6.1 Introduction

In order to critically assess the relative importance of pet owners’ dissatisfaction with their dogs’ behavior in relinquishment of dogs to shelters, it is first worth asking, “How often are dogs relinquished overall? Are dogs being widely discarded by so‐called irresponsible owners, or is the human‐animal bond relatively stable?” The short answer is, we don’t know the answer to this question with any degree of precision, as there is no national shelter census or a single complete list from which a census could be conducted. Besides the lack of a reliable list, the definition of what constitutes an entity that might receive relinquished dogs is also hard to pin down, given the proliferation of small rescue organizations and groups lacking a physical structure that may accept relinquished dogs and keep them in temporary foster homes or otherwise act as intermediaries. Finally, the total size of the US owned dog population is also unknown, with estimates varying over time and by the source of the data. In 2016, the two largest‐scale estimates ranged from 77.8 to 89.7 million dogs in the United States (Burns 2015; American Pet Products Association 2020). And, with the move to online survey platforms (as opposed to surveys by regular mail), the discrepancy seems to be widening (Downing and Lau 2014). Nevertheless, it is still worth asking this question, with the understanding that the answer is at best an extrapolation that itself is based on estimates of unknown reliability, to try to put the problem in some perspective.

A 2019 study used a mark‐capture method from different lists of shelters to try to enumerate the number of shelters in the United States, with the goal of making projections about the numbers of dogs received; they estimated 5.5 million dogs in the United States annually (Woodruff and Smith 2019). Depending on what figure from the estimates mentioned above is used for the total dog population, this would be between 6.1 and 7.1%. This is comparable to that reported by a modeling study in 1991, which estimated that about 7.6% of the US dog population entered shelters annually. The estimate of 7.1% is used here to be conservative (worst case) because it is based on the smaller of the two dog population estimates. Owner relinquishment accounts for an unknown proportion of dogs entering shelters, but some sources have put it around 28% of intakes, or about 1.1% of the total dog population (American Society for the Prevention of Cruelty to Animals [ASPCA] 2020; Zawistowski et al. 1998). If the reality is close to these estimates, people elect to end their relationships with their dogs at an annual rate roughly similar to that of divorcing their spouses, the annual rate of which is about 2% (Amato 2010) (which we use here as more analogous than the commonly alluded to 50% lifetime divorce rate). We can reasonably assume that most of the human‐human break‐ups spring from behavioral incompatibilities. We don’t know, however, what proportion of the sundered human‐canine relationships are due not to incompatibility but rather to circumstances making it impractical for the person to continue to live with and care for a companion animal. Nevertheless, despite the overall stability of human‐dog relationships, the consequences of those bonds that do break are encountered daily by those working in shelters. In this chapter, we will explore the state of the literature on canine behavior that pet owners report as having led to relinquishment and, to the extent possible, on interventions that have been suggested and attempted in an effort to prevent broken relationships and/or facilitate lasting rehoming.

6.2 A Brief History of Relinquishment Data

Understanding the impact of dog behavior on relinquishment can be informed by how shelters and researchers have approached the problem over the years. To the best of our knowledge, the issue of relinquished dogs and stray dogs and the subsequent euthanasia of healthy animals in shelters (so‐called “pet overpopulation”) was first discussed in the modern scientific literature in the early to mid 1970s—nearly half a century ago (Anonymous 1971; Schneider 1975). Growing concern about the problem led to two national conferences in 1974 and 1976, which brought numerous groups of stakeholders together for a discussion about causes and solutions (Anonymous 1974, 1976). The findings of those meetings indicated that a broad range of solutions needed to be explored, including research into methods of non‐surgical sterilization, more effective animal control policies, increased dog license fees to support the latter, sterilization of any intact dog before it was released from a shelter, and efforts to promote more responsible ownership.

A decade later, in 1985, the American Humane Association (AHA), a national advocacy group, began to systematically collect information from animal care and control agencies in the United States to attempt to quantify the problem nationwide; they eventually published a very influential report (Nassar et al. 1992). Those data, collected from more than 100 agencies, indicated that 42.2% of incoming dogs were relinquished (as opposed to being stray), and 62.8% of all dogs were euthanized. Data collected by ASPCA animal control services in New York City provided an even grimmer perspective. Although canine intake rates declined nearly fourfold between 1974 and 1994 (81,627 vs. 23,077 dogs, respectively), the proportion euthanized remained high and showed only a small decline over 20 years (82.7% vs. 74.0%, respectively) (Zawistowski et al. 1998). Nationally, a decade after the AHA study was published, a different convenience sample of 186 shelters suggested some improvement (52% of all dogs were euthanized), but regardless, 39% of dogs were considered unadoptable (Wenstrup and Dowidchuk 1999). The decisions about adoptability that occurred in tandem with such high euthanasia rates may appear almost unfathomable today, when an increasing number of communities in many parts of the United States report saving 85% or more of incoming dogs. But to some extent, those dark days continue to frame our present attitudes toward relinquishment.

In those early days, with the acknowledgment that data might help better characterize the problem of unwanted pets, some shelters also collected the reasons for relinquishment (along with other information about the dogs) at the time of surrender. For example, Rowan and Williams (1987) reported on a study by the Humane Society in Salem, Oregon, which surveyed 1,680 people relinquishing a dog to a shelter in that county. The leading reason was too many pets (27%), followed by other (22%), behavior (20%), old age (19%), and lifestyle changes (12%) (Rowan and Williams 1987). Arkow (1985) reported that in a 1981 survey conducted by the National Animal Control Association (NACA) of 918 relinquishers to 13 shelters distributed across 8 states, behavior was mentioned by 26.4%. Another study in the 1990s published in a major veterinary journal reported behavior as a major reason (30%) for relinquishment; however, it relied upon data from questionnaires distributed to relinquishing owners by shelter personnel and student interns only as time allowed (Miller et al. 1996). Given the non‐random nature of the solicitations and low response rate (56 returned questionnaires from 1,406 dog relinquishers), those results were not generalizable, but they did serve to further educate readers (especially veterinarians) about important aspects of the relinquishment problem and reinforced the notion that behavior was an important contributor.

Despite the good intentions, enumerating reasons for relinquishment probably did little to reduce either intake or euthanasia. The list of stated reasons included all manner of owner lifestyle and dog behavioral factors (e.g., not being trained, illness, moving, receiving the pet as a gift, unwanted barking, housesoiling, allergies in the family, pulling on a leash, family member disliking the pet, new baby, having no time for the pet due to working, destructive behavior, being unable to afford veterinary care, incompatibility with other pets, and many others). In shelter lore, this grew to include more pejorative and fanciful things such as the pet “not matching the owner’s furniture.” The effect of these well‐meaning efforts was largely counterproductive in that it led to shelter staff demonizing people relinquishing a pet, despite any mitigating personal circumstances. Given the high degree of emotional stress and guilt experienced by shelter workers, whose jobs entailed euthanizing large numbers of healthy animals (Arkow 1985; Arluke 1991), it is not surprising that this mindset often carried over into the adoption process. Consequently, to try to ensure permanent homes for adopted pets, these reasons for relinquishment tended to be morphed into factors to be wary of when people were seeking to adopt a pet. This concern was reflected in ever‐more‐restrictive adoption policies, which made the very people shelters needed the most (i.e., those wanting to adopt a pet) the foil for the perceived shortcomings of those relinquishing dogs (Balcom and Arluke 2001).

Contemporaneously with the initial reports about pet overpopulation in the veterinary literature in the 1970s, and prior to the data‐gathering efforts of the AHA in the mid‐1980s, the Humane Society of the United States (HSUS), another national advocacy group, introduced and promoted their comprehensive “LES (Legislation, Education, Sterilization) is More” strategy to reduce the number of companion animals entering shelters (Rowan and Williams 1987). Although there were reports of shelter populations decreasing somewhat, it was clear to those in the shelter community that progress on euthanasia was insufficient.

The discussion about the importance of data for crafting potential solutions was reinvigorated in the late 1980s when Carol Moulton, an executive with the American Humane Association, approached veterinary theriogenologist Patricia Olson to discuss what was going on in US shelters. Coincidentally, in her teaching role, Dr. Olson encountered a veterinary student who challenged her to consider why the veterinary community overall had manifested such a tepid response to a situation that could legitimately be considered a crisis, as it represented the largest single cause of dog mortality in the United States.

Ultimately, those conversations led to two important developments, both spearheaded by Dr. Olson, veterinary epidemiologist M. D. Salman, and Ms. Moulton. One was a special edition of the Journal of the American Veterinary Medical Association (JAVMA) devoted for the first and only time to the topic of pet overpopulation (Vol. 198, No. 7, April 1, 1991; see Olson et al. 1991). This series of articles brought a detailed perspective on various aspects of pet overpopulation to the attention of the veterinary profession. The second development was a series of workshops (in June and November of 1992 and in August of 1993) also spearheaded by Dr. Olson, Dr. Salman, and Ms. Moulton, where scientists and other current or potential stakeholders gathered to further characterize the pet overpopulation problem and brainstorm future actions. One very important outcome of the workshops was the formation of the interdisciplinary National Council for Pet Population Study and Policy (NCPPSP), whose original members were the American Animal Hospital Association (AAHA), AHA, American Kennel Club (AKC), ASPCA, Association for Veterinary Epidemiology and Preventive Medicine, American Veterinary Medical Association (AVMA), Cat Fanciers Association (CFA), HSUS, Massachusetts Society for the Prevention of Cruelty to Animals (MSPCA), and NACA. The NCPPSP later designed and implemented an epidemiological study to better characterize the problem in the United States and to determine which of the oft‐cited “reasons” for relinquishment was actually a risk factor and thus meriting caution and/or intervention (New et al. 2000). To draw any connections between the expression of particular behaviors in dogs and elevated relinquishment risk, we must first know the prevalence of the behavior of interest in the general pet dog population not surrendered or otherwise rehomed. This is of critical importance, because if the trait of interest (let’s say unwanted barking) occurs as commonly in dogs living successfully in homes as in dogs being relinquished, there is no basis to conclude that it represents an elevated risk, even though it may well be a stated reason. As will be discussed later, determining the prevalence of various potential risk factors in the owned population is not easy, and attempts to do this have met with only limited success.

Nevertheless, the practical implications and importance of distinguishing between a reason and a risk factor were highlighted by one finding in particular from the NCPPSP study—that receiving a pet as a gift, long believed to be particularly ill advised, was not a risk factor for relinquishment, as only 2.9% of relinquishers cited this reason compared with 4.5% of dog‐owning households reporting having gotten a dog as a gift (New et al. 2000). This startled shelters, because based on that erroneous belief, some had gone so far as to close or place a moratorium on adoptions around the holiday season, thus denying many pets potential homes.

6.3 Lessons Learned from Risk Factor Studies

Three studies have formally assessed risk and ultimately evaluated some of the more common reasons for relinquishment (Patronek et al. 1996; New et al. 2000; Dolan et al. 2015). However, concerns remain. For example, Lambert et al. (2015) found methodological inconsistencies among studies reporting reasons for relinquishment, including the frequent lack of definition of a particular behavior itself and of behavior problems as a group, the inconsistency and frequent lack of reporting of the number of reasons relinquishers were instructed/allowed to report, and inconsistency in whether respondents were given a list to respond to or given open‐ended questions. They note that when questioning owners, a prompt to provide “the reason” for relinquishment is likely to yield a very different response than one that asks the respondent to “check all that apply.” For example, when “moving” is given as a reason, behavioral reasons are often also cited, leaving the relationship among these issues a matter of guesswork.

As indicated by the above, when given the opportunity, owners may cite more than one reason. Indeed, the NCPPSP provided a total of 71 different reasons for relinquishment for owners to select, with up to 5 reasons allowed per animal. Although behavioral issues were common (cited by up to 46.4% of owners), human health and personal issues, including moving, were cited even more frequently (cited by up to 69.1%) (Salman et al. 1998), reinforcing the fact that relinquishment is often complex (Salman et al. 1998; Scarlett et al. 1999; New et al. 2000). Another study also supported the role of behavior (48% of relinquishers indicated behavior was an important factor), but that study emphasized that owner attachment to the pet was also important (Kwan and Bain 2013). Using factor analysis, Shore et al. (2008) reported that objectionable behaviors clustered into groups they labeled destructiveness, unsociability, and timidity. There were moderate correlations between the factors, suggesting that multiple behavior issues in the same dog were not uncommon. Secondly, although some dogs may indeed be relinquished solely because of behavior problems, data suggest the role of behavior may also vary by geographic location and socioeconomic status. For example, a study at a single shelter in an underprivileged area of Los Angeles, California, reported that economic issues were the overriding factor, something that the authors recognized was potentially resolvable with assistance (Dolan et al. 2015). The relative importance of various reasons may also vary over time, reflecting other social changes, such as changing compliance with recommendations to sterilize a dog and/or the increasing cost of veterinary care.

Zeroing in on the role of behavior with surveys or more sophisticated epidemiological studies is further complicated because studies may lump all behaviors into a single category without distinguishing among different types of behavior, and/or they do not consistently capture the severity and/or frequency of the behavior under investigation, and even if they do, may not measure them in the same way. For example, New et al. (2000) asked owners to estimate whether a behavior occurred “always or almost always,” “most of the time,” “some of the time,” or “rarely/never,” whereas Patronek et al. (1996) asked owners to indicate whether a behavior occurred “daily, weekly,” “≤2 times per month,” or “never,” making it difficult to compare the resulting findings with the NCPPSP study. Neither study captured information about perceived severity or impact of the behavior.

As discussed more fully later, even if the same label for behavior is used in a study, there may be inconsistency in how that behavior was actually defined, with aggression being one particularly problematic term. The choice of controls for comparison also differed among the three epidemiological studies. New et al. (2000) used a national mail sample from members of a consumer survey panel that included owners from across the United States (not just the communities where the participating shelters were located). By comparison, Patronek et al. (1996) interviewed local controls by telephone, whereas Dolan et al. (2015) conducted in‐person interviews with owners bringing their pet to a low cost spay‐neuter clinic for surgery.

6.4 The Importance of Definitions

As mentioned in Section 6.3, when trying to appreciate the role of a particular behavior in relinquishment, it is important that everyone have a reasonably shared understanding of what actions constitute the behavior in question. Thus, the problem with definitions goes beyond the issues with the scientifically imprecise term “behavior” itself, to the consistent lack of definitions of the various descriptors of specific problematic behaviors relinquishers are asked to report on. For example, it is commonly held that “aggression”—which can include, depending on the study, various warning and biting behaviors and/or simply the undefined label itself—is a leading behavioral reason for relinquishment. Unfortunately, there is nothing close to an accepted definition of “aggression,” even on the part of behavior professionals, much less the owners being asked to describe their dog’s behavior or the ultimate readers of the study. In common usage, the term is so pejorative as to be unlikely to elicit a description of an observable behavior (e.g., bite, snarl, snap, freeze, bark, etc.) from a pet owner but instead is more likely to prompt an inference about the dog’s state of mind.

These issues with definitions may also explain inconsistency among and within studies. For example, in the study by Patronek et al. (1996), the odds ratios (OR) for relinquishment with “daily vs. never” aggression to people or toward other animals represented approximately a doubling or tripling in risk of relinquishment (OR = 2.14 and OR = 2.91, respectively), compared to a more than fivefold increase in risk with daily unwanted chewing (OR = 5.59) and a more than eightfold increase in risk with daily inappropriate elimination (OR = 8.52), both of which are more easily defined than aggression. By comparison, in the NCPPSP study (New et al. 2000), when asked about frequency of “growling/hissing/snapping, or attempting to bite,” compared to dogs who rarely or never did this, dogs who did it “Most of the time” were only at a somewhat increased risk of relinquishment (OR = 1.5, 95% confidence interval [CI] = 1.0–2.1), whereas paradoxically, dogs reported as doing this “Always/Most always” were not at increased risk (OR = 0.8, 95% CI = 0.4–1.5). In the same study, 246/2,020 (11.6%) of relinquished dogs had bitten a person versus 154/3,418 (4.5%) of owned dogs (OR = 2.9, 95% CI = 2.4–3.6). However, in a different sample recruited from owned dogs presented for veterinary care, Guy et al. (2001) found that about 10% had bitten a familiar person.

No studies to our knowledge consistently used descriptions of specific and concrete behaviors in their questionnaires for people relinquishing dogs to a shelter. Segurson et al. (2005), for example, employed an abbreviated version of a widely used, but incompletely validated, pet owner questionnaire. That instrument uses some descriptions of specific and concrete behaviors (e.g., “bark,” “growl,” “snap”) in their characterizations of “aggressive” behaviors but then resorts to asking respondents for subjective interpretations of the dog’s emotional state (e.g., “no visible signs of fear or anxiety,” “mild anxiety,” “moderate fear/anxiety,” etc.) in the section that attempts to diagnose fear responses. Other surveys of relinquishers rely either on owners’ interpretations of the meaning of “yes/no” questions, which can imply limitations on appropriate answers even when open‐ended prompts are also included. Open‐ended responses (often prompted in interview‐style surveys) require both accurate on‐the‐spot interpretation and later categorization that actually matches the interviewee’s intent. Again, however, it is difficult to say how much the reported behaviors reflect subjective impressions rather than objectively definable behaviors. Even a novice behavior consultant will have learned that a seemingly concrete term like “bite” can mean anything from teething, puppy mouthing, an accidental nip during play with a toy, to a protracted hold. These still say nothing about the amount of pressure applied, which is a factor in determining whether an injury occurs as well as its severity, nor do they provide any information about context or possible motivation. For example, Guy et al. (2001), in a very large study of dogs being presented for veterinary care in facilities across Canada, found that 41% were reported by their owners to have expressed warning or biting behavior toward a familiar person, and 15.6% had actually bitten. Given that Guy et al. did not include warning and biting behavior toward unfamiliar people, and that findings exist suggesting that directing such behaviors toward familiars and unfamiliars does not typically co‐occur in the same dog (Casey et al. 2014), we can hypothesize with some confidence that the percentage of owned dogs expressing these behaviors is considerably higher. Moreover, none of the dogs in Guy et al. (2001) had been relinquished to a shelter, so it is impossible to know the extent to which their behaviors were considered by the owners to be problematic at all. A more recent internet convenience sample in Finland found owners of pedigreed dogs reporting that 45% of dogs had expressed behaviors categorized as aggressive (barking, growling, snapping, biting) toward unfamiliar and familiar people, not including family members (Tiira et al. 2016). Actual bites to family members were reported at 8.2%. Again, these were not dogs being relinquished to shelters.

Dinwoodie et al. (2019) surveyed people from a self‐selected internet sample and asked about biting specifically. They reported that 4.5% of dogs had bitten a person, and roughly two‐thirds of those bites had broken skin. The survey did not ask about whether any medically treated injuries resulted. Such an injury might, of course, comprise a significant relinquishment risk. But even using our smaller dog population estimate mentioned in Section 6.1, fewer than one‐half of one percent of dogs annually inflict a bite for which the victim seeks medical assessment. Of these, only 2.7% were severe enough to require hospitalization, a sample too small to be considered reliable (Centers for Disease Control and Prevention 2019). Nevertheless, no relinquishment study to our knowledge has examined the injury severity question.

All this renders the reason “aggression” (as well as many other descriptors that may or may not capture similar behaviors) nearly useless scientifically, absent the nuance that can only be acquired through detailed deconstruction of an event. This makes it less surprising that relinquishing owners’ reports of their dog’s behavior problems have been found to have poor predictive value with regard to subsequent guardians’ accounts of the same dogs’ behavior in their new homes (Stephen and Ledger 2007), leaving open the question of whether the difference is due to dogs not consistently expressing the behavior in varying environments and husbandry practices or to varying perceptions and definitions of behavior by owners.

6.5 The Challenge of Determining How and When Behaviors May Threaten Human‐Canine Bonds

The issue of whether dog behaviors, even when designated as “problems,” actually threaten human‐canine relationships becomes even more critical when one considers that multiple studies have found high percentages of dog owners who have not relinquished their pets report living with behaviors they consider problematic. If dogs living successfully in homes are expressing similarly labeled behaviors to relinquished dogs, then it seems reasonable to look to the owner’s perceptions and expectations as explanation for the threat to the relationship, rather than just to canine behavior itself. Indeed, as far back as the 1980s in the United States, behavior researchers found that as many as 40% of owners reported unwelcome behaviors without considering them to be relationship threatening (Voith et al. 1992). More recently, an internet survey of subscribers to a pet supply company in Japan found no less than 86% of respondents reporting at least one behavior their dogs expressed that they found troublesome, with barking and pica causing the most concern for owners (Yamada et al. 2019). Dinwoodie et al. (2019) surveyed an online, global convenience sample of 2,480 dog owners recruited using a variety of sources, including social media, TV, and radio, to assess a variety of behavior problem metrics. After excluding those respondents who said that their pet’s behavior problems were their reason for completing the survey, the authors found that among responders completing the survey for another reason, most (85%) still reported their dogs had behavior problems. Fear and anxiety were the most common problems and showed significant overlap with aggression. At this point, it is unclear whether relationship‐breaking behaviors in owned dogs occur at a different frequency or level of severity or whether relinquishing owners have a lower tolerance for or ability to manage them.

The issue of owners citing multiple reasons (when allowed) as described earlier suggests that relinquishment is often a complex decision, something more explicitly affirmed by qualitative studies (Balcom and Arluke 2001

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