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44/ / Veterinary Focus / / Vol 20 No 1 / / 2010

IntroductionMost people have no difficulty in identifying

overt aggression and fear, but the interaction

between these is less frequently recognized. Fear

is an emotional reaction associated with the

presence of potentially harmful stimuli (by

contrast, anxiety arises from the anticipation of

such events, although the terms will be used

interchangeably here) and is typically expressed in

one of three obvious ways. When an animal judges

that the most appropriate way to deal with such

threats is to avoid them (i.e. take “flight”) then the

commonly recognized fear response is elicited. If

however, it decides to keep still, ("freeze") then the

involvement of fear is perhaps less obvious, and

if it attempts to eliminate the stimulus from its

proximity (i.e. engage the "fight" response), the

dog's behavior may result in inappropriate and

potentially harmful interactions initiated by people, who frequently misunderstand this as

some sort of dominance gesture. A dog’s initial

choice of action may change in both the short term

(i.e. there may be a switch in behavior) or longer term

(i.e. the dog may use a different initial strategy

in future similar contexts) depending on what seems

to happen next from the dog’s perspective (e.g. the

threat continues, intensifies or the dispute is resolv-

ed). Thus, far from being an instinctive impulse,aggression is often a carefully (but quickly)evaluated strategy aimed at resolving a dilemma

for the animal involving some perceived threat.

Daniel Mills, BVSc PhDCBiol FIBiol FHEA CCABDip ECVBM-CA MRCVSEuropean & RCVS Recogni zed

Speciali st in Veterin ary Behavi oural Medicine, Dept of Biol ogical Sciences, Uni versity

of Lincoln, UK

Professor Mills graduated from Bristol Veterinary School in

1990 and was the first individual to be recognized by the

RCVS as a specialist in veterinary behavioral medicine; he

was awarded his Chair at the University of Lincoln in 2004.

His main area of research interest concerns animal cogn-

ition and emotional regulation. He is the program leader of

the University's MSc in Clinical Animal Behavior.

Helen Zulch,BVSc(Hons) MRCVS

Ani mal Behaviour, Cognition

and Welf are Group, Dept of Biol ogical Sciences, Uni versity

of Lincoln, UK

Dr. Zulch graduated from the veterinary faculty of the

University of Pretoria in 1992. The majority of her career

has been spent lecturing, first physiology and then Animal

Behavior. She joined Lincoln University at the beginning

of 2008 where she consults in the Behavior Referral Clinic

as well as lecturing on under-graduate and post graduate

programs.

Appreciating the role of fearand anxiety in aggressive

behavior by dogs

KEY POINTS

Dogs can respond to a potentially harm ful stim ulusby flight, freeze or fight strategies

It is essential to appreciate the factors thatcontribute towards fear inducem ent

Dogs use a com plex of body language that has to betaken together to understand their preferences inconflict situations

There is no direct evidence of dom inance as am otivating factor for aggression in dogs

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Vol 20 No 1 / / 2010 / / Veterinary Focus / /45

This is not to say that all aggressive behavior is

motivated by fear. Indeed, “aggression” is not

consistently associated with any single emotional

state, but may be used to label any behavior that is

perceived to actually or potentially cause harm to

another. This means that behaviors in which harm

is incidental (e.g. if a dog should nip as part of

play) may be described as a form of aggression

(play aggression); as may behaviors associated

with the acquisition of food (predatory aggression).

However, these responses are motivationally quite

distinct and there is an increasing tendency to use

the terms play and predation to describe these

behaviors (1), avoiding the term aggression as this

may give rise to confused thinking about their

cause and management. This clarification may be

one of the first things to address when presented

with a case in which someone or something has

been harmed. It is suggested that the term

“affective aggression” be used to refer to behavior

associated with the presence of negative emot-

ional arousal, such as a state of fear. However

note that, while it is important to recognize the

circumstances that might give rise to fear (Figure

1), it is unwise to consider that any emotion

underlying an aggressive episode is fixed or

necessarily consistent; for example if a dog is

denied access to a resource by an individual who

is perceived as a threatening competitor, (which

may be the owner), then the aggressive response

may include elements of both fear and frustration.

Veterinarians need a greater appreciation of the

risk factors for the involvement of fear in aggres-

sion, since greater provocation will further

compromise the animal’s welfare and potentially

increase the risk to others. To this end there are

two important points to consider in the recog-

nition of fear-related aggression:

• What circumstances give rise to a fear response?

• Why is aggression chosen as part of the strategy

involving fear?

Ci rcum stances givi ng ri seto fear i n dogs

It is worth highlighting that, due to interactions

between genetic and experiential factors, some

individuals are more sensitive to fear than others,

regardless of their experience. Both breeding and

early experience may therefore have important

roles to play in the risk of a fear response being

expressed (all other factors being equal) by a given

individual in certain circumstances, but this

section will focus upon the specific factors which

predispose an animal to show a fear response in a

given situation.

Many specific fears are learned as a result of an

aversive experience, for example the fear of a

veterinarian who has handled the animal roughly,

especially if it was in pain, and the relevance of

this in any given case can often be identified by a

careful history. However there is also a range of

factors that (unless there is specific training to

the contrary) can have an intrinsic threatening

quality. These can help a dog to avoid harm by

providing general rules that aid the judgement

of potential risk and how to respond. These are

particularly important when the animal lacks

clear signals about its safety and they can serve

as triggers for a fear response and possible

aggression as a consequence. These factors can be

broadly divided into stimulus characteristics and

environmental features, whose significance in a

given case can be evaluated and used to help

inform treatment priorities (Table 1).

Stimu lu s characteristics Trajectory. The direction of movement of an

individual towards a dog can have a marked effect

on how that individual is perceived. Direct appr-

Figure 1.

The looming of this owner over their dog is a typical trigger for

a fear aggressive response, even though the owner thinks they

are being friendly trying to pat it.



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oaches are generally perceived as more threat-

ening than indirect approaches and so are more

likely to evoke a fear response.

Velocity. All other things being equal, rapid

movement is more likely to be perceived as

threatening than slow movement

Acceleration. A sudden increase in the speed of

movement is often a sign of impending danger,

and so abrupt movements around a dog may be

perceived as potentially threatening.

Size. Bigger objects are generally associated with

a greater capacity to cause harm and so are more

likely to evoke a fear response than smaller ones.

Direction. In many species vertical movement

across the retinal field is generally seen as more

intimidating than horizontal movement. Why this

should be so is unclear, but this is not limited to the

perception of whole body movements; moving a

hand vertically in front of a dog is often more likely

to elicit a fear response than moving the hand

horizontally at the same speed.

Looming. Many species find the act of being

leaned over by another as intimidating (2). Thus

standing half a meter away from a dog is not the

same as doing this with your hand outstretched

over it at a similar distance.

Envi ronment al cues (adapted from Archer ( 3)) Novelty. An unfamiliar environment or unexp-

ected event is more likely to elicit a fear response

as the animal does not have the necessary inform-

ation about its security (4).

Allocentric spatial thresholds. Allocentric space

(i.e. the location of objects relative to one another

or some arbitrary point) may be used to define the

location of important geographical boundaries

to an individual, such as the limits of a territory.

Crossing of these boundaries by an unfamiliar

individual may be perceived as potentially threat-

ening (5). This area contains important resources

for an individual and so its invasion could signal

their potential loss, and so many territorial defense

behaviors are associated with self-protection and

can involve a fear component. The crossing of the

territorial boundary associated with the home is

perhaps the most obvious allocentric threshold

which can elicit a defensive response. However,

in some cases, dogs may define more arbitrary

The dog is on its bed in the living

room with a toy next to the bed. A

toddler approaches the dog, lifts the

toy and reaches towards the dog to

return the toy to the dog. The dog

snaps at the child (6).

Older dog suffering from arthritis has

previously traveled with a young boist-

erous dog in the back of a car. Older

dog has now started growling at the

younger dog when he tries to climb

into the car.

Young toy breed dog has begun lung-

ing and barking at approaching dogs

when out walking. Has previously beenexposed to puppy classes allowing

uncontrolled free play sessions with

multiple dogs.

Personal space invaded. Possession

threatened. Looming action of child.

Movement of child and its body parts

may be erratic and so include bouts of

acceleration.

Pain associated with the youngster’s

previous actions in the car. Invasion of

personal space.

Pain or fear associated with previous

interaction with other dogs at puppy

class. Owner may have attempted to

correct what they perceive as mis-

behavior, i .e. owner’s behavior is also

threatening to the dog.

Control access by children to dog when he

is resting. Discourage child from picking

up dog toys. Desensitise dog to approaches

to bed. Desensitise dog to looming actions

and accelerations in its proximity. Institute

exchange programs for all those items which

the dog may perceive to be of value so that

human possession of the items becomes

positive.

Control pain. Restrain young dog when in

the back of the car. Counter condition the

older dog to the presence of the young dog

in the car.

Stop punishment and threatening actions

of owner towards their dog. Prevent the

young dog from practicing the behavior.

Desensitise and counter condition the dog

to other dogs in all situations where they

may be encountered.

Table 1.

Examples of aggressive behavior problems involving stimuli which may elicit fear

Scenario Possible threat elementsperceived by the dog

Advice to client



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Avoidance of conflict through yielding /

withdrawal

Appeasement (aiming to re-establish

non-confrontational social contact)

Encourage another to withdraw

(which may still be motivated by fear)

Approach / avoidance or other form of

emotional conflict. This may not signal

a desire for immediate action but

demonstrates a level of discomfort with

the current situation which may indicate

an increased risk for fear motivatedaggression.

• Avert gaze or turn head away • Curve body away and/or move away • Slow down

and/or curved approach • Stop • Tail tuck / arch back

• Lower body / lower neck • Stiffen body • Weight over hindquarters

• Piloerection • Molars exposed with wide open mouth • Retract lips to elongate

commisure • Retract lips to expose incisors in “smile” • Narrow eyes / blink • Fold

ears back • Lie down in lateral recumbence • Raise hind leg whilst in lateral

recumbence • Raise head with gaze averted

• Slow down and/ or curved approach • Stop • Wagging tail • Tail tuck / arch back

• Lower body • Piloerection • Avert gaze • Lie down lateral or dorsal recumbence

• Raise hind leg whilst in lateral recumbence • Paw lift • Yawning / retract lips / liplick • Narrow eyes / blink • Fold ears back • Lower neck • Reach up towards

mouth area of other individual possibly with licking motions

Direct rapid approach • Direct steady tense deliberate approach • Weight over

forequarters • Tail raised above normal relaxed carriage for individual • Wagging

tail / still, stiff tail • Ears pricked / lateral / flattened against skull • Lip commisure

pulled forwards • Incisors / canines exposed with wrinkled muzzle skin • Mydriasis

• Direct stare / widened eyes with tension of surrounding musculature • Neck arched

and head raised / muscle tension • Stillness • Lunge / snap / bite

• Lip licking / yawning • Piloerection • Shaking (as if to rid coat of water) • Other

displacement activities such as sniffing the ground

Table 2.

Interpreting the dog’s body language. These interpretations are putative as few have beenrigorously examined in a scienti fic manner. Postures demonstrated in any given context varyaccording to the individual and its previous experience

Putative motivation for the action Body Language exhibited

“territories”, such as the space around the car that

they are within when it is parked, and respond to

the potential invasion of this space in a similar

way.

Egocentric spatial thresholds. Not all of the space

in which an individual exists is defined by its

physical location; egocentric space is defined by

reference to its location relative to the individual

(2). As humans we are familiar with the idea of

our “personal space”, a certain distance that we

wish to keep from others to maintain our comfort

in normal circumstances. If this space is invaded

then we will often respond (if possible) in some

way, such as backing off. For dogs there are at least

two important egocentric spatial thresholds

that are associated with activation of the fear

neurocircuitry: the invasion of the dog’s personal

space and invasion of its body surface – e.g. touch.

The personal space of a dog appears to be typically

between 1.5 and 2 meters in an open situation, but

it may vary depending on the characteristics of the

environment. Just as we may tolerate people closer

to us in a crowded train carriage, so too may a dog

reduce its personal space in an equivalent situation.

However, in both there is still a minimum accept-

able distance, defined according to the region of

the body concerned. We may tolerate greater

proximity of the body trunk than the face, for

example. In situations such as this it may be part-

icularly important for the individuals to com-

municate their non-threatening intent in order to

avoid inadvertent elicitation of a fear response.

The deci sion t o express aggressionas part of a fear response

As mentioned above, an animal may evoke one

of three strategies to deal with a potential threat:

APPRECIATING THE ROLE OF FEAR AND ANXIETY IN AGGRESSIVE BEHAVIOR BY DOGS



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flight, freezing or fighting. Many animals may

freeze to allow the threat to pass, but this can fail

as a strategy because the owner perceives this

behavior as stubbornness and responds in a

threatening way to the dog, and so escalates the

perceived threat. If freezing does not succeed,

then the animal has little choice other than to try

to withdraw itself or get the perceived threat to

withdraw. Withdrawal may not be possible (e.g. if

the dog is cornered or restrained in some way,

such as with a lead), and so the dog then has no

sensible choice other than to try to get the threat

to withdraw. This is done using a sequence of

conflict-related gestures, which may ultimately

involve overtly aggressive behavior if more subtle

gestures are ineffective at resolving the situation.

In other situations it may be theoretically possible

for the animal to flee, but it is strongly motivated

not to do so. This might be because:

• It wants to protect a resource that it values

highly and/or which it cannot easily take with

it, for example a bitch protecting her puppies

• It anticipates that the other individual will give

way, for example because it is smaller, weaker

and/or has yielded in the past

• It has learned that other strategies do not work,e.g.

when it freezes, the owner continues to tell it off

• It would be painful to do so e.g. concurrent hip

dysplasia

Once again, the response of the individual who

has provoked the response in the dog is critical in

determining what happens next. Do they escalate

the confrontation or not? Escalation may occur

because one or more of the innate triggers of

aggression is presented (such as approaching and

leaning over the dog) or because a direct threat is

made (e.g. the owner gets angry). Ultimately this

may lead to an aggressive display by the dog (7),

but it is important to appreciate that this will be

underpinned by an element of fear, because the

animal feels threatened.

Signal ing to avoid overt aggression An aggressive display should be viewed as a failure

to understand the animal’s needs at a given time,

since dogs have a well-developed communication

system designed to minimize the risk of escalation

and avoid physical conflict in the face of a

potential threat (Table 2). This is because overt

physical attack is a potentially risky strategy,

which, even if successful, may lead to injury or

disruption of the social group to such an extent

that the long term biological fitness of antagonists

will be compromised. Nature does not favor the

tendency to fight unless the situation is perceived

as serious. When there is a potential conflict of

interests, dogs will typically communicate at

least two distinct messages to avoid unnecessary

escalation:

• Their preferred level of engagement in the

conflict (i.e. their desire to yield versus oppose

the other)

• Their level of hostility (intention to inflict harm

or not) to resolve the dispute

Yielding is generally shown through body postures

consistent with withdrawal or inconsistent with

engagement, such as a low, crouched posture with

ears back and tail tucked or the exposure of the

belly and aversion of eye gaze, while opposition is

exhibited by a more forward posture and action.

These are frequently described as submissive or

fearful versus dominant or confident postures, but

note that they relate to preference for engage-

ment in a given situation rather than an exhibition

of general social status, i.e. they are context specific

although they may be shaped by previous experience.

Hostility is evident from an increase in arousal

together with more specific warning signs such as

the fixing of gaze, baring of the teeth, vocalization

and snapping. By contrast, appeasement, which

signals a non-hostile intent and aims to reduce

hostility in others, can be expressed through a

range of gestures such as yawning, increased

blinking, slow movement, reduced ocular apert-

ure, and nose licking.

The expression of yielding and hostility is perhaps

most readily interpreted as a fear-biting scenario,

but it is important to recognize that even an animal

who is willing to actively oppose another may be

fearful of the consequences (8). For example it may

be willing to protect a valued resource but may still

be concerned about the outcome. Therefore the

tendency to interpret the posture of engagement as

a sign of confidence is erroneous. This may explain

the finding by Guy (9) that supposedly dominantly

aggressive dogs are generally anxious and not



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1. De Keuster T, J ung H. Aggression toward familiar people and animals.

In: Horwitz DF & Mills DS (eds). BSAVA Manu al of Cani ne and Felin e

Behavioural Medicine (2nd edn). 2009; pp. 182-210.

2. Graziano MFA, Cooke DF. Parieto-frontal interactions, personal space,

and defensive behavior.Neuropsychologia 2006; 44: 845-859.

3. Archer J . The organization of aggression and fear in vertebrates.

In: Bateson PPG, Klopfer PH (eds) Perspecti ves in Ethol ogy , Vol. 2,

Plenum Press , New York 1976; pp. 231-298.

4. Marler P. On animal aggression: the roles of strangeness and

familiarity.American Psychologist 1976; 31: 239-246.

5. Hediger H. (Sircom G, transl.) The psychology and behaviour of

animals in zoos and circuses. Butterworth, New York 1963.

6. Reisner IR, Shofer F, Nance M. Behavioral assessment of child-directed

canine aggression. Inju ry Preventi on 2007;13: 348-351.

7. Herron M, Shofer FS, Reisner IR. Survey of the use and outcome of

confrontational and non-confrontational training methods in client-

owned dogs showing undesirable behaviors. Applied Ani mal Behaviour

Scien ce 2009; 117: 47-54.

8. Fatjó J, Feddersen-Petersen D, Luís J , et al. Ambivalent signals during

agonistic interactions in a captive wolf pack. Appl A nim Behav Scien

2007;105: 274-283.

9. Guy NC, Luescher UA, Dohoo SE, et al. A case series of biting dogs:

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REFERENCES

confident as might be predicted if dominance was

really underlying the behavior. Indeed, to the

authors’ knowledge, there is no direct evidence of

dominance as a motivating factor for aggression in

dogs, although it is often implied by observers.

Several other important implications follow from

this evaluation of the signaling of dogs. First, if a

dog exhibits signs of appeasement and these are

not acknowledged, then it may either show more

intense signs of appeasement or decide that

hostility is necessary since appeasement does

not seem to work. Appropriate acknowledgement

involves disengaging and eliminating any gest-

ures which could be perceived as potentially

threatening. Unfortunately many owners mistake

appeasement gestures for a “guilty dog who knows

he has done wrong” (Figure 2), and this can result

in further threatening gestures from the owner,

leading the animal to reject attempts at reconcil-

iation and so resort to hostility instead. Unfort-

unately, the dog may learn from such encounters

that appeasement is not a useful strategy and

therefore only offer hostility when afraid in the

future. A similar account could be described in

relation to failure to respond appropriately to

yielding (as opposed to active appeasement)

behavior. In either case the aggression that results

is both normal and a response to continued threat

and so rightly considered a form of fear-related

aggression. Of particular importance to the

effective and humane management of these cases

is recognition that fear may feature within a dog

opposing another in any competitive situation.

Treatments which might potentially escalate the

problem (e.g. those based on punitive or potent-

ially threatening assertive interaction, rather than

consistent sensitive recognition of the animal’s

needs) should be rejected.

ConclusionFear is involved in the expression of aggression

far more frequently than is perhaps generally recog-

nized. It is essential that everyone who interacts

with dogs recognize both the stimuli which may

be perceived as threatening to dogs as well as the

means dogs use to signal their willingness to

engage in different strategies in social situations.

Only then can the risk of aggression and biting be

reduced effectively in the long term.

Figure 2.

An owner may interpret appeasement behavior as a “guilty

look”; note the dog’s crouched body stance, tensed neck,lowered head, narrowed eyes, folded ears and tucked tail.

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