Mind the Muzzle: Using Facial Expression as a Correlate of Stress Level in Domestic Canines

ABSTRACT

The domestic dog is a ubiquitous species having frequent encounters with humans; in the U.S. over 4 million of these result in a dog bite. These injuries might be reduced by improving human-canine communication. Canine responses to alterations of human facial expressions were recorded. The dogs' responses to the presence of a human experimenter were subsequently analyzed against survey data collected by the shelter on the individual animals (time in shelter, age, sex, reason surrendered). Staring at a dog induced more arousal than other human facial expressions (i.e., Averting Eyes, Grinning, or Yawning). Dogs in the shelter the longest looked towards a human the least compared to dogs there 3-6 weeks. Strays and dogs surrendered because the owners did not want them Tongue Flicked, a behavior associated with stress, more than dogs surrendered by owners that could not keep them. Dogs with high tail heights demonstrated Mouth Open, a behavior associated with relaxation, the most, while low tail height dogs displayed this characteristic the least and medium tail height dogs fell in-between. Identifying these and other variables associated with signs of stress in dogs could allow for reduction of aggressive encounters.

INTRODUCTION

The domestic dog, Canis lupus familiaris, is a species firmly entrenched in human daily life. It was estimated that in 2002, 62 million dogs existed in the United States (Yin and McCowan, 2004). Members of the family Canis are present everywhere except Antarctica and some oceanic islands (Clutton-Brock, 1995). Their ubiquitous nature ensures that human encounters with this species are essentially inevitable.

Unfortunately, the close proximity, in which dogs and humans live, carries with it some considerable problems. Over 4 million people annually suffer from a dog bite in the United States. Of these, 757,000 are treated medically and an estimated 3.73 million do not receive medical attention (Weiss, Friedman & Coben, 1998). Oftentimes the victims of these attacks recall them as being unprovoked and initiated without warning. This implies that either dogs are highly unpredictable, or that there was a misinterpretation of the events, on the part of the human and the part of the dog, that led to the incident. We suggest that these encounters can be prevented, in part, by identifying signs of stress in dogs and by attempting to change the dogs' reactions through human signaling.

The potential for miscommunication may arise largely from the phylogenetic enculturation that has occurred between humans and dogs since the time of the dog's domestication which, as suggested by some, might coincide with the evolutionary split between the dog and the wolf (Hare et al., 2002). Archaeological evidence of dog's historic and prehistoric relationship with humans is abundant (Nobis, 1979; Davis and Valla, 1978; Turnbull and Reed, 1974; Budiansky, 2000) and recent mitochondrial DNA evidence, used to determine that the wolf is the predecessor of today's domestic dog, points to an evolutionary split as early as 135,000 years ago (Wayne, 1986).

The extensive historical interactions might contribute to the development of a common system of communication. This is suggested by an experiment done with foxes that were bred over 45 years and selected for tameness. These foxes appeared to be more responsive to human signaling than foxes from a control group (Hare et al. 2005) though the control group displayed a high degree of fear which might have contributed to the lack of responsiveness. This experiment was conducted with the knowledge that both humans and foxes rely on understanding and responding to visual cues to communicate.

Humans use visual signals as a foundation bedrock of social communication. Dogs, as descendents of wolves, and in the same family as the fox, use visual signals as well (McConnell, 2002; McConnell, 2005). If foxes can become more responsive within 45 years it is reasonable to assume that dogs may be uniquely in-tune with human signaling due to their historic and prehistoric interactions with people. Congruently, dogs are more attached to humans than their wolf counterparts that have not had these extensive interactions (Topal. 2005). Multiple studies have also demonstrated the dog's high degree of sensitivity to signaling from humans (Kubinyi et al., 2003; Soproni et al., 2001; Call et al., 2003; Mikloski et al., 2005; Hare et al., 2002; Hare & Tomasello, 1999; Pongracz et al. 2002; Soproni et al. 2002) to the extent that they sometimes perform better in certain tasks than do human's close relative, the chimpanzee (Soproni et al., 2001; Hare et al., 2002). It has also been suggested that many animal species have the same outward physical expressions for internal emotions, humans and dogs included (Darwin 1998).

This potential for viable communication is furthered by both humans' and dogs' extensive use of the face in communication between conspecifics. Humans and members of the family Canidae use facial expression as a powerful means of non-verbal signaling (Bradshaw and Nott, 1995). Aggression between dogs is kept at a minimum partly through the utilization of the face to convey messages in intra-species communication, indicating mood and intent of the signaler (Fox, 1971; Schenkel, 1967). Similarly, humans utilize facial expression in play signaling to conspecifics (van Hooff, 1972). It might therefore be feasible to use the face in human-dog communication, both for sending and for receiving signals related to stress and stress reduction in the hopes that one might limit the number of injurious encounters between the two species.

Stress is shown to be a predictor of aggression in many social species. The dwarf mongoose (Helogale parvula) and African wild dog (Lycaon pictus) both show the highest number of self-initiated aggressive encounters and in dominant individuals heightened levels of glucocorticoid, a hormone used to measure stress level (Creel, 2005; Creel et al., 1996). In another study, in comparison to dogs that had no history of aggression, dogs that have been shown to be aggressive in the past had elevated levels of neurophysiologically-active compounds which are indicators of stress (Juhr 2005).

Behavioral indicators of stress increase congruently with displays of inter-dog aggression when dogs normally housed individually are shifted to group housing (Beerda et al 1999). In order to prevent aggression, one should then be aware of signs of stress in the dog and attempt to reduce the level of stress.

In our experiment, we looked at dog facial expressions as an indicator of stress. Both yawning and tongue flicking are demonstrated more by dogs in a state of stress than dogs that are in an otherwise relaxed state (Coren, 2001). A forward ear position is associated with attention state (De Palma et al., 2005), confidence, and aggression, whereas a backward ear position is often associated with submission and/or fear (Coren, 2001; Abrantes, 2005) and can also be an indicator of stress (Schilder and van der Borg 2004).

In this experiment, we attempted to use these facial signals to monitor the stress level of dogs. We also attempted to alter these stress responses by altering the facial expression of the experimenter. We hypothesized that Yawning at and Averting the eyes from the dog would reduce signs of stress in the dog. Grinning at a dog is interpreted as a threat by some experts and an appeasement face by others, so we hypothesized that we would observe a change in behavior though we had no expectations as to what form that change would take. Stare Alone was used as a baseline posture as this is a thoroughly examined posture known to convey a threatening message to a dog. We hoped to see a difference in the dog's behavior when this posture was exchanged for one of our experimental postures that would be supposedly less threatening. One caveat of this experiment is that there is no truly neutral posture could be used, as the presence of the experimenter could alone incur a response. Demographic and other variables related to the individual subjects were also considered to determine whether or not they have a significant effect on stress-related behavior in dogs.

It is generally agreed that various genetic, demographic, and environmental factors will influence how a dog will react to a certain situation. This is supported by various experiments. Older dogs have an increased incidence of stress-linked behaviors as compared to younger dogs when approached by a familiar person (Beerda et al., 2000). Female dogs show a greater decrease in the amount they look towards a person over time than do male dogs (Wells and Hepper 2000). Females also tend to display higher levels of anxiety, (Beerda et al., 1999; Lund et al., 1996) but males have a higher incidence of aggression (Lund et al., 1996). The amount of time a dog spends in an environment such as a shelter has also been shown to have an effect on stress level measured by behavior and cortisol levels (Stephen and Ledger, 2006; Hennessy et al., 1997; Hennessy et al., 2001; Wells et al., 2002). In this study we investigated the effects of these factors on the responses of dogs to our experimental situation.

MATERIALS AND METHODS

Animals

The subjects in this study were thirty-nine dogs from the Dane County Humane Society (DCHS). All breeds and combinations thereof were permissible, though only dogs classified as "adoptable" were used. The DCHS classifies adoptable as "all dogs eight weeks of age or older that, at or subsequent to the time the animal is taken into possession, have manifested no sign of a behavioral or temperamental characteristic that could pose a health or safety risk or otherwise make the animal unsuitable for placement as a pet, and have manifested no sign of disease, injury, a congenital or hereditary condition that adversely affects the health of the animal or that is likely to adversely affect the animal's health in the future" (DCHS 2005). Dogs that were adoptable, but should not be walked due to a temporary condition such as recovery from surgery were also not used in the study. Dogs less than six months of age were not used due to this being a time of physical, mental, and social development (Scott and Fuller, 1965).

Dogs were selected for the tests on a random basis without repetition. Each of the dog's records were collected. This includes a copy of the results of the behavioral test given at the DCHS, and other forms contained information on age, how and why they were obtained and/or surrendered, sex, intact/altered status, and date of admittance to the shelter.

Set-up

The experiment was conducted in the training room at the DCHS. This is a 9.45 meters x 14.63 meters room with tiled floors. The walls cut in at a 45 degree angle 2.74 meters from the far wall, leaving a 3.96 meter section of wall perpendicular to the path of the experimenter and on the far side of the room from where the experimenter entered. A camera was set up approximately 9.14 meters from the nearest point the test subject could reach and was kept off to the side. It was 1.38 meters off the ground positioned roughly horizontal. The field of view covered the entire area that the dog could move during the trials. The test subjects did not appear to be disturbed by any of these objects in the room, essentially paying no attention to them. The blinds were drawn in the training room and any other windows that might allow for the occurrence of a visual disturbance were covered up. The overhead fluorescent lights in the room were used for illumination.

Upon entrance to the training room the dogs were affixed to a 3.05 meter, plastic-coated cable, giving the subjects freedom to approach/retreat as they saw fit. This cable was attached to a collar that the dog either had on in the kennel in which it was housed or that the experimenter's assistant attached to the dog when retrieving it from the kennel. The cable was attached to a 20.3 cm diameter glass suction cup. In this case, it was affixed to the floor about 30 cm from the wall and centered along the wall's length. A small piece of masking tape was placed 60 cm from the other end of the cable when it made a 90 degree angle with the wall to mark where the experimenter should stop the approach. Most of the subjects were at the end of the cable closest to the experimenter upon presentation of the experimental posture.

When the dogs were not being tested they were kept in the kennels in which they were normally housed. In this space, the dogs could see visitors walking by on the side open to the public, and, on the side open to employees, the dogs could see any personnel walking by in addition to dogs being taken in and out of kennels. There were 19 such kennels adjacent to each other.

Experimental Procedure

Three dogs were randomly selected one at a time. They were tested individually in the order they were selected. The experimenter's assistant went back to the kennels and collected the first dog so the experimenter would have no contact with the dog before the presentation of the first posture. The assistant was asked to interact with the dog as minimally as possible. Vocal communication with the dog was restricted to what was deemed necessary to calm any anxious and/or fearful dogs. The assistant then led the dog to the training room while the experimenter remained out of sight. Upon entrance to the training room the dog was attached to the lead and its leash removed. The camera was then turned on and the assistant left the room to allow the dog two minutes to habituate to the environment. At the end of the two minutes the experimenter entered through the doors directly across from the suction cup to which the dog was affixed and approached at a brisk walk to the piece of tape. One of four experimental postures (discussed under "Human Facial Expressions") was then presented for ten seconds at the end of which the experimenter turned and left the room. The assistant then went into the room, turned off the camera, put the leash on the dog, disconnected it from the cable and took the dog back to its kennel until the dog was needed for subsequent posture presentations. The next dog in line was then retrieved and the process repeated.

In all trials the experimenter, the same person in all trials, wore long jean pants, a long-sleeved black t-shirt, and a pair of brown leather boots. The clothing was laundered in the same type of detergent prior to each day of experimentation and contact with animals was avoided until after the experiment to control for possible scent transfer.

Human Facial Expressions

In an attempt to determine whether the level of stress reflected by dog facial expressions could be altered, reactions of dogs to human facial expressions considered by some to be Calming Signals, that of Grinning, Yawning, and Averting the Eyes. These signals were compared to the Stare Alone posture, as we chose to call it. The direct stare is the most important of all canine facial expressions (Bradshaw and Nott, 1995) indicating a dominant or aggressive position in many instances, or simply communicating to the receiver to not approach any closer (Beaver 1982). It is also widely agreed upon that this signal will ultimately cause agitation in the receiver. The most common and perhaps most widely agreed upon Calming Signal is the Avert Eyes or Look Away. This is enacted by breaking a stare and is believed to diffuse a situation, while holding the stare after one member has deferred can cause agitation, (Bekoff 1977) suggesting that Look Away may have a calming effect.

A signal that has received more recent recognition is yawning. It has been classified as a Calming Signal, (Rugaas, 1997) and is also associated with low level anxiety (McConnell, 2006). There are additional communication signals implemented by the dog through means of the mouth. Dogs are now said to have an expression akin to a smile called the Open-mouth Bared Tooth Display, which is considered a friendly signal (McConnell, 2002). In our experiment we used four human facial expressions; Averting the Eyes, Yawning, Grinning, and Staring Alone, the latter three in an attempt to reduce dog facial expressions associated with stress and the former as a means of comparison.

The order of presentation of postures to each dog was randomized. Each dog would be presented the first of its postures and returned to its kennel. The other postures followed at approximately fifteen minute intervals.

Stare Alone

For this facial expression, the experimenter approached the dog directly, arms hanging loosely at sides. The experimenter's gaze was directed to the face of the test subject with a neutral, and relaxed expression. Once the experimenter stopped at the tape marking the 60 cm distance from the end of the lead the experimenter retained a neutral and relaxed expression directing the gaze towards the dog's head/face for the full 10 seconds. The arms remained hanging loosely at the sides with hands relaxed and open and shoulders parallel with the far wall of the training room. This was used as our baseline posture though no truly neutral posture could be used as the subjects would likely react behaviorally to any posture presented.

Yawn

The approach for Yawn mimicked that of Stare Alone. Upon arrival at the tape marker, rather than retaining the neutral and relaxed expression the experimenter open mouth yawned for a count of four seconds and for the remaining six seconds retained the neutral and relaxed expression used on approach. The body position reflected that of Stare Alone.

Avert Eyes

The approach for Avert Eyes mimicked that of Yawn and Stare Alone except during the approach the experimenter's head was turned approximately 45 degrees to the left (experimenter's left) of the dog with the chin tilted slightly downward. This angle was retained upon positioning at the tape marker. The neutral and relaxed facial expression was again used.

Grin

The approach for Grin was consistent with previous human expressions described. Upon arrival at the tape marker the experimenter took on a large smile showing both upper and lower teeth was given. The experimenter's gaze remained directed at the head/face of the dog though a change in eye shape occurred due to the Grin expression. All other body positioning remained the same.

DATA ANALYSIS

The two-minute habituation period, approach, and posture presentation were recorded on a digital video recorder for all trials. Upon completion, the footage was analyzed by the experimenter. The zoom function on the camera was used so the experimenter's head was not visible in the footage upon data analysis. This was to ensure that there would be no conscious or unconscious bias directed towards scoring due to knowledge of the posture being presented.

The tape was scored for approach (eight seconds) and posture (ten seconds) with the tape being paused every two seconds and being scored for the presence or absence of Stress Related behaviors (e.g. Ears Forward would receive a score of 1 while Ears Middle and Ears Back would both receive a score of 0; behaviors were counted for only the moment the tape was paused unless otherwise specified). These behaviors were qualified as follows:

1) Direction of Gaze

Look Towards: The dog's muzzle and eyes were directed toward the experimenter's head.

Look Away: The dog's position did not qualify as Look Towards.

2) Ear Position

Ears Forward: The dog's ears were directed with the inner surface of the pinna directed rostrally in a dog with erect ears or the ears were pricked with the outer surface of the pinna directed rostrally in droopy-eared dogs.

Ears Middle: The same as Ears Forward but the respective surfaces were directed abaxially.

Ears Back: The ears in all dogs were pulled caudally with the inner-surface of the pinna exposed to some degree on the side of the head.

3) Mouth Position

Mouth Open: The mouth of the dog was open to some degree.

Mouth Closed: The mouth of the dog was completely shut.

4) Yawn

Yawn: The dog was actively yawning at the time the tape was paused.

5) Tongue Flick

Tongue Flick: The dog's tongue projected out of its mouth during the second the tape was paused or the following second.

6) Tail Position

Tail High: The base of the tail made an approximate angle of 15 degrees or more above a line parallel with the floor.

Tail Medium: Tail position between that of High and Low.

Tail Low: The base of the tail made an approximate angle of 45 degrees or more below a line parallel with the floor.

Categorization

The data on each dog were individually entered and therefore associated with the name of the dog and five variables that were deemed appropriate to focus on. These variables were sex, age, reason in shelter, time in shelter, and tail-height (a measure obtained after statistical analysis of behaviors observed). The sex of the dog was categorized as intact male (unaltered at time of admittance to the DCHS), intact female (unaltered at time of admittance to the DCHS), male (neutered at time of admittance to the DCHS), or female (spayed at time of admittance to the DCHS). Age was categorized as young adult (under 1.5 years of age), adult (1.5 years-8 years of age), and senior (over 8 years of age). Reason in shelter was defined as stray or surrender. Surrender was further broken up into three categories, these being "couldn't keep" defined as those where cost, health of owner, time available to owner, landlord issues, and/or moving was listed, "didn't want" defined as simply didn't want, incompatible personalities, and behavioral issues such as running away and snapping. The last reason was "unspecified" simply referring to an unlisted reason. The time each animal had been in the shelter was also taken into consideration. This was measured as consecutive days spent since the last admittance. The time in a shelter spent prior to the last admittance of dogs that were returned or had been transferred from another shelter was not taken into account in this measure. This time was then divided into three groups, Short (0-21 days), Medium (22-42 days), and Long (43 days and above).

RESULTS

We first ran an analysis to determine if a behavior changed over time in regard to approach used. This was to determine if we could safely compare all four postures even though the approach was different for the "avert eyes" posture. No differences were found so we went ahead with further analysis to determine if a behavior changed over time in regards to posture presented. For this we ran a Cochran Q test with a significance level of p less than 0.05 which was altered using a Bonferroni correction for our four postural categories yielding a p value of less than 0.0125. This was done to correct for possible false positives encountered due to the number of separate tests being run. A significant increase over time was detected in the number of times dogs "looked away" from the experimenter when the experimenter performed the Avert Eyes (Q(5)=29.978, p less than 0.0001), Grin (Q(5)=19.541, p=0.002), and Yawn (Q(5)=20.165, p less than 0.001) facial expressions, but not the Stare Alone condition (Q(5)=8.30, p=0.140; Figure1). No other significant behavioral differences over time were found.

Figure 1:  Proportion of the 39 canine subjects that Looked Away in response to an expression cue.  The experiment was scored every two seconds for a period of ten seconds with a total of six scored intervals during which one of four postures was presented by a human experimenter to a canine subject, those being Avert Eyes, Grin, Yawn, and Stare Alone.  A significant increase over time at a Bonferroni corrected level of p less than 0.0125 in the proportion of dogs that Looked Away in an interval was seen during the presentation of all but the Stare Alone posture.

Figure 1: Proportion of the 39 canine subjects that Looked Away in response to an expression cue. The experiment was scored every two seconds for a period of ten seconds with a total of six scored intervals during which one of four postures was presented by a human experimenter to a canine subject, those being Avert Eyes, Grin, Yawn, and Stare Alone. A significant increase over time at a Bonferroni corrected level of p less than 0.0125 in the proportion of dogs that Looked Away in an interval was seen during the presentation of all but the Stare Alone posture.

The data were then presented in the proportion of the ten seconds a particular behavior was displayed. These numbers were arcsine transformed to normalize the proportional data so we could analyze it using tests for parametric statistics.

The arcsine transformed proportional data concerning behavior in response to human facial expressions were analyzed using main-effects ANOVA tests. The posture presented was used as the dependant variable while the behaviors displayed were the independent variables. No statistically significant behavioral changes were found in response to any human facial expression in the study. Therefore, we pooled the arcsine transformed data from the four human facial expressions for the remaining analyses.

Individual Traits and Dog Behavior

Main-effects ANOVAs were run in order to determine if the categorical variables (age, sex, time in shelter, etc.) had a significant effect on behavior. A separate one-way ANOVA was run for the category of reason in shelter. This was done as the sample size for this group was smaller (n=35) than that for the other variables. The reason for this was due to the presence of dogs surrendered to the shelter for an undisclosed or undefined reason. Post-hoc analyses were then run on any tests that proved to be significant. A Fischer LSD test was used for this analysis.

Time in Shelter

With regard to the time in shelter a significant difference was observed (F(2,36)=5.77, p=0.025; Figure 2). Post-hoc analyses revealed that dogs in the shelter the longest Looked Towards the least as compared to dogs in the shelter for the intermediate length of time (p=0.006). The dogs in the shelter for the shortest time period fell in-between these two groups.

Figure 2: Mean arcsine transformed data of the proportion of subjects who Looked Towards a human experimenter.  All subjects were shelter dogs and were categorized as to length of stay in the shelter.  A short span was defined as 0-21 days, a medium span, 22-42 days, and a long span, 43 days and up.  Dogs in the shelter for a medium span responded with a Look Towards significantly more than dogs in the shelter for a long span of time.

Figure 2: Mean arcsine transformed data of the proportion of subjects who Looked Towards a human experimenter. All subjects were shelter dogs and were categorized as to length of stay in the shelter. A short span was defined as 0-21 days, a medium span, 22-42 days, and a long span, 43 days and up. Dogs in the shelter for a medium span responded with a Look Towards significantly more than dogs in the shelter for a long span of time.

Reason in Shelter

Significant differences were found for tongue flicking depending upon the reason a dog was in the shelter (F(2,31)=6.00, p=0.006; Figure 3). Post-hoc analyses revealed that dogs that were taken in as strays Tongue Flicked significantly more than dogs surrendered due to the owner being unable to keep the dog (p=0.003). Dogs that were surrendered because the owner didn't want them tongue flicked more than the dogs of owners that couldn't keep them (p=0.035).

Figure 3: Mean arcsine transformed data of the proportion of subjects who Tongue Flicked in the presence of a human experimenter.  All subjects were shelter dogs and were categorized as to the reason they were in the shelter.  Dogs were in the shelter as they were collected as strays, for reasons of the owners not wanting the dogs, or for reasons that the owners could not keep the dogs.  Four dogs did not fit into these categories and their reasons for being in the shelter were undefined.  Those four were dropped from this analysis.  Dogs that were surrendered because the owner couldn't keep them Tongue Flicked significantly less than dogs that were collected as strays as well as dogs surrendered because the owners did not want them.

Figure 3: Mean arcsine transformed data of the proportion of subjects who Tongue Flicked in the presence of a human experimenter. All subjects were shelter dogs and were categorized as to the reason they were in the shelter. Dogs were in the shelter as they were collected as strays, for reasons of the owners not wanting the dogs, or for reasons that the owners could not keep the dogs. Four dogs did not fit into these categories and their reasons for being in the shelter were undefined. Those four were dropped from this analysis. Dogs that were surrendered because the owner couldn't keep them Tongue Flicked significantly less than dogs that were collected as strays as well as dogs surrendered because the owners did not want them.

Tail Position

Tail position did not change significantly for any of our tests (p greater than 0.05). As this is considered a classic signal in canine behavior, (Smith, 2004; Bradshaw and Nott, 1995; Milani, 1986; Fogle, 1990; Budiansky, 2000; Coren, 2004; Mech, 1999; Beaver, 1982; Schenkel, 1967) it prompted us to use it as a categorical variable to determine if it related to other behaviors significantly. The variable Tail Position yielded a significant difference in Mouth Open (F(2,36)=6.40, p=0.005). Post-hoc analyses revealed that dogs having a low tail height demonstrated Mouth Open less than those with medium tail heights (p=0.002) and high tail heights demonstrated Mouth Open significantly more than low tail height dogs (p=0.007).

Figure 4: Mean arcsine transformed data of the proportion of the canine subjects who displayed Mouth Open in the presence of a human experimenter.  All subjects were shelter dogs and were categorized as to the predominant carriage of the tail.  Dogs that had a low tail carriage had their mouths open significantly less than both dogs that had a high tail carriage as well as a medium tail carriage.

Figure 4: Mean arcsine transformed data of the proportion of the canine subjects who displayed Mouth Open in the presence of a human experimenter. All subjects were shelter dogs and were categorized as to the predominant carriage of the tail. Dogs that had a low tail carriage had their mouths open significantly less than both dogs that had a high tail carriage as well as a medium tail carriage.

Age and Sex

No significant behavioral differences were noted in relation to age or sex.

DISCUSSION

Look Away increased over time during the Yawn, Grin, and Avert Eyes postures, all postures with some evidence as to their use as Calming signals. The Stare Alone posture, a posture that is associated with threat intention, did not produce this effect. This suggests that dogs become more comfortable when one of the former postures is used as compared to the latter. In addition, during the Yawn condition Look Away was lowest during the first four seconds, the period the experimenter was actively yawning, and rapidly decreased after that time when the experimenter was done yawning. Yawning is linked to a calming effect by several people in the field of canine behavior, (Smith, 2004; Rugaas, 1997) and it is likely that attention was directed at the experimenter during the actual action but dropped off immediately thereafter as the signal that no threat was intended was received by the dog. This observed pattern merits further investigation.

Our results further indicate that several demographic and environmental factors were associated with behaviors indicative of stress. Dogs that had been at the shelter for a period of 22 to 42 days showed the highest amount of Looking Towards. This is in contrast to the dogs that had been in the shelter for over 42 days and those that had recently arrived at the shelter, being there for less than 22 days. Looking Towards has been implicated as demonstrating confidence, playfulness, dominance/challenge, and possible aggression in dogs, (Fennell, 2000; McConnell, 2002; Milani, 1986; Smith, 2004; Fogle,1990; Budiansky, 2000) whereas its opposite, looking away, is said to demonstrate submission, lack of confidence, lack of interest, and absence of threat intention (McConnell, 2002; Rugaas,1997; Bradshaw and Nott, 1995; Milani, 1986; Smith, 2004; Budiansky, 2000). This would then suggest that dogs who have just arrived at the shelter experience increased levels of anxiety possibly resulting in a reduction in positive social behavior.

After the initial period in the shelter it is possible that dogs are better adjusted to their environment and more able to engage socially whereas dogs that have been in the shelter for any longer than this time begin to regress in their ability to sustain positive social behavior. It must be emphasized that, although most shelters are very cognizant of the animals' well-being and attempt to foster it as much as possible, the majority of shelters are relatively deprived environments in which the dogs experience limited exercise, direct social interactions, and mental stimulation. They are also kept in close quarters with unfamiliar dogs, along with the sounds and smells of each of these animals. Tests for the stress hormone, cortisol, have been done on dogs in shelters revealing that cortisol levels are initially high, tend to drop after a certain time, and then increase once more (Stephen and Ledger, 2006; Hennessy et al., 1997; Hennessy et al., 2001; Wells et al., 2002). This would support the idea that dogs in the short and long period stay groups in our experiment were under unusually high degrees of stress, perhaps influencing their behavior in the study. It is also possible that dogs that are not quickly adopted, and hence those that stay in the shelter for the longest periods of time, are those that do not initiate and comply with what people may deem positive social behaviors such as looking towards the face of a person and that this could bias our results, especially for the long length stay group. It is more difficult to use this selective adoption theory to explain the findings for our short and medium length stay groups as apparent stress level actually decreased over these categorical lengths of time. It is thus likely that for these two groups the behavior observed was due to effects of stress from the environment and subsequent adaptation to and familiarization with the environment.

Tongue Flicking is another classic behavior said to be indicative of stress and/or anxiety (Smith, 2004; Coren, 2004; Rugaas, 1997) although it is also listed as a Calming signal (Rugaas, 1997). Its meaning, however, is considerably clearer than that of our Look Towards behavior, it not being associated with any aggressive intent, attentional state, or other aspects with less behavioral significance. Stray dogs Tongue Flicked the most indicating that they were experiencing the highest levels of stress in the experimental situation. As we did not have baseline behavioral data, it is impossible to tell if this was a difference seen only in the experimental situation or if it was simply a behavioral disposition of strays in the absence of an experimenter. The dogs that were surrendered due to the owners being unable to keep them showed the least of this stress indicative behavior. It is not known whether the environment these dogs came from produced these affects or rather if dogs that experience more anxiety are simply more likely to be rejected by their owners. A longitudinal study of a reasonably large population of dogs would be appropriate to further investigate these effects.

In the process of recording changes in behavior of the subjects we also ran across a behavior that did not change. Tail height stayed consistent across all trials. This is possibly the most classic of canine behavioral signals, being cited in popular and scientific literature (Smith, 2004; Bradshaw and Nott, 1995; Milani, 1986; Fogle, 1990; Budiansky, 2000; Coren, 2004; Mech, 1999; Beaver, 1982; Schenkel, 1967). We therefore assumed that it was a consistent categorical variable to use and we implemented it in our analysis. The only behavior significantly correlated with tail height was Mouth Open. An open mouth is associated with a comfortable dog (Smith, 2004), unless the dog is opening its mouth in a classic Snarl, which was not observed in our study. Those with a medium tail height expressed mouth open the most indicating a certain level of comfort, consistent with what the literature states about tail height. The dogs with the high tail carriage demonstrated this behavior at an intermediate level indicating a greater level of comfort than the low tail dogs but less than the tail medium. This could be due to the dominant position the tail high dogs are said to take, perhaps making them less at ease in a situation where their status may be perceived as being challenged. The tail low dogs had their Mouths Open the least, indicating the lowest level of comfort among our tail height groups. The significance of tail height remaining consistent for individual animals across experimental postures also supports its use as an indicator of disposition and a particularly useful measure in behavioral testing.

It appears as though disposition and shelter effects play a role in how dogs reacted to our experimental situation. Given that shelter effects played such significant roles, and considering that between 16.3 and 27.1 million dogs are surrendered to shelters every year and between 11.1 and 18.6 million are euthanized (Nasser et al., 1992), the consequence of a shelter environment is an area that merits further study.

When comparison tests were run across experimental conditions none of the dogs' behaviors showed any significant change, either in the first two, six, or full ten seconds that a human facial expression was presented. The ten-second experimental situation, where very little behavior on the part of the experimenter changed, could be considered an unnatural encounter. As environment has already been shown to have an effect on the dogs' stress levels as measured by facial expression it would be reasonable to state that the effects of the experimental situation overrode any effects we might have otherwise seen. It is also possible that changes occurred in cortisol levels or in behaviors that were not measured that would indicate a change in stress level.

In a future study it might be well-advised to use salivary cortisol levels as a measure of stress, although the utility and practicality of this measure for changes over such a short time period may render this an ineffective method. It would also be advisable to obtain baseline behavioral data for the individual subjects when no experimenter is present. However, the present data of a stress/stare posture versus our other three experimental calming conditions is still a valid comparison.

Although we did not see any positive results for the across-conditions portion of our experiment our time-effect results seem to indicate that communication between the human and domestic dog is a feasible goal, that humans can indeed affect the level of stress that a dog is experiencing, and that certain behaviors can be predicted by various individual characteristics of the dog.

ACKNOWLEDGEMENTS

Without the encouragement and help of several people, I would not have been able to complete this research. Dr. Patricia McConnell and Anneke Lisberg have both been inspirations, moving me in a direction to ask more questions about the world around me, and more specifically, about the dogs that are so closely associated with the lives of people. My advisor, Dr. Lauren Riters, has been incredibly flexible and amazingly thoughtful throughout the process of my research. I could not have asked for a better advisor. And, of course, I had two helpers that assisted in running the dogs through the experiment. Thank you, Carley and Kerri for all your help. Without it, I couldn't have proceeded with this work.

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