CLINICAL FEATURE
Is the Bark Worse Than the Bite?
By Jennifer K. Rudolph, BS, and Lawrence]. Myers, DVM, MS, PhD

Veterinary Forum March 2004

While the dog's ancestor, the wolf, has been observed to bark in only a few specific situations, dogs will bark in almost any situation. This behavior divergence raises the question as to why dogs, in the course of their evolution, began to bark so much. Some researchers believe that barking is very context-specific, while others believe that barking essentially serves no function. Despite this discrepancy, what does remain clear is that barking is part of a dog's normal repertoire of behavior. Yet when barking is excessive, it becomes a nuisance that must be addressed. Various treatment options for excessive barking are available.

Although there are over 52 million dogs in the United States alone, very few studies on vocal communication in domestic dogs have heen conducted. Until recently, researchers had agreed that dogs bark frequently, in so many contexts, and for such long periods that barking must simply he a nonspecific way for them to gain attention. However, barking is often considered nuisance behavior, and many counties in the United States have adopted ordinances that address noise from barking dogs. Barking is a major source of noise pollution in kennels as well.
The wolf is believed to bark for only two reasons: as an alarm and as a threat.1 The alarm bark serves as a warning to other pack members that danger is imminent, and the threatening bark is directed at intruders.2 If dogs barked only for these two reasons, then barking might be more tolerable. However, unlike wolves, dogs bark in many other situations as well. Recent statistical analysis' has revealed that barks can be divided into different subtypes based on context and that individual dogs can be identified by their barks. For example, disturbance barks tend to be harsh, low frequency, and unmodulated, whereas isolation and play barks tend to be tonal, higher frequency, and modulated.' These findings suggest that barks may have specific functions in specific contexts, unlike conclusions that have been drawn in previous studies on dog barking.
About 35% of dog owners complain about inappropriate barking as one of the most common behavior problems, so the ability to identify why a dog barks in certain situations can be extremely helpful in trying to eliminate the behavior.4 Because excessive barking is such a prevalent problem, veterinarians and their staff need to be readily able to offer clients advice regarding the management and treatment of nuisance barking. This article focuses on the origin of barking, why dogs bark, and what can be done to manage excessive barking.

The Origin of Canine Barking
Analysis of mitochondrial DNA from wolves and domestic dogs has supported the hypothesis that wolves were the ancestors of dogs and suggests that dogs originated more than 100,000 years ago.1 Although wolves and domestic dogs are genetically quite similar and have similar body shape, there are striking differences in their vocal behavior. While a bark is recognized as the hallmark sound of domestic dogs, wolves very rarely bark. Even when wolves do bark, the actual form of vocaliza-
tion differs from that of the dog. According to Coppinger and Feinstein. 6 dogs bark in long, rhythmic stanzas but adult wolf barks tend to be brief and isolated. Wolf pups may bark repetitively, but wild canids rarely bark for hours like some domestic dogs do. If dogs evolved from wolves and it is known that wolves do not bark much, then something—an event or behavior modification— must have occurred during the evolutionary process to make dogs such prolific barkers. 6 It is believed that humans may have specifically selected dogs that barked more often or that incessant barking could have developed through indirect selection.
According to what science has proven about evolution to date, animals are shaped by natural selection. This mechanism, proposed by Charles Darwin, promotes the tendency for survival and reproduction of animals to occur most likely in those best adapted to their environment.7 Contrary to this classic explanation, however, investigations into vocalization of the canid family have led researchers to believe that evolutionary mechanisms other than direct selection and adaptation are needed to explain the barking behavior of dogs.6 Coppinger and Feinstein proposed that early "dogs" were probably scavengers that hung around human habitations, eating waste produced by humans. Humans most likely took equal advantage of this situation by using dogs for their own food consumption. In other words, it is believed that through a symbiotic relationship with humans, the wild ancestor of the dog might have essentially domesticated itself.

Why Do Dogs Bark?
Typically, animal calls serve as a straightforward form of communication. They convey information about an animal's internal state or trigger specific responses in other animals or people.6 But a dog's bark does not fall directly into a specific category. Barks can occur in such a wide variety of contexts that their meaning is far from being clear.6 Dogs bark when they hear other dogs bark, when their owners come home or they are left alone, while playing, when they want to be fed or go outdoors— even seemingly at nothing at all.
Many biologists assume that when an animal expends energy to make a sound, it must be for a purpose. The sound possibly functions as a signal or element of communication that contains information both the sender and receiver understand.6 One would expect a signal, such as barking, to have clear meaning, but this
might not always be true. In fact, a given signal can have different functions in differing contexts. For example, when a male bird sings, the song functions as a territorial marker warning other male birds to stay away. It can also attract female mates and help maintain the pair-bond relationship.6 Barking could be an example of this context-dependent behavior, but dogs must have developed an extraordinary ability to interpret distinct meanings from just a single signal if this conjecture is true.6
Animal vocalizations can range from having tonal components produced by regular vocal fold vibrations to being composed of completely atonal turbulent noises Biologist Eugene Morton has proposed that vocal signals fall into classes. According to Morton, noisy, low-pitched signals convey aggression, hostility, or dominance designed to force the receiver to withdraw. In contrast, higher-pitched, tonal signals convey appeasement and submission, encouraging approach from the receiver.6 Because the bark contains both atonal and tonal components, it does not fall into a specific class. In addition, the rate at which the vocal cords vibrate dictates the pitch of the bark's tone. Depending on this rate, barks can sound low, high, or even have pitches that rise and fall.6 Therefore, it is not surprising that barks are difficult to understand.

The Theories Behind Barking
• A Product of Domestication
Dogs apparently are not motivated by spite or do not enjoy the sound of their own voice when barking. It may be that the barking behavior is a product of domestication. Wolves, the ancestors of dogs, rarely bark—although they do howl and make other sounds. Although we do not know for sure why early humans preferred dogs that barked, it may have developed as an early warning system to alert a group of humans that another unfamiliar group or a predatory animal was in the area. Thus, genetic predisposition may be one of the reasons certain dogs bark incessantly. The barking behavior that was welcomed 10,000 years ago when small groups were preyed on by wild animals and warring peoples is not, however, very useful today.
• Because They Can
A small band of researchers is finding that dogs almost always bark for a reason, even if that reason is not apparent to humans. However, these noted experts also suggest that barking is simply a manifestation of "juvenile" vocal behavior. The gist of this study is that barking is the hallmark of all dogs being stuck in adolescence and barking merely reflects metamorphic adolescent behavior in the adult. Sources: www.AnimalBehaviorAssociates.com and The New York Times Science Desk, "What Do Those Barks Mean? To Dogs, It's All just Talk," April 24, 2001.

Treatment Alternatives
Behavior Modification
• Desensitization and counterconditioning
• Bark collars (high-frequency sound, shock, citronella)
Medical and Surgical
• Psychotropic drugs
• Surgical debarking

A more recent hypothesis states that dogs bark because they are essentially stuck in adolescence.6'9 All mammals go through a period of growth and change from a highly specialized and adapted infant into an adult that is also highly specialized. Coppinger and Feinstein6 explain that growth patterns are under genetic control and, although some genes are "turned on" in the course of development, other genes are "turned off." Regulatory genes govern these processes, controlling the schedule of the animal's overall growth and the rate at which its individual parts grow. "Heterochronic" refers to any change in the timing of regulatory genes, and heterochronic evolutionary mechanisms can either speed up or slow down the growth rate. Therefore, an animal that is slowed heterochronically might not reach its expected "normal" adult form.6
This heterochronically slowed animal is believed to represent the domestic dog and provide some insight into why dogs bark. Heterochronic change that selects for juvenile traits could essentially freeze the species in mid-metamorphosis, which provides an explanation for the barking evolution of the dog.6 With this hypothesis, the dog develops some but not all of the normal adult maternal behaviors found in wolves. For example, while it is common for a mother wolf to provide food for her pups, this is not usually the case for dogs. Dogs also fail to develop a wolf's full pattern of hunting and predatory behavior.6 The dog's tendency to mix together infant tonal and adult noisy behaviors interestingly parallels the way it brings pieces of infant and adult behavior together. According to Coppinger and Feinstein,6 the bark is a vocalization that arises from no particular adaptive need and one that serves no specific function. Ultimately, it has been concluded, when dogs bark, the behavior is simply a consequence of the fact that they remain a meta-morphic adolescent for life.6'1' When dogs learn to bark, they are essentially using this vocalization to address situations that natural selection has not previously provided a stereotyped signal for. Therefore, barking is believed to
have evolved as a part of various changes that genetically altered the timing of the life cycle of the ancestral canid.6 While Coppinger and Feinstein essentially conclude that barking serves no specific function, Sophia Yin, DVM, of the University of California, Davis has argued that this is not true.5 She states that a dog's repetitive bark compared with a wolf's single bark does not necessarily indicate that the dog's bark is nonfunctional. Many animals actually use repetitive vocalizations on a regular basis, thereby achieving a cumulative or tonic effect.10 Furthermore, closer evaluation of wolf behavior revealed that wolves bark in far more instances than just the previously thought alarm and territorial contexts. Wolves bark in protest, during prey hunting, and while engaged in pair behavior.' Yin maintains that to make a valid comparison between dogs and wolves, researchers must use the same standards and definitions to systematically study both the structure and context of barking.

Controlling Excessive Barking
Just as opinions about why dogs bark vary, the solutions promising to eliminate excessive barking vary as well. Assessing the reason a dog barks is important in implementing proper treatment. A dog's home environment must first be considered because the environment itself might be inadvertently reinforcing excessive barking. Some primary contributory factors are owners who are nervous about their own safety as well as restrictions on a dog's freedom, such as fences or windows." Owners who isolate their dogs as punishment or to avoid some unwanted behavior can inadvertently be encouraging troublesome barking. Correcting the problem that led to isolation in the first place can usually stop this.

Desensitization and Counterconditioning
If a dog cannot be kept away from the physical situation that causes barking but the stimulus eliciting the barking can be identified, desensitization and counter-conditioning can be tried."'12 Desensitization requires owners to teach their dog a sequence of command responses that are performed daily and any time the dog appears anxious about a stimulus outside the property or home. This demonstrates to the dog that the owners are in charge of the situation. Essentially, the dog is exposed to a stimulus at a level that does not evoke a response and is then rewarded for remaining calm.12 The intensity of the stimulus is gradually increased as long as the dog remains calm. Inappropriate responses, such as harking or aggression, result in ending the training session and the dog being led away from the stimulus.12 In 2 to 3 weeks, an improvement should be noticed, even in the owner's absence.
Correcting barking in the owner's absence does require more time and ingenuity. In this situation, coun-terconditioning can be used to substitute an activity that is incompatible with and more acceptable than the undesirable behavior.12 Dog owners should act as if they are leaving the dog alone. In reality, the owner returns to the dog and distracts it the instant any sign of anxiety is displayed. This can be done by using an ultrasound device or by changing the dog's focus of attention and then rewarding it for obeying an alternative behavior, such as sitting.12 The distraction must follow the stimulus that produces barking as closely as possible rather than the barking itself. Hopefully, once this behavior has been achieved several times per day, the dog becomes conditioned toward silence rather than stimulated to bark.11

If a Client Asks: Dealing with Inappropriate Behavior
There is no foolproof way to cure a dog's inappropriate barking behavior, but here are some tips that may help clients succeed:
• Know whether your dog barks while you're away. To
identify exactly when your dog is barking and whether any other behavior is involved, set up a videotape recorder to record its behavior while you are not at home. If barking is accompanied by panting, salivation, restlessness, or excessive activity, the dog may be experiencing separation anxiety, which is a more extensive problem than inappropriate barking alone.
• Hands off your dog while it is being vocal. Any touching or soothing behavior while your dog is barking will only reinforce the barking. Only touch or pet your dog when it is still and quiet.
• Reward the silence. This is the most important part of teaching your dog to be quiet. Each time your dog is quiet when it would normally have barked, make sure you praise it vocally, along with giving a pat or treat. By doing so, your dog will learn that you like it a lot when there is silence.
• Remote punishment may do the trick. Using a garden hose with a pistol-grip sprayer, spray the dog with water spray, never directly interacting with your dog and being careful not to spray the dog directly in the eyes, ears, or face.
• Consider medical problems in older dogs. If your dog develops inappropriate barking in its senior years, deafness or lack of auditory feedback may be the culprit. Decreased sensory capabilities can accompany aging and thus leave your dog feeling more isolated or less able to function, especially at night. If you believe that may be the case, try leaving a hall light on during the night hours.
• Train your puppy early. Puppies and juvenile dogs may show barking tendencies as instinctive protective behavior. Thus, you should not encourage your puppy to bark for security reasons (unless, of course, you have a watchdog). You need to avoid reinforcing barking behavior at a young age.
Source: Beaver BV: Canine Behavior: A Guide for Veterinarians. Philadelphia, WB Saunders, 1999.

"Quick Fixes"
While desensitization and counterconditioning strategies to stop barking might eventually be effective, many people want a "quick fix" to make the barking stop instantly. One behavioral approach is to make a rattling can by dropping 10 to 20 pennies inside an empty aluminum can. When the dog barks, the can is shaken at the dog and the noise will hopefully startle the clog into silence. A spray bottle filled with water or some lemon juice squirted toward the dog's mouth can have the same effect."
Other quick-fix solutions include the use of "bark collars." There are three primary products available: The first emits a high-frequency sound as punishment for barking and comes in two models, a hand-activated collar controlled by the owner and (me that is worn on the dog and is bark activated." Although this product is relatively inexpensive, it usually is effective only 50% of the time/
Another product is the shock collar, which is based on a concept that may draw controversial opinions among dog owners and veterinarians. This collar delivers an electric shock of variable intensity by way of an automatic sensor or remote hand-held transceiver.1' Some shock collars are equipped with a shut-off safety feature. It the dog continues barking despite being shocked, the unit shuts down.12 Although the shock collar has been proven to be more effective than the noise collar, it may inflict slight pain." Thus, some dog owners refrain from using this type of collar. However, owners who may be considering euthanasia as a solution for excessive barking may want to try the shock collar before making a final decision.
The newest product, the citronella collar, may be a kinder, gentler, and more effective solution than the other two collars. In one study," citronella collars were 88.9% effective in decreasing barking compared with 44.4% effectiveness of shock collars. The citronella collar releases a squirt of citronella under the dog's nose after it barks, startling and distracting the dog and hopefully silencing the barking. Because of the dog's keen sense of smell, it is possible that citronella's strange odor might be less tolerated than a painful stimulus, thereby making the citronella collar more effective." Findings have also shown that this type of collar most effectively reduces barking when worn by the dog intermittently instead of continuously.14 Therefore, it is not necessary for owners to place the collar on their pet on a daily basis. The only drawback of the citronella collar is that it might be too cumbersome for a dog weighing less than 10 pounds.

Prescription Medication
The use of medication to treat excessive barking should also be discussed with owners. Some pet owners are already accustomed to administering drugs to their dog. In addition, many behavioral problems can be successfully treated with drugs.
The use of psychotropic drugs, however, should be limited to select cases where barking has been diagnosed as a result of fear, separation anxiety, or a compulsive disorder.12 Amitriptylene, buspirone, clomipramine, and flu-oxetine may be useful adjuncts to behavior modification in the treatment of select cases of excessive barking.12 Some of these drugs, however, have proved to be of minimal use against truly stereotypical behaviors that make animals perform identical actions repeatedly.'1 The drugs work by clamping down on the ability of the basal ganglia to generate movement. Thus, they reduce all movement, not just stereotypical behavior,'1 and can make the animal sluggish. Although psychotropic drugs certainly play a role in treating other behavioral problems, they usually are not the treatment of choice for barking that is unrelated to fear, separation anxiety, or compulsive disorders.

Surgical Debarking
Vocal cordectomy, or surgical debarking, can be a last resort of dog owners who have exhausted all other options and cannot bear the thought of having to give their dog away or euthanize it. When the procedure is correctly performed, the dog still responds to stimuli and engages in barking behavior but at a much more tolerable level.i: Owners should be informed that complete silencing is not guaranteed because of the slight regrowth of vocal cord folds as scar tissue.l: Most owners, however, find the decreased level and pitch of the bark acceptable.

Barking Up the Wrong Tree: Results of a University of California Survey to be Released in July
Sophia Yin, DVM, MS, a lecturer in Domestic Animal Behavior at the University of California, Davis, and Sarah Richardson, DVM, associate professor at Chico State University, recently conducted an "Excessive Barking" survey on dogs that bark too much. Owners who believe their dog's barking is inappropriate participated in the survey. The goal is to obtain an overview of the problem and then characterize the types or contexts of excessive barking. Drs. Yin and Richardson intend to use the data to design and implement studies that will lead to positive solutions. Preliminary results of the survey will be presented at the annual meeting of the American Veterinary Society of Animal Behavior on July 26, 2004.
You may want to recommend to clients who own dogs with barking problems to consider participating in the research project once it is underway. For additional information, contact Dr. Yin at:
Sophia Yin, DVM, MS
Lecturer, Domestic Animal Behavior Animal Science Department University of California, Davis P: 530-757-2383 Email: Sophia@nerdbook.com

More Investigation Needed
Although additional research on canine barking behavior has recently been conducted, the answers as to why dogs bark are still not completely clear. Some believe that barking is a behavior that essentially serves no function. In contrast, others believe that barking takes place in very context-specific cases and does indeed fulfill a specific purpose. Researchers have proposed a variety of hypotheses, but more investigation must occur to reach a definitive conclusion.
One fact that is not disputed is that dogs bark as a part of their repertoire of behavior. Some breeds of dogs are more predisposed than others to barking because of the actual purpose for which they were originally bred. Barking was a desired trait in certain dogs, such as scent hounds bred to bark when encountering the scent trail of their prey. However, it is possible to own a typically "barking" breed that does not fall into this category.
Investigating into the behavior of the dam and sire as well as obtaining the dog as a puppy during the critical period of socialization can improve the ability of an owner to minimize barking in a "classically barking" breed.16 While none of the solutions discussed has been proven 100% effective, many do have some positive
results—an outcome that can reinforce a more loving relationship between dogs and their owners.

Reviewer Comment
This is a sound review of current behavioral and evolutionary hypotheses regarding the barking behavior of dogs. The author(s) describes appropriate and ethical recommendations for managing this behavioral problem.

References
1. Mech LD: The Wolf: Ecology and Behavior of an Endangered Species. Minneapolis, University of Minnesota Press, 1970.
2. Marder A: Gentle ways to quieter dogs. Prevention 48:125-127, 1996.
3. Yin S: A new perspective on barking dogs (Canis familiaris). J Comp Psychol 116:189-192,2002.
4. Campbell WE: The prevalence of behavioral problems in American dogs. Mod Vet Pract 67:28-31, 1986.
5. Vila C: Multiple and ancient origins of the domestic dog. Science 276:1687-1689, 1997.
6. Coppinger R, Feinstein M: 'Hark! Hark! The dogs do bark. . .' and bark and hark. Smithsonian 21:119-128, 1991.
7. Thomas CL: Taber's Cyclopedic Medical Dictionary, ed 18. Philadelphia, Davis, 1997.
8. Tokuda I: Nonlinear analysis of irregular animal vocalizations. ] Acoust Soc Am 111:2908-2919, 2002.
9. Mestel R: Barking dogs are stuck in adolescence. N Scientist 137:9, 1993.
10. Schleidt WM: Tonic communication: Continual effects of discrete signs in animal communication systems. } Theor Biol 42:356-386, 1973.
11. Campbell W: Problem behavior in dogs: Excessive barking. Mod Vet Pract 54:73-75, 1973.
12. Juarbe-Diaz SV: Assessment and treatment of excessive harking in the domestic dog. Vet Clin North Am Small Anim Pract 27:515-531, 1997.
13. Juarbe-Diaz SV, Houpt KA: Comparison of two antibarking collars for treatment of nuisance barking. JAAHA 32:232-235, 1996.
14. Wells DL: The effectiveness of a citronella spray collar in reducing certain forms of barking in dogs. Appl Amm Behav Sci 73:299-309, 2002.
15. Lord A: No way out. N Scientist 173:34-38, 2002.
16. Hart B, Miller M: Behavioral profiles of dog breeds. JAVMA 186: 1175-1180, 1985.

Ms. Rudolph is a veterinary student (Class of 2005) and Dr. Myers is associate professor in the Department of Anatomy, Physiology, and Pharmacology, Auburn University College of Veterinary Medicine in Alabama.