Dog communication is about how dogs "speak" to each other, how they understand messages that humans send to them, and how humans can translate the ideas that dogs are trying to transmit.:xii These communication behaviors include eye gaze, facial expression, vocalization, body posture (including movements of bodies and limbs) and gustatory communication (scents, pheromones and taste). Humans communicate with dogs by using vocalization, hand signals and body posture.
Both humans and dogs are characterized by complex social lives with rich communication systems, but is it also possible that dogs, perhaps because of their reliance on humans for food, have evolved specialized skills for recognizing and interpreting human social-communicative signals. Four basic hypotheses have been put forward to account for the findings. (1) Dogs, by way of their interactions with humans, learn to be responsive to human social cues through basic conditioning processes. (2) By undergoing domestication, dogs not only reduced their fear of humans but also applied all-purpose problem-solving skills to their interactions with people. This largely innate gift for reading human social gestures was inadvertently selected for via domestication. (3) Dogs’ co-evolution with humans equipped them with the cognitive machinery to not only respond to human social cues but to understand our mental states; a so-called theory of mind. (4) Dogs are adaptively predisposed to learn about human communicative gestures. In essence they come with a built-in “head start” to learn the significance of people’s gestures, in much the same way that white-crowned sparrows acquire their species-typical song  and ducklings imprint on their own kind.
The pointing gesture is a human-specific signal, is referential in its nature, and is a foundational building-block of human communication. Human infants acquire it weeks before the first spoken word. In 2009, a study compared the responses to a range of pointing gestures by dogs and human infants. The study showed little difference in the performance of 2-year-old children and dogs, while 3-year-old children’s performance was higher. The results also showed that all subjects were able to generalize from their previous experience to respond to relatively novel pointing gestures. These findings suggest that dogs demonstrate a similar level of performance as 2-year-old children that can be explained as a joint outcome of their evolutionary history as well as their socialization in a human environment.
One study has indicated that dogs are able to tell how big another dog is just by listening to its growl. A specific growl is used by dogs to protect their food. The research also shows that dogs do not, or can not, misrepresent their size, and this is the first time research has shown animals can determine another's size by the sound it makes. The test, using images of many kinds of dogs, showed a small and big dog and played a growl. The result showed that 20 of the 24 test dogs looked at the image of the appropriately sized dog first and looked at it longest.
Depending on the context, a dog’s barks can vary in timing, pitch, and amplitude. It is possible that these have different meanings.
Additionally, most people can tell from a bark whether a dog was alone or being approached by a stranger, playing or being aggressive, and able tell from a growl how big the dog is. This is thought to be evidence of human-dog coevolution.
- See also: coevolution
Mouth shape: Mouth relaxed and slightly open; tongue perhaps slightly visible or draped over the lower teeth - this is the sign of a content and relaxed dog.:114
Mouth closed, no teeth or tongue visible. Usually associated with the dog looking in one direction, and the ears and head may lean slightly forward - this shows attention, interest, appraising the situation.:115
Curling or pulling the lips to expose the teeth and perhaps the gums - is a warning signal showing the weapons (teeth), the other party has time to back down, leave or show a pacifying gesture.:116
Mouth elongated as if pulled back, stretching out the mouth opening and therefore showing the rear teeth - shows a submissive dog yielding to the dominant dog's threat.:119
Head position: A dominant or threatening dog that looks directly at another individual - this is a threat, it is pointing its weapons (muzzle/teeth) at them.:120
A dominant dog turning its head to one side away from a submissive dog - this is calming them, indicating that it is not going to attack.:120
A less dominant dog approaches a dominant dog with its head down, and only on occasion quickly pointing its muzzle towards the higher-status dog - shows no fight intended.:120
Yawn: A dog yawn - as with humans, a dog will yawn when tired to help awaken it. Also, a dog will yawn when under stress, or when being menaced by aggression signals from another dog when it can be used as a pacifying signal but not a submissive signal. Both humans and dogs can defuse an aggressive situation by turning their head away and yawning.:120-122
Licking & sniffing: Licking behavior can mean different things depending on the context and should not be simply interpreted as affection. Dogs that are familiar with each other may lick each other's faces in greeting, then they begin to sniff any moist membranes where odors are strongest i.e. mouth, nose, anal regions and urogenital areas. These greetings and identification sniffs may turn to licking as well. For mating behaviors, this is done more vigorously than when greeting each other.:124 Licking can communicate information about dominance, intentions and state of mind, and like the yawn is mainly a pacifying behavior. All pacifying behaviors contain elements of puppy behavior, including licking. Puppies lick themselves and their litter-mates as part of the cleaning process, and it appears to build bonds. Later in life, licking ceases to be a cleaning function and forms a ritualized gesture indicating friendliness.:124-125 When stressed, a dog might lick the air, its own lips, or drop down and lick its paws or body.:126
Ears: Ears erect or slightly forward - attention or alerted.:130
Ears pulled back flat against the head, teeth bared - anxious dog that will defend itself.:131
Ears pulled back flat against the head, teeth not bared - submission.:131
Ears pulled slightly back and slightly splayed - indecision: uneasy suspicion, may turn quickly to aggression.:131
Ears flickering, slightly forward then slightly back or downward - indecision: more submissive or fearful component.:131
Eyes: Direct eye-to-eye stare - a threat, expression of dominance, or warning that an attack is about to begin.:146
Direct eye-to-eye stare to human at the dinner table, followed by direct stare at food - dog wants some food.:146
Eyes turned away to avoid direct eye contact - breaking off eye contact signals submission.:147
Tail: Tail horizontal, pointing away from the dog but not stiff - attention.:162
Tail horizontally straight out, stiff, and pointing away from the dog - initial challenge, could lead to aggression.:162
Tail up, between the horizontal and vertical position - dominant dog.:162
Tail up and slightly curved over back - confident, dominant dog that feels in control.:163
Tail held lower than the horizontal but still some distance off from the legs, perhaps with an occasional swishing back and forth - unconcerned, relaxed dog.:166
Tail down, near hind legs, legs straight, tail swings back and forth slowly - dog feeling unwell, slightly depressed or in moderate pain.:166
Tail down, near hind legs, hind legs bent inwards to lower the body - timidity, apprehension, insecurity.:166
Tail tucked between legs - fear, can also be a ritualized pacifying signal to fend off aggression from another dog.:167
Tail fast wagging - excitement.:171
Slight tail wag, each swing of only a small size - greeting.:171
Broad tail wag - friendly.:172
Broad tail wag, with wide swings that pull the hips from side to side - special happy greeting for someone special.:172
Slow tail wag with tail at half-mast - unsure of what to do next, insecure.:173
Dogs are said to exhibit a left-right asymmetry of the tail when interacting with strangers, and will show the opposite, right-left motion with people and dogs they know.
Body: Stiff-legged, upright posture or slow, stiff-legged movement forward - dominant dog.:184
Body slightly sloped forward, feet braced - challenge to a dominant dog, conflict may follow.:187
Hair bristles on back of shoulders - possible aggression, may also indicate fear and uncertainty.:187
Lowering the body or cringing while looking up - submission.:188
Muzzle nudge - occurs when a submissive dog gently pushes the muzzle of the dominant dog, showing acceptance.:190
Dog sits when approached by another, allowing itself to be sniffed - signals acceptance of dominance but does not signal weakness.:191
Dog rolls on side or exposes underbelly and completely breaks off eye contact - extreme pacifying or submission signal.:192
Dog sits with one front paw slightly raised - stress, social fear and insecurity.:198
Dog rolls on its back and rubs its shoulders on the ground - contentment.:199
Dog crouches with front legs extended, rear body and tail up, facing its playmate directly - classic "play-bow" to commence play.:200
Long distance contact calls are common in Canidae, typically in the form of either barks (termed "pulse trains") or howls (termed "long acoustic streams"). The long-distance howls of wolves and coyotes is how dogs communicate.
By the age of four weeks, the dog has developed the majority of its vocalizations. The dog is the most vocal canid and is unique in its tendency to bark in a myriad of situations. Barking appears to have little more communication functions than excitement, fighting, the presence of a human, or simply because other dogs are barking. Subtler signs such as discreet bodily and facial movements, body odors, whines, yelps, and growls are the main sources of actual communication. The majority of these subtle communication techniques are employed at a close proximity to another, but for long-range communication only barking and howling are employed.:Ch10
Barks: Barking in rapid strings of 3 or 4 with pauses in between, midrange pitch - alerting call, the dog senses something but not yet defined as a threat.:79
Rapid barking, midrange pitch - basic alarm bark.:79
Barking still continuously but a bit slower and lower pitch - imminent threat, prepare to defend.:80
A prolonged string of barks, with moderate to long intervals between each one - lonely, in need of companionship, often exhibited when confined.:80
One or two sharp, short barks of high or midrange pitch - typical greeting sound, usually replaces the alarm bark when visitor is identified as friendly.:80
Single sharp short bark, lower midrange pitch - annoyance, used by a mother dog disciplining her puppies or by a dog disturbed from its sleep.:80
Single short bark, higher midrange pitch - surprised or startled.:81
Stutter bark, midrange pitch - used to initiate play.:82
Rising bark - indicates having fun, used during play-fighting or when the owner is about to throw an object.:83
Growls: Soft, low-pitched growling that seems to come from the chest - used as a threat by a dominant dog.:83
Soft growling that is not so low-pitched and seems more obviously to come from the mouth - stay away:83
Low-pitched growl-bark - growl leading to a bark is both a threat and a call for assistance.:84
Higher midrange-pitched growl-bark - higher pitch means less confident, frightened but will defend itself.:84
Undulating growl, going from midrange to high midrange - dog is terrified, it will either defend itself or run away.:84
Noisy growl, medium and higher pitch, with teeth hidden from view - intense concentration, may be found during play-aggression, however you need to look at the whole body language to be sure.:84
Howls: Yip-howl - lonely, in need of companionship.:86
Howling - indicates the dog is present, or indicating that this is its territory.:86
Bark-howl, 2-3 barks followed by a mournful howl - dog is relatively isolated, locked away with no companionship, calling for company or a response from another dog.:87
Baying - can be heard during tracking to call pack-mates to the quarry.:88
Whines and whimpers: Whining and whimpers are short, high pitched sounds designed to bring the listener closer to show either fear or submission on the behalf of the whiner or whimperer. These are also the sounds that puppies make as pacifying and soliciting sounds.:89
Soft whimpering - hurting or scared, one of the most heart-rending sounds a dog can make.:91
Moan or moan-yodel, lower pitched than whines or whimpers - spontaneous pleasure or excitement.:91
Single yelp or high-pitched bark - response to sudden, unexpected pain such as a too-hard play bite.:91
Series of yelps - severe fear or pain.:91
Screaming: A yelp for several seconds in length much like a human child, then repeated - anguish or agony, a call to the pack-mates for help, is rarely heard.:92-93
Panting: Panting is an attempt to regulate body temperature. Excitement can raise the body temperature in both humans and dogs. Although not an intentional communication, if the dog pants rapidly but is not exposed to warm conditions then this signals excitement due to stress.:95
Sighs: Sighs are an expression of emotion, usually when the dog is lying down with its head on its paws. When the eyes are half-closed it signals pleasure and contentment. When the eyes are fully open it signals displeasure, something the dog expected has not happened, often associated with the dinner table and the food that the dog expected to share did not happen.:96
Dogs have an olfactory sense 40 times more sensitive than a human's and they commence their lives operating almost exclusively on smell and touch.:247 The special scents that dogs use for communication are called pheromones. Different hormones are secreted when a dog is angry, fearful or confident, and some chemical signatures identify the sex and age of the dog, and if a female is in the estrus cycle, pregnant or recently given birth. Many of the pheromone chemicals can be found dissolved in a dog's urine, and sniffing where another dog has urinated gives the dog a great deal of information about that dog.:250 Male dogs prefer to mark vertical surfaces with urine and having the scent higher allows the air to carry it further. The height of the marking tells other dogs about the size of the dog, as among canines size is an important factor in dominance.:251 Dogs (and wolves) not only use urine but also their stools to mark their territories. The anal gland of canines give a particular signature to fecal deposits and identifies the marker as well as the place where the dung is left. A small degree of elevation may be sought, such as a rock or fallen branch, to aid scent dispersal. Scratching the ground after defecating is a visual sign pointing to the scent marking.:253
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