Communication in Red Fox Dyads:

A Computer Simulation Study

GERALD GENE MONTGOMERY

m

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY • NUMBER 187
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SMITHSONIA N CONTRIBUTION S TO ZOOLOG Y • NUMBE R 187

Communication in Red Fox Dyads:

A Computer Simulation Study

Gerald Gene Montgomery

SMITHSONIAN INSTITUTION PRESS

City of Washington

1974
ABSTRACT

Montgomery, Gerald G. Communication in Red Fox Dyads: A Computer

Simulation Study. Smithsonian Contributions to Zoology, number 187, 30 pages,

16 figures, 9 tables, 1974.—This paper reports on a computer simulation study

of communication that occurs in red fox {Vulpes vulpes ( = V. fulxM.)] dyads

with various means of signalling when the animals move about and signal with

various emission intensities and at various time intervals.

For any two animals, three major factors limit communication: (1) whether

appropriate signal mechanisms are available, (2) whether they are motivated

to communicate, and (3) whether their movements and locations are such that

signals can pass between them. In this study, signal mechanisms and motivation

were not considered as variables, but the role of animal movement in limiting

communication was.

No tactile communication occurred between members of any of the simulated

dyads, and close-range visual or vocal communication (from 16 m or less)

occurred only rarely. Visual communication occurred frequently with reasonably

short visual ranges (20 percent of the time from 306 m), and is probably usually

limited by darkness and terrain. Vocal signals that could be heard from 644

meters gave communication 20 percent of the time when the signaller vocalized

4.7 times per hour. Wild red fox seldom emit loud vocalizations, however, and

vocal communication is probably not of prime importance in maintaining dyadic

social bonds. Communication occurred 20 percent of the time with scent point

signalling (scent marking), when scent remained effective for 8 hours or longer,

when scent could be smelled 96 m from the scent mark, and when the signaller

marked twice per hour. Thus, high levels of dyadic communication may be

achieved through scent marking, and this form of signalling may be of great

importance in maintaining dyadic spacing and social bonding.

The particular movement patterns of the animals that formed each dyad

had a differential effect on the level of communication, regardless of the means

of signalling. Those means of signalling that involved the fewest communication

variables were most severely limited by movements of the animals. Where more

variables associated with emission of signal were available to the animal, emission

could be optimized to minimize effects of movement on communication.

This study suggests that the animals can adjust the distance between them,

the time between them, or both, if prior communication has given mutual

awareness of the locations and movement patterns. In these adjustments, they

can increase or decrease the efficiency of signalling in one or more ways, and

thus control the level of dyadic communication.

OFFICIAL PUBLICATION DATE is handstamped in a limited number of initial copies and is recorded

in the Institution's annual report, Smithsonian Year. SI PRESS NUMBER 5188. SERIES COVER

DESIGN: The coral Montastrea cavernosa (Linnaeus).

Library of Congress Cataloging in Publication Data

Montgomery, Gerald Gene

Communication in red fox dyads

(Smithsonian contributions to zoology, no. 187)

Bibliography: p

Supt. of Docs, no.: SI 157:187

1. Red fox—Behavior. 2. Animal communication. 3. Biological models. I. Title. II. Series:

Smithsonian Institution. Smithsonian contributions to zoology, no. 187. [DNLM: 1. Communication. 2. Foxes. 3. Models, Theoretical. WI SM454N no. 187/QL7S7.C22 M787cl

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Contents

Page

Introduction 1

Acknowledgments 3

Bases for Simulation Models 4

Home Range Space and Individual Movement Patterns 4

Red Fox Movements and Home Range Space 5

Simulation of Individual Movement Patterns 5

Characteristics of Simulated Individual Movement Patterns 6

Communication and the Location of Home Range Space 6

The Communication Models . 7

The Tactile Communication Model 9

The Visual Communication Model 9

The Scent Path Communication Model 9

The Vocal Communication Model 10

The Scent Point Communication Model . . 10

Use of the Models for Simulating Communication . 11

Levels of Communication with Five Means of Signalling 12

Tactile and Close-Range Communication 13

Visual Communication 13

Scent Path Communication 15

Vocal Communication 17

Scent Point Communication 21

Comparisons among the Means of Communication 25

Summary 27

Literature Cited 28

i n

Communication in Red Fox Dyads:

A Computer Simulation Study

Gerald Gene Montgomery

Introduction

This paper reports a study, by computer simulation, of amounts of communication that occur in

red fox dyads when the animals paired to form a

dyad move about and signal in various sensory modalities and in various ways. The reader is cautioned

at the outset that the situations in which wild red

fox communicate were simplified in order to model

movements of the animals and communication between them. In effect, I attempted to model the

case in which the fewest variables affected the

amount of communication that occurred. For example, communication was modeled such that the

word "communication," as used throughout this

paper, is synonymous with reception of signal, although factors other than whether signal is received

surely determine whether or not communication

actually occurs.

Because of this simplification, the results of simulation reported here may only approximate those

that will result when more variables are added to

the models and more complex situations are simulated. As more and more variables that affect communication are added, the simulation models may

become a closer approximation of real situations in

which communication between wild red fox occurs.

The study is an attempt to establish base-line information that can give a basis for comparison as

more and more variables are successively added to

the models and as the simulated situation more

closely approaches the real one. This study is but

Gerald Gene Montgomery, National Zoological Park, Smithsonian Institution, Washington, D.C. 20009.

a beginning of this approach to computer simulation study of communication processes among wild

mammals, with red fox as an example.

In addition to establishing base-line information

and in general pointing up the role of animal movement in communication, the objectives of the study

were (1) to compare the various means of communication available to red fox and estimate the relative amount of communication provided by each

means, (2) to determine some of the factors that

limit communication with various means of signalling, and (3) to learn whether different ways of

moving about have an effect on the level of communication in red fox dyads.

The role of the movements of individual mammals in limiting the amounts and kinds of communication that occur is not well understood. Of the

three major factors that contribute to communication between any two free-living mammals (signal

mechanisms, motivation, and location), only the

first two have been subjects of major reviews (e.g.,

Tinbergen, 1964; Andrew, 1972), which indicates

the relative emphasis in research on the three factors. Emphasis in this paper is on the role of movement and location in communication. This emphasis does not minimize the role of signal mechanisms

and motivation, but will serve to show that all

three factors are necessary for effective communication among mobile, free-living mammals.

Most studies of communication begin with individuals that are at places from which they can

communicate if they are motivated to do so and if

they have the means for signalling and receiving

signal. Yet it is clear that not all members of local
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

species populations or even of loosely organized

social groups can communicate at all times, because distances between them are too great for

signal to pass among them. As an example of the

way in which location of the individuals has generally been ignored in studies of communication,

Altmann (1962a; 1965) studied communication

among wild rhesus monkeys (Macaca mulatto) and

computed the probabilities that certain communicative behaviors would occur in the population.

These computations were made without regard for

the proportion of time that the study animals were

not at locations from which they could communicate. That spatial arrangements of individuals

within a group could influence communication was

mentioned (Altmann, 1965:521), but was ignored

in the exhaustive analysis.

The study of communication among free-living

mammals has centered on those forms which live

in groups (cf., Wickler, 1969:89-90; Rowell, 1969),

and the limitations that movements of individuals

place on communication are less obvious when

the individuals move about together. Even where

the animals under study tend to be solitary, however, observations on communication have been

made (cf., Leyhausen, 1965) only on individuals

that were at places from which communication

could occur.

The movements of individual mammals place

limits on the amounts and kinds of communication

that can take place among them. For communication between any two mobile, free-living mammals

to occur, as defined in terms of a demonstrable

behavioral reaction to receiving signal (Klopfer

and Hatch, 1968:32-33; Mackay, 1972:3-6), locations of the individuals in time and space must of

course be such that signals can pass between them.

Thus, given that signal mechanisms and motivation are adequate, movements of the individuals

must bring them to certain locations before communication is possible.

Given that animals can communicate if they are

at appropriate locations, how much is the amount

of communication that occurs influenced by how

the animals move about? Two kinds of limits are

placed on communication by movements of the

animals and the resultant spacing between them.

First, movements determine the sensory modality

and within the modality the means (Scott, 1968:

17-19) by which communication can or cannot

occur at a particular time (Theberge and Falls,

1967:377). For example, movements may bring

individuals to locations from which they can hear

each other but cannot see each other. To quote

Marler (1967:773):

The usefulness of certain modalities may be restricted by an

animal's habits. A strictly nocturnal species has less use for

visual communication than a diurnal animal has. A solitary

species may have less use for tactile signals than does an

animal in constant proximity with several companions.

Further, Lancaster (1968:442) and Marler (1965:

583) point out that the location of the animals can

affect the range of signals that the animal can use.

As distances between animals increase, there is a

general tendency for less use of multimodal constellations of signal elements and greater use of less

ambiguous signals sent in a single optimal modality.

In the second kind of limit on communication,

locations of the animals limit the amount or kind

of information that can be transmitted once a

communication link is possible. The information

content of messages is determined to some extent

by the sensory modality by which they are transmitted (Klopfer and Hatch, 1968:33; Sebeok, 1967:

367-368; Marler, 1965:547) and movements of the

animals can allow choices in the modalities that

the animals can use at a particular time. When, for

example, both vocal and visual means of communication are possible, an animal might choose to

use vocalizations, which might convey more information than visual signals. Discussion of whether

or not nonhuman mammals do in fact choose the

modality by which they communicate on the basis

of attempting to maximize communication is outside the scope of this paper. Suffice it to say that

movements of the individuals can provide for such

choice.

Within a particular modality, different locations

can continue to affect the amount of communication. Marler (1968:106) points out that problems of transmission of visual signals are lessened

by reduced distance between individuals. Shorter

distance allows greater choice of the visual signal

mechanisms and presumably increases the amount

of information that can be transmitted.

Is it important to know how often animals communicate, as well as to infer what information is

communicated? Rowell (1969:284) points out that

different types of social organization will result

within the same species when the information is
NUMBER 187

communicated at different rates, even though the

same information is transmitted. Thus one of the

factors that determines the social organizational

pattern in a population of mammals is the frequency with which the individuals can communicate.

If the total amount of communication between any

two individuals that form a dyad is important in

maintaining social relations between them, it seems

worthwhile to ask how often the animals are at

places from which they can communicate, and how

often their movements prevent communication.

When the members of a dyad do not travel together, then the opportunities for communication

depend on the interaction of their patterns of

movement and the range of effect of their signals.

Busnel (1963:73-74) recognized this interaction,

but only as it applied to the probabilities of communication among any members of a population,

not between specific individuals:

. . . the probabilities of individuals meeting (male and

female, for example) depend on their density per surface unit,

on their total mobility and on the richness and qualities of

the means of information they have at their disposal enabling

them to increase their individual field of radiation and their

perceptive universe ... . The range of a signal is in direct

porportion to its intensity, other physical conditions of the

medium and signal being equal .. . if the density of the

animal population is high, signals of low intensity will suffice

for the information to be received, while if the density is low,

the emission intensity must be greater to attain the same aim.

Communication can take place at two levels:

universal and individual (Theberge and Falls,

1967:335). In universal communication, some of

the effects of communication may be shown

through influencing other members of a population, regardless of the identities of those individuals and their social relationships with a signalling

animal (Wynne-Edwards, 1962:16-17; Calhoun,

1963:38, 41; Altmann, 1962b:280). However, many

of those effects that relate directly to maintaining

social relationships and social structure depend on

a signaller communicating with specific individuals

(individual communication), rather than with any

individual that happens to be within range when

he signals.

It is useful to analyze social communication in

terms of dyads formed by pairs of communicating

animals, even when a signaller may communicate

simultaneously with several individuals (Poirier,

1968a). In red fox, some dyads are formed by

mated pairs that occupy home range space from

which other red fox are excluded (Sargeant, et al.,

in press; Storm, 1972:73). Yet even within these

dyads, red fox are generally solitary. Red fox in

captivity also move and act independently of each

other (Kleiman, 1967:367). Most of the assumed

communication within red fox dyads must, therefore, involve signalling over relatively long distances or involve signalling by scent over relatively

long time spans. Study of communication in red

fox (Fox, 1971:78-79; Tembrock, 1968:362-368)

has concentrated on signals that function over

short distances. For example, published data on

the distance over which vocal signals from one red

fox are heard and reacted to by other red fox are

not available. The study of communication in this

and other mammalian species has concentrated on

the physical form of various visual and vocal signals, and on responses to signals that can travel

over relatively short distances (usually less than

10 m).

ACKNOWLEDGMENTS.—The research was carried

out in the Department of Ecology and Behavioral

Biology, University of Minnesota. It was supported

by National Institutes of Health Training Grant

No. 5 TO1 GMO1779 and by the U. S. Atomic

Energy Commission (COO-1332-93). The manuscript was prepared during my employment at the

National Zoological Park, Smithsonian Institution.

I am grateful to J. F. Eisenberg for his encouragement and support. D. B. Siniff acted as my advisor,

and some of the ideas on which this paper is based

were developed in conversations with him. I am

grateful for his thoughts, for continued encouragement, and for smoothing the way during my absence from the university. I am grateful to G. L.

Storm and A. B. Sargeant for use of their unpublished data, and to D. B. Siniff and C. R. Jessen

who allowed me to modify their unpublished computer program and advised in these modifications.

V. A. Dirks, W. D. Braddock, and S. G. Curtis of

the University of Minnesota helped with aspects

of computer programs as well, but the sole responsibility for any programming errors is mine. D. B.

Siniff, D. F. McKinney, J. R. Tester, of the University of Minnesota, and J. F. Eisenberg and H. K.

Buechner of the National Zoological Park, Smithsonian Institution, offered suggestions on the manuscript. Linda Forcier typed the paper and helped

with many other details of preparing it. Wyotta
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

Holden prepared and typed many technical pages

for the format requirements of the Smithsonian

Institution Press.

Bases for Simulation Models

HOME RANGE SPACE AND INDIVIDUAL

MOVEMENT PATTERNS

The movements of an individual mammal are

usually confined to a limited area for at least a

large portion of its lifetime. The portion of space

used by an animal has been called its home range

(Burt, 1943). In my view, a major factor that

determines where the animal goes, and thus the

limits and features of the way it uses its home

range space, is a set of learned responses to the local

environment. This view is reflected in the way in

which both home range space and individual

movement patterns were simulated.

The life of an individual mammal occurs within

limits of time and space, the beginning points of

which are controlled by the parent (s). Suitable

places where the animal could go from this initial

point are, in theory, limited only by geographic

and biotic barriers, by the mobility of the individual, and by its lifespan. Most mammals, however,

confine their movements to a relatively small area

for long periods of time, perhaps for their lifetime

(Jewell, 1966). This localization (J. P. Scott, 1963:

241) forms early in the lives of many mammals, but

may form later after dispersal from the natal range

(cf. Storm, 1972:66-122; Hawkins, et al., 1971;

Phillips, et al., 1972). Dispersal movements generally occur in relation to sexual maturity (Blair,

1953:26), a relationship confirmed for red fox

(Storm, 1972:71), and may be an important population regulation mechanism in some species

(Krebs, et al., 1973).

From a beginning point that has been determined for it, or from a point that it chooses after

dispersal, an individual uses particular areas of

space more often than it uses other areas, as time

progresses. Many factors may influence this differential use as, for example, innately determined

preference for unevenly distributed biotic and

structural features of the habitat (Wecker, 1963),

preferences gained through influence of social associates (Terman, 1963; Montgomery and Sunquist,

in press) and responses to the presence of nonassociates and neighbors (Poirier, 1968b:353; Hawkins and Montgomery, 1969:202).

As Burt (1943) conceived the home range, this

differential use of an area that is smaller than the

area potentially available to the animal is a necessary feature for determining whether or not an

individual has a home range. In my view, and in

that of others (J. P. Scott, 1963:241), those places

that an animal remembers, and to which it returns more of less regularly, become part of its

home range. Washbum and Hamburg (1965:616-

617) consider that familiarity with an area is the

prime factor that limits use of space, rather than

availability of food or method of locomotion.

Jewell (1966) in his term "lifetime range" means

the total area with which a mammal has become

familiar. Some areas known to a mammal may

change or be forgotten, and thus will no longer be

included in the home range (Ewer, 1968:65).

In my view, a distinction should be made between how, as observers, we conceive an individual's home range on evidence provided by movements of the animal, and the "concept" that the

animal has of the space in which it lives. I choose

to call the latter concept the animal's "home

range," and the former the animal's "home range

space." Places which the mammal has not visited

but of which it is aware become part of the home

range (but not of the home range space), when

they contribute to orientation of the individual in

the space that it actually uses, its home range space.

In this view, the animal's concept of the space in

which it lives gives rise to the differential way in

which it uses space. Generally, the individual will

spend time in its home range space in a nonrandom manner; its pattern of use of the home range

space will be distinguishable from random movement. As time progresses, radio-marked mammals

of several species, such as snowshoe hare (Lepus

americanus), raccoon (Procyon lotor), white-tailed

deer (Odocoileus virginianus) and red fox, have

been shown to use a series of locations, and the

spatial distribution of these locations is demonstrably different from a random distribution (Tester

and Siniff, 1965; Siniff and Jessen, 1969). That

animals move directly between points on their

home range space has been shown for white-tailed

deer (Rongstad and Tester, 1969:375) and for a

blind raccoon (Sunquist, et al., 1969).
NUMBER 187

RED FOX MOVEMENTS AND

HOME RANGE SPACE

Considerable information is available on the

characteristics of red fox home range spaces and

on the patterns of movement which occur on them.

Sargeant, et al. (in press.) conducted a three-year

study of radio-marked red fox on the Cedar Creek

Natural History Area, near Bethel, Minnesota.

Their work, supplemented with that of Abies

(1959), Storm (1965; 1972), T. G. Scott (1943),

Scott and Klimstra (1955), and Arnold and Schofield (1956), provided generalizations about patterns of movement, size, shape, and spacing of red

fox home range spaces, and other aspects of red

fox biology, which are summarized below.

In general, each red fox home range space is

surrounded by neighboring home range spaces,

except at the limits of the species range and in

other special situations. The total area of a typical

home range space is one to three square miles (259

to 777 ha), the space being about one and one-half

miles (2.4 km) across at its widest point. The

space is usually shared by one adult male, one

(rarely two) adult female(s), and seasonally by

their young. Other red fox are excluded from this

space.

Although the dyad formed by a mated pair

shares the same space, the individuals are seldom

together. They may use the same portions of the

space, but do so at different times—although they

are usually active simultaneously. Most of the activity occurs at night, and the remainder during late

afternoon and early morning. The animals are

typically active for 8 to 10 hours of each 24.

While a fox is active, more than 80 percent of

its time is spent in travel; an individual covers a

major portion of the home range space during the

time it moves each night. Red fox average about

8 miles (12.8 km) of travel per 24 hours, and may

travel as much as 15 miles (24.1 km), all within

the confines of the home range space. Borders of

the space are not patrolled.

SIMULATION OF INDIVIDUAL

MOVEMENT PATTERNS

Simulated movement patterns of 8 individual

red fox were created with a Fortran IV computer

program modified from the program that represents the Siniff-Jessen model of animal movement

(Siniff and Jessen, 1969). All simulations for this

study were done with a CDC 6600 computer at the

University of Minnesota.

The location, size, and shape of the area in

which a simulated animal's home range space could

lie were specified and were controlled by the program. All such areas in this study corresponded to

the same ellipse, which had axes of 1.0 and 1.5

miles (1609 and 2563 m). The movements of each

animal determined where on this area its home

range space actually was. Movements had a high

probability of being confined to the area, because

the animal was programmed so that the probability of moving to areas it had used previously

was higher than movement to areas where it had

never been. Before the simulation of each movement pattern, the animal was given a number of

locations distributed equally over the elliptical

area, and none outside it, equivalent to uniform

use of all the area. Thus at the beginning, the

animal could seek out any part of the area, but

avoided going outside the area. As the simulation

proceeded, the animal differentially used various

portions of the area and tended to seek those places

where it had been most often as it built up its

home range space. For this study, I programmed

the animals to tend to go toward places that were

within 0.15 mile (241 m) of those which had been

used 5 or more times previously. If they failed to

find such a place, they were programmed to tend

to go toward the center of the elliptical area.

The individual's movements on the area were

controlled by a modified random walk procedure,

as follows: With the animal at a location, initially

set by me, the angle that it would turn (resulting

in a direction which it would travel) and the rate

of travel (resulting in the distance that it would

travel during the next regular time interval) were

chosen from probability distributions. Direction of

travel could be biased by where the animal had

previously been, as outlined above. The X-Y coordinates of the animal's next location were computed (based on the direction and distance of

travel), the animal was advanced to that location,

and time was incremented. Subsequent locations

were computed in a like manner until a series of

locations resulted. Additional features of the SiniffJessen model, the logic used in its development,

and examples of simulated movement patterns are
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

given in Siniff and Jessen (1969) and Siniff (1967).

In this study, all animals moved once per 5 minutes, in simulated time, until a series of 900 locations had accrued. This movement pattern, represented by the 900 serial locations, was stored on

magnetic tape until needed.

The computer program tested the simulated

movement patterns against the distribution of locations that resulted from the movement patterns

of radio-tracked red fox (Siniff and Jessen, 1969:

210-213). For this study, a grid-system of 0.10 milesquare (161 m square) grids was superimposed

over the elliptical area. The number of simulated

locations within each square was counted. The

frequency distribution of number of locations per

square was tested, by a goodness of fit procedure,

against the distribution of locations that resulted

when radio-tracking data from red fox were summarized in a like manner. All movement patterns

simulated for this study showed satisfactory fit.

Moreover, visual comparisons of computergenerated plots of real and simulated movement

patterns showed them to be very similar.

CHARACTERISTICS OF SIMULATED INDIVIDUAL

MOVEMENT PATTERNS

Eight movement patterns were simulated, and

each pattern had individual characteristics, which

resulted from the random walk procedure used in

the simulation. Four parameters were used to

distinguish among the movement patterns (Table

1). Two parameters, mean rate of movement and

angle turned between successive locations (Siniff

TABLE 1.—Comparison of four parameters of movements patterns of eight simulated red fox used in

study

Nunfcer of

individual

1

2........ .

3.1."."!

u

5

6

7

a.

Percent of

Mean rate

of

movement

irithin +30°

of straight

ahead travel

K value Total

of ntofcer

negative of

blnanial griddistri- squares

bution used

0.721

0.719

0.731

0.736

0.759

0.697

O.7U8

0.722

32.1

29.8

31*.0

32.2

30.9

29.8

O.562

0.231

0.559

0.675

0.676

0.665

0.39"*

l.lUo

78

56

77

77

77

7U

78

92

and Jessen, 1969:189), were used to characterize

the way an individual moved about its home range

space. Angles turned were compared with respect

to the tendency of an individual to travel straight

ahead, or within 30° of straight ahead, in successive

movements. An animal with a high mean rate of

travel and a high tendency to travel straight ahead

(e.g., No. 5 in Table 1) would cover its home

range space relatively quickly. Siniff (1967:41)

showed no apparent relationship between these

parameters for a particular real movement pattern.

Animals simulated for this study, however, tended

to travel in relatively straighter paths when they

moved at higher rates of travel.

The remaining two parameters, the K value of

the negative binomial distribution fit to the number of locations per square (Siniff, 1967:38; Siniff

and Jessen, 1969:197-199), and the total number

of squares used by an animal were used to describe

each individual's distribution of locations after a

series of movements. With respect to the overall

pattern with which an animal used the elliptical

area, a high K value and use of a high number of

squares indicate that the individual used a relatively large portion of the area, and that it used all

parts of it relatively infrequently. Animal No. 8

(Table 1) provides an example of such a movement pattern. The animal used 92 squares, while

animal No. 2 used only 56, both in their respective

series of 900 locations.

COMMUNICATION AND THE LOCATION OF HOME

RANGE SPACE

The relative locations of the home ranges of any

two individuals have a great influence on whether

or not they can communicate and, if so, on the

constraints that movement patterns and signalling

place on the amount of communication. There is

no possibility for direct communication when two

animals have home ranges that are far apart in

time and space. A red fox that died in 1960 cannot

communicate directly with one born in 1970, even

when they have the same home range space. Likewise, a red fox whose home range is in Illinois cannot communicate directly with a contemporary

fox in Minnesota.

Between these extremes, we might expect that

an individual would move and signal in such a way

as to optimize communication with particular
NUMBER 187

members of the population that are within limits

of time and space. Calhoun (1963:41) has proposed that small mammals will have evolved signal

mechanisms that enable an animal at the center

of its home range space to respond to an individual

signalling from the border. Hediger (1961:54) considers that individuals of a society will be apart only

to some maximum distance, termed the "social distance"; red fox seem to be what he termed "distancetype" animals, which avoid contact and stay at a

distance from each other. Maintaining such a distance implies that the animals communicate regularly. The area about an individual in which it can

influence other animals has been termed a "social

force field" (McBride, 1964:79-84); this field generates the individual distances among animals. That

author discusses social factors that may modify the

extent of such a field, including social position of

the individual, size of the group in which it lives,

and frequencies of agonistic contacts.

Given that any two animals have sufficient motivation and the appropriate signal mechanisms to

communicate, then the relationship among (1)

movement patterns, (2) the spatial relationships of

the home range spaces, and (3) the effective range

of the signals determines whether or not communication can occur. The effective signal range varies

with the mode of communication. Modes of communication listed by Scott (1968:18-19) and classified in terms of the sense organ through which

information is received are considered below, but

electrical and kinesthetic modes of communication

(Busnel, 1963:69) are excluded.

Tactile communication can occur only when

(1) the home range spaces of two individuals overlap in both time and space, and (2) the individuals

move in such a way that they both arrive very near

the same place (s) at the same time(s). Close-range

communication by any means has similar restraints,

except that the animals can be some short distance (s) apart.

Visual communication can occur only when (1)

the home range spaces overlap or when they have

proximal boundaries no farther apart than some

maximum distance over which the animals can

be seen, and (2) the individuals move in such a

way that they are no more than this distance apart

at some point (s) in time.

Vocal communication can occur only when (1)

the home range spaces overlap or when they have

proximal boundaries no farther apart than some

maximum distance over which the animals can be

heard, and (2) the individuals move in such a way

that they are no more than this distance apart

when one of them vocalizes.

Olfactory communication can occur only when

(1) the home range spaces overlap or have proximal boundaries no farther apart than a scent substance can disperse and remain at a concentration

that will elicit a response, and (2) the individuals

move in such a way that one of them arrives at a

point in space, or within some maximum distance

of that point, within some time after the other was

at the point; both the distance and time limits are

determined by dispersal of scent from the point

used by the first animal.

Many variables other than those considered

above surely affect communication. For example,

motivational states of the animals may prevent

communication although the movement patterns

and range of effect of signals are adequate to allow

signals to pass between them. Physical barriers,

darkness, and wind may interfere with signals and

prevent communication even though tlie conditions given above are met. Introduction of these

additional variables, however, would have deterred

the basic aim of this study, which was to simulate

communication with the fewest number of variables. Additional variables, such as those above,

can be programmed into the communication

models at a later time.

The Communication Models

These limiting constraints, which movement of

the animals place on communication, were used as

a basis for programming simple models that describe the way in which red fox might communicate in the various modes. Several simplifying assumptions were used to minimize the number of

variables.

With respect to the location of home range space,

the only case considered was that in which boundaries of the home range spaces of both members of

a dyad corresponded in time and space. The animals of a dyad moved about independently of each

other on this space. Thus, only the effective range

of signals in time and space, the frequency with

which signals were emitted, and the movement pat-
8 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

terns of the individuals affected the amount of

communication that occurred.

I assumed that only one of a dyad (signaller)

could emit signals while the other (receiver) could

only receive those signals. Although I assumed

that communication occurred each time the animal

received signal from the other, the receiver could

not react to such communication by changing its

movement pattern. Signal mechanisms and motivation to communicate were assumed to be always

available when I programmed the signaller to

emit a signal, and whenever the receiver came within range of the signal. Environmental factors such

as terrain, wind, or vegetation were assumed not to

interfere with a signal.

Five models, each describing a means of communication, were developed to simulate communiINCREASE TIME FOR

SIGNALLER AND MAKE

ITS NEXT MOVE

IS

LOCATION

OF RECEIVER WITHIN

LIMITS OF COMMUNICATION

WITH

SIGNALLER?

1—Schematic summary of the flow of processes and

the decision used in the computer simulation models of

communication in red fox dyads. (See text for details of the

different limitations placed on communication between the

animals.)

cation in the four modes. Tactile, visual, and vocal

modes of communication may be envisioned, in

their simplest form, as each fitting one model. However, two models were necessary to exhaust the

simplest means of communication in the olfactory

mode. Scent path communication, as discussed by

Fuller and Fox (1969:472-474) is distinguished

from scent point communication (scent marking)

as discussed by Eibl-Eibesfeldt (1970:310-312). A

schematic summary of the processes and decisions

used in the computer-simulation models for all

means of communication is shown as Figure 1.

In all the models except that for tactile communication, I controlled, through the appropriate

parts of the computer program, one or more of the

variables (communication variable (s)) that influenced the amount of communication between

the animals. The uncontrolled variable in all the

models was where the animals were at particular

times. Descriptions of the models are grouped according to the number of communication variables

that I controlled.

TACTILE COMMUNICATION

FIGURE 2.—Operation of the tactile communication model.

Symbols indicate the locations of the members of the dyad,

with circles representing the signaller and squares the receiver. Numbers inside the symbols indicate the time at

which the animals were at their respective locations. Movements leading to communication at time 2 between a signaller

and a receiver are shown. At time 1 the signaller is at (T)

and the receiver at Q]. At time 2, both animals move to the

same location, and communication occurs. At time 3, both

animals move to locations ®, [3] from which tactile communication cannot occur. Communication at time 2 did not

affect the movements of either animal from time 2 to time 3.
NUMBER 187

THE TACTILE COMMUNICATION MODEL

Tactile communication (Figure 2) occurred each

time the simulated animals were at the same

location at the same time. Animals had point dimensions, thus their locations had to exactly

match. No communication variables were under

my control, because only the movement patterns

determined when the individuals would be at a

particular location. In this and all other communication models, the number of prior times communication had occurred did not affect the receiver's

response to signal; communication occurred each

time he and the signaller were in the same place at

the same time.

THE VISUAL COMMUNICATION MODEL

Visual communication (Figure 3) occurred each

time the animals were within some distance Xt

(visual range) of each other. The visual range was

under my control. The signaller was equally visible

to the receiver at all times from anywhere within

VISUAL COMMUNICATION

FIGURE 3.—Operation of the visual communication model.

The shaded areas around locations of the signaller represent

the simulated visual range and the resulting areas in which

visual communication could occur. Movements leading to

communication at time 2 are shown. The signaller is at ©

and the receiver at Q] at time 1. At time 2, the animals

move to (D and [|] and communication occurs because the

receiver is within visual range of the signaller (within the

shaded area which represents the circle of radius visual

range). At time 3, the animals move to locations (5) and [s|,

from which visual communication cannot occur. In this sequence of movements, there were two times when communication could not occur and once when it did. Communication thus occurred 33 percent of the time. (See Figure 2 for

explanation of symbols.)

a circle around the signaller's location; the radius

of the circle was the visual range. There was no

gradation of effect of the visual signal as the distance from the signaller increased, thus a visual

signal of strength equal to or greater than some

single response threshold occurred throughout the

circle of effect while a signal outside the circle was

below the response threshold.

THE SCENT PATH COMMUNICATION MODEL

Scent path communication (Figure 4) occurred

each time the receiver crossed the travel path of

the signaller within Yi minutes (scent effect time)

after the signaller had used that portion of its

travel path. The travel path was the line that connected successive locations used by an animal. The

communication variable, scent effect time, was

under my control. I assumed that the signaller

constantly emitted a scent substance as it moved

SCENT PATH COMMUNICATION

FIGURE 4.—Operation of the scent path communication

model. Heavy lines connecting circles indicate effective scent

paths, while the open line between circles indicates a scent

path that is no longer effective. Scent effect time is 10

minutes, thus the scent path left by the signaller between

times 1 and 2 becomes ineffective when the signaller moves

between times 3 and 4. Movements leading to communication

between times 3 and 4 arc shown. The receiver moves from

[j] to [|] and no communication results because the signaller

has not yet traveled from © to 0 . When the receiver moves

from g] to ED it crosses a scented travel path, the scent is

still effective, and communication occurs. Had the receiver

crossed the line connecting ® and ® when it moved between

times 3 and 4, no communication would have resulted from

its last move. (See Figure 2 for explanation of symbols.)
10

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

about the home range, thus leaving a path of

scent. The scent was emitted such that the scent

path did not increase in width with time, but had

only line width at all times while scent remained

effective, The scent remained equally effective

during the entire scent effect time, and disappeared

instantaneously (or reached a concentration that

was below response threshold) at the end of that

time.

THE VOCAL COMMUNICATION MODEL

Vocal communication (Figure 5) occurred each

time the animals were within some distance Xi

(vocal range) of each other at a time when the

signaller vocalized; the signaller vocalized after

each regular y«th time interval (vocalization

frequency). The vocal signal could be heard

equally well from anywhere within a circle of

radius Xi about the location of the signaller.

There was no gradation of effect of the signal as

the distance from the signaller increased. Two

communication variables, vocal range and vocalization frequency, were under my control.

VOCAL COMMUNICATION

FIGURE 5.—Operation of the vocal communication model. The

signaller is programmed to vocalize at intervals of 25 minutes (at every fifth location), and the shaded areas around

® and ® indicate the vocal range. Movements leading to

communication at time 5 are shown. At time 1 the signaller

vocalizes at ® but the receiver is outside the vocal range

at Q] and no communication occurs. No communication

occurs when the receiver moves to g] because the vocal

signal is no longer effective. No communication occurs at

times S and 4 because the signaller does not vocalize at those

times. At time 5 the signaller vocalizes from (§)

 and communication occurs because the receiver, at rjj, is within the

vocal range. (See Figure 2 for explanation of symbols.)

THE SCENT POINT COMMUNICATION MODEL

Scent point communication (Figure 6) occurred

each time the receiver was within some distance

Xt (scent range) of a location scented by the

signaller when not more than some time Y< (scent

effect time) had passed after scent was deposited.

The signaller deposited scent after each regular

Zith time interval (scenting frequency), i.e., at

each Zith location that it used. The three communication variables; scent range, scent effect time,

and scenting frequency, were under my control.

I assumed that scent diffused instantaneously out

to scent range Xt and that it was equally effective

throughout a circle about the Zith location for

SCENT POINT COMMUNICATION

FIGURE 6.—Operation of the scent point communication

model. Scent effect time was programmed to be 15 minutes.

Three scent points, in this case those placed at times 2, 3,

and 4, are thus effective at any time. Shaded areas surrounding circles represent the areas in which scent is effective.

Movements which result in communication at time 3 are

shown. No communication occurs at time 2 because the

signaller has not yet reached 0 . Communication occurs at

time 3 because the receiver at [|] is within scent range of ©

and the scent left there at time 2 is still effective. No communication occurs at time 4 because scent left by the signaller

at © is no longer effective. (See Figure 2 for explanation of

symbols.)
NUMBER 187 11

the entire scent effect time y«. There was no gradation of effect with either distance from the scent

source or the time after scent was deposited. Scent

disappeared instantaneously at the end of scent

effect time. When scent circles overlapped each

other, there was no increased effect on the receiver

in the area of overlap.

Use of the Models for Simulating Communication

The movements of each of the five dyads (Table

2) for each range of value of the communication

variables were simulated using each of the five

communication models.

TABLE 2.—Combinations of movement patterns

used to form five dyads used in study (numbers

refer to particular movement patterns; characteristics of the pattern are shown in Table 1)

Dyad

A.

B.

C.

D.

E.

Signaller Receiver

The study thus involved, for each of the five

dyads, simulated communication under a total of

154 different limits on communication. In all,

770 simulations were done for the study.

For each of the dyads, movements with 8 visual

ranges from 0 to 0.01 miles (16 m) were simulated

to study tactile and close-range communication

(total 40 simulations). Movements with 10 visual

ranges from 0.05 to 0.90 mile (80 to 1448 m) were

simulated for each of the five dyads (total 50 simulations) to study visual communication. Movements

with 8 scent effect times from 0.33 to 24 hours

(total 40 simulations) were used for each of the

five dyads to study scent path communication. For

each dyad, movements with 48 different combinations of vocal range and vocalization frequency

(total 240 simulations) were simulated to study

vocal communication; vocal ranges of 0.10 to 0.80

mile (161 to 1287 m) were combined with vocalization frequencies of 0.33 to 6.00 per hour (one

per iy2 hours to one per 10 minutes). Movements

of each of the five dyads were simulated with 80

different combinations of scent range, scent effect

time, and scenting frequency to study scent point

communication (total 400 simulations); scent ranges

from 0.05 to 0.50 mile (80 to 800 m), scent effect

times of 1 to 8 hours, and scenting frequencies of

0.33 to 2.00 per hour (one per li/£ hours to one

per 30 minutes) were used in various combinations.

For each dyad, when a particular communication model and value (s) of the communication

variable (s) were used, the simulation began by

retrieving the movement patterns of the two animals from magnetic tape (Figure 7). The movement patterns were then recreated simultaneously

on the home range space. The initial locations of

the animals were randomized, and they could have

been anywhere on the space. As simulated time

advanced in 5-minute increments, both animals

moved from location-to-location, following their

RETRIEVE MOVEMENT PATTERNS

OF SIGNALLER AND RECEIVER

CHOOSE INITIAL

OF THI

JIONS

INCREASE TIME FOR BOTH

ANIMALS AND MAKE THEIR

NEXT MOVES

COUNT

NON-COMMUNICATION

NOCOULD

COMMUWI CATION

OCCUR FROM THE CURRENT

LOCATIONS OF THE

ANIMALS?

ADD COUNTS OF

COMMUNICATION

AND

NON-COMMUNICATION

COUNT

COMMUNICATION

DIVIDE COUNT OF

COMMUNICATION

BY TOTAL

FIGURE 7 Summary of the flow of processes and decisions

used in simulating communication between a particular pair

of red fox that formed a dyad on the same home range space.
12

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

previously determined movement patterns. The

computer program that controlled these processes

and those described below is included as an Appendix in Montgomery, 1973.

While the animals moved about, the signaller

emitted signals according to the simulation schedule. The interaction of the movement patterns,

the frequency of the signaller-emitted signals, and

the range of effect of the signals, determined the

level of communication that occurred.

I used 540 locations from each movement pattern (the remaining 360 were used to allow the

animals to start from randomly determined locations), thus a simulation was equivalent to the

movements of two red fox for 45 hours (5 days of

9 hours of fox activity each day). The program

counted the number of times the animals' movements brought them to locations from which communication could occur, and how often they were

outside the limits on communication. The number

of times communication was possible was divided

by the total (communication plus noncommunication) to give the percentage of time during each

simulation when communication occurred.

The movement patterns of each of the members

of a dyad remained the same, regardless of which

communication model was used in a simulation,

or of the values of the communication variable (s)

used. Choice of the movement patterns that represented a dyad were made without regard for individual characteristics of the movement patterns;

movement patterns of the animals were thus random variables in each of the simulations.

For each dyad, movement patterns of the animals were controlled variables, allowing comparison of amounts of communication that occurred

with a communication model, when the values of

the communication variable (s) were changed between simulations. Comparisons among the dyads

were also made, for the same communication

model and value (s) of the communication variable (s), to indicate variation in amounts of communication attributable to characteristics of the

individual movement patterns.

To compare movement patterns with levels of

communication, scores for each dyad for the level

of communication that resulted from each means

of communication were ranked. These rank scores

were then compared with rank scores for the four

parameters of the movement patterns. The comparisons indicated- ways in which communication

was enhanced by the slight differences in the way

various simulated animals moved about.

When a particular communication variable or

a combination of variables was held constant for

all dyads, different levels of communication resulted among the dyads (see below), because movement patterns influenced communication and each

pair of movement patterns was unique. The levels

of communication that resulted from each value of

a communication variable (e.g., a visual range of

of 0.40 mile, or 644 m) or for each combination

of communication variables (e.g., a vocalization

frequency of 1 per hour and a vocal range of 0.80

mile, or 1287 m) were averaged for the five dyads.

Many values of the communication variable (s)

were simulated for each means of communication,

and the average level of communication was computed for each value or combination of values. All

the average values for a particular means of communication were plotted (Figures 8, 9, 10) and the

value (s) of the communication variable (s) that

gave, on the average, 20 percent communication

was interpolated from each plot. Then for each

means of communication, the level of communication that resulted, when the value (s) of the communication variable (s) used in simulation equalled

this interpolated value (s), was ranked among the

five dyads. Rank 1 was given to the dyad that

showed the maximum level of communication with

this value (s) of the communication variable (s).

For comparison of movement patterns with

levels of communication, the five signallers and

the five receivers were ranked for each of the four

movement parameters. A rank of 1 for rate of

travel among signallers means, for example, that

the simulated animal had the highest mean rate

of travel among the five signallers. Numerical bases

for the rankings are shown in Table 1, while identities of signallers and receivers are shown in

Table 2.

Levels of Communication with

Five Means of Signalling

Results from the simulation of each means of

communication are presented as follows: The

level of communication that occurred for the various values of the communication variable(s) is shown

in a figure and discussed. Factors that reduced the
NUMBER 187 13

effectiveness of attempts to increase communication are outlined and discussed. Characteristics of

the movement patterns that resulted in higher or

lower levels of communication for particular dyads

are considered. Finally the results of the simulation

are compared with available information on communication among red fox. It should be kept in

mind that simulation was with deliberately simplified models. The simulation results thus may not

reflect levels of communication that occur with the

many variables which affect levels of communication among wild red fox.

TACTILE AND CLOSE-RANGE COMMUNICATION

No tactile communication occurred between

members of any of the five dyads (Figure 8). Tactile communication depended on the animals being

MEAN

y

0 Sat OM JOIO 0 002 406 W>

I - o- 0 -

b0.00 2 XK» am o aoz ow an

2- 2-

D

SIGNAL RANGE (MILES)

FIGURE 8.—Levels of tactile, dose-range visual, and close-range

vocal communication that occurred in five simulated red fox

dyads (A-E) with signal ranges of 0.01 mile (16 m) and less,

and the mean levels of communication for the five dyads.

Note that none of the dyads communicated more than 0.5

percent of the time by these means, and dyads B, C, and D did

not communicate at all.

in the same place at the same time. Close-range

visual and vocal communication was arbitrarily

defined as occurring with visual or vocal ranges

of 0.01 mile (16 m) or less and with continuous or

less frequent vocalization where appropriate. Closerange communication occurred 0.15 percent of

the time or less for the average of the five dyads

(Figure 8). No close-range communication occurred within signal ranges of less than 0.005 mile

(8 m) for any dyad, and three of the dyads showed

no communication with ranges as great as 0.01

mile (16 m).

Tactile and other close-range means of communication were severely limited by movements of

the simulated animals. These results suggest that

communication by close-range means would occur

very rarely between red fox, unless some other

means of communication was first employed to

allow the members of a dyad to move closer together. In the absence of such communication

and coordination of movements, it is doubtful that

close-range communication would occur often

enough to account for social bonding in red fox

dyads.

VISUAL COMMUNICATION

Increasing the visual range, which increased the

area in which the signaller could be seen by the

receiver, increased the level of communication for

all dyads (Figure 9). Because of the specified dimensions of the elliptical area that included the

home range spaces, visual communication would

have occurred 100 percent of the time for all dyads

with a visual range of 1.50 mile (2413 m). With

that visual range a signal from anywhere on the

home range space would have covered the entire

space. The maximum visual range that I simulated

was 0.90 mile (1448 m), and with this range four

of the five dyads communicated more than 80 percent of the time. The maximum rate of communication was 96 percent for dyad B and the minimum

was 75 percent for dyad A.

With linear increases in visual range, increases

in level of communication were nonlinear (Figure

9). On the average, a greater increase in communication resulted from a unit increase in visual range

when the range was less than 0.40 mile (644 m).

For visual ranges of 0.10 to 0.40 mile (161 to 644

m) each increase of 0.10 mile (161 m) in range
14 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

gave an additional 15 percent communication.

For ranges of 0.40 to 0.70 mile (644 to 1126 m),

however, an increase in visual range of 0.10 mile

(161 m) resulted in only 8 percent more communication. This result may indicate that attempts by

a red fox to increase visual communication by

becoming more conspicuous will be more efficient

if the visual signal travels less than 0.40 mile (644

m) to reach a potential receiver of the signal.

With increased visual ranges the curves (Figure

9) showing the relationship between visual range

and level of communication were inflected. This

inflection suggests that some limit on an increase

in level of communication was approached as the

visual range increased. Wastage of visual signal

MEAN

OuB OS U> oe out u>

aa as u>

U M U U 10

VISUAL RANGE (MILES)

FIGURE 9.—Levels of visual communication that occurred in

five simulated red fox dyads (A-E) with visual ranges of 0.05

to 0.90 mile (80 to 1448 m), and the mean levels of visual

communication for the five dyads. On the average, the animals communicated 20 percent of the time when the receiver

could see the signaller from 0.19 mile (306 m).

emitted beyond the boundary of the home range

space accounts for the limit on effectiveness of increasing visual range. For communication within

any dyad by any means, the signal is wasted when

it goes into space not used by the receiving animal.

Such signal may not in fact be wasted, however,

when it is used for communication outside the

particular dyad under consideration. Visual signal

emitted to places on the home range space other

than that place occupied by the receiving animal

was wasted as well, but more visual signal on the

home range space increased the chances that the

receiver would be in a location from which it

could see the signaller.

Signal was not wasted beyond the boundary of

the receiver's home range space when the signaller

was the same distance as the visual range from the

nearest boundary of that space, or more than the

visual range from any of its boundaries. For a

given visual range, there was thus a set of locations

that formed a threshold for such wastage of signal. Beyond these threshold locations, the amount

of wasted signal increased for a given visual range

whenever the signaller moved toward the boundary

of the receiver's home range space or, from a given

location, as the visual range increased. In general,

such a set of threshold locations exist for all means

of communication for each signaller using a given

emission intensity in dyadic communication. Given

that the signaller is aware of the extent of the

receiver's home range space, the locations outline

an area from which the signaller could most efficiently signal the other member of the dyad.

For a particular visual range, only differences

in movement patterns could account for the different levels of communication which were shown

among the dyads (Figure 9), since all other variables were held constant. On the average, the dyads

communicated 20 percent of the time when the

visual range was 0.19 mile (306 m). There was

considerable variation among the dyads in the

amount of communication that occurred with that

visual range, from 7 percent for dyad A to 36 percent for dyad D. For this and a wide variety of

visual ranges, the dyads consistently ranked as

follows with respect to levels of communication

with a particular visual range: D=l, B = 2, E = 3,

C=4, A=5.

It is thus shown by variation in level of communication among the dyads that the way in which
NUMBER 187 15

TABLE 3.—Comparison of level of visual communication provided by pairs of

movement patterns that formed each of five dyads with four parameters of movement patterns of signallers and receivers within each dyad (criteria for ranking

levels of communication among dyads and for ranking movement patterns among

signallers and receivers are given in the text)

Dyad

D

B

E

C

A

Communication rank

1

2

3

1+

5

Rate of movement

(mean)

Signaller

2

5

1

h

Receiver

1

2

3

5

1+

Straight ahead

travel +30°

Signaller Receiver

1 2

5 h

2 1

3 3

h 5

Contagion of

locations

(K)

Signaller Receiver

2 2

5 5

1 3

h k

3 1

Total number of

grid-squares

Signaller

3

1

3

3

5

Receiver

2.5

k

2.5

1

5

one or both members of each dyad moved about

influenced their ability to communicate visually.

There was no apparent rank correlation between

the level of visual communication in a dyad and

any of the four parameters of movement of signallers (Table 3), and the manner in which signallers

moved about apparently did not greatly influence

visual communication. There was a good rank

correlation, however, between rate of movement

of receivers and level of visual communication.

This result may indicate that the way in which

receivers moved about had a great influence on

the level of visual communication, regardless of the

movement pattern of signallers. If this were true,

the signaller could do little to enhance communication except change the visual range, unless he

exerted some control over the receiver's movement

pattern, and in so doing increased the rate at

which the receiver moved about its home range

space.

Although simulation shows that movements of

the animals alone does not prevent significant

levels of visual communication (Figure 9), red fox

are primarily nocturnal, which precludes use of

visual signalling in long-range dyadic communication. Even for short-range location of prey (from

30 m or less), vision was shown to be important

only during daylight hours (Osterholm, 1966:54),

and senses of hearing and particularly smell became more important in twilight and darkness. As

stated by Osterholm (1966:55):". . . the fox's own

daily rhythm has the result that in nature the sense

of sight is not a particularly important receptor

to the red fox." In general, in spite of adaptations

for improved vision in darkness, nocturnal animals

can rely less on vision than other senses for communication (Marler, 1965:547). An additive factor

that would further reduce the effectiveness of

visual signalling is interference by topography and

vegetation. Interference with visual signals by vegetation was shown by Bronson (1964) to seasonally

decrease visual communication among woodchucks (Marmota monax), a diurnal mammal.

Interference, when combined with darkness, would

make visual communication over moderate or long

distance very difficult for red fox. Visual communication is thus probably of little importance in

maintaining social bonds in red fox dyads, not because movements prevent it, but because fox are

primarily nocturnal and because the habitat interferes with visual signals.

SCENT PATH COMMUNICATION

Increasing the scent effect time, which increased

the length of the path of effective scent that was

available at any time, increased levels of communication for all dyads (Figure 10). Amounts of communication afforded by longer lasting scent, however, quickly reached an upper limit. On the average, scent path signalling provided communication

no more than 25 percent of the time, even when

scent remained effective for 12 hours or more. At

the extremes for the five dyads, the upper limit in

level of communication was reached with 18 hours

of scent effect for dyad A and 10 hours for dyads

B, C, and D. At the upper limit in level of communication for the dyads considered separately, the

maximum level was 38 percent for dyad D and the

minimum level was 19 percent for dyad A. Dyad
16 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

A, which could communicate no more than 19 percent of the time by scent path signalling regardless

of the scent effect time, required a longer scent

effect time to reach its maximum level of communication. Dyad D, in contrast, needed a shorter

scent effect time to reach a higher maximum level

of communication.

A limit on the effect of increasing scent effect

times was approached as these times increased

(Figure 10). The limiting factor (s) is unknown;

no scent path signal was wasted by emission outside

the boundary of the elliptical area that included

the home range spaces. The home range spaces of

the two members of each dyad, however, depended

on where within the elliptical area each animal

MEAN 40-

30-

20-

16 20 24

I* 20 24 12 16 20 24

90-

40-

30-

20-

10-

12 I* 20 24

SCENT EFFECT TIME (HOURS)

FIGURE 10.—Levels of scent-path communication that occurred in five simulated red fox dyads (A-E) with scent

effect times of 0.33 to 24 hours, and the mean levels of communication for the five dyads. Note an increase in level of

communication with increasing scent effect times to about

12 hours; further increases in scent effect time did not give

further increases in communication. On the average, the

animals communicated 20 percent of the time when scent

remained effective for 7.6 hours.

actually moved. The home range spaces of dyad

members may have diverged enough so that some

scent path signal could not be received and was

wasted.

As with the other means of communication,

only differences in movement patterns among the

dyads could account for the different levels of communication with the same scent effect time (Figure

10). On the average, the dyads communicated 20

percent of the time when scent was effective for 7.6

hours. Variation among the dyads with a scent

effect time of 7.6 hours ranged from 15 percent

communication for dyad A to 28 percent for dyad

D. For a particular scent effect time, the dyads

consistently ranked as follows with respect to levels

of communication: D=l, E = 2, C = 3, B = 4, A=5.

The variation among dyads, and the consistency

in relative level of communication with each of

many scent effect times shows that the movements

of one or both dyad members influenced the level

of scent path communication. In contrast to visual

signalling, the way in which signallers moved

about while signalling with scent paths apparently

influenced the level of communication (Table

4). Signallers that had a relatively high rate of

travel and, particularly, those that tended to travel

straight ahead at a rapid rate were more successful

in signalling the receiver of their dyad. A critical

factor in scent path communication is the total

length of path that carries effective scent at any

time, because a longer effective path increases the

probability that the receiver will move across it

before the scent becomes ineffective. Where the

animals move over large areas, a second critical

factor is the total area in which scent paths are

effective. Given the same length of effective scent

path, the probability of communication would be

lower when a particular path is concentrated in

one small part of the receiver's home range space

because the receiver may be moving in an entirely

different part of the space while the scent is effective. A movement pattern in which the signaller

moves rapidly and seldom turns would provide

both a longer effective scent path at any time, and

a tendency to distribute that path over a large

portion of the receiver's home range space.

Scent path signalling is potentially an efficient

means for providing moderate levels of communication in red fox dyads. Red fox have interdigital

glands, which produce odor distinguishable even
NUMBER 187 17

TABLE 4.—Comparison of level of scent path communication provided by pairs

of movement patterns that formed each of five dyads with four parameters of

movement patterns of signallers and receivers within each dyad (criteria for

ranking levels of communication among dyads and for ranking movement

patterns among signallers and receivers are given in text)

Dyad

D

E

C

B

A

Comnunication rank

1

2

3

k

5

Rate of movement

(mean)

Signaller

2

1

3

5

h

Receiver

1

3

5

2

k

Straight ahead

travel± 30°

Signaller

1CVI 3

5

k

Receiver

2

1

3

h

5

Contagion of

locations

(K)

Signaller Receiver

2

1

h

5

3

2

3

h

5

1

Total number of

grid-sguares

Signaller Receiver

3

3

3

1

5

2.5

2.5

1

U

5

to humans and which may contribute to leaving a

scent trail as the animals move about (Fox, 1971:

201). Anal and other scent glands may also produce odors that are left as a trail, along with distinctive chemical substances from nonglandular

parts of the fox's body surface. Because a scent

trail is left as the animal moves about, incidental

to its other activities (Ewer, 1968:112-113), a fox

need not spend much additional time and energy

in communication. Scent trails can carry information about the identity and state of the individual

which leaves them (cf., Wilson, 1968:90) and, because of concentration gradients along a trail,

about the direction of travel and the amount of

time that has passed since the trail was laid (Bossert and Wilson, 1963:458-463). Information inherent in scent trails could thus allow fox to maintain a degree of spacing or help to bring them together.

Red fox almost certainly can use information

from scent trails, although good evidence for them

doing so is lacking. Certain breeds of the domestic

dog (Canis familiaris) have outstanding ability to

discriminate among and to follow scent trails

(Fuller and Fox, 1969:472-474). That this ability

is generally developed in canids is indicated by

observations of timber wolves following the scent

trails of conspecifics (Mech, et al. 1971:23; Jordan,

et al., 1967:243).

Simulation indicates that moderate levels of

communication are possible with red fox movements when scent remains effective for about 9

hours, but that further increases in scent effect

time are inefficient in terms of increasing communication. Thus, the optimal level of scent emission

is that which provides communication over a

time approximately equal to the length of the

daily activity period. It seems possible that the

primary function of scent path signalling is to reveal the location of the signaller during the same

daily activity period that scent trails are left. Ambiguity introduced by scent persisting from one

daily activity period to the next may be avoided

by the signaller emitting only that kind or amount

of scent that provides an optimal scent effect time.

VOCAL COMMUNICATION

Changes in the communication variables, which

tended to increase the area covered by signal, the

time covered by signal, or both, resulted in higher

levels of communication for all dyads in the complex relationship among vocal range, vocalization

frequency, and communication (Figure 11). Vocal

communication would have occurred 100 percent

of the time for all dyads with a vocal range of 1.50

mile (2413 m) and a vocalization frequency of 12

per hour. With those values, a signal from anywhere on the home range space covered the entire

elliptical area, and vocalizing 12 times per hour

(once per 5 minutes) was equivalent to continuous

vocalization in the communication model. With

the maximum values that I simulated, a vocal

range of 0.80 mile (1287 m) and a vocalization

frequency of 6 per hour (one per 10 minutes),

three dyads communicated more than 40 percent

of the time and the remaining two dyads more than

30 percent of the time. The maximum rate of com-
18 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

munication with these values was 45.9 percent for

dyad D and the minimum was 34.6 percent for

dyad A.

There was a linear increase in communication

with linear increase in vocalization frequency (Figure 11) for each vocal range from 0.10 to 0.80 mile

(161 to 1287 m). Vocal range and vocalization

frequency interacted such that, as vocal range increased the effect of increasing vocalization frequency became more pronounced. For example,

an increase of one vocalization per hour with a

vocal range of 0.20 mile (322 m) gave 1.6 percent

more communication, while an increase of one

vocalization per hour with a vocal range of 0.80

mile (1287 m) gave 7.0 percent more communication. This result indicates that an increase in the

frequency with which a fox vocalizes will have a

MEAN

FIGURE 11.—Mean levels of vocal communication that occurred in five simulated red fox dyads with vocal ranges of

0.10 to 0.80 miles (161 to 1287 m) and vocalization frequencies of 0.33 to 6.00 per hour (one per \i/2 hours to one

per 10 minutes). Note that a linear increase in vocalization

frequency gave a linear increase in level of communication

for each simulated vocal range. Several vocal ranges and

vocalization frequencies gave an average of 20 percent communication, including 2.8 vocalizations per hour with a

vocal range of 0.80 miles (1287 m), and 4.7 vocalizations per

hour with a vocal range of 0.40 miles (644 m).

greater effect on the level of dyadic communication when the vocalizations are emitted such that

they can be heard from far away.

The effect of increasing vocal range on level of

communication was nonlinear, becoming more

and more limited as the vocal range increased with

a given vocalization frequency (Figure 12). Wastage of vocal signal emitted beyond the boundary

of the elliptical area accounts for a part of this

limit. As with visual communication, signal was

wasted when it went into space not used by the

receiving animal, and a similar set of threshold

locations existed for such wastage of vocal signal.

In contrast to visual signalling, the signaller could

move outside these threshold locations without

reducing the efficiency of signalling, so long as it

did so between the times when it emitted vocal

signals. Given that a signaller is aware of the location of a potential receiver, vocal signalling may

be made more efficient by directional emission of

signal toward the receiver (Busnel, 1963), which

50—

40 —

30 —

20 —

6.00

4.00

10—

I

I • I ' I • I

0 0.2 0.4 0.6 0.8

VOCAL RANGE IN MILES

FIGURE 12.—The relationship between increasing vocal range

and mean amount of communication that resulted for five

dyads with the six vocalization frequencies indicated at the

right of the figure. The inflection of the curves for vocalization frequencies greater than 0.50 per hour illustrates the

limit that wastage of vocal signal placed on the effectiveness

of increasing the vocal range.
NUMBER 187 19

reduces wastage of signal. Directional emission

was excluded from the communication model

when I assumed that all communication was

unidirectional.

For a particular combination of vocal range and

vocalization frequency, only differences in movement patterns could account for the different levels

of communication shown among the dyads. On the

average (Figure 11) the minimum values of vocal

range and vocalization frequency, which gave

communication 20 percent of the time, were 2.8

vocalizations per hour with a vocal range of 0.80

mile (1287 m), and 4.7 vocalizations per hour

with a vocal range of 0.40 mile (644 m). There

was considerable variation among the dyads in

the levels of communication that occurred with

these sets of values. With 2.8 vocalizations per

hour and a vocal range of 0.80 mile (1287 m),

communication ranged from 16.0 percent for dyad

A to 21.2 percent for dyads D and E. Communication ranged from 13.5 percent for dyad A to 26.0

percent for dyads D and E, with 4.7 vocalizations

per hour and a vocal range of 0.40 mile (644 m).

The relative amount of communication per dyad

was consistent among the dyads for these two and

many other sets of values of the communication

variables. Levels of communication among the

dyads ranked as follows: D = E=1.5, B=3, C=4,

A=5.

Although the way in which the animals moved

about influenced their ability to communicate

vocally, there were no obvious correlations between

ways of moving about and levels of communication

(Table 5). Dyads, however, whose members tended

to travel at greater speeds and tended to turn less

often (both members) ranked highest in levels of

vocal communication. Lowest levels of communication resulted when both members of a dyad

traveled slowly and turned frequently. Theoretically, either pattern of movement could have resulted in higher levels of communication if the

movement patterns of the animals had been coordinated such that used the same portions of

the elliptical area at the same times. Where the

movements were not coordinated, the probability

that they were close together depended on chance

alone, and the chance that both animals would be

in the same part of the elliptical area at the same

time was apparently increased when both animals

traveled at high rates in fairly straight lines.

Parameters that summarize the distribution of

locations resulting from a pattern of movement

should show less correlation with levels of communication than do parameters that describe the

pattern of movement per se. Communication by

any means of signalling depends on the individuals

being at certain places at certain times, and the

over-all distribution of locations does not reflect

the timing of the animal's movements. For example, both members of a dyad might concentrate a

portion of their activity on the same part of the

elliptical area without enhancing vocal communication if they were not both in that part at the

same time.

There was an indication, however, that movement patterns that resulted in maximum dispersion of locations (high K values) gave more vocal

communication than patterns that resulted in

greater clumping of locations (Table 5). Unless

the two members of a dyad were mutually aware

TABLE 5.—Comparison of level of vocal communication provided by pairs of

movement patterns that formed each of five dyads with four parameters of

movement patterns of signallers and receivers within each dyad (criteria for

ranking levels of communication among dyads and for ranking movement

patterns among signallers and receivers are given in text)

Dyad

D

E

B

C

A

Communication rank

1.5

1.5

3

k

5

Rate of

(me

Signaller

2

1

5

3

It

movement

an)

Receiver

1

3

2

5

k

Straight ahead

travel ±30°

Signaller

1

2

5

I

Receiver

2

1

k

3

5

Contagion of

locations

(K)

Signaller Receiver

2

1

5

U

3

2

3

5

k

1

Total number of

grid-squares

Signaller Receiver

3

3

1

3

5

2.5

2-5

1*

1

5
20 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

of locations used by the other member and had

clumps of locations in the same portion of the

home range space, or unless clumping in the same

portions occurred by chance, there should have

been an advantage in maximizing dispersion of

locations used by both the members. This is because clumps of locations for the two animals located in distal portions of the elliptical area, when

combined with short vocal ranges, would have resulted in low levels of communication regardless

of when the animals used these clumps.

Vocal signalling could be an effective means

for maintaining social contact in red fox dyads.

As shown by simulation, movements of the animals

allow them to communicate a reasonably high proportion of the time with relatively low emission

intensities and frequencies of signalling. Vocal signalling is efficient in terms of energy cost to the

animal, relative to other means of communication

(Sebeok, 1967:368) and may require less interference with ongoing behavior of the animal than

do other means of signalling (Marler, 1967:773).

In the total energy budget for a red fox, the cost

of vocalizing a few times per hour is probably not

important, regardless of the emission intensity.

High frequencies of signalling with greater vocal

ranges might allow a potential predator of red fox

to better locate its prey (Hall, 1965), and thus promote selective pressure against such vocal signalling. The most probable predator, the timber wolf,

however, generally locates its prey by scent or

sight (Mech, 1966:118-125).

Red fox probably are capable of emitting vocalizations that can be heard over distances at least as

great as the vocal ranges that I simulated. Fox

(1971:43) indicates that auditory signals are well

developed in the more solitary canids for communication over greater distances, notably in the red

fox. That author, however, presents no data on

absolute vocal ranges. The loud vocal signals are

highly stereotyped (Fox, 1971:185) as predicted

(Marler, 1965:583, 1967:772; Nottebohm, 1972:131;

Lancaster, 1968:442) for signals that transmit information over relatively long distance. Timber

wolves respond by vocalizing to the howls of wolves

that are at least 0.50 miles (804 m) away (Rutter

and Pimlott, 1968:138), and farm dogs by barking

to the baying of hounds that are 1 mile (1609 m)

or more away (pers. obs.). Spotted hyenas (Crocuta crocuta) respond to tape-recorded vocalizations from as far as 3000 m (Kruuk, 1972). From

distances of at least 10 m and less, red fox can

precisely locate, on the basis of hearing alone,

slight noises made by prey (Osterholm, 1966:57).

Localization from both short and long distance is

enhanced (Busnel, 1963) by repetition of signalling, which allows a receiver to "home in" on the

direction of the signal source. Red fox are thus

probably capable of both emitting loud vocal signals and using these signals for communication

over long distance. As indicated by simulation,

these loud vocalizations when emitted often

enough could provide high levels of dyadic communication when red fox move about.

Why then do red fox not vocalize more often

with emission intensities that can be heard over

long distances? Nocturnal animals, such as the red

fox, might be expected to rely on audition as the

dominant modality for communication over long

distances (Nottebahm, 1972:131). Timber wolves

apparently use long-distance vocalizations as a

means for maintaining contact among members

of social units when they become separated (Theberge and Falls, 1967). However, Fox (1971:184)

indicates that, unlike domestic dogs, wild canids

in general do not often vocalize. Red fox apparently seldom emit loud vocalizations. Sargeant

(pers. comm.) observed pairs of red fox in a 10-

acre (4-ha.) enclosure and "very rarely" heard

them vocalize. On the fewer than five occasions

during several months of observation when vocalizations were heard, the animals apparently responded either to the presence of the observer or

to other disturbance. Burrows (1968:170-173)

listed all fox vocalizations heard during a oneyear period. Vocalizations, excluding those on

eight dates by cubs at a den, were noted on only

56 dates, and on most of these only a single vocalization was heard. There were long periods of consecutive dates when the foxes did not vocalize; for

example, "during February 1966 I heard foxes on

only three nights" (Burrows, 1968:45).

It is unlikely that red fox would depend entirely

on vocal signalling, or on any other single means

of communication, for maintaining social contact

between members of dyads. Marler (1967:773)

notes that when vision is limited there tends to be

more reliance, in general, on olfaction for both

close-range and distant communication. Red fox

have well-developed scent glands and olfactory
NUMBER 187 21

capabilities (Fox, 1971). As indicated previously,

the movements of red fox can provide for moderate to high levels of olfactory communication.

This study suggests that vocal communication

could be effective in maintaining social contact in

red fox dyads. That such communication occurs

infrequently is explainable in at least two ways.

Levels of communication required to maintain

social bonding in red fox dyads may be very low

or, more likely, other means of communication,

such as those provided by scent marks and trails,

may usually preclude the necessity for using longdistance vocal communication.

SCENT POINT COMMUNICATION

Combinations of the three communication variables that produced relatively sparse, small circles

of scent on the home range space gave low levels

^ ^ \ ' \ ' \

FIGURE 13.—Mean levels of scent point communication that

occurred in five simulated red fox dyads for four scent ranges

(0.05, 0.10, 0.30, and 0.50 miles or 80, 161, 482, and 804 m,

respectively), scent effect times from 1 to 8 hours, and

scenting frequencies of 0.33 to 2.00 per hour (one per H/2

hours to one per 30 minutes). Note that the average amount

of communication increased with an increase in any one or

more of the communication variables. Many values of the

three variables resulted in an average of 20 percent communication including a set in which the signaller deposited

scent once every 30 minutes (2 per hour), scent remained

effective for 8 hours, and the receiver could smell scent from

0.06 miles (96 m).

of communication, while combinations that produced relatively common, large circles of scent

gave high levels of communication (Figure 13).

Higher levels of communication resulted from

increasing the scent range, and for each scent range

they resulted from increasing the number of effective scent points. A greater number of scent points

effective at any time resulted from higher scenting

frequencies, longer scent effect times, or both.

Scent point communication would have occurred

100 percent of the time with a scent range of 1.50

miles (2413 m), a scenting frequency of 12 per

hour, and a scent effect time of 5 minutes. With a

scent range of 1.50 miles (2413 m) other combinations of scenting frequency and scent effect time

would have given 100 percent communication,

such as a frequency of 6 per hour and an effect

time of 10 minutes, so long as one or more scent

points were effective at any time. I simulated lower

scent ranges from 0.05 to 0.50 mile (80 to 800 m),

scent effect times of 1 to 8 hours, and scenting

frequencies of 0.33 to 2.00 per hour (one per 3

hours to one per 30 minutes).

On the average, with maximum values of all

three variables (0.50 mile or 800 m; 8 hours; 2 per

hour), the animals communicated 86.8 percent of

the time. With these high values, there was con0.50MILES. I PER HOUR

0.30 MILES'. I PER HOUR

o.so MILES: as PER HOUR

0.10 MILES: 2 PER HOUR

0.10 MILES: 0.5 PER HOUR

cos MILES: as PER HOUR

SCENT EFFECT TIME (HOURS)

FIGURE 14.—The relationship between scent effect time and

mean amount of communication that resulted for five dyads

with the six combinations of scent range and scenting frequency shown at the right of the figure. The inflection of

the curves for ranges greater than 0.10 miles (161 m) and

frequencies greater than 2 per hour illustrates the limit

that overlap of effective scent circles placed on the effectiveness of increasing the scent effect time.
22 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

siderable variation in level of communication

among the dyads with dyad E communicating 99.8

percent of the time and dyad A 69.8 percent of

the time. The lowest values that I simulated (0.05

mile or 80 m; 1 hour; 0.33 per hour) gave an average of 0.6 percent communication. There was

negligible variation in level of communication

among the dyads, with dyad A communicating 1.1

percent of the time and the remaining four dyads

less than 1 percent of the time.

Increasing the value of any of the three communication variables while the other two were held

constant did not result in expected increases in

communication. Some factor (s) thus limited the

effect of increasing the value (s) of the communication variable (s). The amount of communication

that resulted from the scent point model, given a

particular dyad's movement patterns, should have

been directly related to the area covered by effective scent at any time. A change in any of the three

variables that increased this area should have increased communication in direct relation to the

increase in total scented area, other things being

equal. When the other two variables were held

constant, a linear increase in scent range (the area

increased as the square) should have resulted in a

nonlinear increase in communication. When the

other two variables were held constant, a linear

increase in either scent effect time or in scenting

frequency should have given a linear increase in

communication.

A unit increase in scent effect time gave less and

less communication as more and more of the

home range space was covered with scent because

of higher scent ranges and scenting frequencies

(Figure 14). For a particular combination of scent

range and scenting frequency, the relationship

between scent effect time and percent communication was linear as expected, but only for low scent

ranges and scenting frequencies. A signaller could

thus increase the level of communication by increasing the scent effect time, but would do so

more efficiently when scent ranges and scenting

frequency were held relatively low. This could be

accomplished by scenting with a chemical that

had a low diffusion coefficient and low volatility,

as would be given by a substance with high

molecular weight (Bossert and Wilson, 1963:

454). The resulting slow fade-out time would

have the disadvantage of limiting the rate of information transfer (Wilson, 1968:77), but could increase the overall level of communication in the

dyad.

As with scent effect times, a unit increase in

scenting frequency gave less and less communication as more and more of the home range space

was covered with scent because of greater scent

effect times and scent ranges (Figure 15). The

expected linear increase in level of communication

with linear increase in scenting frequency, for a

particular combination of scent effect time and

scent range, was shown only for low scent ranges

and scent effect times. A factor that may have

limited the effect of increasing scent effect time,

scenting frequency, or both, was overlap of circles

of effective scent. The probability that two or more

effective scent circles would overlap increased as

each scent point remained effective for a longer

time, or, particularly, as scent points were deposited

closer together in both time and space. When

effective scent circles overlapped, the effect of a

unit increase in the number of scent points on the

home range space was reduced because each scent

point covered less than the expected area around

it with effective scent. There was no additional

effect on communication in areas where effective

scent circles overlapped.

100 —

0.50 MILES'. S HOUR!

O.SOMLES:iHOUR

0.30 MH.ES: 2 HOURS

0.10 MN.ES: S HOURS

o.io MILES: 4 HOURS

0.05 MLES: 6 HOURS

0.05 MLES: I HOUR

SCENT POINTS PER HOUR

FIGURE 15—The relationship between scenting frequency

and mean amount of communication with the seven combinations of scent range and scent effect time shown at the right

of the figure. The inflection of the curves illustrates the limit

that overlap of effective scent circles placed on the effectiveness of increasing the number of scent points deposited per

unit time.
NUMBER 187 23

The effect of increasing scent range on levels of

communication was limited by at least two factors.

These were overlap of scent circles, as discussed

above, and wastage of signal emitted outside the

home range space. A combination of these limiting factors resulted in deviations (Figure 16) of

the relationship between scent range and percent

communication from the expected increases.

Scent point signalling could be made most efficient by the signaller adjusting the scent range

and scent effect time to give moderate fade-out

times and moderate scent ranges, by scenting at

least some threshold distance from the boundary

of the home range space, and by distributing nonoverlapping effective scent points over a relatively

large part of the home range space, rather than

their being placed within a small portion of it.

That a red fox moves over a large portion of its

home range space in a single night's travel indicates that at least the last qualification for efficient

scent point signalling may be met by the animals.

Because of the interaction of the three communication variables, there were many sets of values

that, on the average, resulted in 20 percent communication. I used one such set: 2 scent points

per hour; 8 hours of scent effect; scent range 0.06

miles (96 m), for ranking scent point communication among the five dyads. With those values,

S HOURS: 2.00 PER HOUR

8 HOURS'. 0.33 PER HOUR

4 HOURS: 0.50 PER HOUR

2 HOURS 0.50 PER HOUR

2 HOURS: 0.33 PER HOUR

I HOUR*. 0.33 PER HOUR

SCENT RANGE (MULES)

FIGURE 16.—The relationship between increasing scent range

and mean amount of communication that resulted for five

dyads with the six combinations of scent effect time and

scenting frequency shown at the right of the figure. The

inflection of the curves illustrates the limit that a combination of wastage of scent signal and overlap of effective scent

circles placed on the effectiveness of increasing the scent

range.

communication ranged from 15.2 percent for dyad

B to 30.8 percent for dyad D. Communication

ranked as follows among the dyads: D=l, E=2,

C=3, A=4, B = 5. For at least those values of the

communication variables that produced moderate

to high levels of communication, ranking was generally consistent over a wide range of values of all

three variables. The variation in level of communication among the dyads with particular combinations of the communication variables, and the

consistency shown over a range of values shows

that the way in which the animals moved about

influenced their ability to communicate with scent

point signalling.

Dyads in which the signaller had a relatively

high rate of movement combined with straight

ahead travel had higher levels of scent point communication (Table 6). There was a good correlation between level of communication and both

these movement parameters. The speed and directness with which the receiver moved showed no

correlation with level of communication within

the range of speeds and directivity that I simulated.

Likewise, there were no apparent correlations for

either signallers or receivers between level of communication and parameters that describe the

overall distribution of locations (K or total number of grid-squares). When the signaller moves

about rapidly and in straight lines, it tends to both

distribute effective scent points over a large portion of its home range space and to reduce the

overlap in effective scent points. Both effects would

tend to increase the probability that a receiver

would encounter an effective point and increase

the level of scent point communication.

Scent point signalling with red fox movement

patterns can provide dyads moderate to high levels

of communication, as indicated by simulation.

Red fox are known to scent mark regularly as they

move about, the odor persists for several days,

and other fox can detect scent marks from reasonable distances.

Field observations of the number of scent marks

left on snow allow estimation of the rate at which

such marks are placed, because marks left during

the first activity period following snowfall are

attributable only to that activity period, and distances that the animal is tracked can be converted

to travel times by using average rates of fox movement. Murie (1936:11) reported that a fox uri-
24 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

TABLE 6.—Comparison of level of scent point communication provided by pairs

of movement patterns that formed each of five dyads with four parameters of

movement patterns of signallers and receivers within each dyad (criteria for

ranking levels of communication among dyads and for ranking movement

patterns among signallers and receivers are given in text)

Dyad

D

£

C

A

B

Conmunication rank

1

2

3

k

5

Rate of movement

(mean)

Signaller

2

1

3

1+VJl

Receiver

1

3VJl

kCVJ

Straight ahead

travel ±30°

Signaller

1

2

3

kVJl

Receiver

2

1

3VJl

1+

Contagion of

locations

(K)

Signaller Receiver

2 2

1 3

1+ k

3 1

5 5

Total number of

^•id-squares

Signaller

3

3

3VJl

1

Receiver

2.5

2.5

1VJl

k

nated 10 times along one-half mile (804 m) of

track. Sargeant (in litt.) followed the tracks of a

radio-marked male for a total of 3 miles (4827 m)

on two dates, finding 41 places where the animal

urinated and two where it defecated. For urine

marks, these convert to 20 and 13 marks per mile,

respectively, and for feces marks to one per 1.3 miles.

Sargeant, et al. (in press), for radio-tracked red

fox, report an average rate of nocturnal travel of

1.1 miles per hour (1770 m per hour). Using these

figures, I estimate that the animals urine marked

18 and 11 times per hour, respectively, and marked

with feces once per 57 minutes. Interpretation of

these rates is confounded because the data on

rates of urination and defecation were collected

during the time of year when foxes breed. These

estimated rates may thus be inflated because scent

marking by red fox increases during the breeding

season (Fox, 1971:186).

Red fox scent persists, even to humans, for at

least several days after it is placed (Murie, 1936:

13). Feces, in particular, can serve as scent marks

for a long period but may require that a potential

receiver break the scat to increase the scent level

(Scott, 1943:435). As with scent trails, scent marks

containing large molecules with low diffusion coefficients would increase the time over which a

mark is effective, but would generally reduce the

effective range (Bossert and Wilson, 1963:158-163)

and the amount of information transferable to

a receiver (Wilson, 1968:77).

The range of effect of red fox scent marks has

not been experimentally determined. Penned red

fox are able to detect the odor of meat from 1.5

meters (Osterholm, 1966:56), and would probably

detect fox scent from even greater distance. The

range would depend in part on wind direction and

air flow. Busnel (1963:74) reported the upper

limit in range of scent perception for wolves and

dogs as 1500 to 2000 m but did not indicate, as

seems likely, that wind had influenced this range.

Heavy molecules can be carried (Van Arsdel,

1967:1228) by light winds and air flow over much

greater distances, reaching to at least 5 to 10 miles

(8045 to 16,090 m).

I did not simulate conditions in which a large

number of small scented areas remained effective

for periods of several days. Extensive modification

of the computer program would be necessary to do

so. Higher scenting frequencies with short scent

ranges were not simulated, but are possible with

the program I used (Montgomery, 1973). It can

be inferred from the simulation results, however,

(see particularly the upper curve of Figure 16)

that scenting frequencies of 10 or more per hour

would give 50 percent communication or more,

even with scent effect times as short as 8 hours and

scent ranges of 0.025 miles (40 m) or less.

Scent marking could be an effective means for

dyadic communication in red fox. Leyhausen and

Wolff (1959:670) proposed that such scent marks

can allow the individuals to time their respective

movements, and thus provide spacing and "territorial" responses even when home range spaces

overlap. Timing based on scent marks could provide for spacing between mated pairs that occupy

the same space as well.

The major alternative hypotheses for the role

of scent marking (reviewed by Ewer, 1968:104-105,

116-120) is that scent marking by an individual
NUMBER 187 25

mammal serves to orient that individual on its

home range space. Additional hypotheses concerning the role of scent marking are reviewed in

Kleiman (1966). J. P. Scott (1967:379) notes that

there is no evidence that domestic dogs respect as

boundaries the scent marks left by other dogs. The

usual reaction is to cover these marks with scent

of their own. When a domestic dog enters a strange

locality that has not previously been scent marked

by any dog, it will urinate on any objects that are

slightly elevated (Scott and Fuller, 1965:68).

Among canids, red fox especially will urinate or

defecate on unfamiliar objects (Fox, 1971:186).

Once these objects have been marked, they are

ignored for long periods of time, but the scent may

be periodically renewed. Young (1944:304) notes

that timber wolves renew such scent marks each

time they pass by a place that they have previously

scent marked. Because they are so wide ranging

(Mech, et al., 1971:13-18), wolves may not return

to a scent post for several days. Scent marking

could simultaneously serve the dual functions of

self-communication and dyadic communication.

Comparisons among the

Means of Communication

Movements of the animals had an effect on the

level of communication in the simulated red fox

dyads, regardless of the means of signalling. For all

except tactile signalling, some communication was

provided by all models and movement patterns.

Within the range of values of the communication

variable (s) that I simulated, the maximum level

of communication that resulted for any dyad for

each means of signalling ranged from 0 to 100 percent, for tactile and scent point signalling, respectively (Table 7). Visual and vocal communication

would have reached the 100 percent level had I

used appropriate values of the communication

variable (s). As noted earlier, "close-range" communication was a special case of the visual communication model. Scent path communication, which

reached a maximum of 38 percent for any dyad,

would not have reached a higher level regardless

of how long scent paths remained effective.

The maximum levels of tactile and scent path

communication that could be reached were limited

by movements of the animals. Limitations placed

by animal movement on visual, vocal, and scent

point communication could have been overcome

by increasing the value of the appropriate communication variable that controlled the spatial

area of effect of the signal. No such variable exists

for tactile communication, and none was programmed into the simulation model for scent path

signalling.

Movements of the animals had a greater influence on the level of visual communication than

on vocal or scent point communication. For each

TABLE 7.—Summary of values of various communication variables used to

simulate communication in red fox dyads with simple models and of levels of

communication resulting from simulation

Means of

signalling

Tactile

Close-range....

Visual

Scent path

Vocal

Scent point....

Controlled

communication

variable(s) 1

Maximum

value(s)

simulated

Maximum

communication

for any dyad

(percent)

Value(s) for

20 percent

communication

(average)

Range of

communication

among dyads

(percent)^

None

Signal range

Visual range

Scent effect time

Vocal range

Vocalization frequency

Scent range

Scent effect time

Scenting frequency

0.01 miles

0.90 miles

2k hours

0.80 miles

6 per hour

0.50 miles

8 hours

2 per hour

0

1

96

38

U6

100

None

None

0.19 miles

7.6 hours

Various

0.1*0 miles and

U.7 per hour

Various

0.06 miles;

8 hours and

2 per hour

29(7 to 36)

13(15 to 28)

13(13 to 26)

16(15 to 31)

1 Movement of the animals was an uncontrolled variable with all means of signalling.

2 Range when the value(s) that gave an average of 20 percent communication was used for each dyad.
26 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

TABLE 8.—Summary of factors that limited effectiveness of attempts to increase

levels of communication with various simulated means of communication

Means of

signalling

Tactile

Visual

Vocal

Scent point

Controlled

communication

variable(s)

None

Signal range

Visual range

Scent effect tine

Vocal range

Vocalization frequency

Scent range

Scent effect time

Scenting frequency

Optimal range for

maximizing increase

in communication

-

0.05 - 0.U0 miles

0.33 - 7.50 hours

0.10 - 0.30 miles1

0.33 - 6.00 per hour

0.05 - 0.30 miles2

Various^

Various^

Major factor(s)

limiting increase in

level of communication

Animal movement only

Animal movement only

Animal movement; wastage of

signal

Animal movement; divergence

of home range spaces

Animal movement; wastage of

signal

Animal movement only

Animal movement; wastage of

signal; overlap of effective scent circles

Animal movement; overlap of

effective scent circles

Animal movement; overlap of

effective scent circles

Optimal range for a vocal range depended on vocalization frequency.

2 Optimal range for a scent range depended on scent effect time and scenting frequency.

3 Optimal range for a scent effect time depended on scent range and scenting frequency.

•+ Optimal range for a scenting frequency depended on scent range and scent effect time.

communication model, when a particular value of

the communication variable or a set of values of

the communication variables were used in simulation, only differences among the movement

patterns accounted for variability in level of communication among the dyads. Because the same

five dyads were used for all means of signalling,

this variability can be compared among the means

of signalling, and indicates the relative importance

of movement patterns on level of communication.

With the value (s) of the communication variable (s) that gave an average of 20 percent communication, levels of visual communication ranged

from 7 to 36 percent among the dyads (Table 7),

a total range of 29 percent. Comparable total

ranges were 13 and 16 percent for vocal and scent

point communication, respectively. Those means

of signalling that involved the fewest communication variables (i.e., tactile and scent point) were

thus most severely limited by movements of the

animals. This comparison suggests that where more

variables affecting the level of communication are

under control of the signalling animal, variables

could be optimized to minimize the effects of movement on communication.

For the various means of signalling, different

major factors limited the effectiveness of attempts

to increase levels of communication (Table 8).

Animal movement patterns limited attempts to increase communication for all means of signalling,

and were the sole major factor for tactile, closerange, and scent path signalling.

With tactile and close-range signalling, communication levels could be increased by coordination

of movements of dyad members such that they

were seldom far apart. Without rare chance meetings, some other means of signalling would be

necessary to reveal their respective locations so

that they could initially come together and could

find each other after being separated. Levels with

scent path signalling could be increased by coordinating the movements of dyad members such that,

even though the animals were apart, they tended

to travel in the same path with the receiver approximately or actually following the signaller. Scent

path signalling alone could maintain such a leaderfollower set of movement patterns, although other

means of signalling might increase the chances

that the receiver would initially make contact with

an effective scent path. Initial contact, or scent

path communication in the absence of leaderfollower movement patterns, would be enhanced

when the signaller seldom turned and traveled at

high speed (Table 9).

For visual signalling, and for the spatial range

variables of both vocal and scent point signalling,
NUMBER 187 27

communication could be made more efficient by

proper choice of emission intensity (Table 8) and

modification of the signaller's movement pattern.

This modification would involve use of a set of

threshold locations appropriate for the emission

intensity and its signal range, and travel by the

signaller at a high rate of speed (Table 9).

For the temporal variables of scent point communication, communication could be made more

efficient by modification of the signaller's movement pattern through avoidance of slow travel

with many turnings (Table 9) so as to reduce the

overlap of circles of effective scent. It would be

more efficient with proper dual choices of frequency of scenting and scent effect time, such

choices further reducing the probability of overlap

of effective scent circles.

Modifications of movement patterns by an individual to influence levels of communication would

have to be made within the range of patterns dictated by many other factors affecting fox movements. The fox obviously could not afford to

move so fast or far to increase communication that

it expended energy beyond that which it needed

to survive, and modifications should not be made

that would drastically reduce the animal's chances

for finding food.

Many interacting factors influence the movement pattern of an individual fox and, thus, the

movement patterns of a fox dyad. Some of these

influences are genetically controlled, such as limitations that structure and metabolism place on

speed and duration of movement, while some, such

as responses to particular features of the indiviTABLE 9.—Summary of some characteristics of

movement patterns of members of simulated red

fox dyads that enhanced communication with

tfarious means of signalling

Means of

signalling

Visual

Scent path

Vocal

Scent point

Type of movement pattern

that enhanced communication

High rate of travel by receiver

Straight-ahead travel at high rate

by signaller

Not clear; tendency toward straightahead travel at high rate by both

signaller and receiver

Straight-ahead travel at high rate

by signaller

dual's home range space, are learned. Selection

should act to give a range of movement patterns

that are possible for red fox, and the local environment should reduce this range by imposing limitations on individual movement. Still it seems likely

that enough latitude in movement pattern is

permissible under these constraints to allow modification, by an individual, of movement patterns

to enhance communication. As an example of this

latitude, Sargeant, et al. (in press) conclude from

radio-tracking and concurrent field observations

that food gathering rarely is the major determinant

of red fox movement patterns. The animals that

they studied moved much more than was apparently needed for finding and capturing prey, continued to move about after feeding, and showed

similar total amounts of movement during periods

of food scarcity and abundance. Their data support

the view that, at least for one major factor affecting movement of foxes, there is latitude in the

amount of influence that food gathering has on

the pattern of movement.

Summary

Results ef this simulation study suggest that the

way in which red fox move about differentially

affects dyadic communication, the effect of movement depending on how one animal signals the

other. The study further suggests that adjustments

the signaller, the receiver, or both could make in

their movement pattern (s), and the signaller could

make in how it signals can affect both the level of

dyadic communication and the efficiency of signalling. Such adjustments would require in general

that the signaller be aware of the location of the

receiver or have information on the receiver's

previous movement pattern. This awareness of the

pattern of movement of a receiver could result

from bi-directional communication in which both

animals of a dyad act as both signallers and receivers, one major function of communication

being to maintain mutual awareness of the movement patterns of dyad members and promote

further communication between them.

In general, two parameters determined by the

movements of any two animals affect the potential

for communication between them by determining

the optimal means of signalling and by restricting

information transfer via those means. These para-
28

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

meters are distances between the animals at corresponding points in time, where the distance can

range from 0 to a maximum determined by the

dimensions and the spatial relationship of the

two home range spaces; and times between the

animal's use of corresponding areas of space, where

the time can range from 0 to a maximum determined ultimately by the lifespan of one or the

other of the animals. Given that prior communication has given mutual awareness of the locations

and movement patterns, the animals can adjust

the distance between them, the time between them,

or both. In so doing they can increase or decrease

the opportunities for further communication and

can increase or decrease the efficiency of signalling

by one or more means. These adjustments require

changes in the movement pattern of one or both

individuals and will be reflected by changes in

one or both home range spaces. The degree of

mutual adjustment in movement patterns that the

two animals can make to change the level of dyadic

communication will be limited by factors extraneous to dyadic communication, such as communication and social relations with other individuals

and dispersion of life requirements in the respective home ranges of the dyad members.

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