The Natural History of

the Central American Agouti

(Dasyprocta punctata)

NICHOLAS SMYTHE

;

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY • NUMBER 257
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SMITHSONIA N CONTRIBUTION S T O ZOOLOGY * NUMBE R 25 7

The Natural History of

the Central American Agouti

(Dasyprocta punctata)

Nicholas Smythe

SMITHSONIAN INSTITUTION PRESS

City of Washington

1978
ABSTRAC T

Smythe, Nicholas. The Natural History of the Central American Agouti

(Dasyprocta punctata). Smithsonian Contributions to Zoology, number 257, 52

pages, 25 figures, 2 tables, 1978.—In this report the behavioral ecology of the

Central American agouti (Dasyprocta punctata), a large caviomorph rodent,

living on Barro Colorado Island in the Panama Canal Zone is described. This two

phase study includes social structure, activity patterns, maturation, courting,

agonistic and comfort behavior, and acoustic, vocal, visual, and olfactory communication systems, as well as the interrelationship of the animals' behavior with

the environment.

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

in the Institution's annual report, Smithsonian Year. SERIES COVER DESICN: The coral Montastrea

cavernosa (Linnaeus).

Library of Congress Cataloging in Publication Data

Smythe, Nicholas

The natural history of the Central American agouti (Dasyprocta punctata)

(Smithsonian contributions to zoology ; no. 257)

Bibliography: p.

Supt. of Docs, no.: SI 1.27:257

1. Central American agouti. 2- Mammals—Panama—Barro Colorado Island- I. Title. II.

Series: Smithsonian Institution. Smithsonian contributions to zoology ; no. 257

QL1.S54 no. 257 [QL737.R644] 591'.08s [599\3234] 77-608187
Contents

Page

Introduction 1

Acknowledgments 3

Materials and Methods 3

Behavioral Ecology 3

The Trap-Mark-Release Program 6

Phase I: Results of Seasonal Changes on Behavior 6

Seasonality of the Food Supply 6

Effects of Seasonal Abundance of Food 7

Seasonal Changes in Aggressive Behavior 10

Phase II: Results of the Trap-Mark-Release Program 11

Species Trapped 11

Numbers and Age Classes 11

Trapping Locations 12

Life History Curves 13

The Ridgetop Traps 18

Adult Males 18

Life Expectancy of Juveniles 19

Mortality Differences between the Sexes 20

The Use of Space 20

Agouti Territories 20

Territories and Nonreproductive Animals 21

Activity Patterns 22

Feeding and Foraging Behavior 23

Types of Food 23

Foraging 24

Feeding Spots 24

Feeding Techniques 25

Scatterhoarding 25

Comfort Behavior 26

Allogrooming 26

Autogrooming 26

Protection against Biting Dipterans 27

Reaction to Rain 27

Sleeping 27

Courtship and Mating Behavior 28

Introductory Behavior of Captives 28

Courtship of Free-living Agoutis 29

Agonistic Behavior 30

Interspecific Agonistic Patterns 30

Intraspecific Agonistic Patterns 30

Maturation of Young Agoutis 32

Parturition and Nest Selection 32

iii
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

Page

Maternal Care of Nest-bound Young 33

Breakup of the Mother-Young Bond 36

Role of the Male 37

Survival of the Young 38

Communication and Displays 38

Visual Communication 38

Olfactory Communication 39

Marking with Anal Gland Secretions 39

Urine Marking 40

Mechanical Communication 41

Thumping 41

Derivation and Function of Thumping 42

Drumming with the Forefeet 42

Sounds Made with the Teeth 42

Vocalizations 42

The Alarm Bark 43

Reactions of Conspecifics to Alarm Barks 43

The Purr 44

The Creak-Squeak 44

Fight Grunts 44

Rumble 45

Growl 45

Distress Scream 45

Conclusions 45

Competition and Ecological Separation among Terrestrial Frugivores.. 45

Agoutis and Seed Dispersal 47

The Adaptive Value of Monogamous Pairs 48

Limitations Imposed by the Necessity of Hoarding 49

The Status and Future of the Agouti 49

Literature Cited 51
The Natural History of

the Central American Agouti

(Dasyprocta punctata)

Nicholas Smythe

Introduction

Since their appearance in the New World during

the late Eocene, the caviomorph rodents have

undergone an intensive adaptive radiation, so that

today the group exhibits a diversity that is, in comparison with other groups of mammals at the same

taxonomic level, extraordinary. The taxonomic

affiliations of the agouti (based on Simpson, 1945)

are illustrated in Figure 1.

The porcupine (Erethizon dorsatum) is the only

caviomorph that occurs naturally north of the

southern part of Mexico, the remainder being confined to Central and South America, where some

are small arboreal animals, one almost entirely

fossorial, and two semiaquatic. Some of the larger

genera appear to occupy ecological niches similar

to those of various Old World small ungulates.

Thus, as Kirchshofer (1960a) points out, the mara

(Dolichotis patagonum) bears many resemblances to

some of the small, plains-dwelling antelopes. Indeed, the remarkable running gait known as "stotting," which is so characteristic of many ungulates,

also occurs in the mara (Smythe, 1970a). Dubost

(1968) considers some of the similarities between

cavimorph rodents and West African mammals,

and Eisenberg and McKay (1974) discuss convergences with Asiatic forms.

The agouti (Dasyprocta punctata) is similar in

many respects to some of the small forest-dwelling

Nicholas Smythe, Smithsonian Tropical Research Institute,

P.O. Box 2072, Balboa, Canal Zone.

antelopes (Dubost, 1968; Bourliere, 1973) and to

the mouse deer Tragtilus (Morris, 1965). Agoutis

(Figure 2) are large, cursorial, diurnal, principally

frugivorous rodents that occur in broadleafed forests from southern Mexico to northern Argentina.

Their habit of "scatterhoarding" (Morris, 1962)

food items makes them one of the most important

dispersers of the propagules of their food plants. It

appears, in fact, that many of the trees within their

natural range have no other regular means of

dispersal. The importance of the dispersed distribution of Neotropical forest trees, as an adaptive

characteristic, has been discussed by various authors

(Ridley, 1930; Janzen, 1969, 1970). If the dispersal

agents are removed (for example, by indiscriminate

hunting), then the natural distribution will not be

maintained and the character of the forest will

gradually change. Predation upon various parts of

the trees and the pathogens affecting them will increase, recruitment will decline, and the species

composition of the community will change.

Agoutis are an important food source for man

throughout their range. The meat is not generally

considered as desirable as that of their nocturnal

relative the paca (Cuniculus paca), but agoutis are

commoner and are more easily caught. Firearms

are not necessary for a successful agouti hunt since,

due to the unwillingness of the animals to leave

their rather small home range, they can be run to

ground with dogs and then killed with machetes.

For many of the chronically protein-deficient poor

people within the range of the agouti, it is one of

the most important meats.
OLD WORLD HYSTRICOMORPHS

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

SUBORDER HYSTRICOMORPHA

NEW WORLD CAVIOMORPHS

HISTRICIOAE

O.W. Porcupint (4)

ERETHIZONTIDAE

N.W. Porcup»n«(4)

HINCHILLIDAE

Viscocha. cNnchiloO)

ECHIMYIDAE

Spiny rat (14)

ABROCOMIDAE

CMnehllla rat (I)

CAVIIDAE

Guinea pig. mara (6)

CTENOMYIDAE

Tuco-tuco(l)

OCTOOONTIDAE

Bush rat.viacacha rat 16)

Cunteului Stictomv Dn«*procto Mvonroctn

FIGURE. 1.—Taxonomic relationships of the suborder Hystriocomorpha (after Simpson, 1945;

numbers in parentheses indicate number of genera in each family).

In addition to constituting a food for man,

agoutis are also important in the diets of several

carnivorous animals. They are probably a principal

food item for ocelots (Felis pardalis) and jaguaroundis (Felis yaguaroundi), and an important occasional food for jaguars (Panthera onca) and

pumas (Felis concolor), as well as tayras (Eira barbera) and coatis (Nasua narica). Many of the larger

snakes undoubtedly eat an occasional agouti and

M. Alvarez del Toro (pers. comm.) has found agouti

remains in the nest of an ornate hawk-eagle

(Spizaetus ornatus).

In the few remaining Neotropical lowland forests

that have not been severely disturbed by man,

agoutis are the most commonly observed diurnal

terrestrial mammals (Eisenberg and Thorington,

1973:157; pers. obs.). It may thus seem surprising

FIGURE 2.—a-d, Locomotion and general morphology of the

agouti; e, hind foot; /, forefoot.
NUMBER 257

that so little is known of their habits. They are,

however, shy animals and those generally noticed

by a walker in the forest are already fleeing and

have advertized their presence with alarm barks. A

few studies have been made on captive agoutis

(Weir, 1971; Roth-Kolar, 1957) and more detailed

studies have been made of captive acouchys (Myoprocta sp.) (Morris, 1962; Kleiman, 1971, 1972).

Myoprocta is very similar to Dasyprocta though it

is considerably smaller. Practically nothing is

known of Myoprocta in the wild, but in captivity

many of the behavioral patterns are similar to those

of Dasyprocta.

Enders (1935), in what is still the most informative work on the life histories of many Neotropical

mammals, considers agoutis at some length, but he

did not work with a known group of individuals

nor did he study their interactions with such factors as the food supply.

ACKNOWLEDGMENTS.—John F. Eisenberg introduced me to the agouti, suggested it as a subject,

and contributed much to the approach to, and interpretation of, the study. The Smithsonian Tropical Research Institute and my colleagues there

have borne, and borne with, me during the protracted gestation of this paper. To them, and to

others too numerous to mention who have also contributed, I offer my sincerest appreciation. I thank

Michael H. Robinson, Ira Rubinoff, Martin H.

Moynihan, A. Stanley Rand, and Donald M. Windsor for critically reading various parts of the manuscript, but apologize and accept full responsibility

where I have not followed their suggestions.

I thank Arilla H. Kourany and Vielka Vergel for

their considerable efforts in typing several drafts

of the manuscript.

Sections of this paper were submitted as part of

the requirements toward the degree of Doctor of

Philosophy at the Department of Zoology of the

University of Maryland.

Phase II of the study was supported by the

Smithsonian Institution Environmental Sciences

Program.

Materials and Methods

I studied agoutis at the Smithsonian Tropical

Research Institute station on Barro Colorado

Island in the Panama Canal Zone from August

1965 until December 1967, and again from late

1971 until May 1977. Descriptions of Barro Colorado Island may be found in Allee (1926), Kaufmann (1962), and in the literature cited in those

papers. The first phase of my study (1965-1967) was

concerned chiefly with field observations of a small,

known population that lived to the north of the

laboratory clearing.

The second phase is a trap-mark-release study

(which is still going on) and is part of the Smithsonian Institution Environmental Sciences program. It is being conducted in a watershed basin to

the south of the laboratory clearing (Figure 3). I

have also watched wild agoutis in various parts of

Costa Rica; in Chiapas, Mexico; in the Darien

forest, and other parts of Panama. I have observed

captive agoutis at the University of Maryland, Department of Zoology; at the U.S. National Zoological Park; at the Zoological Park in Tuxtla Gutierrez, Chiapas; and in cages on Barro Colorado

Island.

BEHAVORIAL ECOLOGY

During the first phase of the study agoutis were

caught in Tomahawk (National), 23 X 23 X 81 cm,

double-doored traps that were set in a large circle

roughly following the 60-m contour line in the

study area (Figure 3a). Animals were caught chiefly

for the purpose of marking them for subsequent

identification. I have found it impossible, so far, to

regularly trap agoutis at any time of the year except when falling, ripe fruit is scarce. Even at that

time adult animals will seldom enter traps. Thus

the usefulness of traps in the determination of

home ranges and population structures is rather

limited.

During phase I, each captured animal was

marked according to a coded pattern with a black

fur dye (Durafur, I.C.I., U.K.) and, in addition, by

means of a tattooed number in each pinna. The

phase II animals are marked with the tattooed

numbers only. Agoutis molt from mid-February

through April, and the season of fruit shortage,

during which most of them were captured, lasts

from mid-August through January. The dye marks

thus remained visible from two to eight months.

The pinnae are very thin, so the 1-cm-high, tattooed numbers are easily readable at distances up

to 20 m with the aid of good, tripod-mounted

7 X 35 binoculars.
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

100 m

A! PIM M I study oroo

B: Laboratory clearing

C: Photo l study arsa

•<. Habitual agouti trails

"N Location of trta s~t

— Contour(Intor val'ca. .5 m) }

10 motors

• Habitual f••ding spot

"^ Concontrotton of

p undergrowth

\ Spiny bromalM potoh

FIGURE 3.—Barro Colorado Island: a, locations of the study areas (arrow indicates the bait area

and observation platform; watershed basin constitutes the phase II study area); b, phase I

bait area.

Unmarked animals that frequently visited observation areas were initially identified by differences

in the color pattern of the rhinarium, by the condition of the pinnae (which frequently become torn

around the edges) and by whether they were of the

darker or lighter of the two color phases present on

Barro Colorado Island. After a few weeks of observation of the regular visitors it became surprisingly easy to recognize animals by general appearances or differences in behavior. They were assigned

code names consisting of the initials of the description of an obvious characteristic. The numbers of

the trapped animals, or the letter codes of the

others, are preceded by single letters indicating sex.

Mature animals are designated by upper-case letters, others by lower-case ones.

The sex designating letter was assigned to each

phase I animal as soon as I was able to determine

it. If the animal subsequently became mature its

code name was not changed. Thus m22 was a subadult male, the 22nd phase I agouti that I trapped.

He became mature and reproductively active before the end of phase I, but his sex designating letter was not changed.

The agoutis that regularly visited the bait area

below the observation platform were:

Adults Young Comments

MSS

(Scar Shoulder)

FSP

(Spot Nose)

MRE

(Rim Eye)

F13

m22

FSB

(Scar Back)

ml4

mSN

(Scar Nose)

ml8

f29

f27

MSS and FSP were a mated

pair at the beginning of

the study; ml4 was their

only offspring during phase

I that survived to begin

foraging independently

MRE and F13 were mated

at the beginning of phase

I; three of their offspring

survived to begin independent foraging

m22 was subadult at the beginning of phase I, FSB

was adult when first identified but they were not

yet paired; they had two

offspring during phase I,

one of which, f27, survived to forage alone
NUMBER 257

In addition, two other males, MSH (Sharp Ear)

and MVVS (White Shoulder) visited the bait area

often enough that I learned to recognize them. Unmarked animals that did not regularly visit the bait

area, but whose presence in the study area I knew

of, were assigned the appellation DY. (This was to

make the recording of notes easier. Any animal that

I was unable to identify but whose behavior I

noted was identified in the notes as DY. If its sex

was apparent, then it was noted as MDY, mDY,

etc.).

I studied captive agoutis in order to become

familiar with the various components of their basic

behavioral repertoire. In the field I would often see

only a small portion of a behavioral sequence, and

many times my knowledge of the captive animals

helped in the understanding of its context. I used a

4 X 10 in observation cage that was built in the

forest and had eight 1.2 X 2 m living cages attached to its outside. The doors of any combination

of living cages could be opened and the occupants

allowed into the main cage so that I could watch

social encounters.

To supplement direct field observations, I modified four electrically advanced, single-frame (popularly known as "half-frame") 35-mm cameras so that

they could be tripped by animals passing through

their field of view. These, together with small electronic flash units in moisture-resistant boxes, were

placed in different locations in the study area. A

24-hour clock was placed in the field of view and

the area in front of each camera was baited twice a

day with a handful of dried corn. Animals tripped

the camera shutters by touching a wire connected

to a microswitch or by breaking the beam of a

photoelectric switch. Seventy-two frames could be

exposed in each camera before the film was exhausted. In addition to aiding in the determination

of activity periods, the cameras were useful in plotting home ranges and territories since those animals

that were dye-marked were easily recognizable in

the photographs.

Because of their shyness, it is difficult to approach wild agoutis in the forest without affecting

their behavior. The best way to observe them (and

most other local animals) is to sit still and wait for

them to come into view. The probability of seeing

them is greatly enhanced at some times of the year

by putting out bait piles. Depending on the availability of naturally occurring ripe fruit, the animals

in the study area came to such baited areas within

a few minutes of the bait being set out, within one

or two days, or not at all. Once they began coming

it took them about a week to become habituated to

my presence, although they still spent much of

their time watching me unless I was separated from

them by the valley of a creek, by a very steep slope,

or by a tree. Five of these baited areas were set up

in the study area in order to aid in the determination of home ranges. Most observations were made

from a semipermanent observation post that was

set up between the border of two home ranges. It

consisted of a platform about 5 m up a tree. Bait

could be thrown from this platform into a small

natural clearing across a seasonally dry stream (Figure 5b). The fact that I was on a different level

from the floor of the forest had several advantages:

terrestrial animals were much less shy, their reactions toward me being much the same as toward

monkeys foraging overhead. Also I could vary the

quantities of fruit that I dropped at any one time,

thus more nearly simulating a naturally fruiting

tree. By varying the amount and position of the

fruit thrown, I could manipulate, to some extent,

the behavior of animals visiting the area.

I concentrated my observations on the group of

agoutis that lived in the vicinity of the observation

platform from December 1966 until November

1967. Whenever possible, I observed for two periods

of three to four hours each day. In addition, I

watched any animals that I saw while I was working on the equipment in the study area. I observed

the behavior of female agoutis and their young by

sitting as far away as possible from the nest while

still maintaining a clear view.

Observational data were recorded on, and later

transcribed from, a battery-powered tape recorder.

Sounds made by the animals were also recorded on

this machine by means of a microphone suspended

over the bait area at the end of a length of shielded

cable. Field recordings were generally of rather

poor quality because of the high level of ambient

noise made by insects, anurans, and birds, which

precluded the making of sonograms. Some photographic records of the animals visiting the area

were made using a 6 X 6 cm single-lens reflex camera with lenses of 80 to 500 mm focal lengths. The

line drawings included in this paper were made

from the photographs so obtained.

Agoutis are typically almost wholly frugivorous,

living mostly on the soft parts of ripe falling fruit

when this is available, and practically exclusively
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

on the seeds that they buried earlier, when it is not.

(In the mora swamp of the Osa peninsula agoutis

occasionally eat crabs; those living on Ancon hill in

the Canal Zone, an area isolated from surrounding

forest by houses and streets, eat grass when fruit is

not available. The diet is thus not necessarily entirely of fruit, but this is preferred when it is available.) It is thus possible to measure the quantity of

food available to the animals living within a certain area by setting out "traps" to catch a sample

of falling fruit. I set out 75 polyethylene sheets

totaling 175 m2 in area in the phase I study area,

and measured the weight of falling fruits and seeds

over a period of 17 months (Smythe, 1970b).

THE TRAP-MARK-RELEASE PROGRAM

In September 1971, 50 Tomahawk (National),

23 X 23 X 81 cm, double-doored traps were placed

in a rough triangle more or less encompassing the

bed of a creek that drains a 10.01-hectare watershed basin on the opposite side of the laboratory

clearing from the phase I study area (Figure 3).

During the summer (June—August) of 1972, an

additional 50 traps were set out around the perimeter of the watershed basin.

The phase II trapping area is topographically

well suited for occupation by agoutis in that there

are many small creeks that supply potential nesting places for the young. The southeast slope is

covered by older second-growth forest trees and

there are patches of much older forest toward the

south. During the early 1960s there were several

extensive landslips on the northwest slope, so the

forest there is generally much younger. There are

fewer of those fruit trees that the agoutis most prefer in this area than there are in the phase I area,

but I do not believe that the population density is

significantly different.

Each trap is hooked open and baited almost

every day with a handful of dried maize. Every

second Thursday afternoon the hooks are released

and the traps are baited and set. Captured animals

are removed the following morning at about 0900-

0930 hours. They are identified, weighed, marked,

and released. It is difficult to find an accurate

field scale to weigh animals in the 1-10 kg

range. The one that I use is a compact beam balance purchased from a home wine-maker's supplier.

Its capacity is 20 1b (9.1 kg) and, provided it is

kept level, it is accurate to about 1 oz (28 gm).

The animals are marked using the ear-tattooing

method described earlier. This mark proved to be

long-lasting although it was becoming diffuse and

difficult to read in some animals still living in the

area in 1975 that were trapped in late 1971. The

phase II numbering system was started from "1 "

so that the numbers of the phase II animals bear

no relationship to those of phase I. Errors were

occasionally made in the phase II marking, two

animals being tattooed with the same number or

a number being skipped entirely. In the case of

two animals being marked with the same number,

they were subsequently identified in the field by

their sex or by their weight. For record-keeping

purposes they were identified as "a" and "b" and

are shown as such in the weight-curve and range

figures (Figures 10-15).

Phase I: Results of Seasonal Changes on Behavior

SEASONALITY OF THE FOOD SUPPLY

Many aspects of the behavior and ecology of the

agouti are affected by, and appear to have evolved

in response to pressures caused by, seasonal variations in the amount of food available. The chief

manifestations of periodic food shortages, with regard to the behavior of the agoutis that I studied,

were the increased probability of their entering

traps and the increased time that they spent in

the baited areas during those months when food

was scarcest. The time spent together by members

of a pair and the general level of intraspecific

tolerance vary partly as a function of food abundance. As the fruit fall increases, territory holders

tolerate trespassers to- a much greater degree than

they do at other times and maturing individuals

may wander away from their parental home ranges

to strange areas. Wandering males may court any

females that they meet and newly formed pairs may

set up territories in occupied areas. These areas

may be unsuitable because of the lack of seeds

that will last as a hoard.

The seasonal abundance of fruit falling into the

"traps" described earlier varied as in Figure 4. A

total of 72 species of fruits and seeds fell into the

traps, and the number falling into any individual

trap varied from 3 to 14 species. The number of

species fruiting in any given month varied from
NUMBER 257

11 to 26, while the combined weight of fruits and

seeds varied from a monthly average of 0.061 to

1.93 gm/m-/day. Large-seeded fruits, the preferred

food of agoutis, tended to be more seasonal than

those with small seeds (Smythe, 1970b).

There is thus a season of the year, from midApril until mid-August when ripe falling fruit is

very abundant. During the remainder of the year

it is very scarce. Observations over subsequent years

have indicated that the times of abundance and

scarcity are fairly predictable. Evidence from several sources confirms this. For example, about the

middle of each August, coatis (Nasua narica), tapirs

(Tapirus bairdii), and pacas (Cuniculus paca) begin

to frequent the laboratory clearing, especially the

kitchen area, in search of "handouts." On the other

hand the degree of shortage during the lean season

appears to vary considerably from one year to another. During one year only a few beggars will

appear, and they will stay for a short time. Whereas

during another year many will appear and will

not leave without having obtained something to

eat.

EFFECTS OF SEASONAL ABUNDANCE OF FOOD

Figure 4 shows the relationship between the

amount of time spent in the bait area by all the

phase I agoutis using it and the quantity of fruit

falling into the fruit traps. The time spent by the

agoutis in the area was measured as the number

of minutes each animal was present, expressed as

too.

ISO.

0 ' 4 F * A

4

I

C

5

•as

FIGURE 4.—Time spent per month by ail phase I agoutis

in the bait area (solid line) related to the abundance of

fruit fall {broken line).

a percentage of the total time I spent observing.

Thus, if, for example, I observed for 100 minutes,

during which time one agouti was present in the

bait area for 75 minutes and another for 50 minutes, then the total agouti minutes spent in the

bait area would be equal to 125. This would be

expressed on the left ordinate as 125 percent of

my watching minutes.

Figure 5 indicates the time spent in the bait area

by the individual phase I agoutis that regularly

visited it. The observation platform and the bait

area were originally set up near the edge of the

territory held by MSS and FSP. The neighboring

territory holders were MRE and F13, who frequently foraged in the bait area.

The adjacent males, MRE and MSS, spent less

total time in the bait area than did their mates,

F13 and FSP, which were there approximately in

proportion to the abundance of falling fruit. This

is principally due to two factors. First, males spend

more of their time within their own territories

than do females, and secondly, when a male follows

his mate as she goes foraging he usually only eats

a few pieces of fruit before leaving to patrol in a

circle around her. So when FSP and MSS arrived

together, MSS would usually stay only briefly

before leaving to patrol in a circle around her.

During December and January, MRE did not follow F13 very often when she came to the bait area.

As fruit became more abundant, the time spent

together by the members of a pair increased (Figure 6), so that both MSS and MRE appeared in

the bait area more often with their mates. Then,

when fruit was at its maximum abundance, both

males started to spend less time with their mates

in the bait area. This was partly a reflection of the

general increase in attendance by all animals, but

was also probably because both of the females gave

birth at that time, so that, when they visited the

bait area it was only to eat a little and then take

some food back to their youngsters. As fruit became more abundant both members of the pairs

spent more time deeper within their territories,

foraging and scatterhoarding.

The subadult male m22 was living in an area to

the southeast of the bait area in September of 1966

(Figure 7). I believe that he was the offspring of

F20 and that his parents had recently driven him

out of their territory. In December, he became

paired with FSB who came from somewhere to
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

0 1

W 2 2 1 27

mSN MWS MSH

M A M J JASO N D' J F' M A M J J A S O N OJFMAM J JASO N

FIGURE 5.—Time spent per month by individual phase I agoutis in the bait

area {ordinate values are percentages of total observation time).

the south or west of where he was living. FSB was

already an adult female when she first appeared

and could have lost a previous mate before joining

with m22. They occasionally visited the bait area

as individuals until April (Figure 5) when all

0 JT¥»N J JJ i

FIGURE 6.—Percentage per month of time spent in the bait

area by phase I adult females with their mates or offspring

(ordinate values arc percentages of total observation time).

agoutis were generally visiting it less often (Figure

4). From June onward m22 and FSB began defending the bait area as part of their territory and,

when fruit again became scarce, were the dominant

animals there (Figure 7).

The area around my observation platform, especially to the south, where m22 originally spent

most of his time (Figure 7), was used very little by

adult agoutis and thus appeared to be suboptimal

habitat. The fact that I supplied fruit during the

season when none was available in the forest, even

though the quantities that I put out were small,

made my bait area temporarily more favorable than

the surrounding area. As fruit became generally

abundant in the forest, the more central areas of

the surrounding territories became more favorable

to their occupants, who moved there to feed on the

greater quantities and greater varieties of fruits,

as well as to scatterhoard the seeds.

One of the main reasons why the area where

m22 and FSB were living was suboptimal was probably that it contains few agouti food-fruit trees.

So my bait area would still have represented their

best source of food, and it became the focus of

their activities. They hoarded food there, deposited

scent marks, and made more trails, and eventually
NUMBER 257

1966

FIGURE 7.—Phase I territories surrounding the bait area

(large dot) and the changes undergone between the end of

1966 and the end of 1967 {bb = infants that did not survive

to leave the nest).

set up a territory that they were able to defend

when fruit in the forest again became scarce and

the surrounding territory holders attempted to return. I do not know what happened to m22 and

FSB after I terminated the study and stopped putting out bait, but since this consisted of pieces of

banana it would not have lasted as a hoard. I suspect that they had some trouble surviving the

remainder of the season of fruit scarcity.

A similar situation could have existed for the

older subadult males that disappeared. They could

have moved into adjacent suboptimal habitats

when fruit became generally abundant and attempted to set up hoards there. One of the factors

that probably contributes to a habitat being suboptimal is a lack of food plants bearing seeds that,

once scatterhoarded, remain available and edible

until they are needed as a food source. The subadult agoutis could have moved into such areas

and then, when fruit once again became scarce,

died of starvation or other causes related to lack

of food.

Any males that survived the season of scarcity

would be fully adult by its end and perhaps would

challenge the surrounding territory holders for

mates. MWS and MSH could thus have been the

surviving males from the year before, unsuccessfully challenging the territory-holding males for

their mates. Also FSB could have been a subadult

female that survived the season of scarcity in a

suboptimal habitat, joining with m22 in December.

The attendance in the bait area of juveniles

and subadults is represented in Figure 5. Juvenile

male 14 and mSN utilized the area in inverse proportion to the amount of fresh falling fruit, until

the time when it became abundant, and then they

suddenly disappeared. Although the time he spent

in the bait area was more irregular, ml8 also disappeared during the time when fruit was abundant. I saw none of these animals again, and can

only speculate on their fate. Data from phase II

indicate that such animals probably die (Figure 17).

Two strange adult males, MWS and MSH, came

to the bait area early in 1967, were there occasionally until sometime in March, and then disappeared. They both appeared to be in reproductive

condition, for they courted and attempted to enurinatebothF13andFSP.

During both phases of the study the probability

of agoutis (and the other species of animals that

were trapped) entering traps varied approximately

inversely with fruit abundance. During each year

of the phase II trapping program the incidence of

trapped animals has risen sharply about the middle

of August.

In order to further verify the existence of a

seasonal shortage of food I put out small (about

200 gm) conical piles of dried maize at various

points in the study area. During those months

when the fruit sampling data indicated that large

quantities of fruit were falling, these piles would

remain completely undisturbed, except by falling

rain, and the seeds would germinate. This resulted

in a small clump of seedlings that withered and
10

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

died, probably for lack of light. During those

months when very little fruit fell, the piles of

maize would be totally consumed within one to

four hours of their being put out, and the ground

in a 2-m circle around each pile would be rooted

up (by collared peccaries, Tayassn tajacu) to a

depth of 25 cm or more.

I conclude that all animals in this habitat that

depend heavily on fruit for food experience a season when it is in short supply, and so must either

store food in some way or change their diet in

order to survive the season of deprivation. The

fruits with larger seeds (> 1.5 cm in their largest

dimension) undergo the greatest seasonal variation

in abundance, so the animals depending heavily

upon them for food must undergo the greatest

seasonal adjustment.

Frugivores that can climb or fly have the advantage of being able to obtain fruit that is ripe

enough to eat but not yet ripe enough to fall. They

may thus be able to obtain ample food some

months before the purely terrestrial frugivores.

Many trees have protective devices such as spines

on their trunks, apparently to protect the immature

fruits from these attacks, but the protection is often

subverted and the early food supply is utilized by

monkeys, coatis, bats, and others.

SEASONAL CHANGES IN AGGRESSIVE BEHAVIOR

Figure 8 illustrates the ratio between the amount

of aggressive behavior initiated and the amount

sustained by each individual in phase I and the

seasonal changes in this behavior. A monthly index

of aggression for each agouti is derived by taking

the number of attacks initiated against any conspecific by the particular animal per unit time

spent in the bait area and multiplying this by the

number of different conspecifics attacked. Subtracted from the result is the number of attacks

sustained by the same animal per unit time spent

in the bait area multiplied by the number of

agoutis initiating these attacks. The resulting numbers are positive, negative, or zero, and correlate

well with my subjective impressions of which animals were dominant.

In December 1966 the animal with the highest

index of aggression was MSS, who is dominant in

the area upon which the bait area was situated.

MRE, the nearest territory-holding male, initiated

2 0 *

1.5

1.0

0.5

0.5

2.

,ss

OSS

DJFMAMJJASO N

FIGURE 8.—Aggressive indices for phase I agoutis.

only slightly more attacks than he sustained; but,

since falling fruit was scarce in the forest, he continued to exploit the bait that I had put out

(Figure 5). In March there was a decided increase

in the total amount of agonistic behavior exhibited by the group. MSS was still the dominant animal but MRE was also initiating a considerable

number of aggressive encounters. The subadult

males m!8 and ml4 were both sustaining a large

number of attacks (m22 was in the bait area for

only 10 minutes, so the index for him is misleading). Females generally neither initiate nor sustain

much aggression. F13 was more aggressive than

either FSB or FSP, which I believe is due to her

greater age and the possibility that she is a local

"matriarch."

The number of agonistic encounters fell sharply

in April and remained very low throughout the rest
NUMBER 257 11

of the time that fruit was abundant. Agoutis, when

they met, were more tolerant of one another at

this time. In addition, since many more trees were

dropping fruit and the animals were moving from

one food source to another they met less often

and thus had less opportunity to fight.

In September, however, as fruit became scarce,

the surrounding agoutis began to return to the

bait area for food. During the months when fruit

had been generally abundant, m22 and FSP had

been utilizing the bait area and the area around it

as the center of their activities. In September, however, there was an increase in the number of agonistic encounters as m22 defended what had now

become his territory. In October and November,

the neighboring males attempted to utilize the

bait area less, but the females came there approximately in proportion to the decrease in the amount

of available wild fruit (Figures 4, 5).

Phase II: Results of the Trap-Mark-Release

Program

SPECIES TRAPPED

In addition to agoutis, six other species of mammals regularly enter the traps. These are, in approximately descending order of trapping frequency, Cuniculus paca, the paca; Proechimys

semispinosus, the spiny rat; Nasua narica, the coati;

Didelphis marsupialis, the common oppossum;

Philander opposum, the four-eyed oppossum; and

Sciurus granatensis, a red squirrel. In addition,

Tayassu tajacu, the collared peccary, and Diplomys

darlingii, an arboreal rat, have occasionally been

caught, as have several common iguanas (Iguana

iguana). Doves {Leptotila cassini) were frequently

caught.

NUMBERS AND AGE CLASSES

For the sake of meaningful analysis, it is necessary to divide the population of agoutis into reproductive and nonreproductive animals. Among

the animals that I observed during phase I were

several that had achieved the weight of breeding

animals but were not mated, were more nomadic,

and were the recipients of more aggression than

they initiated. So weight alone cannot be a true

indicator of the status of an agouti. Moreover their

reproductive condition is not necessarily immediately evident even when the animal is in the hand.

I therefore decided to label all animals whose

weight was below 2300 gm as "juveniles" and all

those whose weight was greater "adults." As I shall

show, it is often possible to identify nonreproductive "adults" from characteristics that appear in

their trap records.

The results of the trapping program are illustrated in Figures 9-17 and in Tables 1 and 2. (The

apparent discrepancy in Table 1 between the total

number trapped and the highest number marked

is due to some numbers being omitted in the tattooing process.) A grand total of 87 agoutis had

been trapped as of 19 December 1975. Of these,

48 were male and 39 female. According to the age

criterion given above, 34 of the males were juvenile

when first caught, and 14 were adult. Twenty-five

of the females were juvenile and 14 were adult.

FIGURE 9.—Numbers of phase II agoutis trapped during

each month.
12 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

TRAPPING LOCATIONS

Figures 10-12 show the locations at which each

animal was caught during the "winter" (AugustFebruary) of each year. Each figure is a map of the

study area, the narrow lines representing the creeks

that drain it and the dots representing the locations

of the traps. The thick lines join the trap locations

at which individuals were caught, but no attempt

is made to indicate the sequence of captures, nor to

signify multiple captures at a given point.

For those animals that were captured at more

than one location, I measured the maximum distance between their capture points (Table 1).

Reference to the trapping maps of the juveniles

(Figure 11) shows that they tend to occur in groups,

and that there is surprisingly little overlap between

the groups. The data from the observational phase

of the study indicate that there should be a pair

of adults with each group of juveniles. But I also

learned at that time that adults, especially males,

FIGURE 10.—Winter {Aug-Feb) trapping locations of phase II

adult female agoutis: a, 1971; b, 1972; c, 1973; d, 1974.

FIGURE 11.—Winter {Aug-Feb) trapping locations of phase II

juvenile agoutis: a, 1971; b, 1972; c, 1973; d, 1974.

seldom enter traps, so it is not surprising that it is

not possible to identify a pair of adults for each

group of juveniles. There is, however, an adult

female that occurs in the same area as some of the

groups and usually in the same small area year

after year.

The groups of juveniles were most clearly delineated in 1971 and 1973 (Figure 11). If we compare

Figure lla with data for adult females for 1971,

(Figure 10a), we see that female 1 is in the same

area as juvenile male 2 and that adult females 7

and 8 are in the same area as juveniles 5, 6, and

9.* Female 10 is the adult whose area corresponds

with that of juveniles 11, 12, and 18, while female

• fl was below 2300 gm only the first time she was caught,

gaining weight very quickly thereafter. She is more likely

to be a sibling than a parent of m2. She subsequently became established as a dominant female in the same area.

Female 7 started the season as a juvenile, probably the

twin of f9 (Figure 15), so F8 is the locally dominant female.
NUMBER 257 13

FIGURE 12.—Winter (Aug-Feb) trapping locations of phase II

adult male agoutis: a, 1971; b, 1972; c, 1973; d, 1974.

13 (with F21 as a brief visitor) occupies the same

area as juvenile 14.

LIFE HISTORY CURVES

Figures 13—15 represent the weights of each animal each time it was caught, and thus form a

graphical history of each animal's participation in

the study. If an animal was caught more than once

during any given month, its weights during that

month were averaged. In each of the weight-curve

figures for juvenile animals (Figures 15, 16) I have

marked a broken line which represents the average

rate at which three captive-born agoutis grew (with

as great a food supply as they would eat). Those

wild animals that were born during the seasons of

fruit abundance could reasonably be expected to

grow at approximately the same rate as the captives

since, in both cases, a superabundance of food was

available. In fact, wild animals probably grow somewhat more slowly since they must devote some of

their time and energy to the avoidance of predators

and they must move further than across a cage to

collect their food. During the season when food becomes scarce, the growth rate of the wild animals

will be considerably lower, and some may even lose

weight. If, however, the captive growth curve is

fitted to meet the first capture point of those juveniles that were initially caught during, or shortly

after, the season of abundance then an approximate

date of their birth may be derived. (In early versions of these graphs I calculated the probable

growth rate for those animals that were caught for

the first time outside of the period of fruit abundance on the basis of the average growth rate of

others that were repeatedly trapped. The curves

thus derived indicate that practically all of the

juveniles caught in the entire study were born during or very close to the season of fruit abundance.

I have not included the additional curves here

since the figures are already cluttered.)

If the estimated dates of birth derived from the

captive weight curves are taken literally, it is obvious that f 11, ml2, and fl8 were born at too nearly

the same time to have had the same mother (assuming litters no bigger than two and a three-month

gestation period). There are a number of possible

explanations for this (and similar cases): the locally

dominant female could have had a litter of more

than two. I think that this is very unlikely; one is

the usual number successfully raised to the point of

foraging without parental accompaniment, although litters of two, especially during the season

of fruit abundance, do occur. I have never seen

larger litters. A second possibility is that there is

more than one breeding female to an area. This

is quite possible. In the phase I population there

was an older female (F13) who was able to wander

through the surrounding territories with relatively

little chance of being chased (p. 21). I believe that

she was the mother of several of the surrounding

dominants and, while she held an area of her own

(a task chiefly relegated to her mate), she was able

to move freely through those of her offspring. Her

newer young would tend to stick much more to her

home area and not to wander with her. So I do not

think that the discrete groups of juveniles in phase

II had more than one set of parents involved. The

remaining possibility is that the estimated birth
14 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

TABLE 1.—Statistics on each phase II agouti {asterisk indicates that the animal was caught

for the first time during the winter of 1975, which was not over at the time of this analysis)

No. of

times

Animal trapped

Months

betw. 1st

and last

capture

Maximum

distance

betw. trapsites (m)

No. of

times

Animal trapped

Months

betw. 1st

and last

capture

Maximum

distance

betw. trapsites (m)

m2

m5

m6

ml2

ml9

m23

m24a

m26

m30a

m34

m4l

m42

m44

m49

m50

m55

m59

fl

f7

f9

fll

fl4

fl8

f28

f36

f37

f38

f39

f43

f45

M3

M4

M15

Ml6

M17

M20

M25

5

16

7

5

2

6

18

3

1

4

5

3

2

1

11

1

10

15

11

11

4

6

1 h

5

1

1

3

3

8

4

1

1

17

1

2

4

18

4

4

10

7

17

17

12

3

4

2

2

20

28

39

28

4

29

3

28

29

3

1

1

4

29

22

50

5

ADOLESCENT MALES

56

121

121

55

25

102

117

121

62

_

^5

91

11

128

-

153

-

ADOLESCENT

62

77

51

93

151

109

83

136

60

25

-

30

47

m66

m67

m68

m70

ntfl

m74

*75

m80a

m80b

m8l

m82

m84»

m87*

m88*

m89»

m90

m92

FEMALES

f46

f48

f5l

f52

f60

f69

f73

f79

f85

f86*

f97*

f98*

ADULT MALES

121

89

-

-

93

-

0

M53

M54

M57

M65

M78

M83

M93*

ADULT FEMALES

8

4

2

3

1

3

4

5

3

4

1

2

3

2

4

2

2

6

2

1

4

7

5

1

3

1

3

1

1

1

2

1

1

1

2

2

17

5

6

2

14

5

6

2

4

3

5

2

4

4

1

11

3

21

18

4

3

3

94

53

0

53

62

123

98

249

87

100

76

49

147

47

41

37

F8

F10

F13

F21

F24b

F27

F30b

15

8

8

1

11

12

7

50

44

26

-

23

17

14

109

108

96

-

70

213

76

P31

F40

F47

F58

F76

F77

F91*

2

1

3

1

4

1

1

7

3

14

_

-

164

_

_

106

-
NUMBER 257 15

Kg

2IO

76

I

r : -

D'J

1972 O'J | 9 7 3 O'J 1974 O'j 197S

FICURE 13.—Life history curves of phase II female agoutis that were adult when first caught

(stippled areas = seasons of fruit abundance).

Kg

©20

• 16

( I m [, ,, A.

lJ 1972 Olj 1973 C*<* 1974 O'J 1975

FIGURE 14.—Life history curves of phase II male agoutis that were adult when first caught

(stippled areas = seasons of fruit abundance).

ol
16

SMITHSONIAN CONTRIBI'TIONS TO ZOOLOGY

Kg

2 —

I —

92

•r*

1972 1973 1*74 lt7B

FIGURE 15.—Life history curves of phase II female agoutis that were juvenile when first caught

(broken line = average growth rate of 3 captive-born agoutis; stippled areas = seasons of fruit

abundance; no weight data for f39).

dates are wrong. This is the most likely explanation,

although I believe that the error occurs in a predictable fashion: very young agoutis, while under the

care of their mothers, may grow at the same rate as

captives that have access to superabundant food

supply, but as they become older and must spend

more time guarding against attack by conspecific

aggressors and predators, their rate of growth falls

below that of captives of the same age. Thus the

estimated dates of birth should be displaced more

to the left (i.e., earlier in the year) the older an

animal was when it was first captured. So fll and

£18 were probably twins born in August, and ml2,

who weighed about 300 gm more when first captured, was born 3 months earlier.

In 1973 (Figures 10c, lie, 12c), the groups are not

as clearly delineated, but there have been some interesting developments since 1971 (Figures 10a, lla,

12a). Now adult fl still occupies the same area and

juveniles m41 and f43 appear there (Figure lie)

Now adult f7 has reached adult weight; she and fl

were the only adult females trapped in 1972 (Figure

106), but F8 was almost certainly still present for

she appears in precisely the same area again in 1973

(Figure 10c). In fact, F8 is probably the oldest female in the study, since she was fully adult when

first trapped in November 1971 (Figure 13). Now

adult f9 appears in the same area as F8 in 1973, but

looking back to Figure 15 we see that f9 has a similar history to that of f7; she was born during the

season of abundance of 1971, and was first captured

during October of that year. She grew to adult

weight at approximately the same rate as the captive animals, remained in the area for a while and
NUMBER 257 17

Kg

It72 |97S ~ " l»74 " " It7 9

FIGURE 16.—Life history curves of phase II male agoutis that were juvenile when first caught

(broken line = average growth rate of 3 captive-born agoutis; stippled areas = season of fruit

abundance).

then was suddenly absent from the traps. The

juveniles appearing in F8's area in 1973 are f37 and

f45 (possibly twins born in September) and f48 and

£52 (twins born in June or early July). F24b appears

early in 1973 (Figure 13) and achieves adult weight.

It appears that she is the locally dominant female,

but then we see (Figure 13) that FIO was retrapped

in May 1975. A range map has not yet been prepared for the 1975-1976 period of deprivation, but

FIO was caught in the same trap that she entered

in November 1971. She was limping rather badly in

May 1975 and did not appear very healthy, although her weight did not indicate this. During the

first part of 1975, F24b gained weight steadily; probably partly as the result of pregnancy. Her apparent

thriving condition, as opposed to the poor condition of FIO the last time she was caught, may have

indicated that F24b was in the process of displacing

FIO as the locally dominant female.

Some general conclusions can be drawn from the

weight-curve figures. It is evident, for instance, that

not all seasons of abundance or deprivation are

equal in their effects on the animals. During the

winter (August through February) of 1971, most

animals showed some increase in weight. Food

could not have been actually abundant at this time

or the animals would not have entered the traps;

nor, I believe, could the food used in the prebaiting

program have contributed substantially to the general weight increases. The same quantities of bait

were used during the winter of 1973 and during

that time there was a general loss of weight throughout the population; a loss that was fatal to some

animals. This indicates that there was probably a
18 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

general lack of hoardable food items during the

summer of 1973.

THE RIDGETOP TRAPS

The outer ring of traps, which follows the ridgetops that form the boundaries of the study area

basin, has always been less productive than the

inner ring. This is what I would have expected

from my earlier observations, which indicated that

agouti activity is generally concentrated toward the

beds of creeks rather than toward the ridgetops.

Nevertheless, analysis of the few captures in the

outer ring is informative. In 1973 (Figure 10c),

F27 appeared and was fairly regularly trapped

there. F58, who was barely heavy enough to be

designated an adult, was also trapped there once.

But no young juveniles (who were not first caught

lower in the creekbed areas) appeared there. Then,

in 1974, F27 reappeared (Figure lOd) in the same

area and so did two juveniles, f60 and m80b (Figure lid), but they were not trapped in the lower

area. Reference to the weight curve of F27 (Figure

13) indicates that her weight was high when she

was first caught (in August 1973, at the end of that

period of fruit abundance). Then her weight fell

sharply in the ensuing lean period. She gained

weight again as food became more abundant and

almost certainly gave birth around the end of June,

for at that time her weight again dropped sharply.

Since F27's weight loss in late 1973 was too great

to be caused by parturition alone (many other

agoutis lost significant weight at the same time),

and since it occurred at the time of minimum food

abundance, I believe that the following conclusions

are warranted. When first trapped in August 1973,

F27 was a nonreproductive young adult, probably

born during the period of fruit abundance of 1972.

Her parents lived in the creek drainage area that

runs in the opposite direction from the study area

creek (i.e., on the other side of the ridge on which

she first appeared). She survived the winter of 1972

living on and around her parents' territory, and

reached adult weight in the spring of 1973. When

she achieved potential breeding size she was harrassed by her parents and, taking refuge in the less

desirable ridgetop area of their range, discovered

the trap line. The prebaiting program assisted her

survival, in spite of a severe weight loss, through the

winter of 1973. She then mated and settled somewhere on her home slope (either by replacing or,

more probably, living near her parents). During the

winter of 1974, she continued to exploit the traps,

having become familiar with the area. At the same

time her offspring, f60 and ni80b, as well as an

adult male, M83, who could well be her mate

(Figures lOd, lid, I2c[), followed her there.

ADULT MALES

As I had discovered during the first phase of the

study, adult males will seldom enter traps. The data

concerning them are thus rather sparse; however,

some interesting information can nevertheless be

gathered about them. Only one, Ml7, has been

trapped regularly since the inception of phase II,

and he was already a full-grown adult at the time.

His area almost exactly coincides with that of fl

throughout the study and it is very probable that

they are a mated pair. At the beginning of the study

another adult male, M3, lived in the same area, and

was somewhat heavier than M17. It is thus possible

that M17 was one of those animals that had

achieved adult weight but was not yet reproducing

at the time that M3 was reaching the end of his life.

As fl became old enough, she and M17 mated and

began to take the area over from M3 and his mate,

who remains unidentified. M3 was not trapped

again until the end of 1973, at which time his

weight went into steep and almost certainly fatal

decline.

Adult male 55 may have been born in August or

September 1973 and is probably the offspring of F8.

He weighed only 1300 gm when first trapped in

January 1974 (Figure 16). This means that he was

born very late in the season of food abundance of

1973, and would still have been small when food

began to grow scarce. Difficulty in competing with

larger juveniles (at a time when, judging by the

number of animals that lost weight, food must have

been very scarce indeed) probably drove him to explore further afield than would normally have been

the case for one of his age. Thus he found the outer

ring of traps and exploited the food that was available there. He, m26, f36, f46 were the only animals

caught during the lean period of 1973 who showed

any significant gain in weight each time that they

were caught. Most of the rest of the agoutis caught

during that period lost some weight. Juvenile female 36 was first caught in June of 1973. She was
NUMBER 257 19

caught again just over a month later and had

gained weight at approximately the same rate as

captive animals. She was not trapped again until

November and at that time weighed very little more

than she had in July. Actually she had probably

gained weight through July and early August and

had then lost some of it before the next time she

was trapped. In February 1974, she was caught in

the outer ring of traps for the first time. She was

caught again in March and showed a slight loss of

weight. Thereafter she gained weight to become a

large adult (3670 gm) by April 1975. The weight

increases that she showed in early 1975 may well

have indicated pregnancy and it is probable that

she has successfully established residence as a reproductive dominant in the area. Whether she, and

the other animals that have been moved apparently

as the result of my prebaiting program to less favorable areas, can continue to survive there is difficult

to say. It would seem that their reproductive success

will probably be lower on account of there being

fewer nesting refuges for the young. The adults,

however, may continue to live there for some time.

LIFE EXPECTANCY OF JUVENILES

Figure 17 shows the length of time over which

individual agoutis that were juveniles when first

caught were trapped. The left axis shows the

number of survivors, divided according to their sex,

and the right shows the cumulative precentage that

dropped out of the study after a given period of

time. Table 2 shows the number of months spent

by the members of each class in the study.

Figure 17 can also be interpreted as a curve of

probability of survival for those young agoutis that

leave the nest to begin foraging on their own. If it

is accepted as such, we see that the times of greatest

mortality in the population of growing animals

occurs at those times when food is scarcest and that

few young survive to become reproductively active

animals. We have seen from Figures 15 and 16 that

most of the young that survive to leave the nest and

begin foraging on their own are born during the

time when food is most abundant. As the season of

abundance ends and food becomes more difficult

to find, agoutis (especially the younger ones) begin

to enter the traps. At the same time there is heavy

Porcontoa* dropping our (cumulative).

© — -O Number of surviving moist

©.....O Number of surviving fomatos

•evc 9 99

•KX>

SO

8 0

7 0

6O

SO

4 0

3 0

2 0

10

8OM -

10 10 20

Tim* :

2 0 3 0 SO 4 0

FIGURE 17.—The time between first and last entrapment for phase II agoutis that were juveniles

when first caught.
20 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

TABLE 2.—Average number of months between first and last

capture for each age class of phase II animals (the last two

entries show the average for adults caught more often than

in only one month)

Age class

All adults

Adult males caught more than once

Adult females caught more than

Average number

of months

6.53

8.00

8.83

15-50

11.75

7.68

18.50

24.20

mortality so that about seven months after food

begins to grow scarce, more than 70 percent of the

original population of subadult agoutis has died.

Food becomes scarce about the middle of August

(Figure 4). If August is taken as the hypothetical

point of initiation of the time axis in Figure 17,

it can be seen that this first seven months represents

the first season of deprivation for a growing young

agouti and the subsequent increases in mortality

occur predictably at roughly those times when food

would be expected to be growing scarce.

In terms of probability of mortality, an animal

suffers a 70 percent chance of dying during its first

period of deprivation (months 1 through 7), but a

less than 5 percent chance of succumbing during

the succeeding season of plenty (months 8 or 10

through 13 to 15). By the end of that season any

surviving agoutis will be potentially sexually mature and thus subject to increasing aggression from

locally dominant animals. As food becomes scarce

again there is another increase in mortality with the

males suffering more than the females. (In Figure

17, the curve for males drops to zero surviving in

month 20. This, of course, would not happen for

the entire population. It is an artifact of the number of animals participating in the study.)

MORTALITY DIFFERENCES BETWEEN THE SEXES

In the population making up the study group

there were nine more males than females when they

began entering traps. But, by the end of the first

lean season, the numbers of the sexes were equal.

The number of males and females remains equal

through the following period of food abundance

and then the number of males drops to zero. Sixteen to 20 months after their first becoming old

enough to forage from the nests, all the animals

would be potentially sexually active. The more

rapid extinction of the young males could possibly

be caused by their receiving a greater amount of

aggression from the adult population.

The Use of Space

AGOUTI TERRITORIES

Among the agoutis that I have watched, the social units for reproductive adults consists of a mated

pair. The amount of time that the members of the

pair spend in one another's company may vary

seasonally, being greatest when falling fruit is least

abundant (Figure 6), but the pairs seem to be permanent and to last until one of the members dies.

Each pair occupies an area of approximately one

to two hectares (Figures 7, 10-12), within which

they are aggressive against and normally dominant

over conspecifics, and in which they spend most of

their time.

I speak of agoutis as being territorial many times

in this paper. It is not my intention to cause confusion in the minds of those who reserve the term

to describe the defense of an area from which all

conspecifics of the same sex are excluded. In order

for that situation to pertain it is necessary for the

defender to maintain better communications with

the limits or boundaries of the defended area than

is possible for forest-dwelling, terrestrial animals.

Other agoutis can, and regularly do, enter adjacent

defended areas. If a tree comes into fruit on a given

territority it is regularly visited by the agoutis living in the surrounding areas. Both reproductive

and nonreproductive animals trespass. When the

resident animals detect the presence of intruders

they may attempt to drive them away. The rigor

with which they do this varies seasonally; being

most pronounced when falling fruit is scarce, and

greatly reduced when it is abundant.

At times when food is scarce the male will usually

drive away any strange agoutis that he detects, but

he is more aggressive toward other males. Females

are less active in the defense of their territory but

they will usually drive away other females. Both

sexes harass any subadults that they meet and will

attack the juvenile offspring of adjacent territory
NUMBER 257 21

holders, even when they meet them on their parents' territory.

The defensive activates of the residents are more

concentrated within the territories than around the

edges, and the deeper into a territory that an intruder goes, the more likely he is to be attacked.

The boundaries of the territories are not absolutely

defined and, moreover, they may vary seasonally,

the areas of heaviest use shifting as trees in different parts come into fruit. As marked in Figure 7

the boundary lines connect points from which I saw

residents successfully drive off adult conspecifics, or

they represent paths along which patrolling residents moved or did not cross (or they join each of

these types of indicators).

There is considerable individual variation in the

behavior of adult dominant animals as far as their

defenses of a home area is concerned. Female 13,

who I believe was the oldest animal in the phase I

study group, was able to wander through the surrounding territories at any time of the year, with

far less probability of suffering an attack than was

any other agouti. In this respect she was similar to

the founding female of the group of agoutis in the

900 m- enclosure in the zoological park at Tuxtla,

Mexico. This female could closely approach, and

successfully compete for food with, any other group

member and received practically no aggression in

return.

The young animals are continually harassed by

reproductive adults but they (especially the young

females) nonetheless seldom move very far away

from their parents' territory. Unless they are able to

set up a breeding territory of their own their chance

of survival much past the age of normal sexual

maturity is slight (Figure 17) and the likelihood of

a maturing animal being able to set up a territory

is also slight unless a local territory holder dies at

the appropriate time. It thus seems probable that

the territory of an old animal will be surrounded

by those of its offspring, and that, even though territories are maintained, there will be interterritorial dominance heirarchies set up as well. Female 13

was probably the mother of several of the surrounding territory holders and may have maintained her earlier dominance over them and thus

have been able to move with relative impunity

through territories that they rigorously defended

against others.

The "territories" are thus not, in the strictest

sense, territories. But they are much more than

merely home ranges. It might be more accurate to

speak of "local, long-term dominance hierarchies

amongst reproductively active animals" but repetition of such terminology becomes tedious. In subsequent discussion I therefore refer to areas that

are occupied for long periods, and defended (with

seasonally varying vigor) by reproductive agoutis

against some or all conspecifics, and upon which

food is hoarded (not necessarily only by the dominant resident) but upon which conspecifics regularly trespass, as "territories"!

TERRITORIES AND NONREPRODUCTIVE ANIMALS

Agouti territories usually include a length of

creekbed, and it is here that the nests of their young

are generally situated. Most of the scatterhoarding

done by reproductive agoutis is done within their

own territories, though they may occasionally bury

a piece of food on a neighboring territory when

they are foraging there. Each territory also includes

a number of agouti food trees. The subadults (after

they leave the care of the mother) generally live

and sleep outside of the areas most heavily used

by the adults, even though they must do most of

their foraging there.

As they grow older and gradually move further

from their nests, young agoutis remain within the

territory of their parents, exploring by themselves

if the mother is raising a second litter, or in her

company if she is not. When the level of aggression

of the parents and other adults increases, the young

animal must spend much of its time avoiding them,

and so is forced into the peripheral regions of the

surrounding territories or into areas that get little

use from reproductive dominants. The result is that

the home ranges of the subadults are less well defined than are the territories of the adults, and they

overlap the edges of the surrounding territories.

Subadults do not defend a specific area, but if approached by a smaller agouti when feeding, especially during the season when food is scarce, will

attack and drive it away.

Agoutis become potentially sexually mature -at

the age of about six months (Roth-Kolar, 1957:369).

This appears to depend upon the sufficiency of the

diet, for many animals in the phase II study passed

the age of six months and were obviously not big

enough to be sexually mature. On the other hand,
22 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

some of the animals that I observed in both phases

passed the age and weight necessary for sexual

maturity and still retained many of the behavioral

characteristics of juvenile animals: fleeing at the

approach of the territorial adults and living largely

in the areas between territories. Such animals remain unmated, but those of the same sex establish

a loose dominance hierarchy among themselves.

Thus, in December of 1966, the oldest phase I subadult agouti regularly visiting the bait area, mSN,

was dominant over ml4, who in turn was dominant

over ml8. This relationship held no matter where

these animals met one another in the surrounding

territories. The juvenile m22 was about the same

age as mSN, but the former did not begin to visit

the bait area until February of 1967, at which time

his status was changing to that of an adult territory holder, and he was forming, or already had

formed, a liaison with FSB. I do not know where

FSB came from, but it was somewhere to the south

of the study area, so that when the opportunity

arose, she was more available to m22 than to mSN.

Those animals older than six months are apparently able to change their status very quickly

should a local reproductive adult die or become

unable to maintain its dominance. The consistent

harassment the subadults suffer from the dominant

animals and their resulting inability to maximally

utilize marked trails and food resources places them

under increased selective pressures, so that mortality is high. But when the opportunity arises to

acquire territory-holding status it is practically

guaranteed that an animal of potentially high fitness will be available to fill the gap.

Activity Patterns

Agoutis begin to move about shortly before

dawn, when light levels in the forest are still too

low to permit observation (Figure 18). The activity

period becomes extended when food becomes scarce,

and they may even forage until shortly after dark.

Younger, nonbreeding animals are often active at

times when the territory holders are sleeping or

resting. On very cloudy days, or on mornings when

it is raining, the beginning of the activity period

is postponed. Leaving the sleeping spot is preceded

by a lengthy bout of stretching and grooming. In

the wild, the members of a pair of agoutis usually

sleep within a few meters of one another, and

when the female has finished grooming, she leaves

her sleeping spot to begin foraging. The male follows her, often circling her at a distance of 5—20

meters, apparently attempting to detect the presTim* of day

FIGURE 18.—Activity periods {the number of times an automatic camera was tripped by agoutis

during each hour).
NUMBER 257 23

ence of any other agoutis that may be in the area.

The male also occasionally approaches the female

and attempts to enurinate her (see p. 28).

After a period of foraging, the length of which

depends upon the abundance of available food, the

female follows one of three patterns: (1) if she has

an infant, she picks up a piece of food and goes

to the nest; (2) if she has none, she sits or lies in

a feeding spot and rests, often appearing to doze;

or (3) she may set out on "patrol." If she goes to

the nest, the male either approaches as close to

the nest as she will allow him, and then he sits

and rests, or continues patrolling the territory,

forages, or rests elsewhere. If the female rests near

the foraging area, the male may rest near her or

he may continue to patrol in a circle around

her. If she sets out on patrol, he follows, usually

within a meter of her, occasionally sniffing at her

rump.

The action of patrolling appears to enable the

animals to maintain familiarity with the territory.

Patrolling agoutis follow habitual trails, biting

small vines and other vegetation that have recently

fallen nearby. They may stop and eat, but they

generally walk more quickly and along more regular trails than do normally foraging animals. They

may patrol for an hour or more, often moving

from one side of the territory to the other, or

circling it, several times. But they usually stop and

rest before starting to forage again sometime between 1030 and 1200 hours.

A female with a nest-bound infant leaves it

around 1030-1100 hours and goes to forage. If her

mate has been waiting, he usually joins and follows behind her. From about 1200 or 1230 hours

until 1300 or 1330 hours agoutis usually rest and

then begin actively foraging until dusk. They continue foraging until darkness falls in the forest,

gradually moving toward a sleeping spot. Having

reached a sleeping spot, they sit and groom for

some time before lying down and sleeping. If they

are disturbed during the night they quietly leave

and generally move to a point that is higher than

the surrounding area, such as upon a large log,

where they sit quietly. If approached, they flee in

much the same manner that they do in the daytime. (This behavior may partly account for descriptions of agoutis as being nocturnal, since the

dull red glow of the eyes is easily spotted in the

light of a headlamp.) I heard only one alarm bark

during hours of darkness and this was too far away

for me to find out what circumstances elicited it.

Young animals and unmated adults spend much

of their time in cautious exploration of the area,

for they are in constant danger of attack from the

resident pair. They were usually the first to enter

the bait area in the morning but they seldom fed

for more than a few minutes before they were

interrupted and driven off by the residents.

The activity pattern described here may undergo

considerable variation, depending on the availability of food or the presence of various disturbances,

such as snakes, which may cause agoutis to spend

several hours in alarm reactions. Figure 18 shows

the times when agoutis visited baited cameras, and

indicates that they were active throughout the day.

But this figure represents the activities of about

20 individuals at a time of the year when falling

fruit was very scarce (they were not attracted to

the baited cameras except when food was scarce).

The frequency and duration of resting periods depends upon the abundance of falling fruit, and

much of the time spent by agoutis in the bait area

when fruit was abundant was devoted to resting

or sleeping. As fruit becomes more abundant, an

increasing amount of time is also spent scatterhoarding (see p. 25).

Feeding and Foraging Behavior

TYPES OF FOOD

I tested captive agoutis with the object of finding out what types of food they would eat, and

found that they react to any approximately spheroidal object, within a wide range of sizes, as

though it was food. They prefer objects of greater

than approximately 1.5 cm in the largest dimension, but they will eat, or attempt to eat, objects

as small as 5 mm, and often eat fruits as large as

10-15 cm in diameter. The agoutis that I tested

would eat apples and pears upon first encountering them. They also treated such things as drawing pins (thumb tacks) and glass marbles as though

they might be food items. They reacted to such

objects by picking them up with the mouth (with

considerable difficulty in the case of the marbles),

manipulating them and going through the motions used in peeling fruit, and then burying them.

Although fruit and seeds form the vast majority
24 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

of the food of the agoutis that I studied, they did

browse occasionally. I saw agoutis eating leaves

only three times, all during the period when falling

fruit was scarce. They are reputed to eat roots

and sugar cane (Cabrera and Yepes, 1960:44,45;

Walker, 1968:1027). The only roots that I saw

them eat in the wild were those projecting from

germinating seedlings, although captive animals

eat carrots, potatoes, and cassava (locally called,

"yucca"). I think it entirely possible that they eat

such things in areas where the forest has been

cut to such an extent that there is not enough

fruit to hoard against times of deprivation. None

of the captive animals that I tested would eat

sugar cane. They occasionally ate a little ground

beef and, like the animals studied by Roth—Kolar

(1957), preferred cooked to raw meat. On one occasion, an adult male Liomys pictus escaped from

its cage in the same room as a group of captive

agoutis. It wandered into the agouti cage, where

it was killed and almost entirely eaten.

FORAGING

Agoutis are attracted to the sound of fruits falling to the forest floor, and will travel 50 meters

or more to pick up one that they have heard.

Native hunters drop stones from trees to attract

agoutis within the range of their weapons (Goldman, 1920:130). Agoutis also follow bands of monkeys for short distances, picking up fruits that the

monkeys drop. This may be an important source

of food at some times of the year since the monkeys, particularly spiders (Ateles paniscus "geoffroyi") and howlers (Allouatta palliata) are able

to reach many fruits that are not yet ripe enough

to fall but are ripe enough to eat. The monkeys

typically take only one or two bites from a fruit

before letting it fall.

The sound of falling fruit also appears to act

as a stimulus to feed. On several occasions when an

agouti had fed in the bait area and then had laid

down to rest, I threw a piece of banana so that

it landed 3-5 meters away from the animal. Upon

hearing the falling fruit, the agouti would usually

get up, walk past or over other pieces to the one

that had just fallen, and eat it.

The sound of another agouti eating will also

attract agoutis to a food source, and they also find

fruit by its odor. I set up temporary observation

stations at several points in the study area. Each

was baited with a pile of banana (about 2 kg) cut

into short pieces. I sat 20 or 30 meters away and

was able to watch approaching animals from before

they had apparently detected the bait. On several

occasions an animal walking tangentially to the

baited area would suddenly pause, sniff the air,

and turn and walk directly to the bait pile.

An agouti approaching a food source that is

within another territory, or in an area of disputed

territory in the season when fruit is scarce, usually

circles the food area before approaching it. It will

often pause about 10 meters from the food, thump

a few times (see p. 41), get up and make a complete

circle of the food area, returning to the spot where

it first thumped, sit and thump again for a few

minutes, and finally get up and enter the area.

The first piece of fruit that is encountered is usually carried out of the immediate vicinity, often

to the place where the agouti sat and thumped

before entering the area, and is eaten there. Subsequent pieces may also be carried out of the area

and eaten, but after carrying away the first two or

three, the agouti usually starts to eat them nearer

to where they fell.

FEEDING SPOTS

When agoutis find a fairly steady source of falling fruit, such as my bait area or a fruiting tree,

they habitually carry fruit to regular spots to eat

it (Figure 36). Whether by active removal, or from

normal wear, these spots become smooth and devoid of litter, so that they are easy to identify.

They are similar to, and may double as, sleeping

spots (see p. 27). The feeding spots may be on

small elevations in the open, giving the animal a

view of the surrounding area, or they may be under

vegetation such as large leaves.

A feeding agouti seldom eats more than two or

three pieces of food in a single feeding spot, but

moves from one to another after picking up a

piece of food. The spots apparently become marked

with agouti odors, for not only will other agoutis

from the immediate area make mutual use of them,

but those passing through the area will eat and

mark on them the first time they visit the food

source.
NUMBER 257 25

FEEDING TECHNIQUES

Agoutis sit on their haunches to eat (Figure 19),

in the same manner common to many other rodents

(Eibl-Eibesfeldt, 1958). The forepaws are used to

manipulate fruits and seeds. Fruits are generally

systematically peeled and the peel either chewed

to extract the juice (e.g., as in the case of Aslrocaryum), or discarded. Seeds may be held so that

the animal can gnaw a very tough seed coat at the

same point consistently.

SCATTERHOARDING

When an agouti encounters a concentrated food

source, it usually eats a few of the fruits or seeds

and then starts to bury them. If the fruit consists

of a hard seed surrounded by a fleshy pulp, the

animal usually eats or peels off the pulp before

burying the seed. Seeds are occasionally buried

near to where they fall, but more often are carried

individually for distances up to about 50 meters,

in various directions from the source, and placed

in carefully dug holes from 2 to 8 cm deep. They

FIGURE 19.—Feeding behavior: a, b, c, typical feeding postures; d, food held in mouth while animal sits up to observe

surroundings; e, agouti browsing; /, placing a leaf over a

buried food item.

are then covered with soil, which is smoothed with

the forepaws, and a leaf or twig is usually placed

on top. This is very similar to the behavior described in the green acouchi (Myoprocla pratti)

by Morris (1962).

The buried seeds may be dug up again almost

immediately or not until up to about eight months

later. An agouti other than the one that buried

the seed will often come along and dig it up within

a day or so, take it away, and then rebury it. In

this way a single seed may be transported and

buried as much as 150 meters away from the parent

tree. When falling fruit becomes scarce, agoutis

live almost entirely on scatterhoarded seeds, though

not necessarily on ones that they themselves buried.

Most of the seeds that a territory holder digs up

are from within its own territory, but many of

them were buried there during times of abundance

by young animals, not necessarily from the same

territory, that have since died or moved elsewhere.

I do not have data to show the percentage of the

scatterhoard that is retrieved; but, during times of

abundance, all agoutis hoard considerably more

than they eat. When a large, multiseeded fruit

such as Gustavia or Tontalea is encountered, the

animals may bury from one to five seeds for each

one that they eat. They may also partly eat some

of the seeds before burying them, which could prevent germination. When single-seeded fruits with

a hard exocarp and a surrounding sweet pulp are

found, the pulp is removed and the remainder

usually buried.

Since the population, all of whom are hoarding

more than they are eating, is highest during the

latter part of the six-month period when fruit is

most abundant and since many members of that

population do not survive to exploit the seeds that

they have hoarded, it seems logical to assume that

many of the seeds are never disinterred. Moreover,

it seems highly probable that many of them will

be under excellent conditions for germination.

Thus many agouti food plants have their seeds

efficiently dispersed.

The question arises as to how agoutis find seeds

that they have buried when they need them. It

is possible that the slight disturbance of the soil

that remains after the seed is buried acts as a clue.

But it seems unlikely that such a disturbance could

remain visible for several months, since all that

would appear necessary to obliterate it would be
26

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

a heavy rainshower. The perineal region of an

agouti usually contacts the ground at some time

when burying is in progfess- Hoards are thus

marked, whether intentionally or inadvertently,

but the odor mark could iTMt last for very much

longer than the signs of disturbance.

Howard, March, and Cc>le (1968) showed that

Peromyscus can smell bufied seeds and Murie

(1977), working in my pha«e I study area, has recently shown that agoutis can find buried seeds,

apparently using predominantly olfactory cues.

They usually bury seeds near fallen trees or at the

bases of small clumps of palms or other undergrowth, and it is near sufrh structures that they

tend to search in later months when fruit is scarce.

Therefore, it may be that they find buried seeds

at this time by searching ii* similar situations and

detecting the odor once they are over the spot

where the seed is buried.

Comfort Behavior

ALLOGROC>MING

Like acouchies (Myoprpcta pratti) (Kleiman,

1972), female agoutis frequently groom their young

(p. 33). Some allogrooming also occurs between

members of a pair, but agoutis would generally

be classed as "distance animals" in the sense of

Hediger (1955:66).

AUTOGRCK)MING

Murray (1961) demonstrated the importance of

autogrooming in rodents.

 A s

 might be expected

in a tropical, terrestrial ?nimal, agoutis devote

considerable time to grooving and apparently remove many ectoparasites. Trapped animals that

appear to be in poor phy?cial condition are usually infested with ectoparasites whereas those in

good condition are generally almost entirely free

of them. A heavily infested animal may be host

to more than 100 ticks of various sizes, have small

areas of the body covered with orange mites, and

have upwards of a hundred fleas.

When grooming themselves, agoutis sit on their

haunches and use the forelimbs and incisors to

manipulate the hair of tlie ventrum and flanks

(Figure 20). The forefeet ai"e used to rake the hair

and to draw it within reach of the incisors, which

FIGURE 20.—Comfort behavior: a, combing rump hair with

incisors; b, grooming face with surface of forefeet; c, grooming face with "parasite combs"; d, e, sleeping posture or

position assumed for protection of ventral parts from biting

dipterans; /, stretchingare then used as a comb. The top, the sides, and

the back of the head are groomed with the forelimbs, which are used either singly or together.

Between each sweep of the forelimbs, the animal

may lick the inside surface of the wrists, where

there is a small oval patch of skin, bearing short

fine bristles (Figure 2). At certain times of the year

small ticks and ectoparasitic mites are very abundant in the forest and may attach themselves to

any animal that moves through the undergrowth.

The short bristles on the wrist patches would appear to function as combs to remove these pests.

Agoutis may have so many small orange mites on

them that they have been described as having a

"bright orange, fungus-like growth" (Enders, 1930:

287). These mites and the many small ticks that

the agoutis sometimes have, however, are usually
NUMBER 257 27

situated in regions that the "parasite combs" cannot reach, such as the soft skin in the cleft Ijelow

the cheek bones.

Agoutis often scratch themselves with the hind

claws. This is usually done while the animal is

in a sitting position, but occasionally also while

it is standing. Each claw is carefully cleaned with

the incisors after a bout of scratching.

PROTECTION AGAINST BITING DIPTERANS

Mosquitoes and tabanid flies often cause agoutis

a great deal of apparent discomfort. The most

vulnerable areas seem to be the pinnae, the rhinarium, the perineal region, and the extremities

of the hind limbs. In response to biting insects,

agoutis twitch their pinnae rapidly back and forth.

They will do this even when in the freeze position

after having been alarmed, often giving away their

positions to an observer. When bitten on the rhinarium, agoutis wipe at it with either forepaw,

and often do this while walking along, hardly

breaking stride.

Insects biting their perineal region seem to cause

much discomfort. When the insects are abundant,

agoutis will sit in such a way that the perineum

is pressed close to the ground (Figure 20d, e). When

insects are biting their hind legs, agoutis will lift

the foot off the ground and give it a quick flick.

If the biting persists, they will sit down and attempt to bite the insect or the spot where it is

biting.

REACTION TO RAIN

The approach of heavy rain showers is usually

signalled by a noticeable darkening within the

forest, the roaring of howler monkeys (Alouatta

palliata), the noise of the rain on the vegetation

and occasionally by thunder. Agoutis generally

left the bait area at these times before the rain

actually arrived and went out of my sight. On

those occasions when they stayed in view, they

moved under large leaves and lay down, or sat

and groomed, until the rain was over. They paid

little attention to lighter showers, the water from

which takes some time to penetrate the canopy if

it comes through at all. One subadult went into

a mild frenzy dance (p. 28) when it was raining

lightly and animals foraging under such conditions often wipe their faces with their forepaws

and wrists.

SLEEPING

Each agouti has several habitual sleeping spots

on its home range. These are usually in hollow

logs, shelters formed by buttress roots or under

vegetation such as large leaves or tangles of vines.

They are recognizable as circular patches from

which the ground litter has been removed, either

purposefully or as a result of continued use. Some

sleeping spots are not in sheltered places but are

small bare areas similar to the feeding spots; these

may be utilized by the animals for both feeding

and sleeping. Agoutis often use one sleeping spot

for a few days and then move to another. Territoryholding animals may sleep anywhere within the

territory; nonterritory-holding younger animals tend

to sleep near to the area of the holes that they

inhabited as infants.

I did not observe any adult agoutis sleeping in

burrows, but since most of the burrows in the

study area were in the banks of the creeks, they

were difficult to observe. I set up an automatic

camera outside four different burrows in an area

where I knew that a pair of agoutis was sleeping,

but the only animals entering the burrow were

an armadillo (Dasypus novemcirtctus), a pair of

motmots (Electron platyrynchiim), and an iguana

(Iguana iguana).

Sleeping agoutis commonly lie on the ventrum,

with the forelegs folded so that the feet are under

the chest (Figure 20d, e). This posture exposes a

minimum amount of the areas commonly bitten

by insects and may be adopted for that reason.

Agoutis in captivity, housed in insect-proof cages,

usually lie flat or curled on one side to sleep.

When they awaken, agoutis stretch in a similar

manner to many other mammals, first arching the

back while stretching the legs, then stretching the

forelegs alternately forward, often while yawning,

and finally taking a step forward while extending

a hind leg stiffly to the rear. Stretching is often

followed by a bout of grooming before the animal

leaves the sleeping spot.

Agoutis rest often while they are foraging, but

territory holders rest more than nonterritory holders. They generally rest on one of the feeding
28 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

spots in the area or may leave a foraging area and

go to a sleeping spot on their territories. The female of a territorial pair rests more than the male.

He often lies clown near her when she rests, but

he seldom remains resting for more than a few

minutes, and continually gets up and makes short

patrols around her. The postures adopted for resting are the same as those used for sleeping. Resting agoutis often fall asleep, but usually awaken,

raise the head, and look around every few minutes.

Courtship and Mating Behavior

INTRODUCTORY BEHAVIOR OF CAPTIVES

In mature, captive agoutis that have not been

previously introduced to one another, contact,

courtship, and attempted mating behavior follow

a usual pattern (Figure 21): (1) brief naso-nasal

contact; (2) urine spray or enurination (Southern,

FIGURE 21.—Courtship behavior: a, b, naso-nasal contact;

c, d, e, enurination; /, frenzy dance; g, h, dorsal grooming

of female by male.

1948:177) attempt by the male, followed by front

foot trembling; (3) following or driving of the female by the male; (4) enurination and foot trembling; (5) attempted mount; (6) mount with thrusting; and (7) intromission and ejaculation. Steps

6 and 4 are commonly repeated whether or not

they are followed by steps 5, 6, and 7.

The naso-nasal contact may be initiated by either

the male or the female, and it is often accompanied

by "purr" vocalizations by either. It usually lasts

for no more than a second; then the female breaks

off contact and avoids the male. It is interesting to

compare this behavior with that of Myoprocta.

Nothing is known about this "miniature agouti"

in the wild, but it is said (Morris, 1962; Kleinman,

1971:261) to be considerably more socially tolerant

than its larger cousin. Kleiman (1971) has studied

the sexual behavior of captive Myoprocta and report that females tolerate and indeed intitiate contact with males to a much greater degree than occurs in agoutis.

In his attempts to approach her, the male agouti

walks obliquely toward the female, rears up on his

hind legs, pivots toward her, erects his penis and

squirts urine at her from a distance of up to about

1.5 m (Figure 21a-c). As he rears up the female usually jumps out of his way, so that his initial spray

seldom hits her. The male then starts to follow the

female as she walks about. He may make squeaking

noises (p. 44) at this time and, when he pauses, his

front feet may be vibrated in a rapid trembling

motion. Every time the female pauses to eat, to

rest, or to groom he attempts to get in position to

enurinate her. He usually succeeds on the second

or third try.

Being sprayed with the urine of the male has an

interesting effect on young females, causing them

to go into what I call the "frenzy dance." At first

the female appears to ignore its occurrence; then,

after 15 or 20 seconds, she begins to toss her head

and to prance around. She sometimes; leaps into

the air, twisting as she does so, and lands on her

side or on her back. Then she jumps up and starts

to run in circles, apparently aimlessly, for she

crashes into any object in her way. At first the male

merely watches her, then her behavior appears to

infect him for he starts to act in the same manner

and the two animals rush about together.

After a minute or so of this behavior the female

suddenly stops and begins to eat or to groom. The
NUMBER 257 29

male also stops and attempts to get into position for

another enurination. After receiving the first few

sprays, the female gradually allows the male to approach more closely until he is eventually able to

crouch over her in the mounting position, but without actually touching her. He also grooms her back

with his incisors when approaching her closely

(Figure 21g). Subsequent to each enurination the

male sits and trembles his forefeet. During the

process his scrotum becomes enlarged and there is

a noticeable increase in his odor.

Of the four captive females that I observed, none

would tolerate contact by the male during the day

of their introduction. On the fourth successive day,

one of the females allowed the male to mount

briefly, although I do not believe he gained intromission, and another engaged in some mutual

grooming with the male. Since my major concern

was with the behavior of wild animals and it appeared that copulation would not occur in the

captives for some time. I did not persist in observation beyond this stage. Copulation in captive

agoutis is described in Roth-Kolar (1957:369) and

in Myoprocta by Kleiman (1971:268).

COURTSHIP OF FREE-LIVING AGOUTIS

In the group of wild animals that I watched, two

pairs were already established at the beginning of

phase I and remained so throughout, although the

animals spent varying amounts of time in one another's company (Figure 6). One phase I pair (m22

and FSB) formed during the study, but I did not

see the initial behavior involved in its formation.

The remaining animals, with few exceptions, engaged in no sexual behavior. One exception was

ml4, who, when he was about 5—6 months old, attempted repeatedly to copulate with his mother,

FSP. It is interesting that, at the time, FSP had

recently given birth and ml4 would meet her when

she left the nest area to forage. Her mate, MSS,

would also meet her and, if he encountered ml4,

would drive him away. But ml4 was often able

to remain with FSP for some time before MSS detected him. Sometimes he would nudge his mother

over onto her side and would nurse; at other times

he would attempt to copulate with her. On three

occasions I saw her stand still while he mounted,

made a few rapid pelvic thrusts and then dismounted or slid off when she moved. I do not know

whether any of these attempts represented complete copulations.

The most commonly seen courtship behavior in

wild agoutis consists of the male "driving" the

female. Wherever she goes, he follows at a distance

of a meter or less, occasionally coming close enough

to sniff her anal region. Except on rare occasions,

even in established pairs, the female avoids all but

the briefest contact with the male and will generally

not allow him closer than about 0.5 m. The only

physical contact that I observed between the paired

animals in the study area consisted of mutual

grooming of the ear region and of the male occasionally attempting to take food from the female

in the same way that juvenile agoutis do. Males

frequently attempt to get into position to enurinate

their mates, but succeed only about 20 percent of

the time. After each attempt they usually sit with

their front feet trembling.

I did not observe the frenzy dance in enurinated

females in the wild, probably because the pairs that

I watched were well established by the time I was

aware of their existence. A milder form occurs

under the following conditions:

1. In young animals (about 3-8 weeks of age)

when they are engaged in practice and exploration behavior. Both single young and members of a

pair of twins occasionally engage in abandoned

rushing about in response to no apparent external

stimulus.

2. In response to light rain. I was observing phase

I f27 when a light rain began. She began to prance

in a manner very similar to that seen in the frenzy

dance.

3. As an after effect of submissive behavior when

confronted by an obviously stronger animal. On

separate occasions during phase I MRE and ml4

were feeding in the bait area when a group of collared peccaries arrived. Each started toward a piece

of banana at the same time as a peccary, which

made a short rush at the agouti, frightening it

away. In both cases the agouti sat for a few seconds

outside the bait area, and then jumped up and performed a mild version of the frenzy dance. On another occasion, when ml4 was driven away from

his mother by MSS, ml4 sat for a few seconds and

then started to leap and prance around in a manner

similar to that seen in the frenzy dance.

In all cases where this behavior occurred it was

in response to a situation that probably involved
30 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

an inability to follow through on an aggressive impulse either because the object arousing the aggression was absent (in the case of the rain shower)

or because it was inappropriate (in the case of meeting an obviously stronger competitor for food, or a

conspecific that transmitted a sexual rather than an

agonistic signal).

Between the time that young agoutis leave their

parent and the time that they become territory

holders, all their encounters with conspecifics involve some aggression. Young animals are either

harried by territory holders or are involved in competitive situations with other nonterritory holders.

Each agouti spends several months learning to

avoid contact with all conspecifics regardless of

their gender. As the age of potential sexual maturity is attained the situation becomes aggravated and

territory holders expend considerable energy seeking out and driving away potential usurpers of the

same sex. The maturing animal must now learn to

be prepared to fight, but to flee before suffering

significant damage from a stronger animal. It seems

unreasonable to expect that the initial exchange of

sexual signals between potential partners could suddenly abolish months of learning that the prospective mate is a potential threat. It seems more likely

that, by the male's transferring his odor onto the

female through enurination, both members of the

pair come to recognize one another as nonthreatening, but, during the initial period when this is

being accomplished, each recognizes the other as

simultaneously threatening and attractive. The sexual overtures serve to decrease the threat but not

entirely to negate it. This would also help to explain why the male periodically enurinates the female throughout the year even when not actually

engaged in mating behavior; it is a means of maintaining the pair-bond.

The frenzy dance thus consists of in vacuo fighting during which both aggressive and defensive behavior patterns appear in each animal. The abandoned running is accompanied by jumping and

head flinging which are similar to the movements

of an animal trying to jump over and to bite another, and also by kicking backwards with the hind

feet, avoidance jumps and rolling on the back while

kicking upwards, which are defensive movements.

Kleiman (1974:177) in a general review of Hystricomorph behavioral patterns states that the frenzy

dance (termed by Kleiman "frisky hops" after

Rood, 1972) is a play pattern with practice predator-escape as its major component. In agoutis,

components of flight behavior are certainly present,

but flight behavior is an important part of intraspecific hostility. Of course, many aspects of fighting

between conspecifics and of predator avoidance of

behavior will be similar; but, because of the factors

mentioned above, I believe the frenzy dance to be

principally a manifestation of frustrated intraspecific aggression.

Agonistic Behavior

INTERSPECIFIC AGONISTIC PATTERNS

Except in the defense of their young against coat is

and what is possibly redirected aggression when

they are driven away from food by peccaries, I saw

very little interspecific aggressive behavior on the

part of agoutis. In a foraging situation, they reacted

to the direct approach of practically any other animal as they would have to the direct approach of

a conspecific, i.e., by retreating. One reason for this

is probably that most of the animals that agoutis

come into contact with are larger than themselves.

I saw only one encounter between an agouti and a

smaller mammal. This occurred when two agoutis

were feeding on some maize that I had put out and

a squirrel (Sciurus granatensis) came down a nearby

tree and began to eat some of it. One of the agoutis

made a brief lunge toward the squirrel, which retreated up a liana but quickly returned and began

eating again. The agouti drove it off several times,

each time in a less energetic manner, and finally the

squirrel was tolerated at a distance of about 2

meters.

I found that wild-trapped agoutis never attempted to bite. On one occasion, when a subadult

male escaped from my handling net, I caught him

in such a way that my index finger was in his

mouth, and he still did not attempt to bite. The

chief means of fighting back against predators is

with the hind feet, with which agoutis can exert

a powerful and damaging kick. Agoutis also "mob"

potential predators of particular types (p. 41). This

behavior might be considered to have some aggressive components.

INTRASPECIFIC AGONISTIC PATTERNS

When one agouti walks toward another, this
NUMBER 257 31

constitutes a simple act of aggression and, if the

aggressor is an adult male, such behavior will elicit

appeasement squeaks from females, juveniles, or

subordinate males as they get out of its way. Under

situations of higher apparent aggressive motivation

the aggressor may rush at the other with the rump

hair erected and /or the anal glands everted. An attack against a conspecific of the same sex and approximately the same age consists of a rush and an

attempt to bite, or, at a higher intensity, of rushing

and jumping over the other animal and lashing out

at it with the hind feet when directly overhead

(Figure 22).

A type of aggressive behavior that is initiated by

all age classes in captivity, but which I saw used

in the wild only by adult females against younger

agoutis, consists of the aggressor running at the

other and drubbing it with the forefeet. This is the

first overtly hostile act performed by a mother

against her maturing offspring as it attempts to take

food away from her. A young animal sustaining this

a

FIGURE 22.—Agonistic behavior: a, chasing; b, c, rump hair

fully erected; d, jumping over and striking with hind claws;

e, biting attempt; /, jousting.

type of attack usually crouches and remains stationary, which probably inhibits a more damaging

attack since, if the young animal flees when the

female first threatens, she is liable to attack it more

vigorously, chasing and biting it.

If an agouti, when approached by another, turns

and flees, the one approaching is liable to attack.

On several occasions subadult males were feeding

in the bait area at the same time as, and obviously

within sight of, territory-holding adults. A sudden

movement made by the adult (or a sudden, quite

unrelated noise) would cause the subadult to flee,

and only after it had started to run away would

the territory holder pursue it. An agouti, chasing

another that is fleeing, attempts to bite it on the

rump, usually uttering a series of grunts similar to

those that precede the alarm barks (p. 43). The

fleeing animal often receives superficial wounds

from the biting of the pursuer. On one occasion a

large adult male (but obviously not territory holding) escaped from his cage and went into the forest

early one morning. I left the cage open and, in the

evening, he returned and was cowering inside,

bearing many wounds of the type received by an

agouti that is bitten while fleeing from another.

Either the animal attacking, or the one fleeing,

or both, may have the rump hair erected during

an aggressive encounter (Figure 22). When both

are in the same age class and/or reproductive state,

both will raise the hair to the maximum level. In

such a case, the one that is furthest from the center of its territory will usually flee; but if it does

not, an elaborate form of fighting, similar to the

"jousting" that has been described in rabbits

(Southern, 1948:181), may take place. The following excerpt from my notes describes an encounter

during phase I between MSS and MRE, both reproductive males. MSS was normally dominant

over MRE at this time in this area, but MRE had

just succeeded in driving off ml4, which apparently

raised his fear threshold and lowered his aggressive

threshold, and MSS had just driven off mSN,

which had a similar effect on him:

16 March 1706 hrs: F13 appears 5 m north of the north

end of the log [Figure 3fo] and goes straight into the bait

area. Her mate MRE returns to the bait area after a lengthy

chase of ml4, sees F13, raises his rump-hair and chases her

out of the bait area. MSS is sitting just south of the bait

area, after chasing mSN into the creckbed 30 m to the south.

MSS turns when MRE makes fight grunts as he chases F13,
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

and runs into the bait area. MRE apparently hears him

coming and turns to meet him. MSS stops about 1.5 m

from MRE and they circle one another, stepping sideways,

both with the rump hair fully erected. They suddenly rush

together, leaping into the air just before meeting and lashing out with the hind feet. MSS is thrown off balance by

this and lands on his side. MRE jumps on him and tries

to bite him, but MSS jumps up and flees with MRE chasing

him and trying to bite his rump. MSS turns and attacks

MRE about 20 m north of the bait area. They chase one

another in large circles for nearly 10 minutes, to the north

and east^ of the bait area. F13 has meanwhile returned and

eats in the bait area. MSS returns alone and attempts to

eliminate F13, but she jumps out of the way. MSS goes

off south.

1721 hrs. MRE returns to the bait area. His fur is tufted

out on the flanks and he has a bleeding spot on the top

of his nose. He enurinates F13, and sits with his front feet

trembling.

This was the only time that I saw this type of

fighting behavior in the wild. It did occur in my

observation cage, either between adult males or

between adult females. Severe wounds are liable to

result from the fighting use of the claws of the

hind feet. One of the females hit the other on the

haunch, leaving a wound nearly 5 cm long and

more than a centimeter deep. I found a dead adult

male, outside my study area, that had been disemboweled. The body was still fresh and undamaged (apart from the long gashes in its ventrum)

by either predators or scavengers, and I suspect

that the animal died as the result of a fight with

another agouti.

Maturation of Young Agoutis

I did not witness actual parturition in the group

of agoutis that I studied. The process has been

described by Enders (1931) for a semi tame animal

that lived in the laboratory clearing on Barro Colorado Island. I observed the development of three

captive-born agoutis from shortly after they were

born until they reached maturity, and watched the

early development of six wild ones (two pairs of

twins and two singles), four of which were killed

or disappeared before reaching potential maturity.

PARTURITION AND NEST SELECTION

I believe that parturition in wild agoutis occurs

in one of the habitual sleeping spots of the mother.

Three of the six infants that I saw shortly after

birth were born sometime during the night, and

the mother and young were resting when I first

observed them in the morning. Single births seem

to be more common than twins in the Barro Colorado Island population. Of the 12 litters that I

saw, six consisted of single young, three others

probably were single but I did not observe them

for long enough to be certain, and three were

twins. As in most other caviomorph rodents (Kleiman, 1974:190), the young are extremely precocial

at birth. They are fully furred, with their eyes

open, and are able to run, though somewhat unsteadily, within the hour of their birth. At first

they have some difficulty finding the nipples of the

mother, but suck a little by the end of the first day

and by the beginning of the second day they are

attempting to eat solids.

The two phase I mothers that I observed on

the morning after they had given birth followed

a slightly different pattern. The one (FSB) with

the single youngster (f27) got up from her sleeping

place under a dense clump of bamboo at 0645

hours on 14 March 1967, stretched in the usual

manner, then started walking straight toward what

would become the nest of the young animal: a

small hole under an abandoned water tank in the

forest bordering the laboratory clearing, about 15

m from her sleeping place. The infant followed,

running close beside her front feet and continually attempting to nuzzle her in the side of her

mouth as she walked. She went straight to the hole

and put her nose near it. The young one went into

the hole and did not reappear. The female lay

down outside the hole (which was far too small for

her to enter) and rested until 0950 when she got

up and put her nose near the hole again. At the

time, the ambient noise level was too high for me

to hear any noise she might have made but later,

under the same conditions, I could hear a short

purr. The baby came out of the hole and, when

the mother lay down on her side, nuzzled in her

fur, obviously attempting to find a nipple.

One of the workers on Barro Colorado Island

told me that the hole that this baby used had been

used by agoutis repeatedly in the past and it has

been used by others since. I think it likely that

FSB used it as an infant and that there may be a

traditional use of such nesting places in agouti

populations.

The other case during phase I was further from
NUMBER 257 33

the laboratory clearing, and I observed it from

the tree platform. I had been aware for some days

that F13 was about to deliver, for the movements

of the fetus are clearly visible within the female

for about two weeks before parturition. One evening FI3 was very restless and had spent some time

lying on her side with one hind leg elevated, which

is an unusual position for an agouti. She had also

been licking her perineal region.

The next morning, as it became light enough

for observation at 0630 hours, I saw her lying in

one of her sleeping spots just east of the bait area,

with two newborn young. At 0645 she got up and

started walking north, up the hill. Both young

followed her and showed the same nuzzling of the

side of her mouth that was shown by FSB's baby.

They turned west across the hill about 25 m north

of me, and she put her nose into a small hole.

Both young animals went into it, but they came

out again almost immediately. The female continued west across the hill, followed by the two

babies, and they went out of my sight. Only three

minutes later a large band of female and young

coatis came down the hill from the direction that

the three agoutis had taken. The next day F13

came to the bait area and ate there, but did not

take any food away with her. Females that were

suckling new young visited the bait area for only

brief periods, and almost always took a piece of

food with them when they left. F13 did not appear

to be lactating in the weeks that followed. Nor was

she provisioning young. So I concluded that both

of her young ones died in some manner, and that

it is quite possible that they fell prey to members

of the band of coatis.

When the young agouti is three to five weeks

old it becomes too large for its first nest entrance

and moves to another burrow. In the three cases

where I observed this, the young animals moved

to burrows that were already in existence. I presume they would dig their own if none was available, although I believe that nest sites are largely

traditional, females eventually using the ones they

were born in, and there is seldom a need for digging fresh burrows. The only digging I saw in

agoutis (wild or captive) occurred in the burying

or digging up of food. On several occasions I kept

wild-trapped individuals for a few days for observation in cages with soil floors. None ever attempted to dig out.

MATERNAL CARE OF NEST-BOUND YOUNG

Female agoutis do not sleep with their young,

but instead go to one of their habitual sleeping

spots. They go to the nest after a brief period of

early morning foraging, usually carrying a piece

of food, remain with the young most of the rest

of the morning, feeding and glooming it or merely

resting, and then usually go foraging again at

1030 or 1100. Sometimes they wait until early afternoon before going off on the second foraging trip.

I was not able to watch agouti nests with young

occupants during the time when fruit was scarce,

but observations of mothers who bore young during this period indicated that they spent more

time foraging and less time resting near the nest.

The behavior of individual females differed in this

respect too. FSB would visit the nest, feed and

groom the young, rest, and then return to foraging. She would eat food where she found it and

would occasionally rest while foraging; then she

would return to the nest, usually carrying a piece

of food. FSP generally spent less total time near

the nest but visited it more frequently. She would

go foraging, eat one or two pieces of food where

she found them, and then carry one back to the

nest. Then she would eat the piece of food, let

the baby eat it or bury it near the nest entrance,

and go foraging again. She would rest both near

the nest and while she was foraging. The females

generally left their nests about 1300-1400 and foraged from that time until about 1730, shortly before dark. Then they would return to the nest,

and feed and groom the baby before going to one

of their sleeping spots to spend the night.

When female agoutis arrive at the nest, they call

the infant with a sharp purring noise (Figure 23)

and then sit and wait for it to come out, which it

usually does within a few seconds. It may then

attempt to eat some of the food that the mother

brought with her or, if she has eaten some of it

while waiting, may eat pieces she dropped. The

first thing she does is to start grooming it. Sometimes she begins by grooming it around the ears,

but wherever she starts she works quickly back to

its perineal region which she begins to lick very

energetically, often lifting the baby off the ground

if it is standing, or rolling it over on its back

(Figure 23). When licked on the perineum, the

baby urinates and defecates and the female ingests
34 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

FIGURE 23.—Parental care: a, female waits for infant outside

nest; b, nest building by infant; c, d, perineal grooming by

mother; e, f, infant seeking solid food brought by mother;

g, h, i, nursing; /, infant autogrooming.

all the products, then nudges the baby out of the

way and licks the ground underneath it. After it

is a few days old, the young agouti seems to try

to avoid the perineal grooming, running in small

circles, jumping out of the way, sometimes even

kicking its mother in the face as she tries to lick

its perineum. But sooner or later the baby comes

close to suck and she will not permit it to do so

until she has groomed it, and has ingested the

urine and feces. On several occasions the baby was

very slow to defecate, taking 15 minutes or more

and several grooming sessions to do so. As soon

as it begins to defecate it is allowed to suck (Figure 23). The pattern of grooming the perineum

of the baby is repeated shortly before the female

goes away to forage again. The morning sessions

of sucking are often very short, lasting no more

than a minute or so, and there may be two or

three of them. When the female returns to the

nest before dark there is usually a longer session,

lasting 20 to 30 minutes.

During the first week the baby never comes out

of the hole unless the mother is there. After the

first week it begins to look out. when the mother

is not there, and then to come out for longer and

longer periods. At the age of about two weeks the

infant begins to follow the female as she leaves

the nest. At first it merely follows her to her resting spots, but then attempts to follow her as she

leaves to go foraging. She often turns and lunges

briefly at it as it tries to follow her and, initially,

this is enough to chase it back into the nest. Eventually the infant retreats into the nest only when

it is frightened by something other than the

mother, and at this time (when it is 5-7 weeks

old) will sometimes venture with her all the way

to a foraging area. During the initial exploration

of the area the young animal finds, enters, and

occasionally plays in, the progessively larger holes

that will become its subsequent nest sites as it

grows out of the smaller ones.

In spite of this exploratory activity, during the

first three weeks of its life, most of the time of an

infant agouti is spent around the mother as she

rests outside of the nest. It carries nesting material

into the hole, leaps or climbs onto or over her

(Figure 24), or merely runs around in short, rapid

bursts. She pays little attention to this, but sometimes turns and grooms the baby with her tongue

and incisors, mostly around the head and ears,

but occasionally over the rest of its body surface.

The baby also grooms her around the back of her

head and on the sides of her face, and usually

follows this by grooming itself. Mutual grooming

occurs between mother and young up until the

time that they become separated.

Two other important behavioral patterns that

appear during the second week are sitting up on

the haunches to eat and food burying. Up until

this time baby agoutis eat small pieces of solid

food from the ground, neither picking it up nor

resting on their haunches to eat. Week-old babies

also begin to bury small pieces of the food items

that the mother brings to the nest. At first they

dig holes that are much too shallow to conceal

the food, but by about the third week they are

efficiently burying seeds.

Adult male coatis (Nasua narica) often attempt

to get into nests housing young agoutis (Smythe,

1970c). If the female is present when they arrive

she gets up and moves a short distance away,
NUMBER 257 35

a b

FIGURE 24.—Parental care: a-e, rubbing over; /, four-monthold juvenile stealing food from its mother; g, six-month-old

agouti nursing; h, male adult, having enurinated infant, attempts to mount it.

erects her rump hair, and growls. She also may

make short rushes at the coati, and sometimes succeeds in driving it away. Sometimes the coati will

charge the adult agouti, and the frequency of such

attacks increases as fruit becomes scarcer.

Occasionally, when the infant is sitting with its

hind end near the female's face, it will suddenly

leap up, lashing out with its hind legs as it does

so and kicking her in the face, before dashing

away a meter or so. In adults a similar behavior

is sometimes seen in one agouti that is being

chased either by another agouti or by a running,

potential predator, but an interesting difference is

that the hair on the rump of the animal that is

being pursued is always erected, whereas in young

animals it is not. A similar case is seen when a

litter consists of twins. When they play they sometimes go through the complete fighting sequence,

including the mutual leaping into the air and

lashing out with the hind feet (p. 31); but, whereas

adults always have the rump hair fully erected

during such an encounter, juveniles do not.

One advantage of the infant's selecting a nest

the entrance of which will only just admit it is

that potential pedators of any greater size are excluded. As the young animal grows, however, it

begins to have difficulty entering the nest itself;

finally reaching the point when it must crawl in,

holding the hind legs straight out astern. The age

at which this occurs is not the same for all animals,

since the size of the initial nest hole varies from

one to another. As the young animal begins to

experience difficulty entering its nest, or somewhat

before this happens, it begins to spend more and

more time in a nearby {5-30 m away) larger burrow. Finally it abandons the original nest altogether, although it may still occasionally return

and play outside it. As with other aspects of the

ecology of agoutis, there is considerable individual

variation in the number of times the growing animal moves and the amount of time it spends in

each of the burrows. One that I watched lived in

four successive burrows, while another moved directly from its first to a considerably larger one,

which it occupied until it was subadult and was

living most of the time above ground.

Any time after the young one is about 15 weeks

old, its mother may have another litter. When this

happens the older offspring begins to spend more

time foraging alone, gradually moving farther away

from its nest, but returning to it if frightened.

Much of its time is now spent exploring the edges

of the area with which it is familiar, apparently

learning the system of trails used by the other

agoutis in the area. It will often walk along one

of these trails, moving away from the familiar area,

and then will turn suddenly and run very rapidly

back to the familiar area; then, as often as not,

it will turn around and run back along the trail

again. This type of erratic running is strongly

reminiscent of that seen during initial sexual encounters. An exploring juvenile sometimes misses

the trail and runs into the undergrowth. I saw

one get its front feet momentarily entangled in a

small vine and fall down. Had there been a predator nearby it could easily have reached the agouti

before it was able to recover, which illustrates the
36 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

adaptive value of what otherwise seems like aimless

behavior.

Exploring juveniles also cut small branches with

their incisors in much the same way that adults

do, but the adults only cut them when they are

across one of their trails, whereas the juveniles

may cut them anywhere. They also scent-mark frequently as they are exploring, though this behavior

does not appear until they are four or five weeks

old (cf., Roth-Kolar, 1957).

BREAKUP OF THE MOTHER-YOUNG BOND

A young agouti may forage with its mother until

it is four or five months old. If she has not had a

subsequent litter, the young animal remains with

her constantly from the time it is 3.5-4 months

old, sleeping with her in one of her sleeping spots

and following close behind when she goes foraging. Females with small, nest-bound young are

often joined by their older offspring as the females

leave the nest area to go foraging, and they allow

the older young to nurse occasionally when they

are away from the nest (Figure 24).

Nest-bound young agoutis take food out of their

mother's mouth whenever she brings some to the

nest. This behavior persists as they follow her on

foraging trips. Each time a foraging female picks

up a piece of food she utters a single, loud "purr"

similar to the noise made when she calls the

younger animal out of its nest. When the adult

makes this noise, the young animal immediately

runs over and takes the food out of her mouth.

Even if it has already found a piece of food and

is eating, the juvenile will drop its own and take

whatever the mother is holding. At first the female

willingly gives up her food to the young animal;

but, as it grows older, she seems progressively less

inclined to do so, eventually mixing a high-pitched

whine with the purr and holding onto the food

so that the youngster has to pull quite hard to get

it away from her. The juvenile persists in taking

her food and, after some time, she begins to attack

it whenever it approaches her when she is feeding,

drubbing it with her front feet and not allowing

it to take the food. Even at this stage she makes

the purr whenever she picks up a piece of food,

as though she cannot help doing so. Finally, she

attacks the young animal whenever she sees it and,

since it persists in attempting to approach her,

there is a period when she shows more aggressive

behavior toward her own offspring than toward

any other animal from the immediate area.

At this time a young animal is chased by almost

all the other agoutis that it meets, and spends much

of its time avoiding them. It is also in more danger

than usual of predation at this time because of

unfamiliarity with escape routes and because of

the possibility of blundering into a predator during

one of the frequent flights from a conspecific. My

data, both observational and from trapping, indicate that of the agoutis that survive infancy, few

survive the period between leaving their mother

and obtaining a territory of their own (Figure 17).

On the other hand, several animals in the secondphase trapping area were trapped as adults four

years earlier. Therefore, the probability of mortality falls sharply as an agouti achieves reproductive

status.

The disintegration of the mother-young bond

is accelerated by two factors: the female giving

birth to subsequent young and/or the food supply

decreasing. If a second infant is born at the time

when fruit is abundant, the first has a better chance

of surviving since, during the time when it is

learning the characteristics of the environment,

the territories are less assiduously guarded and the

predators are not as hungry (some agouti predators,

such as coati and tayra, are also frugivorous). All

four mother-young pairs that I watched extensively

through the process of disintegration broke up at

a time when the food supply was beginning to

dwindle. The two young animals that attempted to

join foraging mothers when the period of deprivation was further advanced appeared to suffer more

than the two who were already foraging with their

mothers when it began.

I observed the phase I group of agoutis through

1966 but did not begin intensive observations until

December of that year. Only three juveniles survived the 1966 period of fruit scarcity, and all were

males. The oldest, mSN, was foraging by himself

by the time fruit began to grow scarce, but the

other two, ml4 and ml8, were still with their

mothers. In 1967 two juveniles survived and both

were females. I was able to observe some of the

behavior involved in the breakup with their mothers of the two youngest males and the two females.

A brief synopsis of my observations in each case

follows.
NUMBER 257 37

About the middle of May 1966, FSP had a male

baby, ml4. She had a subsequent litter (which I

did not see, but the existence of which I inferred

from her behavior) in August, but it did not survive for more than two weeks. Thus, ml4 remained

with her as he grew up, sleeping and foraging with

her from late July until fruit began to grow scarce

in October. They spent less time together through

the time when fruit was in lowest supply. By January 1967, m!4 was potentially sexually mature and

began to attempt to copulate with his mother,

even though he still showed occasional nursing

behavior. By the end of January and in February,

his father, MSS, began to show serious aggressive

behavior toward ml4 and would actively seek him

out and chase him. MSS's aggressive behavior toward ml4 became still more pronounced in March,

although FSB still tolerated him, and then he

suddenly disappeared.

In late July 1966, F13 also had a male baby,

ml 8, which was not ready to leave the nest and

forage with her until the end of September, by

which time fruit was becoming very scarce. Both

F13 and her mate, MRE, showed considerable

aggression toward ml8 the first time he came to

the bait area. During the months of January, February, and March, ml8 sustained more attacks

than any other animal that I had under observation. He survived until the end of May, when he

disappeared. But he was always easily recognizable

up until that time because of his small size. He did

not gain significant weight through the three most

severe months of food scarcity. The last time I

trapped him was toward the end of December, but

before he disappeared he did not look much larger.

It seems reasonable to attribute his puniness to

lack of food when he was young, and this, in turn,

to parental aggression.

In early June 1967, F13 had another baby, and

this time it was a female, f29. I was away in July

and August, but by the first of September the two

were foraging together and f29 was regularly taking food from her mother's mouth. F13 tolerated

this until the middle of October, when she began

showing signs of aggression. By the end of the first

week in November she would attack f29 on sight.

During the third or fourth week of June 1967,

FSB had twins, of which one (a female, f27) survived to leave the nest and start foraging with its

mother in late September. I saw very little aggression between these two animals, but f27 spent

considerably less time in the bait area with her

mother than did f29 with F13 (Figure 6), and by

late October came to the bait area alone.

It thus appears that a juvenile that joins its

mother while fruit is still relatively abundant will

be tolerated by both parents for a longer time

than one that attempts to do so later. Aggression

toward male young seems to be initiated by their

fathers and toward female young by their mothers.

The onset of parent-young aggression appears to

occur earlier if fruit is scarce and, if it is scarce

enough, either parent may become aggressive toward a youngster of either sex.

The first phase of the study terminated in November of 1967, so I do not know what became of

f27 and f29.

ROLE OF THE MALE

During the first three weeks that the baby is in

the nest, the female will not permit another agouti

to come close, even keeping her mate and any

previous offspring at a minimum distance of about

5 meters. During the third week the male sometimes comes to the nest when the female is off

foraging, and the young one will come out of the

nest and attempt to interact with him. The male

apparently recognizes the smell of his mate on the

juvenile and he treats it as he would her. Each

time the young animal runs toward the male he

rears up and enurinates it, so that by the end of

a few minutes it is thoroughly soaked with his

urine. He also attempts to mount the juvenile,

but it runs out from underneath him, and he

stands and trembles with his front feet in the same

way he does when frustrated in his attempts to get

nearer to his mate.

There is apparently a postpartum estrus in

agoutis, for the male is in almost constant attendance just before parturition, in spite of the increasing aggressiveness of the female, and he shows

a greater amount of sexual excitability than usual

whenever he is with the female immediately after

parturition. In addition, subsequent litters are

usually born about three and one-half months later,

which is approximately the length of the gestation

period (Roth-Kolar, 1957:369) Roth-Kolar (1957)

found similar behavior in her captive animals, and
38 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

says that subsequent litters generally followed parturition by from 110-190 days.

SURVIVAL OF THE YOUNG

Although there is a definite increase in the number born from March through July, I observed

young agoutis during almost every month of the

year on Barro Colorado Island. But, of those

born outside of the March—July period in the

phase I study area, none survived to leave the nest.

The chief factor involved in their mortality was

that, in the absence of falling fruit, adult male

coatis turned from being primarily frugivorous

to a primarily carnivorous way of life and spent

much of their time hunting juvenile agoutis

(Smythe, 1970c). The fact that the coatis experience

considerable success in this pursuit is attested to

by my witnessing three actual captures by them

from the observation platform.

I believe that the time of survival of those

agoutis that do leave the nests to begin foraging

is also rather short, although they merely disappeared from the bait area and I am not sure of

their fate. They suffer a very high level of aggression from the older animals which, together with

the seasonal shortage of fruit, contributes to their

undergoing considerable hardship from September

through December. These conclusions are substantiated by the data gathered in phase II (Figure 17).

It would seem likely, therefore, that unless maturing agoutis find an unexploited area where they

can establish a territory and accumulate a food

hoard, which they would have to do by emigrating

unless a local territory holder died, their chances

of survival are not good.

Communication and Displays

VISUAL COMMUNICATION

The act of walking toward another agouti is

regarded by the one being approached as an aggresive gesture. The animal being approached almost always avoids the other by walking or running out of the way. (As might be expected, this

leads to difficulties when a male is attempting to

get close enough to a female for copulation.) Occasionally a juvenile is frightened by something or

will inadvertently run toward an adult male. In

this case the adult runs out of the way of the approaching juvenile, as it would if attacked by

another adult, but it then generally circles and

attacks.

There seems to be little or no recognition of

mates or other individuals by visual means. An

excerpt from my notes during phase I serves to

illustrate this:

24 April, 1730 hrs: An unidentified agouti chases F13

toward the bait area itself. MRE (the mate of F13 and a

high-ranking male) is eating in the bait area and, as she

passes him, she suddently turns and rushes at him. He runs

away for about 3 m, with his lump-hair fully erected, then

turns around and rushes at F13. She wheels and flees, making appeasement squeaks. He slows down, so docs she. He

approaches and tries to enurinate her, but she avoids him.

He sits with his front feet trembling (a sign of sexual

arousal).

Such cases are common. An agouti would be

aggressively aroused and would attack the next

one it encountered, which would often be its mate.

Then recognition would suddenly occur when the

animals were close together, I believe, by one recognizing the odor of the other.

Exaggerated piloerection of the rump hair (Figure 22b, c) occurs as a manifestation of readiness

to flee, even though it invariably appears in both

animals engaged in aggressive encounters. It is a

graded response, in its lowest intensity consisting

merely of raising the long rump hairs to an angle

of about 30° from the body. At the highest intensity the hairs are raised to nearly 90° so that they

form a fan of hair on the rear end of the animal,

and the display may be accompanied by eversion

of the anal scent glands.

The fullest degree of piloerection is seen when

one animal flees from another. It also occurs in

the pursuer, but in such cases the one fleeing will

usually turn and attack the one pursuing, i.e., their

dominance relationship is uncertain. In such cases,

both animals keep the hair raised during the entire

encounter. Full piloerection also occurs in an

agouti that is being chased by a potential predator.

I saw it in several chases by coatis (Nasua narica)

and peccaries {Tayassu tajacu), in one by a tayra

(Eira barbara), and one by a jaguaroundi (Felis

jaguaroundi). The first time I saw MRE enter the

bait area, FSP was sitting there eating. MRE

walked slowly into the area in the investigative

posture, with the neck outstretched and held low,

ears forward, and hindquarters slightly crouched.
NUMBER 257 39

FSP paused and looked at him with her ears forward, and both animals were still, about 2 m from

one another. A large branch suddenly fell off a

tree about 50-60 m away, and both animals fled

in opposite directions with their rump hair fully

erected.

A lesser degree of piloerection is liable to occur

in situations of mild alarm. For instance, an agouti

eating in the bait area would occasionally hear a

noise made by another animal, such as a bird,

moving in the foliage nearby but out of sight, and

would raise the rump hair to an angle of about

60° from the body surface. A similar response occurred when F13 came upon an infant of FSP's

that had just been killed by a coati; she raised

her hair to about 60° and thumped her hind feet

on the ground, while sniffing at the carcass. (I had

inadvertently driven the coati off while looking

for it after hearing the distress squeals.) Hair erection also occurs when an agouti smells a spot where

a stranger has marked. The further the marker

had come, and thus the less familiar it is, the

higher the hair is raised. The lowest intensity of

the hair-raising response occurs when an unfamiliar

but distant noise, such as a gunshot, is heard or

when a familiar but loud noise, such as a thunderclap or the sudden crashing of monkeys in the

overhead foliage, occurs.

The function of the exaggerated piloerection is

uncertain. It may have some signal value, but if

so I believe that this is secondarily derived from

a more probable function: that of protecting the

rear end of a fleeing animal from the teeth of a

conspecific, or making the target less definite for

the teeth or claws of a predator. (Similar behavior

is obviously advantageous to other caviomorph

rodents: the porcupines).

A certain amount of visual communication must

also occur during fighting behavior in agoutis, especially in the highly synchronized "jousting" (p.

31), since this requires the cooperation of both

animals. I am not sure what signals are exchanged,

because the whole bout is over very quickly.

OLFACTORY COMMUNICATION

Marking with Anal Gland Secretions

Odors play an important role in the communication system of agoutis. Both sexes possess eversible anal glands that are used to mark various

structures in the environment (Figure 25) and secrete a substance that, to the human nose, has a

powerful and long-lasting odor. After I had handled an agouti, especially a male, it would take

repeated scrubbing with soap and water to remove

the odor from my hands.

Males mark more frequently than females, but

the frequency of marking by both sexes increases

with the unfamiliarity of the situation. Thus a

totally foreign object, such as a freshly placed trap,

will elicit more marking than will a newly fallen

branch. Even though the animals will not go near

the trap, they will mark frequently at a distance

of a few meters while looking at it. The smelling

of the mark of an unfamiliar animal causes an

agouti to increase the frequency of its marking,

the increase being most pronounced when one

adult male smells the mark of another. In such a

case the perineal drag is often accompanied by

FIGURE 25.—Marking behavior: a, perineal drag; b, e, marking while sniffing unfamiliar odor, c, marking while thumping; d, f, marking with rearward scratching; g, marking on

newly fallen tree trunk.
40 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

alternate rearward scratching of the hind feet, and

also by thumping (Figure 25c). The same behavior

pattern is sometimes seen during lulls between bouts

of fighting or aggressive chasing, when the participants are out of visual contact but are about to

seek one another out to continue the fight. Also

during fighting the anal glands may be everted

and, at such times, I was able to smell agouti odor

from a distance of 10 m or more.

The only other times that I was able to smell

agouti odor while watching wild animals was when

a feeding animal was suddenly and violently surprised. On one such occasion, MSS was feeding in

the bait area when a large male coati came within

5 m of him without his apparently being aware

of its presence. (Coatis occasionally move slowly

along, snuffling at the ground, apparently ignoring

their surroundings. In this way they are often able

to get quite close to feeding agoutis, who sit and

watch them, probably relying on their much superior speed to escape if necessary. If able to approach within 5 m or so of a feeding agouti, the

coati may make a sudden lunging rush at it. In

most cases the agouti escapes, but at least one

phase II male (ml9), who was of "adult" weight

and healthy, was caught and killed.) In the case

of MSS on this particular occasion, the coati suddenly rushed at him and he fled making full alarm

calls. A strong smell of agouti scent reached me

within a few seconds. Similarly, an unidentified

feeding agouti that was surprised by a jaguaroundi

left a noticeable odor when it fled.

Scent marking of a home range by an animal

that is potential prey for many predators might

seem maladaptive, since the odor could provide

clues to the prey animal's whereabouts. It is also

possible, however, that the sudden release of a

cloud of scent could have a confusing, "smokescreen" effect on the predator by masking the specific location of the animal that released it. Scent

marking is always performed by an animal that

is thumping (Figure 25c), but it may be done without involving a perineal drag. An agouti that

buries food probably also marks, but this is rather

difficult to ascertain since the anal region is in

contact with the ground anyway when the animal

is digging. Feeding spots seldom seem to be intentionally marked, but if a strange agouti comes to

one it will sniff at it and then mark, so it apparently recognizes the odor of the resident.

The rubbing-over behavior of young agoutis is

probably a form of marking, in that there is a

mutual exchange of odors. The behavior of its

father toward a juvenile indicates that the odor

of the mother is on it, and the male reacts as

though the infant actually was the female. Later,

when the juvenile no longer rubs over its mother,

the male recognizes it as a different animal and

reacts toward it aggressively rather than sexually.

Urine Marking

Besides the secretion of the anal glands, urine

is also an important agent of communication. In

sexual behavior (p. 28), urine is sprayed onto the

female by the male from a distance of up to 1.5

meters. Males enurinate other males in aggressive

encounters in captivity; but, although I have seen

wild males briefly erect the penis after an aggressive encounter, I have never seen male-male en urination in the wild. Captive females, apparently in

a high state of sexual arousal, will assume the

crouching position typical of an enurinated male,

and may urinate copiously on the ground. However, they are apparently not able to aim a stream

of urine either forward or backwards, as are some

other female caviomorph rodents (Kirchshofer,

1960b; Kleiman, 1974:186). In male agoutis the

penis points backwards in its relaxed position, but

males do not spray urine backwards.

Females with nest-bound young urinate repeatedly (at intervals of one or two days) on a spot

outside the nest, and the baby lies on this spot

when it comes out of the nest and the female is

not there. In a sense it looks as if the spot is being

treated as a surrogate mother. Adult males will

perform a full ventral rub on the ground on the

spot where their mate has urinated, and will sometimes sit and look at this spot and tremble their

front feet. A male performing a ventral rub first

smells the spot on the ground, then places his

chin on it and, pushing himself forward with the

hind legs, slides on the ventrum over the spot

until the hind legs are almost straight out behind

him. Then he pulls himself forward and into a

standing position with the front legs. The whole

pattern is strongly reminiscent of an agouti infant

rubbing over its mother. All of these behavior patterns reinforce the contention that odor plays an

important part in individual recognition by agoutis.
NUMBER 257 41

A mother agouti, before she permits her infant

to nurse, licks the perineum and stimulates it to

eliminate its metabolic wastes, which she then

ingests. The infant, when the mother is not present,

seeks out the place where she has urinated and

lies there. Thus, from birth on, odors are of primary importance in an agouti's social gratification

and communication. The rubbing over by a young

animal probably functions in the establishment

and maintenance of an odor bond between mother

and young. The function of enurination during

courtship is a means of overcoming the female's

natural tendency to avoid the approach of her

prospective mate. By spraying his urine onto her,

the male transfers his own odor to the female.

When he subsequently attempts to approach her,

she has become accustomed to his odor and her fear

of him is reduced. The original function (from

the point of view of selection pressures) of a female's removing of the infant's metabolic wastes

was probably to make the search more difficult

for a potential predator. Later, urine becomes

important in sexual bonding.

The constant marking of conspicuous objects

within the animal's home range probably serves

several functions. One is to give the animal a sense

of security as it moves from one patch of its own

identity to another. Roth-Kolar (1957:363) says

that one of her captive females froze to death (in

winter, in Germany) rather than enter a nest box

in which the bedding material had been changed

and so no longer smelled familiar. The facts that

recognition of one member of the pair by the

other is by means of odors, and that both male

and female frequently mark in the home area,

show that mutual use of the area is facilitated by

the scent marking. The male marks more often

than does the female, and he is also more active

in driving off strangers. Anywhere that he has

marked can be treated by her as being open for

exploitation of food and living space. Because of

his defense activities, she is less likely to be attacked

by another agouti while she is within the marked

area. At the same time, a strange agouti coming

into the marked area may recognize the "ownership" of the residents and be ready to assume a

submissive attitude during, or retreat from, an aggressive encounter. The smelling of a strange

agouti's odor induces rump-hair erection (an indication of fear, hence of readiness to retreat) and

an increase in scent marking by a potential trespasser, This results in each agouti's creating a

border zone around each territory in which the

adjoining residents have marked and within which

each is prepared to be submissive. This may also

result in reducing potentially damaging aggressive

encounters. As either animal trespasses further into

the territory of the other, he smells less and less

of his own odor, and his readiness to flee probably

increases proportionately. The resident, smelling

more of his own familiar odor (or, if olfactory accommodation occurs, less unfamiliar odor) is more

confidently aggressive.

MECHANICAL COMMUNICATION

Thumping

Agoutis exhibit thumping behavior in response

to an unfamiliar stimulus that is not moving toward them or that they are are unable to locate.

In certain situations an agouti will lift both hind

feet and rap them more or less simultaneously on

the ground. This is usually done while the animal

is sitting or crouching but occasionally occurs in

a standing animal, in which case the front legs may

also be thumped, so that the agouti actually jumps

clear of the ground and makes the thumping noise

as it lands.

Thumping is a graded response. A mildly disturbed animal sits and thumps with both hind

legs, raising the legs from the ground, but not

appreciably raising the rump. A more highly

aroused animal, or one stimulated to thump by the

thumping of another, will raise the rump slightly

as it thumps, will evert the anal glands to some

extent, and may exhibit some perineal dragging.

At its maximum intensity, thumping of both hind

feet (rarely both front feet as well) is accompanied

by: (1) marking with full eversion of the anal

glands, and (2) alternate rearward scratching of the

hind feet.

Thumping occurs when an unfamiliar stimulus

cannot be localized; for example, when a resident

detects the odor of a fresh scent-mark of an unfamiliar animal. It also occurs when a presumably

unfamiliar or potentially dangerous animal such

as a snake, or a man, is detected but does not move.

In this situation, it may be socially contagious and

develop into mobbing behavior. When one agouti
42 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

detects a snake it begins to thump, to mark, and

to erect its rump hair. Apparently in response to

the thumping noise, other agoutis (often individuals that would otherwise be aggressive toward one

another) join together and mob the snake. They

come close (about 1.5—2 m) to the snake, not necesarily facing it, but never facing directly away,

and thump on the ground. On one occasion I

placed a 2.2 m boa constrictor (Constrictor constrictor) in a net in the bait area. Agoutis mobbed

it continuously for five hours, after which I removed it. The same agoutis continued to show

mobbing behavior toward roots and branches near

the area where the snake had been (presumably

because they have a similar shape to the snake)

for a further two hours, at which time I discontinued observation.

An agouti going into an unfamiliar area will

thump. This is usually seen when one comes into

an area where another is dominant. The thumping

acts to attract the attention of the resident, who

usually goes and tries to drive away the interloper.

Occasionally a juvenile animal (recipients of aggression from almost all adults) will be frightened into

fleeing upon hearing another agouti thumping.

Subadult males, who are beginning to show some

aggression to other agoutis, will sometimes thump

after they have been driven off by a dominant animal. This often has the effect of re-arousing the

aggression of the dominant and results in further

chasing of the subadult.

Derivation and Function of Thumping

An animal moving into an unfamiliar area, or

an area where a conspecific is dominant, is usually

in a state of readiness to flee. Agoutis achieve most

of their running thrust from their hind legs; presumably using many of the same muscles involved

in thumping, which may thus have been derived

from flight-intention movements (Daanje, 1950).

Thumping is usually a response to a stationary

or slow-moving stimulus that is potentially threatening but which is not actually attacking. If this

is a predator or a conspecific that is preparing to

attack, then there will probably be a state of psychological tension. The sudden thump may serve

to startle the attacker into attempting its attack

at a time when the thumper is maximally prepared

to escape. It would be advantageous for other

agoutis hearing the thumping to gather around

the thumper in order to determine the whereabouts

and intentions of the potential attacker. They, in

turn, will begin to thump, which results in the

predator being mobbed. Since some confusion

would result if the predator did attack, the probability of one of a group of prey animals being captured would be less than for one alone. Also, in this

respect, it is interesting to note that mobbing most

often occurs in response to snakes, which are more

sensitive to substrate-borne vibrations than to airborne sounds (Oliver, 1962:163). By thumping on

the ground, agoutis are able to transmit a stronger

signal to the snake than they would by vocalizations.

Drumming with the Forefeet

A sexually aroused male agouti will often tread

rapidly with his forefeet (Kleiman, 1974:184). Occasionally this is done so rapidly that a pattering

noise can be heard.

Sounds Made with the Teeth

Noises made by an animal moving its mandible

so that the teeth rub or click together are hard to

identify precisely. Agoutis make a chattering noise

with their teeth; I believe that it is made with the

incisors. It is often made after a soft fruit is eaten.

Is is also made during agonistic encounters, usually

between bouts of fighting.

When gnawing a hard seed, agoutis make a loud

rasping noise that can be heard for 50 m or more.

This acts as both an intra- and an interspecific

signal. Conspecifics upon hearing this noise often

move closer to the animal making it, either to chase

it away or to partake of other food that may be

in the area. On one occasion a jaguaroundi (Felis

jaguaroundi) heard this noise and immediately

began to stalk the animal making it. The tame

jaguaroundis of Dr. R. F. Ewer on Barro Colorado

Island regularly listened for the sound of agoutis

rasping nuts and began to stalk as soon as they

heard it (pers. comm.).

VOCALIZATIONS

Eisenberg (1974) summarizes the sounds produced by agoutis, compares their vocal repertory
NUMBER 257 43

with that of other caviomorph rodents, and discusses various ecological correlates.

The Alarm Bark

The best known vocalization of the agouti is

the alarm bark. As usually heard by a person walking through the forest it sounds much like a repeated, rather high-pitched, bark of a small dog.

If the observer is closer to the animal, however,

he will hear that each bark, or pair of barks, is

preceded by several deep grunts, "uh-uh-uh . . . ,"

which are usually made as the hind legs thrust

forward at each bound. The alarm bark is always

made by an animal running at a full gallop, never

by one sitting still (and never by one in an enclosure too small to permit full-speed running).

It is also made under particular circumstances.

When an agouti detects the approach of an unfamiliar animal it will usually freeze. (If the animal is approaching directly, the agouti will sneak

silently off into the underbrush.) If the angle of

approach is such that the unfamiliar animal does

not come within a critical distance (which varies

from agouti to agouti, being longer in younger

animals), then the agouti will remain still until

after it has passed. If, however, the angle of approach is such that the critical distance is broached,

the agouti will make alarm barks as it runs off on

one of its habitual trails. The alarm bark is also

given if the agouti is suddenly surprised, as by the

rush of a predator.

Agouti alarm vocalizations are graded. At the

lowest intensity only the preliminary grunts are

uttered. This occurs when the agouti is frightened

or surprised by a peccary or a feeding coati (i.e.,

one that does not attack, but is eating fruit); these

are animals with which the agouti is familiar but

which exert an interspecific dominance in a feeding situation and are potentially dangerous. The

second intensity consists of the preliminary grunts

along with one not very loud bark. This occurs

when an agouti is chased by a potential predator

(e.g., a coati or a peccary), but is not surprised and

is easily able to outdistance the attacker. The

third intensity is the loudest bark, repeated several

times, singly or in pairs and preceded each time

by the grunts.

Reactions of Conspecifics to Alarm Barks

If an alarm call was sounded while agoutis were

in the bait area their reaction was generally not

very pronounced. They would usually pause for

one or two seconds, listen in the direction of the

calling animal, and then return to what they were

doing. Occasionally the rump hair might be

erected to about 30°, which indicates a low state

of arousal. If the alarm bark was sounded by one

of the agoutis actually in they area, they might

react to it a little more strongly. The following

excerpt from my phase I notes is illustrative of

this and other aspects of agouti behavior.

1 March, 1712 hrs: A male coati comes up the dry creek

below the observation platform. An unidentified agouti

starts thumping out of sight, east of the bait area, and

ml4 sits beside the north end of the large fallen log that

is on the west edge of the bait area (Figure 3b). Then ml4

sniffs in the direction of the coati, which is making a wide

circle of the bait area. The coati reaches the north end of

the log, jumps onto it and walks down it to the center of

the bait area.

1717 hrs: The coati eats in the bait area. ml4 goes east

and then north. The unidentified animal still thumps out

of sight.

1718 hrs: ml4 stops at the north end of the log, thumps,

and then goes east. He thumps again, then remains sitting

about 3 m northeast of the log.

1720 hrs: mSN appears just south of ml4 and walks

toward the bait area. He stops and eats something on the

way and then goes west to the path leading from the northern end of the log to the bait area. He goes down the path

into the bait area, sees the coati and raises his rump-hair

to about 45°. Then he picks up a piece of banana and

moves to the east side of the bait area to eat it. (The

coati eats on the west side of the bait area, on the other

side of the log from mSN.)

1722 hrs: MSS and his mate FSP enter the bait area from

the northeast. mSN thumps, and then thumps again.

1723 hrs: FSP goes toward mSN and then turns toward

the center of the bait area. MSS suddenly chases mSN, who

runs in a small circle. MSS makes a high-pitched grunt as

he chases mSN, who goes up to the feeding spot at the

north end of the fallen log and sits just on the east side

of the log. MSS returns to the bait area. FSP has seen the

coati and sits looking at it.

1724 hrs: MSS marks with a perincal drag. The coati walks

toward MSS who moves a few steps out of its path. mSN

has begun to gnaw a hard seed and the sound is clearly

audible to me. ml4 is walking slowly toward mSN. The

coati goes north on the west side of the log, and jumps up

onto it less than 2 m from mSN. This startles mSN and

he leaps up and runs northeast, almost colliding with

ml4, then dodging out of the way and continuing northcast. m!4 runs west directly at the coati, apparently only

seeing it when about 1 m away. He veers southeast, in-
44 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

creases his speed and makes full alarm barks. The coali

jumps away and freezes with his tail vertical. MSS and FSP

freeze for about 30 seconds.

1729 his: MSS has walked in a circle under brush cover.

He returns to the spot where ml4 veered upon seeing the

coati, and thumps and marks over the spot.

1730 hrs: MSS comes south into the bait area. He thumps,

then thumps again, then marks. He walks straight through

the bait area and goes east, out of sight.

Animals making alarm noises usually run for

about 30—40 m, then stop, sit down and remain

quite still for 15 to 40 minutes. They will then

start to groom for a few minutes before getting

up and walking back along the path they followed

when making the alarm noises.

The Purr

Another sound in the vocabulary of the agouti

is the purr. This resembles one "syllable" of the

purring of a domestic cat but is usually rather

louder. It may also contain some louder vocal interjection, the volume depending upon the context. The purr is essentially a contact noise and

occurs in the following contexts: (1) by a nursing

mother when arriving at the nest, while being

groomed by the juvenile, upon picking up a piece

of food when foraging with the juvenile, or when

the juvenile takes food out of her mouth; (2) by

the juvenile when being groomed by the mother,

or during naso-nasal greeting of the returning

mother; and (3) by adults when being closely approached by their mate, when being groomed by

their mate, or when picking up a piece of food

after searching some time for it.

When a nursing mother visits the nest, she puts

her nose into the nest entrance, makes a single

purr, and then sits down nearby. The juvenile

usually comes out within five seconds, although I

have seen a mother wait for as long as two minutes. All agoutis, in response to contact with their

mate, their mother, or their young offspring, make

the purr. Tame agoutis will make the same sound

in response to the contact of a human.

Upon first hearing this noise I thought that it

was made by the animal grinding its teeth together. Later (when a tame agouti made the same

noise) I could see that, while the sound is not

accompanied by any movement of the mandible,

there is some thoracic movement, and so I conclude that it is a vocalization. It is a difficult noise

to describe, sounding rather like a very squeaky

door that is moved rapidly at first and then more

slowly, the resulting noise having two definite

components: a high-pitched squeak followed by a

definite staccato creak. This vocalization is repeated

at very short intervals by a young animal following its mother, so that it is almost staccato in

form.

The longer a juvenile has been separated from

its mother, the louder the initial squeak is made.

On two occasions I thought that I heard an adult

female make the same noise when she was separated

from her young; but because of the high level of

insect noises in the forest, I could not be absolutely

sure. The noise is made by adults in potentially

aggressive situations and appears to have an appeasement function. If an agouti is attacked by

another that does not have its rump hair fully

erected and is not making "fight grunts," it will

make the creak-squeak. It is typically made by

subadults that fail to move out of the way of an

approaching adult until it rushes at them. It is

also made by adult females whose mates attack

them "by mistake." In each of these cases the sound

appears to decrease the aggression of the attacker.

An adult male approaching a female to enurinate

her may make creak-squeaks. The frequency of

the sound appears to increase with the number

of times she avoids him. Occasionally, if a male has

been attempting to enurinate a female and she

leaves the area without his knowledge, he will sit

in one spot and make creak-squeaks with his front

feet undergoing violent trembling. The same behavior sometimes results when an adult male attacks his mate. She may flee, making appeasement

squeaks, while he sits and trembles his front feet.

The Creak-Squeak

A juvenile that is temporarily out of contact

with its mother, or is following her as she walks

along, makes a noise that I call the "creak-squeak."

Fight Grunts

The fight grunt is a short grunt that is repeatedly uttered by one agouti when pursuing another,

usually while attempting to bite the fleeing animal's
NUNfBER 257 45

rump. Animals making fight grunts usually have

the rump hair raised to its maximum height.

Rumble

A trapped, wild agouti sometimes makes a very

deep rumbling sound when approached. This

sound is of a very low frequency, and must be

near the lower limit of human audition. I have

not heard the rumble in natural circumstances in

the wild.

Growl

Between bouts of an aggressive encounter agoutis

will utter a noise that sounds like the growling of

a very small dog but is rather smoother. The same

sound is uttered by a female when a coati is attempting to dig her young out of the nest.

Distress Scream

Agoutis of all ages make a distress scream, similar to that of a rabbit, when a predator has actually

caught them. I use a nylon net to handle trapped

agoutis. When in the net, none of them made distress screams. On two occasions animals escaped

from the net while being marked, and I caught

them by one hind leg. Both of these animals made

distress screams. I have seen three infants and one

adult agouti captured by male coatis but have seen

no other actual case of predation. In each case of

coati predation the agouti made loud distress

screams that lasted five to ten seconds. In one case

a nearby band of cebus (Cebus capucinus) monkeys appeared to become very agitated by the

agouti vocalizations and in another a pair of

creasted guans (Penelope purpurascens) called

loudly for some minutes after the agouti screamed.

The uttering of distress screams by agoutis that

have been caught by any predator probably has

been selected for because other animals are attracted to the scene and occasionally interfere with

the predator, permitting the agouti to escape.

Hunters throughout the range of the agouti fashion

a simple whistle out of wood, plastic, or sometimes the caps of soft-drink bottles, with which

they are able to render the distress scream with

startling fidelity. I have been assured by a number

of independent sources that a wide variety of animals can be lured within very close range by use

of these whistles.

I was recently watching an apparent dominance

contest between two agoutis outside both of the

study areas. One of them eventually chased the

other under a rather dense pile of fallen foliage—

palm fronds and other material. There was apparently no easy exit from the space underneath since,

when the aggressor entered, the aggressee remained

inside. I could see nothing of what went on theie

but I could hear the animals scuffling about. Suddenly, one of them started to make distress screams.

A male coati that I had not previously noticed

trotted up to the pile of foliage and climbed partly

onto it. The distress screams stopped and both

agoutis erupted out of their cover and ran off in

different directions. The coati remained motionless where it was until both agoutis had disappeared. This is the only occasion that I have heard

distress squeals given in an intraspecific encounter.

Conclusions

COMPETITION AND ECOLOGICAL SEPARATION AMONG

TERRESTRIAL FRUGIVORES

During that part of the year when fruit is most

abundant, a surprising array of mammals, including some that are generally considered to be carnivorous (e.g., tayra and coati) or browsers (e.g.,

tapir and deer) subsist on it. There is a period

during most years when fallen ripe fruit is superabundant, so that much of it rots where it falls.

During this period the frugivores cannot be considered to be competitors in the strictest sense.

As fruit becomes seasonally less abundant many

of the facultative frugivores turn to other food

sources but, since fruit is comparatively nutrient

rich in terms of the effort expended to procure

it, they will eat fallen fruit when they can obtain

it. Thus, during the season when fruit is scarce

it may be a factor in limiting the numbers of the

animals exploiting it, and they must therefore be

considered as at least in potential competition with

one another.

The largest biomass of primarily ground-dwelling or terrestrial mammals of the forest of Barro

Colorado Island consists of the following species:

the common opossum, the coati, the agouti, the
46 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

paca, the spiny rat, the collared peccary, and the

tapir. All of these mammals are either primarily

or faculatively frugivorous and, in fact, during the

period of fruit abundance they are all probably

primarily frugivorous.

Of the above species, the agouti, collared peccary,

and coati are diurnal, whereas the opossum, paca,

spiny rat, and tapir are nocturnal. If we assume

(and I believe it is reasonable to do so) that ripe

fruit falls from a tree without regard to the time

of the day, then at least during the time when

fruit is abundant, the diurnal and nocturnal animals can be considered to be ecologically separated

by the fact that they are active at different times.

When fruit is the principal diet, the major potential feeding competitors of the agouti would be

the collared peccary and the coati. (In recent years

on Barro Colorado Island the local forest squirrel,

Sciurus granatensis, has increased markedly in number. It can eat most of the same food items as the

agouti and is thus a potential competitor. But the

total biomass of squirrels is low enough that their

effect is small.)

Coatis are unable to break through the seed

coats of many of the agouti food plants (Kaufman,

1962:101) and so are excluded from these as a food

source. I have seen peccaries, however, breaking

Astrocaryum seeds with their powerful molars;

therefore, they must be able to eat almost any

seed that agoutis can and are their most serious

food competitors.

The principal way in which agoutis contend

with competition by peccaries, and to some extent

by coatis, is by cleaning off any soft, odoriferous

exocarp, and dispersing and burying the seeds as

they fall. During the season of abundance, peccaries

move from one fruiting tree to another, generally

eating whatever fruit is on the ground when they

arrive and then moving on. A band of peccaries

has a home range that covers many times the area

occupied by a pair of agoutis; so, if a pair of

agoutis scatterhoards the fruits as they fall, it will

be uneconomical for the peccaries to search for

each item in the dispersed food source. The same

holds true for a band of coatis.

During the season when falling fruit is scarce

the situation is quite different. Since the supply of

fruit is now inadequate to feed all of the animals

that it supported through the season of plenty, the

probability of there being competition between

diurnal and nocturnal animals is increased. The

feeding habits of the terrestrial friigivores become

more diverse and each adopts different methods

of compensating for the lack of available fruit.

There are four major ways of coping with seasonal shortage of food: (1) entering torpor and

slowing the metabolic processes, (2) broadening the

activity period and increasing the time spent foraging, (3) changing the diet and eating something

that is more abundant, and (4) storing food in

some way while it is abundant and then utilizing

it when the supply diminishes. None of the animals under consideration appears to go into torpor.

The agouti and probably the spiny rats store

food at times when it is abundant. Agoutis scatterhoard food items and spiny rats larderhoard in

their burrows (pers. obs.). When fruit becomes

scarce, agoutis spend less time resting and more

foraging, and depend heavily upon the seeds that

they buried earlier. I do not have enough data

regarding the spiny rat to be able to state whether

it alters its activity pattern or how much it depends

upon its hoard.

Pacas neither scatterhoard nor larderhoard. They

do store some food in the form of fatty tissue,

which is a course presumably not open to agoutis

since they rely upon their acceleration, speed, and

stamina to escape predators. Pacas also change

their diet and browse more, especially on seedlings,

many of which probably grow from the seeds that

agoutis have buried.

Peccaries do not store food. During times when

fruit is scarce they browse and root more, and

they also extend their normally diurnal activity

period into the night. Any time that they find a

concentrated food source during this period they

"camp out" on it, exploiting it day and night, and

making it essentially unavailable to agoutis or

pacas. Male coatis also extend their activity period

and change their diet, becoming more carnivorous

(Smythe, 1970c). They also tend to camp out on

a supply of fruit if they find one at this time

(Kaufman, 1962:175). Female coatis seem to change

their activity period very little, but they tend to

eat more small litter animals, and they travel further for food than at other times of the year

(Kaufman, 1962:174). The common opossum appears to keep to its normal activity period, but it

may spend more time foraging. It also broadens
NUMBER 257 47

its diet and eats small, moderately hard, seeds that

it rejects at the time of abundance.

Coatis and opossum (as well as other arboreal

mammals) are able to climb and reach fruit at a

time when it is ripe enough to eat but not yet

ripe enough to fall; that is, while it is still unavailable to the strictly terrestrial species. The extent

to which this benefits the climbing and arboreal

species is not known; but the potential advantage

is great; for example, coatis and other animals can

eat the unripe fruits of the palm Astrocaryitm

standleyanum in January, when ripe, falling fruit

is very scarce indeed.

The relationship between the terrestrial and the

arboreal or aerial frugivores is complex. I will not

discuss it further, beyond pointing out that there

may be some mutual benefits involved. Agoutis

often follow bands of monkeys as they move

through the trees, picking up fruits that they drop.

Cebus, spider, and, to a lesser extent, howler monkeys eat many of the agouti preferred fruits and

might thus be considered to be potential competitors. Monkeys habitually drop many food items

after taking only a single bite from them. Agoutis

benefit from such behavior at times when falling

ripe fruit is in short supply Similarly, I have

watched peccaries (and, in darkness, pacas) going to

the fruits dropped by arboreal feeders. Scatterhoarding of the seeds thus obtained by the agoutis

enhances the survival of the trees, which in turn

benefits the arboreal animals.

AGOUTIS AND SEED DISPERSAL

Three important characteristics of the forest

are relevant to a discussion of agoutis as seed dispersers: first, the relationship between the spacing

of static organisms (the trees, their leaves, or their

seeds) and the ease with which they may be encountered by potential predators or disease vectors;

second, the relationship between forest maturity

and seed size; and third, seasonality in the pattern

of fruiting.

As Ridley (1930) and more recently Janzen (1970)

have pointed out, the probability of plants suffering predation or disease decreases with distance

between individuals. The same principle holds for

seeds, seedlings, or adults, but is probably most

important in the case of the seeds, which are not

only most vulnerable as individuals but also contain the most concentrated source of high-value

food. The density of fallen (nonself-dispersed) seeds

is highest in the "seed shadow" directly under the

parent and, in the absence of any kind of dispersal,

would remain at zero elsewhere. Assuming roughly

random dispersal in the direction away from the

parent, the average density of the seeds of a particular species will eventually reach the point where

it will be lowest, half way between fruiting conspecifics. It is along the line so described that the

seeds and resulting plants will be minimally encountered by host-specific predators and disease

vectors. Seed dispersal is thus of critical importance.

With regard to seed size and the maturity of the

forest, Salisbury (1942:4-36) pointed out that, in

general, seed size increases with the average height

of the individuals in a given stand of vegetation.

This is probably primarily due to the fact that the

light levels on the forest floor decrease as the average height of the trees increases. Therefore, germinating seeds are more successful if they contain

greater reserves of nutrient.

So we see that survivorship of a forest tree species is intimately related to two factors: the distance

of dispersal of its seeds and their size. But the

larger a seed becomes, the more difficult it is to

move. A small seed can be blown by the wind,

flung by an exploding pod, hooked onto a passing

animal or swallowed and later deposited with a

small amount of rich fertilizer far from its parent.

As seeds become larger, each of the above dispersal

methods becomes less efficient. How then can the

largest seeds be transported? They can be made to

float but, unless the water ebbs and flows (as it

does over large areas of Amazonia), the distribution of the seeds will be unidirectional and thin.

One occasionally reads of "gravity dispersal." Reliance on this would result in a gradual descent of

the species in question until it existed in maladaptive densities at the lower ends of valleys. Animals could carry the seeds, but why should they?

This brings us to the third consideration: seasonality.

The long-venerated assumption that tropical humid forests are aseasonal and constantly benign is

gradually being put to rest, and we now know that,

although the temperature may remain fairly constant, there are nonetheless fairly predictable seasonal changes throughout many, perhaps most, of
48 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

the lowland tropical forests. These are usually underlain by changes in the annual pattern of rainfall and through much of the range of agoutis

there is a wet and a dry season each year. It is

during the dry season that there is the greatest

shedding of leaves from the trees, but decomposition of the forest floor litter is slowest then because

of the lack of water. When the rain begins again

the rate of decomposition is accelerated and, for

a brief period, the soil surface becomes rich in its

products. This is the optimal time for the germination of seeds and is thus the height of the fruiting

season. After some months of heavy rains most of

the surface litter is washed away and, as there is

little or no topsoil, seeds dropped at this time

would have a lowered probability of survival. They

would also be more likely to be eaten since the

seed-eating animals are short of food outside of

the main fruiting season.

Climatic variation causes a season of scarcity and

the agoutis hoard seeds to overcome this. The seeds

are large enough to constitute a food resource during times of scarcity and are protected against decomposition, or attack by unspecialized predators,

by a tough seed coat. (Or, perhaps in some cases,

by toxins that may deteriorate after some months

in the ground.) Agoutis are able to chew through

this seed coat with their incisor teeth and, in this

case, the embryo is destroyed. More seeds are

hoarded, however, than are recovered, so dispersal

is accomplished. The seeds have evolved so that, in

most cases, a dual reward is offered to the potential disperser. The primary reward consists of a

soft, sweet pericarp or pulp surrounding the seed

and serves to attract the animal to the fruit. It is

usually consumed immediately. The second reward

is in the rich endocarp which, protected either by

the tough exocarp or containing its own toxins,

remains edible until it is needed some months after

being hoarded. The agouti could not survive without such a hoardable resource; the plant could

probably not survive without its agent of dispersal.

The average distance that agoutis move the seeds

that they hoard might seem small, but since the

spacing of the seeds only increases until they are

moved halfway toward the nearest fruiting conspecific, the distances are probably perfectly adequate.

THE ADAPTIVE VALUE OF MONOGAMOUS PAIRS

The adaptive value of remaining mate-tolerant

throughout the year probably arises from the following factors. Since seeds are scatterhoarded to

protect them from exploitation by other animals

and to constitute a food source in times of scarcity,

they must also be guarded from exploitation by

conspecifics. This necessitates the maintenance of

a fairly high level of intraspecifiec aggression.

Moreover, the maximum survival rate of offspring

occurs when parturition takes place near the beginning of the season of fruit abundance. Since the

agouti has a gestation period of approximately

three months, this means that conception must

have taken place at a time when there was practically no fresh fruit available, and defense of the

hoarded seeds was most rigorous. It would be difficult for the animals to mate at that time if they

lived separately, defending separate hoards. Animals remaining together throughout the year do

not have to go through the lengthy courtship that

would be necessary to overcome the high level of

intraspecific aggression and they can produce young

when their chances of survival are greatest. Kleiman (1974:190) has suggested that agoutis probably

have a very short period of estrous. If this is the

case then it also is of obvious advantage for the

pair members to be in one another's company at

the time of estrous.

The manner of partitioning energy expenditure

may also favor the formation of a long-lasting pair

bond. Most of the defense of the hoard is performed by the male, but the fitness of the population is a function of the well-being of the female.

The most highly adaptive strategy is probably for

the male to defend the hoard and for the female

to derive the greater proportion of nutritional

energy from it, and to expend her energy in the

raising of their young.

It may also be advantageous for the species as

a whole if some young are produced throughout

the year. Very few of the young born outside of

the period of abundance survive but, while the

seasons and the degree of food deprivation are usually fairly predictable, aberrant years are not uncommon. In the population of agoutis that I

watched, some young were born in every month

of the year and mortality was high for those born

between September and March (when food is gen-
NUMBER 257 49

erally scarce). It is probably, however, that there

are years when food is more abundant during what

is usually the lean season, and that the young born

at that time suffer reduced mortality. The survivors

would be at an advantage over young born later,

since they would be larger at the beginning of the

regular season of abundance and more able to

profit from it.

LIMITATIONS IMPOSED BY THE NECESSITY

OF HOARDING

The necessity of hoarding food against times of

scarcity also contributes to the placing of a size

limit on the agouti. Since the hoard is scattered it

is reasonable to assume that there is an optimum

density of buried seeds. If the mean distance between individual buried seeds is too low, the hoard

will be concentrated enough that it will be profitable for peccaries to exploit it. If the mean distance between seeds is too high, there will not be

sufficient food within the area of the hoard to

support the resident agoutis.

Since the hoard must be defended, the resident

must be able to detect the encroachment of a conspecific over a certain distance. This does not

mean that he must be able to detect the other animal anywhere within the defended area, but he

must have a high probability of doing so during

one of his periodic patrols, and he cannot spend

all of his time patrolling. The distance over which

one animal can detect (or communicate with) another is a function of such environmental factors

as visibility, air movements, and ambient noise

levels. These factors are thus important in delimiting the maximum size of the defendable area. A

larger agouti living in the same environment would

need a greater quantity of stored food to tide it

over seasonal shortages, but it would not be able

to economically defend a larger area. Nor could

it benefit from storing seeds at a higher density.

For the same reason, the strategy of raising the

reproductive potential by polygyny would be impractical, if the area defendable by one male can

only support one additional animal.

THE STATUS AND FUTURE OF THE AGOUTI

In conclusion, I feel it necessary to express my

opinion as to the status and future of the agouti.

Since it is the commonest and one of the most

widespread of those Neotropical forest mammals

that are considered to be desirable food by man,

many factors affecting its well-being are generalizable to other animals that are also considered to

be desirable food.

A range map of the genus Dasyprocla serves

equally to illustrate the distribution of the Neotropical, moist, lowland, and premontane forest.

The comparison is supported on a microgeographic

scale: the agouti is absolutely dependent upon the

existence of this type of forest. The conservation

journals are constantly reminding us of a fact that

is all too evident to any naturalist who has traveled

in Latin America: the forests are disappearing at

an almost incredible rate. The cult of progress

holds as one of its most sacred tenets that a standing tree is anathema, and there is probably no way

to stop the destruction of most of the forests. With

them will go all their dependent species and we

will be left with those that have the potential to

exist as man's commensals.

The foregoing view is held by many to be cynically pessimistic. Perhaps that is true. There are

still, even in Central America, vast tracts of forest

that look, from an airplane or to the casual visitor,

as though they are practically unmolested by man.

I have visited some such areas to attempt the observation of agoutis in conditions even less artificial than those of Barro Colorado Island.

In 1966 I traveled with a botanist, Dr. James

Duke, some 160 km up the Chucunaque, a river

that bisects part of Darien Province, in eastern

Panama. It is an area widely regarded as being

among the most pristine in Central America. Along

the river, as far as we went, we met several canoeloads of natives every day. As they traveled the

river, particularly if they were going downstream,

the women and children remained in the canoe

while the men with their dogs hunted both banks

of the river. Periodically we stopped and went

ashore and I searched the area within a few hundred meters of the riverbank for signs of agoutis.

During the entire trip I found one footprint and,

at another location, heard one alarm call. During

the same year the Atlantic-Pacific Interoceanic

Canal Studies Commission was investigating the

possibilities of building a sea-level canal across the

Isthmus in Darien Province (Route 17). I had the

opportunity to visit the area for a week. A road was
50 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

being built along the proposed route, and I spent

the days and much of several nights around the

head of this road, about 10 km inland from the

tiny village of Santa Fe, walking as far into the

forest as I could get, searching for agouti signs. I

employed a local hunter to take me out with him

and to show me the areas where his experience

indicated we would see the most agoutis. During

the entire time that I was in the area I caught

glimpses of two agoutis, heard two alarm calls, and

saw six different sets of tracks. I found more domestic dog tracks than agouti tracks!

In 1976 I paid two separate visits to the site

of a proposed dam (La Fortuna) in Chiriqui Province in western Panama. The proposed damsite is

a 2- to 3-hour walk, through progressively older

looking forest, from the nearest village. This village

of a few houses is itself about an hour's walk from

the end of a very rugged dirt road. I walked around

the damsite in all directions during a total stay

of 10 days. I did not see an agouti, nor even a

track. The tracks of domestic dogs were common.

Local hunters asured me that it was only necessary

to go 5 or 10 km further into the forest before

game became plentiful; not as plentiful as it was

a few years ago, and somewhat further away, but

with a good set of dogs and perhaps a headlamp,

one could be certain of shooting agoutis, pacas,

peccaries, tapirs, etc.

Agoutis undoubtedly exist in all of these areas,

but their numbers are abnormally low. The point

of the foregoing is to show that complacency about

there being plenty of undisturbed forest left is

unwarranted. Moreover, it is not true of Neotropical forest game animals that, if their habitat is

left more or less intact, their populations will survive in spite of indiscriminate hunting. This is

because dogs and headlamps are being increasingly

used and the mammals have evolved no defense

against such things. Agoutis have no natural predator (and therefore no natural responses to one)

that combines the abilities of high-speed odor-trail

following with interindividual cooperation in the

hunt. A hunter can visit the same area repeatedly

with two or three dogs and can eradicate the local

agouti population. Similarly, no mammal has

evolved defenses against predators using lights.

The use of headlamps is not as widespread as the

use of dogs, but it is becoming increasingly common to meet hunters who live a day's walk from

the nearest battery supplier and who regularly use

headlamps.

A few countries in Latin America have instituted

hunting regulations, but I have not seen more than

token enforcement. (I have visited two "reserves"

where the men charged with the enforcement of

the regulations were, by their own admission,

regularly hunting on the reserves.)

Thus, agoutis and the other game animals are

indiscriminately hunted throughout the year, and

the reduced populations have little chance to recover. If it was possible to preserve reasonable

tracts of forest and to enforce regulations prohibiting the use of dogs and headlamps, and restrict

hunting to the season of minimum reproduction

(which may vary from one region to another, but

probably is similar for most species within a given

region), then there would be a fair probability of

preserving the game animal species.

If the remaining forested areas must be exploited

to produce food for burgeoning populations, it

may well be that cutting down the trees is the

less productive method of exploitation. In most

cut-over areas where agoutis, pacas, tapir, and

brocket deer would have thrived, cattle have been

found to do poorly. It is possible that, by efficiently

managing these areas and exploiting the naturally

evolved ecosystem, a higher protein yield could be

sustained. Management and law enforcement would

be difficult and some species would suffer, but it

would be better to preserve at least incomplete

ecosystems, containing some of the animals, than

to destroy them all.
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