Can Dogs Tell Lies with a Growl?

SC Psychological Enterprises Ltd.

When a dog growls it is sending a message. The main message is "I feel threatened, but I will defend myself if you come closer. Back off!" If a dog is acting aggressively, intending to attack, he usually does not growl in advance. That makes evolutionary sense, canines such as wolves do not growl before they attack their prey. That would be silly and non-productive because it would give their targets a warning and a chance to escape. However, like most communications, more than one message may be sent, at the same time. Specifically, information about the individual sending the message (who is doing the growling) is also conveyed. And as in most communications the message can contain deliberately deceptive information, even in dogs, as was demonstrated in a recent study by a team of researchers headed by Péter Pongrácz at Eötvös Loránd University in Budapest, Hungary.

Sound Dimensions in Growls

Like most vocal communications, several important dimensions in sounds make up growls. They are:

• Pitch: Whether the sound is high or low is determined by its wave frequencies. High frequencies produce high-pitched notes like those on the right side of a piano keyboard, while low frequencies produce lower, more booming, sounds like the left side of the keyboard. Experimentally, the pitch of a growl is best characterized by the fundamental frequency, which is the lowest frequency in the mix.
• Timbre: This is a measure of the complexity of the sound and is characterized by the specific mix of sound frequencies that make it up. This gives sounds their identity since you can recognize a middle C note as being recognizably different when played on a trumpet, a guitar, or a xylophone. Experimentally, this is sometimes reflected in the measure: formant distribution. This measures the intensity of each sound frequency in the growl. A wider formant distribution can make a growl sound more gruff and hoarse.
• Duration: The measure of how long or drawn out the growl is.

Research has shown that how aggressive a dog's growl appears depends strongly on pitch and duration. Lower-pitched sounds are more threatening, as are longer sounds.

Dog Size and Growl Sounds

Over the past two decades, research has established that the physical characteristics of a dog alter the nature of its growls. Specifically the pitch of sound coming from the dog's mouth varies with the size of the animal making it. This is possible because of a basic physical principle. The larynx, or voice box, of a larger animal is bigger. Sound resonating in a large chamber tends to be lower in pitch, as can be observed by noting that the pitch of the sounds from a cello is lower than those made by its smaller cousin the violin. This means that the growl of the larger animal will be deeper and lower than the corresponding growl of a smaller animal.

Thus the growl contains important information about who is doing the growling. From the viewpoint of evolution, it is certainly helpful and adaptive to recognize the size of the animal producing a particular growl, even before it is visible. The most obvious reason is that larger animals are likely to be more dangerous and when you hear one of them growl it may be time to take cover or head for the hills. Dogs recognize this, and several studies have shown that dogs react differently when approaching a hidden speaker, depending on the size of information contained in the growls issued.

Can Dogs Lie with Their Growls?

The main question posed by these researchers was whether dogs modified the sound of their growls in a way that might affect the perception of their body size, depending upon the current situation. For example, if a dog is approached by a man who seems threatening he will growl. Perhaps he is approached by a larger, more threatening man. Would he alter his growl to make himself appear larger and more threatening? Some research has suggested that this is the case since dog growls sound a lower pitch when confronted with a more threatening situation. But is this change in the acoustic nature of the growl enough to make people think that the sound is coming from a larger dog?

In this study, researchers assembled pairs of growls where both recordings originated from the same dog exposed to varying degrees of threat. The threat was provided by male or female experimenters who differed in size. As a control condition, they also assembled pairs of sounds from pairs of dogs of different sizes.

Do Altered Growls Deceive?

To answer this question the researchers assembled 311 human participants. They listened to many pairs of growls and had to indicate which growl came from the larger dog in each pair. The analysis of the results was extensive and detailed, beyond the scope of the space we have here, however, certain highlights were clear and easily described.

First, for the control growls (where the dogs were physically different in size), the human listeners were quite good at detecting which of the dogs was larger, confirming earlier research showing that growls convey recognizable information about the size of the growler.

Specifically, the researchers found that all three of the dimensions of sound made a difference in this judgment. Growls with lower pitch, timbre with more frequencies packed in the lower range, and longer duration growls were all identified by human listeners as being associated with larger dogs.

But now the critical question is, when there is a greater threat, do the dogs alter their growls to make listeners misperceive them as larger? When the human observers heard the growls emitted when dogs were presented with a threat from a larger person, they interpreted those growls as coming from a larger dog. In other words, when presented with a greater threat the dogs altered the pitch, timbre, and duration of their growls to make themselves appear to be larger and thus more formidable.

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If this bluff works it is very adaptive, since it may stave off an actual attack by a potential aggressor who wants to avoid suffering too much damage to himself. It is all very reminiscent of political posturing in today's volatile world, where a country claims to have a larger army or more powerful arsenal of weapons to make it less likely that other nations might attack it. A threatened dog's growl simply announces, "Beware, I am large and dangerous."

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