within species, however, the examples of deception are few. We know deceptive communication occurs within a number of primate species. Interestingly, some recent work using ravens has shown that, much like many primates, birds may also be capable of intentionally deceiving conspecifics.

This result came as a bit of an accident during an experimental study on social learning and scrounging in foraging ravens. The researchers provided their ravens with a series of covered plastic boxes that served as food caches (some containing pieces of cheese; some empty). The boxes were arranged in clusters and ravens were videotaped during their foraging explorations. Right from the start, the researchers noticed an interesting pattern between a pair of male ravens: rather than search for his own food, a dominant male relied on a subordinate male’s explorations, following the subordinate male around and eating the food that he discovered.

It eventually became apparent to the researchers that the subordinate raven wasn’t the only one being exploited in this situation. He had developed a strategy to trick his competitor. Whenever the subordinate male found a cluster of boxes containing food, he would quickly move on to a different cluster and start opening boxes there. The dominant male would soon follow, leaving the subordinate free to return to the other boxes and enjoy his snacks at leisure.

The parallels here to primate behaviour are interesting: chimpanzees have been known to walk away from a food site in order to induce other group members to do the same, and then return later to enjoy the food in privacy. Does the ability to communicate deceptively say something special about the cognitive evolution of a species?

You can read the raven study here.

Language Instincts: Human impacts on animal communication

Bird song

From November 5, 2006

As a change of pace from previous posts, I’d like to look into some of the ways that the human-altered environment may be impacting avian communication. Recently, a number of articles have been published that examine the impacts of human activities on bird song.

Some background on bird song

Bird song is a surprisingly complex communication system that we are only just beginning to understand. In most species, male birds use song for two reasons: to defend territory, or to attract a mate. In either case, song is thought to be an honest signal of individual quality, much like sexually-selected plumage.

When defending territory, males will often sing short, simple songs, and face off in vocal battles with rival males. Because singing is costly in terms of energy and time, only a male in good condition can sing loudly and continuously. When attracting a mate, however, males change their tune and sing longer, more complex songs. The function of song in sexual advertisement is very similar to elaborate plumage ornaments in that it signals individual quality to potential mates. For example, in many bird species, females prefer to mate with males who sing more complex songs or have larger repertoires. Experimental work with zebra finches has shown that males subjected to stress during development sing less complex songs later in life than males whose development was trouble-free. Thus, song complexity may be a good signal of genetic quality that females can use when picking a partner.

Bird song and background noise

The acoustic environment in a city is much different than in a natural setting. The background noise in human-altered environments is louder and generally lower in frequency than it is in natural habitat. This presents a problem for animals trying to communicate.

In the last few years, a number of studies have been published showing that birds in cities alter their song characteristics in response to urban environments, for example by singing at a higher frequency to communicate efficiently over low-frequency background noise. This is probably not the result of natural selection favouring birds with innately different songs in urban populations. Instead, it is probably due to birds born in cities learning to sing at a higher frequency in order to communicate effectively in their acoustic environment.

It has been suggested that local changes in bird song may lead to the divergence of communication systems between different populations. Because many female birds choose mates based on song characteristics, this divergence could lead to reproductive isolation between urban birds and surrounding populations. Cities therefore provide a unique opportunity for researches studying bird song in a number of different ways. Understanding how communication is altered in these environments may help us understand the evolution of signal diversity. At the same time, this work could help us understand the best ways to manage urban animal populations.

Language Instincts: The evolution of sexual signals

From October 28, 2006

This Thursday Al Uy from Syracuse University came to talk to the Ecology, Evolution and Behaviour group at Queen’s. Al spoke about his research on the ecology and evolution of visual signaling in birds.

Plumage colour in birds is known to be involved in conspecific communication, including the signaling of quality to potential mates. In many species, females can gain information about the condition or health of a certain male just by assessing the colour of his feathers. Sexual selection for honest signaling is often implicated in the evolution of brightly coloured plumage, much like the evolution of the peacock’s tail described in my last post.

Al Uy is interested in understanding how sexual selection might contribute to the speciation process, since changes in sexual signals can lead to reproductive isolation between two populations. He pointed out that this idea originated with Darwin, who noticed that often the only difference between closely related species is a sexually dimorphic trait such as male plumage colour. To understand why this might be, Al studies the plumage colour of small birds called the bearded manakins with an interesting mating system: the males gather at display sites called leks, where they clear an area of the forest floor and dance to attract females. There are several subspecies of bearded manakins, all with striking differences in male colouration (whereas the females are all plain and look alike). Here are two of the manakin subspecies Al works on (golden-collared and white-bearded males):

Golden-collared manakinWhite bearded manakin

The signal function of manakin beards

Al began his talk by discussing his investigation of the signal function of colour in the golden-collared manakin, which formed the groundwork for his research in signal diversification. Al and his students have found that the yellow colour of the male ‘beard’ plumage functions as a signal of male quality that females assess during male dancing displays, since males with brighter yellow beards tend to be larger, have higher display rates, and obtain more matings than their dull-bearded counterparts.

Al also tested whether the brightness of the male plumage translated into conspicuousness from the point of view of the female manakins. He used a model that took account of avian perception, ambient light during male display, the reflectance of male plumage and the reflectance of the visual background during display (the dancing court). Consistent with the predictions of sexual selection theory, male conspicuousness as calculated by this model was related to male mating success. In other words, more conspicuous males obtained more matings. Unexpectedly, Al found that the darkness of the visual background was actually more important in explaining the variation in mating success than plumage reflectance, suggesting an important role of the visual habitat in shaping conspicuousness and the evolution of lekking. Al thinks that the lek mating system might have arisen from males becoming more competitive for the specific areas of the forest providing the best visual background for display. In the near future Al plans to test this idea by comparing the reflectance properties of the lek habitat with other areas in the forest.

Why are there so many beard colours?

The next part of Al’s talk focused on his main research interest: understanding what factors might promote the diversification of sexual signals like manakin beard colour. The basic hypothesis he is testing is that changes in the visual habitat can drive the diversification of visual signals. In order for plumage colour to be conspicuous (and therefore most effective as a signal) it needs to match the available light, contrast the background, and be tuned to the receptivity of the target individuals (females). Changes in any of these factors could have promoted the evolution of the four different male colour types found in the bearded manakins.

Al plans to test this hypothesis in several ways. First, he will examine whether or not the evolution of retinal physiology might be driving the diversification of male colour. He plans test this idea by comparing the abundance of retinal cones between the different manakin subspecies. If females from different subspecies have retinas that are optimally sensitive to the beard colours of their mates, then changes in female perception might be driving changes in male beard colour.

Al is also testing his ideas about colour diversification by studying a hybrid zone of golden-collared and white-bearded manakin populations. This is an area of Costa Rica where a river divides populations of the two manakin subspecies, although the yellow plumage trait (found in golden-collared manakins) extends slightly into the white-beaded population. One hypothesis Al is currently testing is whether this trait introgression has occurred because yellow plumage is intrinsically more attractive to the manakin females, although at this point he can only speculate as to why this might be. Al is testing this possibility by examining mate choice in the area where both yellow and white males are competing for the same mates.

The other question Al would like to answer is: what stops yellow males from sweeping further into the white population? It seems unlikely that the river is a physical barrier isolating these populations since birds are certainly capable of crossing it. Instead, Al is looking into the possibility that a change in the visual habitat on either side of the river is maintaining the separation between these two populations. In other words, white birds in succeed in their habitat (despite some introgression of yellow males) because white is the most conspicuous and best colour for displaying in that habitat.

Although Al’s talk was a bit long, it was enjoyed by the audience at Queen’s for telling a complete story without being overly technical, and some went so far as to claim it was the “best talk ever” (Dev Aiama). You can read more about Al Uy’s research here.

Language Instincts: Sex and honesty, or the mating scene for peacocks

Choosing between two males

From October 28, 2006

It doesn’t take an expert to realize that the extravagant song, dance and plumage of male birds (see videos in my last post) are intended as some sort of communication to potential mates. However, the insight that sexual ornaments are signals was a critical one that provided a mechanism for sexual selection and vindicated one of Darwin’s most important ideas. Darwin, of course, was the first to point out that extravagant male traits persist despite their probable costs because females prefer them. The example Darwin often referred to is the enormous and flashy tail of the male peacock (you can see for yourself at this online collection of all of Darwin’s writings).

It wasn’t until the 1970s when Amotz Zahavi suggested his handicap principle that we really began to understand why females prefer certain males. Zahavi’s idea was that extravagant sexual ornaments should be thought of as signals, and these signals are not selected in spite of their costliness but because of their costliness. A costly signal is an honest one; only the highest quality males can express it to its fullest extent. Females should be selected to prefer traits that are costly for males to produce because preference for an honest signal should yield the most benefits. Preference for a dishonest signal (one that a low-quality male could fake) should be weeded out by natural selection.

Darwinians had to wait a long time for honest signaling theory, and they had to wait even longer for someone to test these ideas with respect to the peacock. In the late 1980s and early Marion Petrie began to study what peahens actually look for in a mate. Following the love lives of peafowl in a London zoo, Petrie found a correlation between the number of eye-spots on a male tail and the number of peahens willing to mate with him.

Petrie’s next step was to test this correlation experimentally by decreasing the number of eye-spots on the tails of some males (by simply cutting them off). The question was whether the number of eye-spots directly influences mating success. Her results? Males who had eyespots removed were significantly worse off in terms of their number of mates compared with their mating success in the previous year.

Petrie also looked at the quality of peacock offspring, and found that the larger the eye-spots of a peacock dad, the better his offspring survive, suggesting that males with more extravagant tails are high quality individuals. This means that peahens gain a genetic benefit for their offspring by mating with well-plumed males. So the tail of the peacock would appear to be an honest signal of male quality rather than an arbitrary preference after all.

One other intriguing result of the work done by Petrie and her colleagues is that peacocks tend to display close to their kin. This suggests that kin selection has shaped males to aid their kin in attracting more females, and may provide a reason why poor-quality males who don’t get any mates bother to display at all. Interestingly, experimental work has shown that peacocks are able to recognize their brothers even when they do not hatch from the same nest. My question is: is it possible that birds might use some sort of visual cues that involve plumage for kin recognition?

Language Instincts: Advertising sex

From October 24, 2006

…bird sex, that is.

Male birds will do some pretty bizarre things in the name of sex. Here are some examples of displays put on by males in order to advertise their quality to potential mates (all the clips are from David Attenborough’s “Life of Birds” series for the BBC).

The superb lyrebird of Australia builds a small mound in the forest and sings a complex tune combining his own songs with songs (and noises) that he picks up from his environment:

Superb Lyrebird

The birds of paradise of Papua New Guinea are a strange bunch. Here are some clips of the extraordinary visual displays performed by these males:

Birds of Paradise

Wilson’s bird of paradise also has a very strange pattern of ornamental plumage (this video is also hilarious because of Attenborough’s sneaky hiding places):

Wilson’s Bird of Paradise

More to come on the topic of sexual signaling soon!

Language Instincts: “Run, run as fast as you can, you can’t catch me…”

Motmot

From October 5, 2006

What does the racquet-shaped tail of a turquoise-browed motmot (the bird seen at right) have in common with the tail of a deer and the rhyming gingerbread man of fairy tale fame?

They are all important signals in the communication with predators.

The turquoise-browed motmot has a strange looking tail. The two central tail feathers are elongated and designed with weaker barbs towards the ends of the feathers. These barbs wear away to give the feathers an unmistakable tennis-racket shape. When faced with a predator, the motmot will repeatedly wag its tail from side to side in an exaggerated, pendulum-like way (see video of a related motmot species performing the wag display here). Bold move, you might think – and you would be right. The wag display will often draw the one’s eye to a motmot that might not have been seen otherwise, and no doubt it has the same attention-grabbing effect on predators. So why do it?

A researcher from Cornell University, Troy G. Murphy, recently looked into this problem, studying motmot colonies that nest in abandoned quarries and wells in Mexico. He developed several hypotheses to explain the tail wagging behaviour, and then performed careful observations of the context of over 100 wag displays to discriminate between the explanations.

His hypotheses were as follows: (i) The motmot wags its tail as a warning alarm signal to other motmots, alerting them to the presence of the predator. This means that the signal would be beneficial to nearby individuals (such as kin or mates) even though it might be dangerous for the signaler to draw attention to himself. (ii) The motmot wags its tail as a self-preservation alarm signal. The signal should still be directed to other motmots, but instead of being dangerous for the signaler it might benefit him by encouraging other nearby motmots to move closer together or even mob (attack) the predator. (iii) The motmot wags its tail as a pursuit-deterrent signal directed at the predator itself. Much like the gingerbread man, the tail wag would say, “Run, run as fast as you can, you can’t catch me…” This kind of predator-prey communication would actually benefit both adversaries: the prey gets to stay where he is while the predator avoids wasting energy on what would probably be futile chase.

Murphy found that when presented with a predator, the turquoise-browed motmot will perform the wag display even if it is alone and not within sight of other motmots. He also found that motmots are just as likely to tail-wag when they are alone as when they are near their mate, or near any other motmots. These observations allow us to reject (i) since the display is obviously not intended for motmot receivers. Murphy was also able to reject (ii) since the birds do not move closer together or mob when a predator approaches.

From this evidence we can conclude that the tail wagging must be a signal to the predator, communicating that the motmot has spotted the threat and is ready to escape. Interestingly, the tail of many ungulates has a similar pursuit-deterrence function. For example, some white-tailed deer will signal to chasing predators by flagging their conspicuous tails. Pursuit-deterrence signals have also been observed in lizards (arm-waving to deter predators) and fish (swimming right up and inspecting predators directly to deter them). Too bad for the gingerbread man – if he had stayed in one place and relied on his signaling he might not have been eaten after all.

Language Instincts: A bug’s life

From September 30, 2006

The colony of the leafcutter ant is a strange parallel to human civilization. These ants can often be seen in tropical America parading down trails they create in the forest carrying small leaf clippings. When they return to their nest mound, the ants use these clippings as a substrate for growing fungus; the fungus is used to feed leafcutter larvae. Amazingly, ants are the only group besides humans to have developed agriculture. And leafcutter agriculture is more advanced than you might think – the ants use feces as fertilizer and they even secrete antibiotics to protect their crop from mould.

Leafcutter ants at work in Costa Rica

Leafcutters hit the trail in Costa Rica

Biologists and naturalists have often wondered how relatively simple insects like this can maintain complex social systems; systems that have been around longer than any human civilization and will probably still be here long after we’re gone.

On one level, these systems work because social insects have evolved caste-specific division of labour. Within a colony, individuals are morphologically and behaviourally specialized to carry out specific jobs. A leafcutter ant colony will include a reproductive queen and various sub-castes of workers. Workers are content to give their lives to the colony without any hope of reproduction because of a quirk of genetics that makes them more closely related to the queen’s offspring than their own.

But that still leaves open the question of how simple animals can organize themselves without any obvious authority to command them. How are the activities of various castes coordinated? To address this, scientists in the 1980s began to apply self-organization theory to the behaviour of social insects. This is the idea that a group of simple individuals following basic rules can produce a complex pattern. Self-organization theory has been successfully applied to explain everything from spiraling patterns formed by molecules to the movement of schools of fish and cars in traffic (see here for more). All insects would need is some simple built-in rules to govern their behaviour and the capacity for sharing information with others; if so, the adaptive complexity of the insect colony could be explained by the theory. Indeed, as early as 1989 researchers were able to demonstrate that self-organization explains how a group of foraging ants are able to pick the best path to a food source. They performed an experiment where ants were given the choice of two available routes to their food. Eventually the ants converged on the shorter of the two paths. And this happened without any individuals having knowledge or prior experience of either path!

How could the ants in the experiment accomplish this? The answer is chemical communication. Research into chemical communication in insects took of in the 1960s when E.O. Wilson showed that foraging trails used by ants can be maintained by a positive feedback system of pheromones deposited on the substrate. Trails are reinforced by the deposition of positive pheromones. The more the trail is used by successful foraging individuals, the more the attractant pheromone is deposited and the more additional foragers will be encouraged to try that trail. In the experiment described above, ants traveling on the shorter of the two paths took less time, so pheromones accumulated faster on that route. This set up a positive feedback cycle, resulting in all ants making the right choice for the shorter path regardless of past experience – just as self-organization theory predicts.

More recently, research has revealed chemical communication in social insects to be more detailed than was first imagined. For example, ants generally possess an arsenal of different trail pheromones for different purposes – repellent signals to mark unprofitable branch points that should be avoided, alarm pheromones to signal predators or other dangers, and often different short-lived and long-lived versions of their pheromones. Thus, foragers can communicate a surprising amount of detail just by excretion.

And chemical communication isn’t the end of the story. Insects can also share a great deal of information through tactile and vibrational means. The classic example of this kind of communication is the waggle dance of the honey bee forager, which was shown in the 1940s by Karl von Frisch to convey information regarding both the distance and direction to a food source. Scientists have shown that ants use vibrational communication as well. For example, leafcutter ants that find a good leaf will rub their appendages together (called stridulation) in order to attract tiny hitchhiking workers. These hitchhikers ride on the leaf fragment on the way back to the colony and defend the forager from parasitic flies.

Social insects are remarkably adapted for communication and one can imagine how the combination of various signals and modes of transmission allows insects to share the range of information necessary to run a colony (or farm, as it were). Indeed, the capacity for advanced communication is what sets animals apart from the simple units in other self-organizing systems (like molecules in a beaker or cars in traffic). Understanding communication in social insects is critical to helping us understand how these insect microcosms evolved in the first place, and may even teach us something about our own societies.

More on communication in social insects can be found in articles here, and here.

Language Instincts: What’s in a name?

From September 18, 2006

The study of animal communication is the study of how – and why – information is transmitted between living organisms, whether of the same species or not. The bottlenose dolphin is one example of an animal studied for its chatty behaviour – it was recently shown that the signature whistles used by these social mammals may function like human names.

The name of this blog, on the other hand, is based on Steven Pinker’s book “The Language Instinct”. Pinker argues that human language is an evolutionary adaptation “hard-wired” into the human brain; what I plan to do here is explore the evolutionary reasons for various communication systems in the animal world. My goal is to post weekly on a different avenue of research in this field.

I have to admit that I’m no expert when it comes to the study of animal communication – the reason I chose to write about this topic is that it’s something that I’m interested in and would like to learn more about. Nevertheless, I hope this blog will be a good source of current findings to others who share my interest in biology and animal behaviour.

As a side note, one type of communication that will not be covered here is that between animals and humans, since it isn’t a major part of the scientific study of animal communication (although apparently a career can be made of the talent to communicate with animals, even by telepathic means!).