in social communication and pheromone assessment (Adams and Wiekamp 1984). Distinct from the main olfactory epithelium, the VNO is located below the nasal cavity, and its receptors also carry information to the olfactory bulb. This chemosensory organ is ordinarily viewed as responsible for pheromone detection in urine, feces, and saliva as well as glands in the anogenital region, mouth, and face. Using odor cues, dogs can discriminate conspecifics as well as identify something unique about themselves compared to other odors (Bekoff 2001; Horowitz 2017). Horowitz (2020) also found that dogs can distinguish their owner’s odor from that of a stranger. Additionally, dogs appear to take note of human odors associated with fear or happiness (D’Aniello et al. 2018).
Dog social encounters are marked by close olfactory inspection, particularly of the head and anogenital area. Body sniffing is common between dogs when they first meet, either on or off leash (Bradshaw and Lea 1992; Westgarth et al. 2010). Initial encounters are typically short, and dogs often explore the environment instead of furthering the interaction, a phenomenon that has been described in free‐ranging dogs and at dog parks (Howse et al. 2018; Ward 2020). In the samples studied, often self‐selected groups at dog parks or open spaces, post‐greeting aggression and even play were relatively rare. Direct encounters between dogs at shelters may be rare, and dogs tend to be on leash (or in kennels), and interactions might be thwarted due to shelter operational protocols. Without the opportunity for direct olfactory investigation, these dogs might experience tension, restraint, or frustration upon seeing other dogs, which could affect subsequent intraspecific interactions.
Olfaction also plays a role in dog interactions with people. For example, the anogential and thigh areas of unfamiliar people are investigated more than those areas of the owner, who is already known to the dog (Filiatre et al. 1991). Unfortunately, humans may thwart olfactory investigation, for example, reaching out or descending a hand on top of a dog’s head, instead of allowing the dog to approach and sniff.
Communication via scents is common by depositing secretions and excretions in the environment. Urination is more than waste expulsion; canids gain valuable social information by attending to these splatterings and pay considerable attention to unfamiliar urine (Lisberg and Snowdon 2009). Scent marking can even be performed differently between dogs of the same sex. Small male dogs have been found to mark higher than they are tall; hypotheses for why they do this have not yet been tested (McGuire et al. 2018). Depending on the surface, scent marks could be visual, olfactory, or even, possibly, auditory (Bekoff 1979).
Olfaction is essential to the dog umwelt, or perceptual world (Horowitz 2009b). Providing dogs with opportunities to actively use their noses—for instance, through nosework—can enhance well‐being. Duranton and Horowitz (2019) found that dogs who participated in nosework for two weeks displayed a more optimistic outlook—measured via cognitive bias test—when compared to dogs who participated in heelwork practice. Engaging in sniffing is good for dogs. Humans’ jobs, as their observers and caretakers, is to know that the dog's nose is constantly engaged, to actively provide them with smelling opportunities, and to not discourage them from using their nose in species‐typical ways.
1.5 Complex Behaviors
Behavioral and physiological parameters help assess canine negative and positive affective states. This section focuses on the former, particularly multi‐modal behavior patterns relevant for dog welfare and well‐being both in and out of the shelter.
Despite the good intentions of people and organizations, shelters are awash in stressors. While adaptive in that the stress response and fear prompt physiological and behavioral changes when something is perceived as frightening or indicative of danger (Boissy 1995), stressors (or the perception of such) can also be unrelenting. Persistent or chronic stress challenge short‐ and long‐term well‐being, and studies identify relationships between stress and a decrease in immune function (Glaser and Kiecolt‐Glaser 2005), a decrease in lifespan (Dreschel 2010), and an increase in arousal, fear, and aggression (Dreschel and Granger 2005).
Stress‐related behaviors summarized by Mariti et al. (2012) overlap with fear, anxiety, conflict, or appeasement. Snout/lip licking, yawning, whining, and panting are oral behaviors. Dogs may avoid eye contact, look away, or have their ears back. Trembling and body shaking are often indicators of high psychological stress and could be accompanied by a lowered body posture, cowering, and hiding. Dogs paw‐lift in both social and asocial contexts, when alone and distressed, and also during social (inter‐ or intraspecific) conflict, confusion, or fear (e.g., of punishment). Periods of continual barking, whining, and howling suggest frustration or distress, although vocalization could also be socially mediated and serve other functions. Dogs with either low or high activity should be monitored for additional behaviors of anxiety. Dogs may also be excessive or under‐consumers of food and water. Individual differences are common, and behaviors presented can be affected by stressor type, such as social or non‐social context, as well as severity and duration. Overt indicators such as trembling and whining may be more recognizable than subtle behaviors, for example, turning away, yawning, and licking (Mariti et al. 2012).
Stress‐related, fear, and aggressive behaviors can be connected. If pressed, dogs exhibiting fearful postures may freeze, continue to withdraw, flip onto their backs in a display of passive submission, or display a defensive attack. Defensive aggression differs from an offensive display in that the defensive dog’s posture is pulled back, with ears back and tail tucked. Ultimately, the dog is attempting to increase distance from the fear‐inducing stimulus but may come forward to bite prior to retreating. Alternatively, dogs displaying more offensive aggression may lean forward with a fixed stare, raised tail, and stiff or frozen body and present a “hard eye” with a closed mouth or offensive pucker, in a sense making themselves appear bigger.
Dog bites to people can occur in any context where dogs and humans overlap, such as situations where resources are present (like food or toys), on private property, in play, and during seemingly “normal” interactions (like petting or being in a dog’s presence), as well as in occupational contexts such as those involving entering the dog’s home environment, or veterinary or shelter work, among others. People are often familiar with the dog who bit them, and young children, who are often bitten on the face or upper body, constitute a large number of those bitten (Reisner et al. 2011). Breed, neuter status, age, and sex are often explored as contributory factors to bites, yet relationships between these factors and bites are not always clear and should be interpreted cautiously (Newman et al. 2017). Instead, the conditions under which a dog is reared, kept, or managed—such as lacking socialization experience or being left unsupervised with children—could increase bite risk. A UK survey found that numerous factors influence the presence of aggressive displays, and a dog who shows aggressive behavior in one context, such as outside the home, might not do so in another context, such as in the home (Casey et al. 2014). Dogs cannot be characterized as universally “safe” or universally “dangerous,” as people might like.
Human behavior prior to a bite is an important piece of the puzzle. Owczarczak‐Garstecka et al. (2018) analyzed dozens of bites from YouTube videos and found that human contact‐related behaviors increased approximately 20 seconds prior to the bite. Petting, restraining, and “standing over” the dog were observed frequently. On the dog’s part, behaviors such as low body position, head turning, and panting, as well as staring and stiffening, increased approximately 30 seconds prior to the bite. These findings are valuable: they suggest that bites are not “coming out of nowhere,” highlight the value of the “ladder of aggression” theory (Shepherd 2009), and suggest that people could notice dog signals and respond in turn. The ladder of aggression suggests that dog responses to threatening or stressful stimuli (social, environmental, or other) tend to be graded. A dog is apt to yawn, lick, look away, or move away before growling, snapping, or biting. These cues, proceeding from subtle to overt, aim to increase distance, and while not all dogs will exhibit all signals, the ladder concept provides a general or average progression. These subtle behaviors demand attention because if ignored, dogs might learn that these behaviors are ineffectual and develop a lower threshold for more overt distance‐increasing indicators, like growling, barking, baring teeth, lunging, and even biting.
Abnormal