Signal and Cue—What is the Difference?

Male Lion (Panthera leo) and Cub eating a Cape...

Secondary sexual traits, as the mane of the male lion, are powerful cues (Image via Wikipedia).

In the behavioral sciences, there is some confusion about the meaning of the terms signal and cue (as with so many other terms) and some authors use it interchangeably. To make it even more difficult, communication theory also uses the same terms with slightly different meanings and in the theatre and movies world a ‘cue’ is actually a ‘signal.’

However, in behavioral sciences, the general consensus (see references below) is that signal and cue have the following meanings.

signal is a perceivable behavior or feature that has evolved and has acquired the specific characteristic of conveying information about the signaler or the signaler’s environment. Information (communication) changes the behavior or the beliefs of the receiver.

This definition of signal implies that if a signal changes the behavior of an organism, this change of behavior must be profitable to both sender and receiver more often than not, or otherwise, signalers would cease to send the signal and receivers would cease to respond. This definition distinguishes, in principle, a signal from coercion, although some signals may be coercive, e.g. threats.

In general, signals must be honest and reliable, or otherwise they cease to have any effect (receivers don’t behave appropriately) and they undermine communication (honest senders will not benefit from sending the signals). However, some signals can tolerate a certain degree of dishonesty, all depending on the costs and benefits for all parties. H. W. Bates discovered in 1861 that some (palatable) butterflies had an advantage in mimicking (Batesian mimicry) poisonous butterflies, which is detrimental to the poisonous butterflies inasmuch as it turns their signals of unpalatability less reliable. On the other side, some species use the same signals to convey the same information and they all benefit from it (Mullerian mimicry).

cue is any feature that an organism can use as a guide to display a particular behavior or series of behaviors. The classical example is the mosquito seeking a mammal to bite and flying up wind when it detects CO2. The CO2 is a cue for the mosquito, but it is surely not a signal sent by the mammal, which would prefer to remain undetected and not be bitten. Intentionality is the key element to distinguish signals from cues.

A cue is a regularity, a pattern that either is permanently ‘on,’ or is ‘on’ and ‘off” depending on specific conditions, e.g. a rock, a tree, or the position of the sun in the sky cues us of directions, and dark clouds cues us of impending rain. The rock, the tree, the sun and the clouds are not there to give us information, but they do if we interpret them correctly. A signal is more malleable, more intentional and we can turn it ‘on’ and ‘off’ in response to relevant cues in the environment, e.g. the warning cry that many species (signal) issue in response to the appearance (cue) of a feared predator.

Cues are traits or actions that benefit the receiver exclusively. The sun and the rock do not profit from us getting our bearings. When a mouse by accident makes a rustling sound in the leaves and attracts a predator increasing the risk of being killed, the sound is a cue for the predator about the location of its prey. When an alert animal deliberately gives a warning call to a stalking predator resulting in the predator giving up the hunt, this sound, the alert call, is a signal both for conspecifics and the predator. Different species can, thus, communicate by means of signals which both recognize and behave accordingly.

Secondary sexual traits are features that distinguish the two sexes of a species, but that are not directly part of the reproductive system. They are probably the product of sexual selection for traits, which give an individual an advantage over its rivals in courtship and competitive interactions. Secondary sexual traits are also cues for the opposite sex. They are not directly related to a better production of offspring, but are normally good indicators of better sperm quality or egg production, e,g, manes of male lions (Panthera leo) and long feathers of male peacocks (Pavo cristatus). In humans, visible secondary sexual traits include enlarged breasts of females and facial hair on males.

The study of signals and cues is more complex that it may appear at first sight. Cues can become signals. In 1952, Niko Tinbergen described ritualization as the evolutionary process whereby a cue may be converted into a signal, e.g. the canine behavior of baring teeth. In 1975, Zahavi described the handicap principle where the reliability of some signals is ensured because they advertise greater costs than absolutely necessary, e.g. the exaggerated plumage of the peacock.

We must understand correctly what the intentionality of signals means and not to confound the intentionality of the signal itself with its origin, development and evolution. Signals do not origin by design with a determined purpose. Some features or behaviors just happen at a certain time to be efficient for an organism in generating in another organisms the right behavior at the right time. If they convey an advantage to these organisms in their struggle for survival (and reproduction), they will spread in the population (provided these organisms reproduce). With time, they gain intentionality and become true signals, but their origin was accidental like everything else. This is the reason why I had to modify (some extensively) the definitions I use in this text and I had to create new ones—to make them compatible with the Darwinian theory of evolution.

Applying the principle of simplicity, as always, I suggest the following definitions:

signal is everything that intentionally changes the behavior of the receiver. A cue is everything that unintentionally changes the behavior of the receiver.

These definitions open for the possibility to better distinguish between the intentional signals (proper signals) we send and the unintentional ones (which are cues). For example, many dog owners say “no” to their dogs meaning “stop what you are doing,” but their (unintentional) body language (cue) says “yes.”

In conclusion: signal is the most correct term to denominate what we use when we communicate with our animals; and signals may assume many forms, auditory (the words we use), visual (the hand movements and body language we use), olfactory (in canine detection work), tactile (a touch, very common in horse training) and probably also palatable.

So, enjoy the consequence of your (intentional) signals and be careful with any cues you may be (inadvertently) sending to your favorite animal. Enjoy as well your further studies of this fascinating topic: animal communication.

Keep smiling!

R-

 

References and further readings

  • Dawkins, M. S., and T. Guilford (1991). The corruption of honest signalling. Animal Behaviour 41:865–873.
  • Donath, J. (2007). Signals, cues and meaning (February draft for Signals, Truth and Design. MIT Press)
  • Hasson, Oren (1997). Towards a general theory of biological signaling. Journal of Theoretical Biology 185: 139-156.
  • Hauser, Marc D. and Mark Konishi, eds. (1999). The design of animal communication. Cambridge: Bradford/MIT Press.
  • Maynard Smith, John and David Harper (1995). Animal signals: Models and terminology. Journal of Theoretical Biology 177: 305-311.
  • Maynard Smith, John and David Harper (2003). Animal signals. Oxford University Press, UK.
  • McFarland, D. (1999). Animal Behaviour. Pearson Education Limited, UK.
  • Otte, D. (1974). Effects and functions in the evolution of signaling systems. Annual Review of Ecology and Systemat- ics 5:385–417.
  • Saleh, N et al. (2007) Distinguishing signals and cues: bumblebees use general footprints to generate adaptive behaviour at flowers and nest. Arthropod-Plant Interactions, 2007, 1:119–127
  • Schaefer, H. M. and  Braun, J. (2009). Reliable cues and signals of fruit quality are contingent on the habitat in black elder (Sambucus nigra). Ecology, 90(6), 2009, pp. 1564–1573.
  • Searcy, W. A., and S. Nowicki (2005). The evolution of animal communication. Princeton University Press, Princeton, New Jersey, USA.
  • Tinbergen, N. (1952). The curious behavior of the stickleback. Scientific American December 1952.
  • Zahavi, A. (1975). Mate selection: a selection for a handicap. Journal of Theoretical Biology 53:204–214.

 

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22 comments on “Signal and Cue—What is the Difference?

  1. Thank you so much for taking the time to share your knowlege. Each post is so helpful, clear and easy to understand. they have been a great resourse to me and the young people I work with. Thank you again.

  2. Hi Roger
    Thanks for clarirying this difference. I was going to say that I try to use cues rather than commands to my dogs. On reading your post above, I wouold like to say that I use signals. However, I do not think that I am capable of giving signals, as everything that i do is unintentially not as clear as I would like. My dogs train me. I do understand what you are saying. I think the main thing is that I do not expect my dogs to “obey” me, just to respond to words that I have attached to behaviours I have rewarded. Phew – I have had a few drinks , so I hope I have made sense.
    Liz

  3. This is a very interesting exposition of terms and definitions and goes to show how confusing things can actually get. I thought I had it more or less right, but actually less than more, when it comes to the definition you have outlined for cue. Thank you for making a useful word even more useful!

  4. Hi everyone,

    Thanks for your comments. And, yes, Liz, you make sense, so you can still have one more drink. Most of our body language is unintentional, they are cues that emphasize, confirm or deny our spoken words (our signals). When we communicate with our dogs we use a lot of unintentional body language (cues). Most of them work because they are in unison with our (intentional) signals, but sometimes they don’t because they contradict our signals (words or hand signals). This is the reason why you should always mean what you say and say what you mean; and you should always keep a clear mind-set when you train animals.

    Cheers,

    R-

  5. Hi everyone,

    I had to update once again my “Signal and Cue—What is the difference?” because I got so many messages from my Facebook friends with so many good questions that I couldn’t leave unanswered. I decided to improve my blog with more and better explanations and examples, more links and a more comprehensive further readings list to help you to continue your study of this fascinating topic: animal communication. Sorry for the inconvenience and thank you all.

    Keep smiling!

    R-

  6. This is really interesting, You are a very skilled blogger. I have joined your feed and look forward to seeking more of your wonderful post. Also, I’ve shared your website in my social networks!

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