Dogs can modify their growls to make themselves appear larger.
When a dog growls, it's sending a message. The main message is"I'm scared, but I'll protect myself if you get too close." Back off!" If a dog is acting aggressively, intending to attack, they usually don't growl beforehand. That seems logical, dogs such as wolves don't growl before they attack their prey. That would be silly and non-functional because it would give their targets a warning and a chance to escape.
However, as with most communications, more than one message may be sent at the same time. Specifically, information about the individual sending the message (who is growling) is also conveyed. And as in most communications, the message can contain deliberately misleading information, even in dogs, as was demonstrated in a recent study by a team of researchers led by Péter Pongrácz at Eötvös Loránd University in Budapest, Hungary.
Key Aspects in Growls
Like most vocal communications, several key aspects in sounds make up growls. They are:
1. Pitch: Whether the sound is high or low, determined by its wave frequencies. High frequencies produce sharp notes, while low frequencies produce deeper sounds. Experimentally, the pitch of a growl is best described by the fundamental frequency, which is the lowest frequency in the mix.
2. Tone: This is a measure of the complexity of the sound and is described 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 distinctly different when played on a trumpet, a guitar, or a xylophone. Experimentally, this is sometimes reflected in the activity: formant dispersion. This gauges how strong each pitch is in the growl. A wider formant dispersion can make a growl sound more rough and raspy.
3. Duration: This gauges how strong each sound pitch is in the growl.
Studies indicate that the tone and length of a dog's growl greatly affect its perceived aggression level. Lower-pitched sounds are actually threatening, as are longer sounds.
Dog Size and Growl Sounds
Over the past few decades, research has outlined that the physical characteristics of a dog affect the nature of its growls. Specifically, the pitch of sound coming from the dog's mouth varies with the size of the animal producing it. This is possible due to a basic physical principle. The voice box of bigger animals is larger, causing their growls to be deeper and lower compared to smaller animals because larger chambers produce lower-pitched sounds, similar to how a cello produces lower sounds than a violin due to its size difference.
Therefore, the growl carries significant details about the growler's identity. From an evolutionary standpoint, it is certainly advantageous and adaptive to recognize the size of the animal producing a particular growl, even before it is visible. The clearest reason is that larger animals are likely to be more dangerous and when you hear one of them growl it may be time to seek shelter or head for the hills. Dogs understand this concept, and research indicates that dogs respond differently when they approach a concealed source of sound, based on the size cues present in the growls they hear.
Can Dogs Deceive with Their Growls?
The main question posed by these researchers was whether dogs changed their growls in a way that could affect the perception of their body size, depending on the immediate situation. For example, if a dog is approached threateningly by a man, he will growl. Perhaps he is approached by a larger, truly threatening man. Could he change his growl to make himself appear larger and more threatening? Some research has suggested that this is the case because dog growls sound a lower pitch when faced with a truly threatening situation. However, is this alteration of the acoustic nature of the growl to the point of making people think that the sound is coming from a larger dog?
In this study, researchers collected pairs of growls where both recordings came from the same dog exposed to varying levels of threat. The danger came from male or female researchers of varying sizes. As a control condition, they also collected pairs of sounds from pairs of dogs of different sizes.
Do Altered Growls Deceive?
To address this question, the researchers recruited 311 human participants. They listened to many sets of dog growls and had to pick which growl belonged to the bigger dog in each set. The study of the findings was thorough and detailed, but some key points were evident and simple to explain.
First, for the control growls (where the dogs were truly disparate in size), the human listeners were quite good at determining which of the dogs was larger, confirming previous research showing that growls convey distinct information about the size of the growler.
Specifically, the researchers found that all three of the aspects of sound had an effect on this judgment. Growls with lower pitch, tone 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 fundamental question is, when there is a greater threat, do the dogs change their growls to make listeners misperceive them as larger? When the human listeners heard the growls emitted when dogs were given a threat from a larger individual, they interpreted those growls as coming from a larger dog. In other words, when faced with a greater threat, the dogs changed the pitch, tone, and duration of their growls to make themselves appear larger and therefore more powerful.
If this bluff works, it is highly adaptive since it may deter a real attack by a potential assailant 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 to make it unlikely that other nations could attack it. A threatened dog's growl simply announces, "Beware, I'm big and dangerous."