Introduction to Canine Behavior

CHAPTER 1 Introduction to Canine Behavior

Understanding the dog requires that one understand where it came from, so it becomes necessary to go back to the wolf and beyond. The dog began its association with humans well over 10,000 years ago, a period longer than for any other domestic animal. Since dogs came into our lives, they have filled a number of roles: from companion to food, from alter ego to special sense. It is the great genetic plasticity in Canis familiaris that has permitted so much variation in its sizes, colors, and behaviors. In modern times, breeds have been developed for specific purposes, such as herding cattle, retrieving a hunter’s kill, and pulling a sled. Although there are behavioral variations between breeds, often related to purpose, the core behaviors of the domestic dog are very similar across breeds and are often similar to those of its closest relative, the wolf. The wolf can serve as a basis for understanding the dog, but it is also important to remember that thousands of years of selective breeding have changed a lot of the behavior too.


The oldest known ancestor of the domestic dog is the Miacis, a small, weasel-sized carnivore that lived approximately 40 million years ago in the Eocene.60,88,89,211,239 The miacid was probably a forest dweller with a long tail, short limbs, and a plantigrade stance.60,210 Already at this time, the teeth that would come to be called the carnassial teeth had taken on their characteristic shape. By the late Eocene period, the Cynidictus had evolved, and it probably gave rise to the Hesperocyon (formerly Pseudocynonsides).60,89,182,211 This latest group existed approximately 3 million years ago in the Oligocene and was distinguished by its larger size, longer limbs, better developed carnassial teeth, and larger brains.60 The line of ancestors that followed is less clear. Some propose that the Cynodesmus of the Miocene gave rise to the Tomarctus of the Pliocene, and the Tomarctus eventually gave origin to the canids.60,89 Others theorize that Hesperocyon gave rise to the Leptocyn, one possible ancestor of the dog, or to the Tomarctus, another possible ancestor.182,211

Regardless of the exact ancient line, all modern predators (fissipeds) belong to one of three superfamilies: Miacoidea, Feloidea (Aeluroidea), or Canoidea (Arctoidea). Cats, hyenas, and Old World civets belong to the Feloidea. Dogs, wolves, foxes, and jackals belong to the canine subfamily of Canoidea.60,78

Even narrowing down the phylogenetic subfamily does not settle another age-old question. What animal is the immediate ancestor of the domesticated dog? Most experts agree that the wolf played a major role in the dog’s genetic pool, but there are 32 subspecies of Canis lupus.211 Of the canids, only the wolf, coyote, and jackal have the same number of chromosomes (78) as the dog and can interbreed to produce fertile offspring.57 A question remains about other common early ancestors or another possible ancestor species.89,90,318 Dogs and wolves share 71 of 90 behavioral patterns, more than are shared by any other two species.279 Early DNA tests have provided limited information that the domestic dog, wolf, coyote, and jackal are the most alike among the canids.69,317,326 Newer isoenzyme genetic distance indicates that the dog is more closely related to the wolf than to other canids.119,183,314,323

Assuming the wolf (Canis lupus) begot Canis lupus familiaris,211 which begot Canis familiaris, which of the many subspecies of wolf started the process? Again, considerable disagreement exists. Some authorities argue for a single origin in northernEurasia,278 the Near East,69 or North America.119,211 Others argue for the possibility of the occurrence of domestication in different species in diverse locations.55,57,85,190 How the first dogs gradually changed into the many breeds we have today has been the subject of much speculation over the years. Most people believe that the Arctic breeds probably came first because their physical appearances are very similar to wolves. Others believe that “village dogs” were first.35,65 These were followed by livestock-guarding dogs and hunting companions, and then by sled dogs, herding and gun dogs, and household dogs.65 The most current studies of DNA microsatellite subtypes find at least four distinct groupings representing unique “adaptive radiations” (Fig. 1-1).230 The four groups with similar genetic clusters also tended to share geographic origin, morphology, and/or genetic closeness to the wolf of Southeast Asia, following humans to different parts of the world.35,230,267 Research into common behaviors also shows some similarities within the four groups. Those closest to wolves show more aggression and less demand for affection than those farthest away.111

Exactly when humans started interacting with wolves is difficult to determine. Some of the earliest hominid sites with Canis lupus remains were found in Zhoukoudian, China, dating back between 200,000 and 500,000 years; in Kent, England, dating back 400,000 years; and in Nice, France, dating back 125,000 years.59,211 As evidence of domestication, scientists have pointed to (1) the smaller size of bony remains compared with those of indigenous wolf populations; (2) certain anatomic differences in the skull, mandible, and teeth; and (3) phylogeographic variation. According to these criteria, dogs separated from wolves up to 40,000 years ago. However, DNA evidence for the delineation suggests that dogs originated approximately 135,000 years ago and that occasional wolf back-crosses have occurred.313

Domestication probably occurred in more recent history, but exactly when and where is not clear. Burial sites are the most likely source of information, but some researchers question if burials truly indicate early domestication, or if they were started somewhat later. A German dog burial site dates back 14,000 years.58,93,238 Another burial site in Siberia goes back 10,650 years.93 Evidence of the dog’s existence has been found at the Palegawra Cave in Iraq, dating back some 10,000 to 12,000 years,55,56,211,212 although there is some question about this date.69 At Ein Mallaha in northern Israel, scientists excavated a tomb dating back to 9350 to 9750 BC that contained a burial of an old human, probably a woman, and a 3- to 5-month-old puppy.57,59,69,71,190 In China, domesticated dogs have been dated back to 7355 ± 100 BC.211 The earliest European site is Star Carr in Yorkshire, England, which contained evidence of dogs dating back to 7538 ± 350 BC.69,211 Swedish and Danish sites date back to 5000 to 6800 BC.211 In North America, dogs probably accompanied humans over the Bering Strait land bridge from Asia and spread out from there.165,230,238 Dog burial sites date back 8500 years in western Illinois and 7500 years in Benton County, Missouri.69,199,210 The ancient Chiribaya dogs of Peru were apparently very prized and recently found mummified bodies date back about 1000 years.61 Domesticated dogs probably did not exist in Australia more than 12,000 years ago.57,69 That was the approximate time Tasmania separated from the Australian mainland, and the absence of canids there supports this theory. The dogs that did come to the Australian continent probably did so as recently as 5000 years ago,70 and eventually reverted to the feral dingo.

How and why domestication of wolves occurred will always be speculative. Some theories about domestication in general suggest that a mutually advantageous relationship between wolves and humans would allow for the loss of such wolf behaviors as self defense and self protection. At the same time, there would be the gain of other behaviors, such as access to food or shelter.40 Perhaps wolves and humans shared hunting success. Wolves might have followed hunters initially to find game. The wolf that was allowed to share a kill made by its two-legged benefactor would have become somewhat tame.211 Hunting skills as well as ease of being tamed—traits that benefited the humans—could then have been selectively bred owing to proximity because the most successful wolves took on a favored status and were more apt to be around others with similar traits.

Early humans may actually have taken young cubs from the den to be hand-raised, as was done by Native Americans even into the eighteenth century, and as some people still do.56,100,182,280 Without a parent to teach hunting skills, the wolf/dog would have become dependent on the humans for food.40,190 Some probably became scavengers, responsible for keeping the camps clean.57,90 As suggested by evidence from the Israeli burial site, some wolves may have first shared space with humans simply to provide companionship.57,69 The relative lack of canid bones at most sites indicates that dogs were probably not a major food source.69 Other roles these animals could have filled would have been as an occasional “watchdog,” religious symbol or sacrifice, draft animal, or source of hides, meat, or warmth at night.57,90,182,190

Domestication is a complicated process that involves genetic changes in a large number of animals that are selectively bred over many generations to intensify certain traits and make others secondary. The result is a species that is biologically changed in its morphology, physiology, and behavior.94,157 The dog became smaller than the wolf, had different colored hair, and was less alert to its environment. Over time the quantitative nature of the various responses change so that rather than a behavioral trait being completely lost, its threshold is heightened or lowered by lack of or consistent exposure to specific stimuli.249 Many more generations of continued selective breeding modified the dog into a wide variety of shapes, sizes, colors, and behaviors based on the goals and desires of those responsible for mate selection.

The domestication process can occur relatively rapidly in a canid when strict criteria are used.249 The Russian geneticist D.K. Belvaev was able to create major changes in a group of silver foxes through intense selective breeding only for tameness over approximately 20 generations.26 By the end of that time, his animals were reported to have sought contact with humans, licked human hands and faces, changed their breeding cycle to twice a year, developed drooping ears and erect tails, and displayed the submissive behaviors of whining and tail wagging.182,190 In the case of wolf-to-dog evolution, the timeframe was probably much longer than in Belvaev’s experiment, because the selection criteria were far less distinct; however, the social structure of the wolf is the closest of any of the wild canids to that of the human, making the wolf the best candidate for domestication.278

The physical and behavioral features that tended to be retained in the wolf-to-dog transition were those most associated with juveniles, a phenomenon called paedomorphosis.* In the dog, those wolf cub–like physical features include a smaller size, shorter muzzle, relatively wider cranium or more domed head, reduced tympanic bullae, more convex mandible, larger eyes, smaller teeth, floppy instead of erect ears, and less developed temporalis and masseter muscles. The retained behavioral characteristics include increased frequency in care-soliciting behaviors, submissive food begging (such as face licking), relative lack of fear, timing of activity periods, curiosity, playfulness, lessened territorialness, and increased seeking of social contacts.40,87,119

On the other hand, some distinct differences also developed between wolves and dogs that were unrelated to paedomorphosis. Many of these features were not selected for or against but probably tagged along genetically. The curly tail of some dogs was one of the most obvious early changes. It, in turn, has been followed by a great variation in the size and shape of the tail, its amount of curl, and the position in which it is carried. Unlike other canids, dogs sometimes have the first digit on the rear limbs.57 The scent gland from the dorsal aspect of the base of the tail is greatly reduced or absent in dogs.57,94 Reproductively there are differences too. Sexual maturity occurs between 6 and 12 months of age in dogs versus almost 2 years in wolves. Female dogs experience twice as many estrous periods as female wolves in a year, and estrus can occur at any time during the year. Thus, males are reproductively interested throughout the year instead of during a wolf-like 2-month breeding season.57,278 Dogs have developed better social-cognitive skills than wolves and are able to read human signals, including those that indicate the location of hidden food.105 Even wolves raised with humans do not show that behavior. Coat colors have increased in dogs. It has been shown in foxes that the change in the color of fur can be related to behavior changes. The amber fox is less aggressive than the gray fox. Also, at least some amber foxes have smaller adrenal and pituitary glands.57

Seven thousand years ago, there were specific kinds of dogs. Three thousand years ago heavy hunting dogs, short-legged dogs, and Greyhounds existed.57,58 Soon dog breeds proliferated. Small dogs share a single insulin-like growth factor I (IGF-I) allele that suggests a specific sequence variant is the major reason for their body size.298 But dogs now come in a wide variety of sizes, colors, and working skills. Dogs were an integral part of Roman culture and could be found throughout that empire. Probably the first systematic breeding of dogs occurred there. The Romans had fighting dogs, sheepdogs, guard dogs, and small lapdogs.56,57 As a side note, the cave canem signs in Pompeii and Rome were the first “Beware of the Dog” signs; their intent was to warn visitors not to step on the small Italian Greyhounds.239 Columella, a Roman agricultural authority, is said to have advised the breeding of dogs that did not look like wolves, including black farm dogs that barked at intruders and white sheepdogs.56

The licensing of dogs was started by King Henry III of England around the middle of the thirteenth century when he singled out mastiffs.239 The first competitive dog show was held in 1859 at Newcastle in Britain but was limited to Pointers and Setters. With the start of the shows and the British Kennel Club in 1873, breed standards were gradually tightened until they reached what we know today.57


Dogs have been used to meet more human needs than any other domestic species (Table 1-1), and humans keep finding new things for them to do. The original list of four roles animals typically fill—food, clothing, shelter, and transportation—were to be greatly expanded as dogs came to be associated with other cultures and time periods. A recognition of the human-animal bond allows for consideration of activities animals do with us, as well as for us. Probably the longest service that dogs have performed is the guiding and guarding of livestock. Even today the use of livestock-guarding dogs is an effective method of managing predation, with 82% of them considered to be an economic asset.103 Guide dogs for the blind are the most common type of specially trained service dog, extending the sensory capacity of the human with whom they work. But service dogs help humans in much more than the physical sense. They have been shown to provide a tremendous psychologic boost and to facilitate community integration. Their use has been correlated with better attendance at work or school, while reducing the number of human assistance hours needed.5 Dogs are also an integral part of many search-and-rescue teams.118 They have served with honor in the military as sentries, smell detectors, early warning systems, and communication go-betweens.4 Dogs are used as research models and as a child’s teacher. Psychologically, they can contribute to good mental health, help bridge social interactions5,168 and serve as a warm, fuzzy therapist for those who need a feeling heart to listen.

The genomics of dogs is currently a hot research topic, but ultimately the understanding of the genetics of behavior will take a lot longer. Behavioral genetic research peaked in the late 1960s and early 1970s and has been spotty since then. It is recognized that there are critical aptitudes, and the military and police in other countries have done some work in using genetics and behavioral selection tools.43 The heritability of a few traits in hunting dogs has been reported, but these represent only five traits in four breeds.130,300 Some is known about the interrelationship of certain polymorphic genes as they affect temperament and psychic diseases in humans.300 We could speculate that there may be a relationship to certain conditions in dogs as well (Table 1-2). Time will tell if any of these relationships exist. Unfortunately, bad genetic traits that can be passed on with desired ones can lead to the culling of working dogs or aggression in pets, as examples.128,170

TABLE 1-2 Genetic associations with temperament or psychic diseases in humans that may relate to similar problems in dogs

Target gene Temperament/psychic disease(s)
5-HT transporter Anxiety, harm avoidance, novelty seeking, depression
5-HT2A receptor Anorexia nervosa
5-HT2C receptor Reward dependence
5-HT6 receptor Alzheimer’s disease
Dopamine transporter Attention-deficit hyperactivity, novelty seeking
Dopamine D2 receptor Reward dependence, harm avoidance
Dopamine D3 receptor Novelty seeking
Dopamine D4 receptor Novelty seeking, attention-deficit hyperactivity, harm avoidance
Catechol-O-methyltransferase Obsessive-compulsive disorder, attention-deficit hyperactivity
Monoamine oxidase A Impulse aggression, panic disorder
Tryptophan hydroxylase Impulsive aggression, aggression (anger-related traits)
Tyrosine hydroxylase Deliberation, dutifulness

HT, Hydroxytryptamine.

Modified from reference 300, pp. 356-357.

Throughout the world, the cultural views about dogs vary tremendously, and this can be true even within a single country. Where dogs are highly regarded, they may be given human names, allowed to share human beds, and fed human food. At the other end of the spectrum are cultures that consider dogs to be pariahs—social outcasts. In between these two extremes are cultures indifferent to the well-being of dogs.

Although the United States has one of the highest dog ownership rates, it also has a large number of people who refuse to accept any of the responsibility that normally accompanies such ownership. Stray animal populations and euthanasias in animal shelters are statistical proof. For every 415 babies born each hour in the United States, there are 2000 to 3000 new puppies and kittens.81 That means 60,000 animals must die each day just to maintain a stable population.81 Surgical sterilization helps, but it is not the solution to the problem of overpopulation.

Exact statistics on dog population in the United States are impossible to get, but over the last 35 years, several groups have made well-researched estimates (Table 1-3). Beginning in 1972, with an estimated dog population of 36.1 million, the numbers rose gradually, reaching 55.6 million dogs in 1983.131,240 Since 1987 the number of dogs in this country has increased slightly, reaching 61.6 million by 2001.7,51,52,98,332334 Even the best efforts to obtain valid data are challenged,235 so any “data” are really estimates.

Worldwide, there are no reliable canine population data either, but surpluses are a concern everywhere.156 The United Kingdom had an estimated 6.3 million dogs in 1986, and approximately 700,000 puppies are born there each year.66,308 Certainly, with the size of the pet food market, manufacturers must have some estimates on dog numbers, but this information is not widely available and the use of manufactured food is not universal.

The number of households having dogs and the average number of dogs for each is another way to look at population statistics (see Table 1-3). In the United States, Australia, Belgium, France, and Ireland, approximately 40% of all homes have at least one dog.176 In contrast, in Germany, Austria, Sweden, and Norway the number is estimated to be between 12% and 15%.176

Approximately 2000 distinct dog breeds have existed at varying times throughout history, and there are currently around 400.230,259 The American Kennel Club recognizes 152 breeds. Slightly over half the dog population in the United States and some European countries are purebred but not necessarily registered.66,303,330

Popularity of breeds changes constantly, and only a few breeds account for a large portion of the new puppies (Table 1-4).52,55,66 The general trend over the past 35 years has been toward large dogs. The success of a dog actor or image can create a sudden demand for a specific breed. Lassie, Rin Tin Tin, Eddie, and the 101 Dalmatians moviehave each triggered the extreme popularity of their breed. Unfortunately, the sudden popularity of any individual breed can result in a lot of behavior problems in those dogs. Behaviors, even within breeds, can change over time.299 The American Cocker Spaniel breed was considered to be a good family dog in the 1950s. At the peak of this popularity, it became an aggressive dog and fell out of favor. Cocker breeders worked hard to get rid of the aggression so by the early 1980s, the breed rose in popularity again. By the middle 1990s, the breed regained a reputation for aggression and fell out of favor once more. Current studies find that correlation between behavior and function of the breed’s origins no longer exist, but the behaviors now relate to the breed’s current use.299 There is a positive correlation between use in working dog trials and the playfulness and aggressiveness in the sires, and between dog show use with social and nonsocial fearfulness. A negative correlation exists between dog show use and playfulness, curiosity, and aggressiveness. Popular breeds also have higher sociability and playfulness scores than less popular breeds, which probably relates to why they became popular. Careful selection of breeding animals can be helpful in the overall success of producing consistency in service dogs of certain breeds.331

It is logical to expect behavioral and medical disorders to differ somewhat among breeds, because selective breeding tends to concentrate specific traits. Over 350 inherited disorders have been reported in dogs.230 Breeding for appearance does not take into account the genetics of temperament. Moreover, most books about a breed are written by fanciers of the breed, so there is a tendency for each book to indicate that dogs of that breed are good with children, easy to train, and make wonderful pets. Relatively few authors have approached the subject with a scientific basis and real objectivity.112,114,115,280

Veterinarians tend to see a skewed population of dogs, although the patient trends are gradually approaching the norm. In 1983 at least one in four dogs did not visit a veterinarian. By 1997 the number had dropped to approximately one in six dogs.51,52,301 The average life expectancy for a dog is 13 years,243 but the mean age of dogs in the United States is about 4 years.7,329 In fact, over half of all dogs are under 6 years of age.7,51,52,332 Many dogs die at a young age to balance with the geriatric populations veterinarians usually deal with. The oldest authenticated age worldwide is 29 years and 5 months for an Australian Cattle Dog.243 At least as evidenced by necropsy data, there is a trend for the mean age of death for neutered dogs to be older than for intact dogs.36

Approximately 75% of the dogs that go to veterinary clinics have been spayed or castrated,1 but over the entire population, only 66% of the animals have been neutered. There is a significant difference between sexes, in that 12% of the males and 47% of the females are neutered.303,330 Yet estimates, based on owners’ responses, run as high as 92% for spayed females and 62% for neutered males. Exact figures are impossible to obtain175,233; data suggest that young dogs are less likely to be neutered than older dogs and male dogs less likely than females. Almost one third of dog owners have not neutered their dog because they “just have not gotten around to it.”303

In this era of genomics, researchers have found that dogs and humans share approximately 25% of their gene sequences.149 Although that is nowhere close to the shared genes of humans and chimpanzees, it is cause to wonder if this may peak human interest in dogs. The human fascination with and expectations from dogs have been investigated. Results indicate that 68% to 80% of people got the dog for companionship, and about 50% of dog owners say they are emotionally dependent on their animals.2,7,335 This finding parallels the finding that 76% let their dogs sleep on or by their beds.2,296 Almost all dog owners talk to their pet and feel that the animal understands them.296 Studies have shown that people who express little affection for dogs also express little for people. Men who expressed little affection for dogs were also found not to desire attention.38,168 When dog owners were studied specifically, three to five attitudinal segments were identified.166,330

Several years ago the Pet Food Institute did a study of pet owners and described five types of people having a dog. Certainly the distribution within categories has changed over time, but the basic descriptions are still true today. Dog owners categorized as “Companionship Owners” (27% according to the original survey) considered their dogs to be major sources of friendship, companionship, and affection.330 They usually took their dogs on vacations and generally reported few problems with them. If they had to leave their dogs, these owners would be the most likely to support a pet hotel,260 or have a pet sitter stay with the dog. This group of owners derives very important psychologic benefits from their dogs.330 Human names had been given to 52% of the pets, and names of endearment were common, like “Sweetie” and “Baby.”2,96,97 Most dogs with companionship owners have human names, with “Sam,” “Max,” “Heidi,” and “Ginger”being among the most popular.96 Interestingly enough, 75% of people who have dogs feel that they are more tolerant of the pet’s shortcomings than the shortcomings of their spouse or children.296 Over 50% of companionship owners feed their pets premium brands of food and give them gifts on their birthday or on holidays.99,193

“Worried Owners” (24% of the original survey sample) like their dog, but they have a fear that their pets are potentially harmful and that they lack control over them.330 They often allow their dogs to roam such that they may be gone for a day or two at a time. Worried owners often describe their dogs as “stupid,” “dumb,” or “spoiled,” and they may be embarrassed by their animal’s sexual behavior.330 Veterinarians recognize these owners as they get pulled into or out of the clinic by the dog. Owners subconsciously recognize these dogs because they hate taking the dog for a walk.

For “Valued Object Owners” (19%), the dog is considered an extension of self and given the same quality of care in selection and maintenance as otherpossessions.330 Although there is no significant psychologic investment by these owners, neither do they complain about the dog’s physical characteristics.330 With personification of image, castration of male dogs is generally strongly resisted by most of these owners. Even within this group there could be a great deal of diversity, from the aristocratic ownerof an Afghan or Pembroke Welsh Corgi, to the black-leather-jacketed owner of an American Pit Bull Terrier or Rottweiler wearing a spiked leather collar. The first group might use regal names like “Sheik” or “Cognac” for their pets, whereas the latter would prefer power names like “Fang,” “Brutus,” or “Killer.”

The fourth group of dog owners from the Pet Food Institute study were those called “Dissatisfied Owners” (19% of the original study population).330 The general view held by people in this category was that the dog was more trouble than satisfaction. The owners tended to complain about everything from doggy smells and shedding of hair to the dog being a nuisance, overly affectionate, or too expensive. Because any investment in the animal’s health was considered too expensive and time consuming, veterinary care was minimal for the dogs of these owners. Interestingly, these owners often had received the animal as a gift or had procured it as a pet for their children.330 Names chosen for these dogs often reflected the owners’ negative or noncommittal attitudes. “Stinky,” “Budweiser,” and “Dog” were examples.

“Enthusiastic Owners” (17%) were the fifth group identified in the Pet Food Institute study. These people took good care of their dogs and appreciated the friendship and companionship they received.330 They had few complaints of either physical factors or behavior problems. Though sharing many of the characteristics of the companionship owners, enthusiastic owners were defined as having a less pronounced psychologic commitment to their dogs.330

A later study divided pet owners into three groups. The “Pet for Child” owner group (29%) viewed their dogs as guardians and playmates for their children.166 The “Pet Lovers” (30%) viewed their dogs as companions.166 The “Pet Dispassionates” (41%) viewed their dogs as serving mainly functional purposes.166

People acquire dogs for a number of reasons and from a number of sources. The most common reason for dog ownership seems to be the presence of children between the ages of 6 and 17.241,250,301,330 The most common sources are breeders, friends, or family members (Table 1-5). When asked why they acquired a specific dog, owners gave a variety of reasons and sometimes more than one. Most (24.0%) chose the dog because of its sex, 17.1% said it was friendly and affectionate, 15.0% cited pity, 14.3% said it was cute, 12.8% liked its color, 12.8% picked it for its size, and 13.7% chose it for certain other physical characteristics or appearance in general.53

TABLE 1-5 Common sources for pet dogs

Source of pet Percentage
Breeder 30
Friend/family 20
Pet store 10
Humane society 9
Newspaper ad 8
Animal shelter 6
Other 17

Data from reference 304.

The human-animal bond does have its ups, downs, and “say that agains.” One owner euthanized her dog and had it stuffed because she was afraid her son’s dog would hurt it!294 Overall, dog owners spend billions of dollars each year on their pets. In Japan, people can actually rent dogs by the hour because owning one is so expensive.256 Typical expenses of ownership are primarily for food and routine health care, but treatment for illnesses and injuries also requires sizable investments. Of dogs presented for emergency treatment at a large city’s teaching hospital, approximately 53% had been hit by a vehicle, and two thirds of those dogs were males. Among owned dogs the number decreases as cities enforce leash laws. Another 10% had been injured in animal interactions, primarily fights with other dogs, and 77% of those dogs were male. Of the 11% admitted because of trauma by a sharp object, two thirds again were male. These dogs overall were significantly younger than those of the typical hospital population, and more of them were male.154,155

The source of the pet has been studied relative to development of future health and behavioral problems. In general, the prevalence of problems does not differ according to source of the dog269; however, of those adopted from a humane society, fewer were returned by owners who had taken their dogs to a veterinarian.146 Even when people in that group did return the dog, it was much later and after a more serious effort to solve problems than was the case for owners who never made the veterinary connection.146

Dogs that are relinquished to shelters end up there for a variety of reasons. Some owners bring their dogs in requesting euthanasia (16% to 27%), usually because of advanced age, illness, or aggression.102,144,202 People relinquishing their dogs are often asked to fill out a questionnaire. Confidential questionnaires reveal significantly more behavior problems in the dogs than would be found with nonconfidential questionnaires or in the general dog-owning public.282,283 Major themes do occur as reasons for surrendering a dog. Lifestyle can make ownership difficult. That can involve everything from working too much to moving (Box 1-1). Certain factors are more apt to predict which dogs will be given up to a shelter. These include an owner who did not participate in an obedience class, lack of veterinary care, sexually intact dogs, a minimum of dog-human shared activities, inappropriate care expectations, at least once weekly episodes of housesoiling, received as a gift or at low cost, and acquired from a shelter.28,234,264,270

Older dogs were less likely to be either surrendered to a shelter in the first place or to be returned to the shelter later.104,205 If the adult dog was rejected, the usual reason given was unacceptable behavior,so it appears that the unsatisfactory placing of dogs is more often due to incompatibility than to disease.15,104,328 In an effort to decrease the number of dogs returned, shelters give advice to new owners, and some even offer postadoption behavior assistance. Studies show that after the first 12 months 14% to 20% of the adopted dogs are no longer in the home. Of those, 10% were returned, euthanized, or rehomed for behavior reasons.15,75,232 Overall, 55.4% of adopters reported behavior problems and 54% of those had moderate to severe problems during the first 6 months. During the next 6 months, the actual number reporting minor behavior problems increased, too.15 Researchers are studying ways to predict which dogs are most likely to develop behavior problems after being placed in a home.316 The subjective evaluations used in the test predicted 75% of the potential problems and were better than the objective opinions of the animal shelter staff, which predicted only one third.316 Studies indicate that the most frequent problems in dogs adopted from humane societies included housesoiling, aggression toward human adults, separation anxiety, aggression toward other dogs, car-related problems, pulling on the leash, and disobedience. Other researchers found that dogs that were acquired from shelters, kept in crates, or at least 6 months of age were also at higher risk of being relinquished.234 In the first month postadoption, 39% to 68% of owners experience a behavior problem with their dog.177,329 Housesoiling occurs in 51% of the homes and destructive behaviors in 28%.177 The aggression and separation anxiety problems were the ones most likely to result in the dog being returned. Returns are frequent enough that states have even attempted to legislate the idea of a warranty for buyers of dogs from pet dealers.244 Retention studies find a better prognosis if the dog and new owners attend a puppy class; the puppy has early handling; the owners use a head halter instead of regular collar; the dog responds to cues; the dog was expensive; there are no children in the home; the dog is female; and the dog sleeps on or near the bed.75,76,234

Although Canis familiaris has become an important part of our society, only 38% of dog owners keep their pet long term.244 Every year millions of dogs are disposed of either by sending them to new homes, surrendering them to animal shelters or pounds, or turning them loose to create strays. The stray is defined as a wandering domestic dog that is given unsupervised freedom to travel, either on a regular or intermittent basis.62,100 The typical reason dogs become strays is because of irresponsible management by dog owners. Evidence indicates the majority of roaming dogs are owned.200 In this country there are probably few truly feral dogs—ones that have reverted to total self-sufficiency—among the large number of stray dogs.100 Of the 10 to 17 million dogs entering shelters, 36% to 59% are strays. About 30% are relinquished to the shelter by their owners, and 13% to 20% enter for other reasons.192,199,201,203,306 Behavior problems are givenas the single most common reason for giving up the animal and thus are responsible for up to 70% of the deaths—more than all infectious diseases combined (Table 1-6).102,129,133,142,162

TABLE 1-6 Reasons for relinquishment of dogs to animal shelters

Reason Frequency
Behavior problems 46.4%
Human housing issues 30.4%-38.8%
Human health/personal issues 27.1%
Request euthanasia 16.0%-17.7%
Human expectations 14.0%-14.6%
Animal housing issues 12.7%
Moving 12.5%
Animal’s health 7.8%-8.2%
Human lifestyle 6.8%-25.4%
Animal characteristics 4.3%-4.5%

Data from references 202, 206, 265, 270.

The exit rate from shelters is revealing. Approximately 19% to 25% of the dogs leaving the shelter are placed in a new home, 15% are reclaimed by the original owner, and 55% to 66% are euthanized.* Of owners who returned their dog to the shelter, 89.7% did so because of an undesirable behavior.328 Shelters are looking for better ways to predict success of dogs adopted. Some provide counseling. Others are looking for behavioral or endocrine tests that are significant.121 The perfect answer seems a long way off, however. The annual euthanasia rate is 10% to 20% for the overall U.S. dog population; 4 to 9 million dogs are killed in U.S. animal shelters and pounds each year.

The causes of dog overpopulation are numerous and complex, and this book is not intended to address all the possibilities. In general terms, though, excess dogs mean more puppies are being born than there are homes available. It has been estimated that 1000 to 2000 puppies are born every hour in this country.24 That means that 70,000 puppies are born each day, compared with 10,000 human babies.306 A single intact bitch can directly and indirectly give rise to 67,000 dogs over a 6-year period.306,307 The lifetime rate of production for a female dog is only slightly lower for spayed females than for intact ones, because 20% of all neutered animals have been allowed to reproduce before being neutered.175,213

If each dog litter averaged five puppies, it would be necessary to terminate 1 to 2 million pregnancies each year to prevent an excess of puppies.213 Although spay/neuter programs have reduced the degree of the overpopulation problem, at least in certain areas, these surgical procedures would be most effective if they occurred before any litters were sired or whelped.142 It has been argued that the cost of surgical neutering is a deterrent, but studies show that to be true only about 5% of the time.303 The irony is that the rate of intact animals increases in direct relationship with the income of the owners.175,273 More than surgery is needed to control dog numbers. It may take education of the next generation of dog owners and regulation of the demand.142,273

Stray dogs pose several problems for society. In addition to the unpleasant aesthetics of mass euthanasias, there are public health and nuisance problems.62,306,307 Stray dogs account for 20% of dog bites to humans.20 They can carry zoonotic diseases, especially rabies. Stray dogs can be traffic hazards, and they can be predators of livestock and wildlife populations, even upsetting the ecologic balance. Finally, roaming dogs foul the environment by tipping over garbage cans and leaving excreta. The estimated 61.6 million dogs in the United States weigh an average of 14.5 kg and produce 40 ml of urine per kilogram of body weight per day.191 The result is 35.73 million liters of urine deposited by dogs each day. These same dogs produce 20.94 million kilograms of feces per day, assuming each dog eliminates 0.34 kg of feces.25 If 144 flies can hatch from each defecation;25 there is a potential for 17.7 billion flies hatching daily.20


There is a strong tendency to think of veterinary behavior in the realm of a treatment, rather than as a list of preventive services that can be offered to dog owners. Preventing problems is even more important than treating them. A practice can offer a number of services that help strengthen the human-animal bond, generate revenue, and do not require large amounts of time,33 and all members of the staff can contribute to the success of the programs. For new pet owners, a clinic team can help with preselection consultations, preventive behavior counseling, puppy socialization classes, community-related events like vaccination fairs or National Pet Week parties, and recommending preventive management products and services.159,223

Preselection Consultations

Preselection consultations can take a number of different forms and can be available to specific clients or to the public as a whole. The most obvious form of these consultations would be to offer appointments for individuals and families who are seriously considering getting a dog and want to be sure they are selecting the right breed for their family and lifestyle. How to make this service known is the biggest challenge, because most puppies are obtained as spur-of-the-moment purchases. Technology is increasing our ability to reach potential pet owners. By putting general information on clinic websites and in client newsletters, writing a column for a local newspaper, or hosting a local radio or television public service show, veterinarians can educate the whole public, not just current clients. Then specific questions can be dealt with during a preselection consultation targeted to a particular family’s concerns. There are a number of subjects that potential dog owners should consider before getting a dog. The most obvious is the breed, although they often have their minds already made up. However, they need to think of things like anticipated yearly costs for dog food, veterinary care, preventive medicines, and grooming; care when the owner is gone; requirements for obedience training, specific elimination areas, and exercise; amount of time available to interact with the dog; and amount of shedding, brushing, and upkeep. Future owners should then put their expectations up against the actual characteristics of the breed or breeds they are considering to see if they fit. Books like The Perfect Puppy114 are nice additions for future dog owners to see. It is important that books recommended are unbiased as to the traits of a breed.

Preventive Behavior Consultations

Preventive behavior counseling begins the first time the new dog enters the clinic. Because most people have one dog at a time,303 many of the basics should be covered. Those basics include what to feed, vaccinations schedules, parasite control information, housetraining and crate training techniques, proper socialization procedures, basic puppy obedience training, and techniques to help the dog successfully view the owners as its leaders. With the large amount of information that needs to be shared, most veterinary practices find that handouts help emphasize points mentioned in the clinic. This information can also be made available through a lending library of books and videos, and with website information. It is also helpful to have a checklist in the record so that information can be spread out over several visits and for consistency between the various staff who may interact with the puppy.

Products to Help Prevent Behavior Problems

Clinics can sell or recommend a wide variety of products that help prevent behavior problems. Of these, most will fall into four categories. Crates and exercise pens keep the dogs confined when owners cannot actually watch them. In addition, once the puppy gets used to these products, it will often spend part of the day in them without coaxing. This makes the crate or pen a nice product for traveling with the dog by taking along the smell of home and the familiar surroundings in a safe environment. The second category of product that helps prevent behavior problems is the head halter. Even 6- to 8-week old puppies can learn correct behavior and simple obedience lessons with the head halter. This is a humane way to hold a puppy’s attention, without putting pressure on the trachea or forcing prongs into the neck. More is discussed on this topic in Chapter 2. Chew toys, the third category, that can dispense food treats give mental stimulation to puppies. In some of these toys, the center is hollowed out so that a food treat like cream cheese or peanut butter can be smeared inside. These keep the puppy busy trying to get all the treat out. When frozen, it takes even longer to get out. Other forms of the hollow-center toy allow the owner to put in kibble, which is then dispensed slowly as the puppy rolls the ball around. A low-cost variation of this would be to put some kibble into an empty 2-liter soda bottle that has been flattened. Other chew toys allow food treats in the crevices of the surface or simply allow the puppy to chew on them. The fourth category included other types of toys that can encourage human-puppy interactions and puppy exercise. Ropes with which the puppy can play tug-of-war with the owner, tennis balls for chasing, and Frisbees to catch are examples. Articles in each of these categories will decrease the opportunity and need for puppies to get into trouble with destructive chewing.

It is also important to ask each time the dog is seen if there are any undesirable behaviors that the owner has noticed. Early identification can prevent long complicated behavior workups later and greatly decrease the time needed to diagnose and treat a particular problem. Some basic questions can be added to the admission form or to routine history-taking, or special behavior questionnaires can be added to preadmission information.224 Approximately two thirds of pet owners feel that their animal is well behaved, but 85% report specific problem behaviors.242 As with similar studies in the past, problems noted tended to be nuisance ones (barking/growling 17%, jumping on people 13%, begging for food 11%, digging 8%, running away 6%, destructive behavior 5%).242


Within the last 30 years, veterinarians have become more comfortable in working up animal behavior problems. Many recognize their obligation in this discipline because of their responsibilities in diagnosing mental conditions in addition to physical ones, appreciating the interconnection between behavior and medical conditions,33 and ability to modify behavior with psychotherapeutic drugs. Much of this need to help dogs with behavior problems reflects the change in society’s major role for the dog, from a working farm animal or backyard inhabitant to a four-legged family member. Approximately 90% of owners surveyed feel that the dog is or is almost a family member.10 An equal number want help managing a pet’s behavior problems.197 An animal is not capable of seeking help alone or describing its problem16; it takes an owner, too. Unfortunately, owners may not know what is normal canine behavior or may have unrealistic expectations of the dog,82 because they have known individual dogs only as family members and have not observed the more universal aspects of dog behaviors. But when a behavior is considered problematic, pet owners agree it can have a big impact on their lives.207

Animals show behaviors based on their reflexes, instincts, and learning, although it is usually a combination of all three.245 Exactly what behavior is shown will depend on external factors, such as environmental stimuli, and internal factors, such as mood, hormones, physical capabilities, previous experience, and sensory capabilities. Even such things as the presence or absence of the owner in the examination room influences the physiology and behavior.229 Usually when an owner is present, heart rates are lower and aggressive behaviors are significantly more common. Animal behavior problems can be related, then, to the biology of the species and to its environment.266 Another aspect is important in veterinary medicine too—the role of pathologic processes.186

A full understanding of animal behavior problems may not be possible until we understand its deepest-level biologic interactions, in descending order from phenotype, neuroanatomy, neurophysiology/neurochemistry, molecular, genotype, or the levels of “causality.”221,226 But behaviorists have come a long way from the days of tranquilizers and euthanasia solutions. Today we recognize many of the complexities that contribute to behavior problems and can proactively work to make things better.

The scope and severity of behavior problems vary greatly. In general, 70% to 75% of dissatisfactions pet owners have with their animals are classified as nuisances rather than serious or dangerous problems.9,10 The most common nuisances are territorial defensive behavior, overprotection of the owner, and excessive vocalization.22 Destructive behaviors, barking, overexcitement, rushing at people or dogs, and jumping on people are also common complaints.* Veterinarians can proactively work to prevent those behaviors from developing. The veterinary behaviorist sees problems that are more serious, with more than half related to aggression,14,72 and visits to a behavioral specialist are often a last-ditch effort by the owner to avoid euthanizing an animal. Euthanasia is the leading cause of death of companion animals, and behavior problems are the leading cause of euthanasia.24 Thus, a behavior problem can be viewed as a “terminal disease” and correcting it as the only way to save the animal’s life.312,322

Aggression, separation anxiety, and housesoiling are the most common behavior problems seen as referral cases.22,72,336 Among breeders of purebred dogs, abnormal temperaments were listed as one of the top 12 important issues.120 More than 35 years ago, the veterinary profession was encouraged to deal with behavior problems by breeders and dog owners, making animal behavior a unique specialty that grew from the public asking for help.45

At least 40% of pet owners take their animal to a veterinarian once or twice a year, and another 32% make three to four visits.1 Just over half the owners say they have discussed a behavior problem with the veterinarian,1,297,335 and 78% would seek help for a developing problem from the veterinarian.303 Of owners who had adopted their dog from an animal shelter, 89% felt it was helpful to have an office visit just to discuss behavior.122 Because early intervention is best, veterinarians should include questions at the yearly visits to screen for the development of problems.126 Questions could cover areas such as presence of unruly behavior, development of signs of aggression (protection of objects or food), housesoiling, and other areas that are commonly associated with behavior problems.

Different researchers have looked at different ways to categorize animal behavior problems.27,132 Perhaps the most descriptive uses three large categories and then subdivides those (Box 1-2).27 It may be helpful to use these broad categories to think of appropriate questions to ask during routine examinations to be sure early signs of behavior problems are not already showing up. Under each of the three categories described in Box 1-2, more is known about the owners most likely to make the complaints. For aggressive dogs, owners who complained were likely not to consider themselves to be the primary caregiver, and the dogs were more likely to have come from pet shops or shelters.28 Dogs that were considered to be disobedient were more likely to be associated with homes having more family members, men, and owners not having previous experience with dogs. The dogs were more likely to be considered purebred and small in size.28 The complexity of responses about the reactive behaviors made it difficult to find common factors among owners.

Obedience training is a common recommendation to make for owners of new dogs, but its relationship to the development of behavior problems is confusing. Some studies suggest it has no relationship with the development of problems,324,325 but others suggest there is.54,138 Agility class attendance is significantly correlated with a reduced number of behavior problems.29 Formal obedience training at home is negatively correlated, perhaps because it is more likely to be associated with punishment rather than rewards.29 It is appropriate to recommend obedience training classes for all dog owners, but there are important things that need to be part of that recommendation. First, and most important, is that the owner be the person working the dog. It should never be sent off for training, even if the owner then comes to work with it for a few days. In the best case, the dog learns how to obey the trainer, but in the worst case bad things happen. Obedience classes are more about training the owner than the dog, so the owner must be part of the lessons. The second factor is that the trainer uses only positive training methods. Telling a dog “no” may stop a behavior, but it does not show the correct or expected response. Shaping a behavior by allowing only the desired outcome and rewarding that outcome is more satisfying to the owner and not stressful for the dog. Heavy leash corrections, shouting, and swatting are not good training techniques. They only vent frustrations.

Behavior problems can present a dilemma for the practitioner, because it can take a long time to adequately work up a case. In some cases, owners may view it as being easier to get rid of the dog than have to work up or treat the problem. For early and simple problems, like a puppy defecating in the house, the time required for the history, diagnosis, and recommendations may be only 15 minutes. But for the adult dog that is showing aggression, the history-taking alone may require 2 hours.

Handling the behavior case adequately can take excessive amounts of time if the situation is not well planned. The shorter and simpler problems may be handled successfully during a routine office call, but for those where more time is needed, the client should be asked to return when an appropriate number of appointment times can be merged. In this way, the veterinarian can devote proper attention to the client. The client, in turn, would be expected to pay for the time required, just as if the veterinarian’s time were involved in performing an ultrasound or surgical procedure.50


For any veterinary case, the first information acquired should be the signalment. Alone it can provide a great deal of information for a behavior case, as it can for a medical case. The age of the dog can be helpful, particularly if the dog is very young or very old. For example, a case of housesoiling by a 3-month-old puppy would be worked up and treated differently than one involving a geriatric patient. Incomplete or improper housetraining is the highest differential for the puppy. Medical problems, including neurologic changes, head the list for the senior. Similar variations according to age can also apply in cases of aggression and other behavior problems. The typical dog presented for a problem is a young adult, around 3 years of age.336

The sex of the dog can vary the list of differentials for a problem. Dominance aggression, intermale aggression, and roaming are much more likely to occur in intact male dogs. Maternal-protective aggression is characteristic of bitches with puppies. More than 50% of dogs presented for behavior problems are intact males.317,321,336 This fact suggests that testosterone may be important in the development of behavior problems. The effects of neutering and the relationship of gender to various problems will be discussed in later chapters.

Breed differences do occur in regard to behavior. Problems with a particular breed, however, may vary according to its popularity, its general location, and over time. National trends do occur, but the fact that a certain breed ranks high on a list of problem dogs may not be significant. Popular breeds (see Table 1-4) will necessarily be represented in higher numbers for any given problem. Only when the rate of a certain problem in that breed is higher than the distribution of the breed in the canine population can it be considered a breed-specific problem. As an example, if excessive barking is considered, 10 owners of Rat Terriers complain and three owners of Beagles complain. It is easy to assume that barking is a bigger problem for Rat Terriers. But, if you knew that there are 100 Rat Terriers (incidence of barking = 10%) and five Beagles (incidence of barking = 40%), you would view the problem differently.

The relative incidence of a specific behavior problem in a breed can vary by location.162 One reason is that sometimes a breed is more popular in one area than in others. Another reason is that a particularly popular sire can spread a genetically based problem, establishing a regional emphasis or occasionally a national one. In a few cases, the breeder chooses to ignore or at least not acknowledge the presence of the problem, allowing it to become well established within a breed.

The incidence of a behavior problem within a breed can change over time. Not too long ago, American Cocker Spaniels, which were extremely popular, became known for various types of aggression.19,162 An interesting contrast can be made with the same breed 50 years ago, when Scott and Fuller chose to breed the Cocker Spaniel as the model for nonaggressiveness in their 13-year behavioral genetics study.280 After a breed loses its popularity, conscientious dog breeders continue to select dogs carefully to mate using more rigorous criteria. The people who were trying to make a fast dollar through indiscriminate breeding selection have moved on to other breeds.

One clue to behavior problems may be the pet’s name. The name of the dog can provide an interesting insight as to its role within the family. Endearing and human names are probably most common when the dog is considered to be a family member. Noncommittal or derogatory names may indicate a neutral or negative relationship. These relationships could be contributing to the development of the problem behavior and will likely determine the willingness of the owner to participate in achieving a successful outcome.

Case History

For most behavior cases, the majority of information will come from the history, so the importance of history-taking cannot be overemphasized. The main goal is to obtain an accurate description of all important aspects of the problem, including relevant information about the pet, the associated humans, and the environment.134,320,323 It is important to not let owners use judgmental descriptions because of their biases.30,167 “The dog is guilty” or “he did it to get even” are examples. Another goal is to identify the immediate consequences of the behavior, understand the development of the behavior, and uncover other related problems that may be present.323 There is evidence linking the owner’s relationship to the dog and the development of behavior problems.209 Dominance aggression has been tied to the anthropomorphic involvement of the owner. Owner anxiety can be related to overexcitement and displacement activities in their dog, but not to the development of phobias.

General background information should be part of an inclusive history for dogs with behavior problems because, in many cases, past events can direct future actions. Specific information would include where they got the dog; how well was it socialized; how much, when, and what type of food/treats it gets; how much and what type of training it has had; other animals in the household; and people in the household and their general schedules. The medicalhistory needs to be included as well. A dog not current on its rabies vaccination that is presented for problems with aggression has some significant liability issues. Those with chronic diseases may require lessons on how to be frequently medicated, may have chronic pain that increases their aggressive tendencies, or may be on medications that limit the choices for psychotherapeutic agents.287 An early puppyhood history may not be available for dogs adopted from animal shelters or rescued, and that can make understanding the depth of the problem difficult. Food and treat information is very useful, because both can be used as rewards during behavior modification sessions. In fact, using different treats during both the history-taking and treatment discussion sessions can provide information about how successful food rewards will be. The goal is to find a treat the dog “would die for” so that very tiny pieces can be offered as rewards. Because eating also satiates hunger, training sessions are best timed to occur before a meal rather than after. Many owners describe their dogs as moderately well trained, but then go on to say it will only respond to “sit” commands, while on leash, about 50% of the time. Dogs that have been obedience trained will have a different incidence of behavior problems than will dogs without training.54 Note, however, that although this information is important historically, no statistical correlation exists between either obedience training or spoiling and the incidence or type of any behavior problem.324,325 Information about other animals and people in the household can be useful for problems involving the social behaviors.

For some practitioners, a history form is useful to be sure that all pertinent data are obtained (see the Appendix).23,134,150 Others prefer an open format wherein owners are invited to discuss their perspectives first, and additional questions by the practitioner elicit missing information. For the recently developed but less serious types of problems, a structured questioning style may be suitable. In a referral setting, however, the owners will usually want to describe the problem as they see it. Having them fill out a form before the visit can provide useful information. It also can be useful to start discussions by asking owners where they got the pet and if they know anything about its parents. Then ask for a description of the pet’s life history up to the present day. It is often necessary to refocus a discussion to get owners to describe the actual behaviors, rather than provide their interpretation of what the animal is doing or why.30 It is also important to clarify vague descriptions. “The dog is destroying the sofa because I don’t spend enough time with him” needs to be divided into information about the sofa (how, when, where, what parts) and what is the human-dog interaction schedule. Other vague descriptors, like “all the time,” “a lot,” “alpha,” and “tried everything,” must be better defined.

The writing of the history for the patient’s record can tax even the fastest note taker, but this technique gathers a lot of information that might otherwise be missed, assures the owner of the veterinarian’s interest in the pet, and helps the owner focus on particular events when more specific questioning follows. Newer techniques can include making a video record of the session. Questions during the owner’s narrative can be asked, but for clarification of a point or to redirect the narrative as the owner continues. After the owner has completed his or her segment, it is appropriate to ask for more details about specific episodes.320 Some practitioners choose to ask about the latest episode first.68,320 Others want the descriptions to occur in the order of occurrence. It should also be noted that different owners may have different perspectives about the problem or memories of the events. For this reason, it can be helpful to have all the people involved present for this visit, if possible.68

The six general questions to be answered in any history-taking session involve what, how, where, when (two different “when” questions), and who. We will look at each of these questions next.18,23 Based on the answers to these questions, many more-specific questions can help focus on the total scope of the problem.

< div class='tao-gold-member'>

Jul 24, 2016 | Posted by in SMALL ANIMAL | Comments Off on Introduction to Canine Behavior
Premium Wordpress Themes by UFO Themes