The Behavior of

Ocellated Antbirds

EDWIN O. WILL

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY • NUMBER 144
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SMITHSONIA N CONTRIBUTION S T O ZOOLOG Y • NUMBE R 14 4

The Behavior of

Ocellated Antbirds

Edwin 0. Willis

SMITHSONIAN INSTITUTION PRESS

City of Washington

1973
ABSTRACT

Willis, Edwin O. The Behavior of Ocellated Antbirds. Smithsonian Contributions to Zoology, number 144, 57 pages, 25 figures, 1973.—A ten-year study of

color-banded Ocellated Antbirds (Phaenostictus mcleannani) on Barro Colorado

Island, Panama, showed that they persistently follow army ants for arthropods

flushed by the ants. Dominant over the smaller antbirds that follow ants, they

take the best zone low over the center of an ant swarm and drop to the ground

for prey. They rest and preen for long periods of maintenance behavior each

day, probably because as dominant birds they get food easily. Alarm behavior is

similar to that of other antbirds. Agonistic behavior contrasts with other antbirds in having a silent challenging display and an unusually wide spectrum of

submissive calls and postures. Courtship is mainly courtship feeding and singing;

monogamous mates stay together for years.

The nest is probably sunk in the ground between tree buttresses. Males incubate in the morning and late afternoon, females in the early afternoon and at

night. Males and females feed nestlings and fledglings. Pairs renest repeatedly

during the rainy season, April to December, but nest predation is high. Young

are feeding themselves a month after appearing at swarms with their parents,

but then irregularly stay with their parents up to several months (females) or

years (males). Loose patrilineal clans form, in which gene transfer between

clans is mainly by movement of young females. Daughters-in-law are tolerated.

Clan members sometimes forage together, but use much submissive display. They

close ranks or "bunch" in disputes with other pairs or clans. The social system

is somewhat like that of chimpanzee groups and perhaps like that of early man—

two other dominant animals dependent on local and varying sources of food.

The clan system permits complete overlap of home ranges of pairs. The parental pair in an area tends to dominate trespassing pairs and their own offspring.

This social system permits great local concentration over good ant swarms. It

is facilitated by tolerance for related birds, silent (and thus less disturbing) challenging, and by a wide variety of submissive displays. The Ocellated Antbirds

on Barro Colorado concentrated at ant swarms on escarpment zones near the

center of the island. Even with these concentrations, however, the species declined to near extirpation between 1960 and 1971.

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

in the Institution's annual report, Smithsonian Year. SI PRESS NUMBER 4774. SERIES COVER

DESIGN: The coral Montastrea cavernosa (Linnaeus).

Library of Congress Cataloging in Publication Data

Willis, Edwin O.

The behavior of ocellated antbirds.

(Smithsonian contributions to zoology, no. 144)

1. Ocellated antbird—Behavior. I. Title. II. Series: Smithsonian Institution. Smithsonian

contributions to zoology, no. 144.

QL1.S54 no. 144 [QL696.P2] 591'.08s [598.1'11] 72-13261

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402

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Contents

Page

Introduction 1

The Ocellated Antbirds 3

Molt 4

Voice 4

Postures and Movements 8

Wandering 10

Foraging 11

Foraging Competition and Grunting 14

Maintenance Behavior 16

Preening, Stretching, Resting 16

Bathing 17

Anting 17

Reactions to Army Ants and Other Insects 17

Antipredator Behavior 18

Freezing 18

Panicking 19

Mobbing 19

Reactions When Captured 21

Flight, Tameness, and Curiosity 21

Agonistic Behavior 22

Submissive Displays 22

Aggressive Displays 25

Other Agonistic Behavior 27

Reproductive Behavior 28

Loud-singing 28

Courtship Feeding and Copulation 28

Traveling with the Mate SI

Searching (for Nest Sites?) . 32

The Nest 32

Incubation and Brooding 33

Care of the Fledglings 33

Growth of the Fledglings 34

Clan Formation 35

Nest Survival, Renesting, and Breeding Seasons 37

Spatial Behavior 38

Spatial Distribution: Territoriality, Superimposed Pairs, and

Superimposed Clans 38

Spatial Distribution: Escarpment Zones Versus Flat Areas 46

Detailed Spatial Relationships—A Day at a Swarm of Ants 46

Discussion 49

literature Cited 55

The Behavior of

Ocellated Antbirds

Edwin 0. Willis

Introduction

Ocellated Antbirds (Phaenostictus mcleannani,

Formicariidae) are the largest (about 50 g) and

least common of the three main species of antbirds

that persistently follow army ants and capture

arthropods flushed by the ants in the undergrowth

of humid tropical forests from Honduras to Ecuador (Johnson, 1954; Howell, 1957; Slud, 1960,

1964). Earlier (Willis, 1967, 1972a) I reported on

the medium-sized (30 g) Bicolored Antbird (Gymnopithys bicolor) and small (17.5 g) Spotted

Antbird (Hylophylax naevioides). The social organizations of these two species allow them to follow ants all or part of the time even though large

species of antbirds dominate smaller ones. This

report examines how the social and other behavior

of the domineering but specialized Ocellated Antbirds allows them to follow army ants.

Ocellated Antbirds are of special interest to the

student of behavior because mated pairs flock over

ants, even during the breeding season. Most birds,

even ones that flock during the nonbreeding season, separate as pairs on isolated territories when

nesting. A few birds, such as Mexican Jays (Brown,

1963), form group territories and nest cooperatively,

while a fair number of species, such as gulls (Tinbergen, 1953), nest communally on small territories.

Bicolored Antbird pairs form groups over army

ants even in the nesting season but are still territorial; the pair on its own territory dominates trespassers (Willis, 1967). Brown (pers. comm.) has

Edwin O. Willis, Department of Biology, Princeton University, Princeton, New Jersey 08540.

theorized that this kind of "loose territoriality" is

a stage in the evolution of communal nesting. The

study of Ocellated Antbirds now shows a step beyond the stage in Bicolored Antbirds—a stage of

separate nesting but formation of altruistic loose

families or "clans"—and suggests that group territoriality could also evolve from clan organization.

The clans of Ocellated Antbirds resemble in organization the loose clans of chimpanzees (LawickGoodall, 1968). Such clans are in some ways more

social than the more tightly organized groups of

jays and baboons or the aggregations of gulls and

cedar waxwings; for instance, clan animals have

larger vocal repertoires and greater emphasis on

individual recognition of many individuals. The

independent evolution of loose clans in animals as

different as chimpanzees and Ocellated Antbirds

deserves study to see if ecological or behavioral

causes are similar, particularly since humans may

have developed language and social behavior in a

chimpanzee-like system rather than as tightly

grouped animals like baboons or gorillas.

I have attempted herein to completely describe

the behavior of Ocellated Antbirds. Such "ethograms" or "life histories" normally are boring to a

reader in some places and interesting in others, for

few readers interested in preening are interested in

social behavior and vice versa. I ask patience of

the reader, or that he or she skip over sections of

little interest. The text first gives a "picture" of

the bird from the visual and vocal standpoints; if

I had information on odors or other things the bird

could use in behavior I would have included them.

Second, I describe simple changes in the static picture—locomotion, simple movements, etc. Third, I

1
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

look at complex sequences of movements. These

complex sequences are divided into six sections,

which should cover all possible behaviors: foraging

behavior to the small and positive; maintenance

behavior as a reaction to things that are small and

negative; antipredator behavior to the large and

negative; agonistic behavior to things medium-sized

and negative; reproductive behavior to the mediumsized and positive; and spatial behavior to the large

and positive. When an activity could be placed

in two or more sections, it is described in the section of main interest and mentioned briefly in the

others. Social behavior and communication can

occur in all six sections. I think that the sixfold

way is more desirable than division into social and

nonsocial behavior, for behavior must be related to

environment rather than studied in isolation as

one would do if he merely looked at interactions

between animals or lack thereof. The contexts as

well as the structures of the animals can, I hope,

explain such things as the independent evolution

of clan systems in antbirds and chimpanzees.

Common and scientific names of birds here are

from Meyer de Schauensee (1970). The common

name of the Ocellated Antbird was often "Ocellated Antthrush" until Meyer de Schauensee's earlier book (1966:294). Anatomical evidence (Ames,

1971) suggests that "antthrushes" of the genus Formicarius form a rather distinct group; the Ocellated

Antbird is not a terrestrial walker like them but a

clinging, hopping bird of the low undergrowth,

more like the Bicolored Antbird.

ACKNOWLEDGMENTS.—For support, I thank the

Woodrow Wilson Foundation, National Science

Foundation (including Grants GB-21442 and GB30776), Frank M. Chapman Fund of the American

Museum of Natural History, Sigma Xi, and Oberlin College. The staff and facilities of the Smithsonian Tropical Research Institute and of the

Compaiiia Minera Choco-Pacifico (at El Tigre)

were most helpful. Drs. James R. Karr and Alexander Wetmore provided unpublished information

on Ocellated Antbirds. Steve Anderson, Ronn

Kistler, Steve Kistler, Jeff Strassenburg, and Douglas Wechsler helped census in 1971. My wife, Yoshika Oniki, helped in many ways.

STUDY AREAS.—The main area for field work was

the lowland forest of Barro Colorado Island in the

Panama Canal Zone. I have described this forest,

dates of visits, and methods of study elsewhere

(Willis, 1967, 1972b). Here I will note only that

birds are mist-netted and banded with individual

combinations of color bands for later recognition

through binoculars. I have found Ocellated Antbirds at six other localities in Panama (Cerro Campana 900 m, Madden Forest Reserve, Pipeline

Road, Rio Agua Salud, Bohio Peninsula, Rio Medio) and at five in Colombia (Tucura, Boca del

Rio Verde, Cano Remolina, Filo de Abibe, and £1

Tigre). A total of some 40 months of studies on

Barro Colorado, 1960 to 1971, contrasts with a

total of less than a month of observations at other

areas.

ARMY ANTS.—The Ocellated Antbird never, so

far as I know, forages more than casually away

from swarms of army ants. Eciton burchelli and

Labidus praedator, the only two species that form

wide swarms in tropical forests and clearings from

Mexico to Argentina, flush large numbers of arthropods. A few other species flush small numbers of

arthropods. Ocellated Antbirds follow Eciton

burchelli almost exclusively, but sometimes follow

other species of ants near colonies of burchelli.

The behavior of Eciton burchelli is described by

Rettenmeyer (1963) and Schneirla (1957). A swarm

raid emerges from a bivouac, or interlocked mass

of ants around the queen and larvae, every morning during a "nomadic" phase of about two weeks.

The raid moves outward on the ground all day,

and often the whole bivouac moves that night to a

new site located by the raiding ants. After two

weeks of nomadic raiding the ant larvae pupate

and the colony settles for three weeks of the "statary" phase, usually inside a hollow tree. The raids

radiate from the statary bivouac like spokes from

a wheel, except that on some days the ants fail to

raid. Birds often shift to nomadic colonies as soon

as the ants fail to swarm, but may return to the

statary colony occasionally. The ant pupae and

new eggs hatch, and the ants begin another nomadic phase. The five-week cycles continue all

year long, dry season and wet season. Because of

the greater abundance of organisms in the leaf litter (Willis, MS) in the rainy season (April-December) the ant colonies increase in size during that

time. A few colonies then split into small colonies

in the dry season, but there is a decrease in average colony size from the splitting. Also, some
NUMBER 144

colonies are lost because of decreases in numbers

in the dry season. On Barro Colorado Island there

are about three colonies of Eciton burchelli per

square kilometer throughout the year (Willis,

1967:7); but the ants wander without regard for

territorial boundaries, so that there may be several

to none within a given square kilometer of forest.

The Ocellated Antbirds

Ocellated Antbirds are strikingly colored, longtailed antbirds. Specimens have been painted in

color in poses that look like submissive behavior

(see later) for Howell (1957: opposite p. 73) and

Meyer de Schauensee (1964: PI. XI). A color photograph of a live bird is in Dunning (1970). Dunning's photograph shows a pallid-faced bird in

alarm behavior, captive in a photographic box.

A few species in other antbird genera also have

bare, blue faces; but the closest relatives of Ocellated Antbirds are currently considered to be redfaced "bare-eyes," Amazonian antbirds of the genus

Phlegopsis. It is not certain that the bare-eyes are

closely related to Ocellated Antbirds, for their similar ant-following habits may have led to convergence. The Pale-faced Antbird, Skutchia borbae, of

central Brazil is a white-faced ant follower that

may link bare-eyes, Ocellated Antbirds, and the

small White-plumed Antbirds, Pithys albifrons

(Willis, 1968a). Short-tailed medium-sized antbirds

of this and several other genera, especially Rhegmatorhina (Willis, 1969) and Gymnopithys (Willis,

1968b), also seem to bridge the gap between Phaenostictus and Pithys but may be convergent genera.

All of these are ant-following antbirds, and all (as

do a few other antbirds) consistently "flick" (Willis, 1967:39) the tail upward and lower it slowly

when excited.

The six genera just mentioned might be combined under Pithys, the oldest name, were it not

that they are almost as diverse morphologically as

any birds in the Formicariidae. However, the present taxonomy expresses reasonably well that several

rather distinctive forms and groups of forms occur,

and that the single species of Phaenostictus is distinctive.

There are several subspecies of Ocellated Antbirds. Wetmore (1972) considers that gray-crowned

nominate P. m. mcleannani range from near the

Canal Zone east on both slopes of Panama into

northern Colombia, as far as the central Simi and

Cauca drainages, then grade southward on the Pacific slope into dark P. m. pacificus from the central Atrato drainage into northwestern Ecuador.

Dark-crowned P. m. saturatus range from Code in

Panama along the Caribbean slope through eastern

Costa Rica and Nicaragua to the forests of southeastern Honduras (Monroe, 1968). This form

ranges somewhat onto the Pacific slope in central

Panama and in the region of the Cordillera de

Guanacaste in northern Costa Rica. All of the

forms stay in humid lowland or foothill forests, up

to as high as 1300 m on Cerro Tacarcuna in eastern

Panama.

In accordance with Bergmann's Rule, but contrary to Allen's Rule and Schoener (1971), Ocellated Antbirds become slightly smaller in wing and

bill toward the equator (Table 1). Females are

generally slightly smaller than males, but the differences in length are not reliable for sexing birds

in the field. Females, however, usually weigh 44-50

g, males 50-58 g, based on a few weights of specimens and of live birds on Barro Colorado Island.

In a few cases, I used weights as a method of sexing

birds but only as an auxiliary to the method of observing mated pairs, in which the male consistently

feeds the female. Five Barro Colorado weights

ranged from 44 to 57.8 g. James R. Karr (pers.

Place

Honduras-Nicaragua

Costa Rica

Panama

North Colombia

S. Colombia-Ecuador

TABLE 1.—Culmen

no.

4-4

SO-SO

39-35

26-29

8-6

and wing lengths of Ocellated Antbirds

Males

oilmen

24.2 (23.6/24.7)

24.4 (22.9/25.7)

24.4 (223/25.7)

23.8(22.1/25.4)

23.6 (22.8/24.7)

wing

91.2 (85/95)

92.4 (86/97)

91.3(88/95)

893 (85/95)

86.8 (85/90)

no.

2-1

17-17

32-32

18-19

9-5

Females

culmen

23.5 (23.4/23.6)

24.1 (223/25.9)

23.8(21.9/255)

235(21.7/24.6)

22.6(22.1/23.6)

wing

87 (-)

895 (85/94)

87.5 (84/93)

86.4 (82/90)

83.0(81/87)
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

comm.) weighed six birds seven times at the Limbo

Hunt Camp, in the Panama Canal Zone, and found

a range of 46.9-57.3 g (average, 51.4 g).

Young birds in juvenal plumage molt slowly into

adult plumage in the first few months of life (see

later); they can be recognized as young until the

pale gape angles and the last juvenal feathers are

gone. Instead of the pearly gray or brown crowns

of adults, the young have mottled crowns of blackish feathers with whitish tips. The forecrown is

sometimes bare in very young birds. The mottled

feathers disappear last at the rear of the crown.

The young have pale gape angles and dusky faces,

not the bright blue faces of adults; the base of the

lower mandible is whitish rather than the whole

bill being black as in adults. Young almost lack

the rusty nape and breast so prominent in the adult,

although both young and old have black throat or

bib feathers. Instead of the black-centered rusty

belly feathers of adults, the young have buff or

orange-centered blackish feathers. This is the reverse of the pattern of the adult ocellation. The

back feathers are black as in adults, but with buff

or rusty rather than whitish-brown edges. The

greater wing coverts are rather white-tipped in

young birds, forming an indistinct wing bar. Black

and other colors are duller than in adults, partly

because the juvenal feathers have fewer barbs. Most

of the color differences from adults can be explained on the basis that juvenal colors should

differ from adult colors in characters that are important in adult agonistic behavior (see later).

Molt

Ocellated Antbirds are among the many species,

including several antbirds (Snow and Snow, 1964;

Oniki, 1971), that molt when they are nesting.

There is a complete postjuvenal molt, including

wing and tail feathers, in the first four or five

months of life; one must be careful to exclude

these birds when determining molting seasons.

Some 201 dated seemingly adult specimens from

museums in the eastern United States show molting ratios (number in wing molt/number not in

wing molt) for the months from January to December, respectively, of 5/19, 3/28, 5/30, 4/30, 8/9, 3/4,

4/3, 7/7, 12/3, 5/0, 7/1, 3/1. Thus, although some

birds are in wing molt in every month of the year,

few are in wing molt from January to April. This

is the dry season in Central America, the source

of most of the specimens. Most birds are in molt

in September to December, which in much of Central America is the last and rainiest part of the

wet season.

Many of the May birds in molt come from eastern Panama and northwestern Colombia, a region

with a short dry season; however, the few birds

from the constantly rainy western part of Colombia

south into Ecuador seem to have the SeptemberOctober molting season of Central American birds,

rather than the April-May molting season that is

characteristic of most birds of other species south

of the climatic equator. Perhaps any tendencies of

the few southern birds to an austral molt season

are swamped out genetically because the main pop

ulation of Ocellated Antbirds lives north of the

climatic equator, where the boreal molt season is

more advantageous. It may also be that, despite

climatic differences, the food supply in the litter in

western Ecuador peaks at about the same time as

the June peak in Panama (Willis, MS); if so, nesting and the following molt (Snow and Snow, 1964)

might be arranged so as to divide the available food

peak in both areas.

On Barro Colorado Island, the few data indicate

wing molt in every month checked; the molting

ratios for the months of January to December are

2/3, 0, 0, 0, 1/0, 5/2, 11/1, 11/5, 2/0 1/0, 0, 0.

Two birds were recaptured during a single molt;

one had # 7 from the end of each wing in molt

on August 2, and # 1 and # 3 on each wing in

molt on August 8. Another had # 3 on one wing,

# 4 on the other in molt on July 17. On August 2,

# 5 and # 2 were in molt on diose wings. Irregularities in molt sequence are probably common, as

the Snows (1964:11) noted for another antbird, the

Barred Antshrike.

Voice

Calls of Ocellated Antbirds are much like those

of Bicolored Antbirds (Willis, 1967:13-16). Ocellated Antbirds, however, apparently lack the aggressive calls of snarling, bugling, and hissing, as

well as the submissive call of whimpering. They

add, however, a wide variety of intergrading moreor-less submissive calls here described as chittering,

whining, screaming, and squawking. In Ocellateds

but not Bicolors there is also a special call, "carol-
NUMBER 144

ing," when the male feeds the female. I recognize

16 named calls for Ocellated Antbirds, compared

to 14 for Bicolored Antbirds and 12 for Spotted

Antbirds (Willis, 1972a). All three species of antbirds have two additional subtypes of calls, plus

various minor modifications and combinations of

calls. The number of separate calls are like those

or somewhat greater than those for many passerines

that have been studied, except for the antisocial

Plain-brown Woodcreepers (Willis, 1972b) and the

groupterritorial Mexican Jays (Brown, 1963), both

of which have 5 or so named calls. The increased

number of calls from the subordinate Spotted Antbird to the subdominant Bicolor to the dominant

Ocellated probably reflects the increasing degree of

social interaction from Spotted to Ocellateds.

Group territoriality in jays apparently leads not to

increases in the number of calls but to decreases.

However, one of the less social jays (Hardy, 1971)

has only 3 named calls.

CHIRRING.—A loud buzzy descending cheeeee'yuk

(Figure 1H) is the normal reaction to large terrestrial animals, and thus it is the call usually

reported for Ocellated Antbirds (Eisenmann,

1952:36; Slud, 1964:222). The bill is often raised

slightly for the note, and the tail may be flicked.

A deep version (Figure ID) is also used by large

aggressive males being held in the hand or being

badgered by a subordinate bird. The sound is

often muffled, especially if chipping is being given

too. The audiospectrographic chirrs show decreases

from about 4000 to 2000 Hz; there are about 50-60

frequency modulations per second, fewer than the

80 or so per second in chirrs of Bicolored Antbirds.

The end of every Ocellated chirr is a burst of white

noise, centered about 2000 Hz; this noise is so

weak that it shows only on the audiospectrograph

for the bird held in the hand. (The "grunts" of

another distant bird, Figure 1H, also lack the introductory white noise seen in grunts from a closer

bird in Figure 1c).

KEENING.—A faint, whistled teeeeeee, very like

the keeeeeee whistle of Bicolored Antbirds but

higher in pitch, is the reaction to such distant and

uncertain danger as a passing large bird or an alarm

call of another species. At times teeeeeee, teeeee!

or even three notes are used.

CHIPPING.—Sharp, rather irregular chip-ip or

chip-ip-ip calls are given as a bird flees to cover, is

chased by another bird, or sees a hawk fly past. The

chipping of an alarmed bird waiting in a safe place

becomes a muffled chut-ut and sometimes seems to

intergrade with muffled chirring, which is also given

persistently at such times. The chipping bird often

jerks its tail upward violently with each set of

notes. Each chip of the trio in Figure IK is 0.03

second long, and the first goes from 300 to 4500,

1000, and 3000 Hz as a complete sharp-cornered

sine wave or Z-wave. Much noise, some of it probably not an artifact, obscures the pattern.

GRUNTING.—Scratchy, short chaic grunts, sometimes chaic-chaic double-grunts, greet small competitors like Bicolored Antbirds whenever they

move near a foraging Ocellated. Four times per

second was the maximum rate; usually the grunts

are irregularly spaced, almost syncopated, and come

at one to three per second. The tail rises slightly

with each grunt, and the throat is slightly ruffled.

Grunts (Figure 1G) show an introductory burst of

white noise about 2000 Hz and up to 0.06 second

long, plus a terminal descending chirp (with many

overtones) about 0.02 second long. Peak-to-peak,

the grunts are 0.22 second or more apart. The pattern of the grunt is more or less the reverse of that

of the chirr (in which the first part is musical and

the last part is noise).

SONGS.—Both sexes give three types of songs,

though the female's songs tend to be less loud and

at a higher pitch than those of the male. The striking and far-carrying but seldom-heard "loud-song"

is a piercingly loud but thin series (Figure 1A-B)

that, like a loud-song of Bicolored Antbirds, rises

in pitch and then drops back to rough terminal

notes that begin to resemble chirrs: a short one is

Eeeee, eeee, eeeh-eeh-hee-hee-hee-hee-hi-chee, cheeer,

cheeer'k, cheeeer'k, cheeer'kl The graphed loudsong shows three parts: (1) seven eeee notes, each

slightly under 0.2 second long, the whole part taking 1.5 seconds and rising from about 3000 Hz at

the start to 3500 Hz at the end; (2) sixteen rapid

eeih or ee notes, accelerating from 0.17 to 0.07 seconds peak-to-peak (at numbers 11 and 12) and then

decelerating, over a span of 1.6 seconds, with the

highest pitch of the song 4200 Hz; (3) a terminal

flourish of five long eeeeeeyip notes, declining from

3200 to 2900 Hz as they go from about 0.2 to 0.4

and then 0.35 seconds. Since the terminal five-note

flourish lasts 1.8 seconds, the graphed song (an
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

/T * t

0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 r "T 1 1 r

..»•!# • ft

I I I I I

± oL

T I i i i i i r

* I < i « « :

G J H

i

i r

V»

"i ' -\—i—i

2 5 0 5 i—i i—i—i—i

1.0

i—i i—1—1—r

1.5

Time in Seconds

2 0

FICURE l.-Audiospectrographs of calls of Ocellated Antbirds, from Barro Colorado Island: A, B,

loud-song, arrows mark note no. 15 in the song; c, faint-song; D, chirr of male held in the hand;

E, strained chirr and two chips from a subordinate bird; F, truncated chirr and whine of a subordinate bird; c, grunts, showing normal spacing; H, chirr, with two grunts, from distant birds;

i, whining; j , scream and a whine; K, triple chip.
NUMBER 144

unusually long one from a bird excited by a recorded playback) is 4.9 seconds in length. Even a

bird excited by a tape recorder rarely loud-sings

more than 7 or 8 times per minute. The loud-song

is given when mates are separated, when rivals are

separated, or when a bird leaves a swarm of army

ants. The bird changes position little to sing: the

tail quivers slightly, and the throat pulses as the

bill stays open.

The far more common "faint-song" is used often

when a single bird or group of birds is about to

travel, so commonly so that I called it the "go-song"

for many years. It is a faint series of 3 to 10 or so

whistles, rising in pitch and then dropping at the

end. There are usually many notes in the ascending first part of the song, one or a few in the descending last part. Each note is accented by a slight

downward movement of the tail. Whee-kee-ki-chew

is what I called a "3-1" faint-song, 3 notes upscale

and 1 down. Eisenmann (1952:36) noted a "6-0"

song, probably actually a "5-1" song; faint-songs

often follow chirring at a human intruder. The

longer faint-songs (such as "7-3" and "10-4" songs)

tend to be louder, and the loudest and longest add

introductory and terminal eeeeee notes and become

loud-songs. The graphed faint-song (Figure lc) is

a "7-2" song, about 0.9 second long, and rises from

2000 Hz at the start of the first note and about

1500 Hz in the clicks at the end of all other notes

to about 4000 Hz at the center of the seventh note.

The ninth note is a heavy chew, which drops from

2400 to 1500 Hz. The first note is about 0.09 second

long, the eighth only 0.04 second, but peak-to-peak

intervals are about 0.11 second throughout; thus,

spaces between notes are longer at the end of the

song. The faint-song seems like the central section

of the loud-song.

"Serpentine-songs," as in Bicolored Antbirds, are

musical series in which calls rather like faint-songs

are connected by low-pitched chirping notes: ee,

hee, hee, hi, hew, hew-hew-hew-hew-hew, over and

over. Possibly "caroling," described later, is a truncated serpentine-song, for serpentine-songs are

phrases that attract a mate or young to a site or to

be fed.

WHIRRING AND SNAPPING.—The only sound by a

dominant bird besides an occasional chirr is likely

to be a surprisingly loud whirr of the wings and

multiple snapping of the bill as it supplants a subordinate of its own or a smaller species. I have not

detected hissing by dominant Ocellateds, although

both Spotted and Bicolored Antbirds use that sound

in their snapping attacks.

CHITTERING.—Stuttering i-i-i-i or a-a-a-a-a chatter

is one of the complex set of calls of subordinate

Ocellated Antbirds being crowded out by silent

dominant ones. At times the chittering becomes

like a faint-song, as a "chittering faint-song," and

may be related to it.

WHINING.—Starting as grunts that become more

and more strained and scratchy, aaah (Figure li)

sounds verge into whining kraihh whines as a subordinate bird bounces about and tries to avoid being ousted from a swarm. The two graphed whines

are 0.3 and 0.25 seconds long, and are bands of

noise between 1800 and 2800 Hz. Both whines end

in harmonic chirps much the way grunts do.

SCREAMING.—Whines grade into variable piercing

squeals, eeeieehl and the like (Figure Ij). The

first note graphed is a whining scream, the second

one a whine. The scream is a burst of white noise

from 500 to 4500 Hz, with a main whistle about

2000 Hz; it ends in a harmonic chirp much like the

harmonic chirp at the end of a grunt, but a chirp

that tends toward the frequency modulation of a

chirr. It is possible that these harmonic chirps are

actually verging on low-intensity chirrs, for subordinate birds use strained chirrs and chips as part of

their whining and screaming at times. For instance,

Figure 1E graphs a strained cheeyk chitik chitik, a

chirr followed by two double-chips, and Figure IF

gives a chee-aik, a truncated chirr and truncated

whine. Sounds similar to screaming are sometimes

given by birds in the hand.

SQUAWKING.—A bird that is chittering, whining,

and screaming may give a sudden CHWAIHK!

squawk when supplanted.

PEEPING.—As in other antbirds, young separated

from their parents or begging for food sometimes

peep. The main kind of peeping later grades into

singing and is a rising pee-pee-pee-pee-pee-pee.

Often each note quavers, pee'e, as a "quavering

peeping."

SQUEAKING.—Young squeak waiaih when fed, and

resume peeping after feedings.

CAROLING.—The male or female feeding a young

bird, or male feeding a female, usually gives at

the moment of feeding a distinct but not con-
8 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

spicuous series of 1-15 whistled notes, the first few

at a higher pitch than the last few: chee chee chew

chew! or the like. Caroling often sounds irregular,

as if two birds are calling, but it is definitely given

by the feeding bird and not the fed one when a

male feeds a male or a young bird. If the feeding

bird holds back with the food, however, the other

may give a faint caroling, often chee chee chee notes

that do not descend in pitch. (These notes may be

"chirping.")

GROWLING.—When a well-fed female antbird refuses the food and caroling of her mate, she growls

a brief chah-ah-ah-ah series. The series is somewhat like one kind of chittering.

CHIRPS.—Faint cheur chirps go back and forth

between mated Ocellated Antbirds at times. There

seem to be many such faint sounds, but they are

inaudible at a distance and hard to tell from the

chirps of other antbird species with them. When

the female Ocellated sees her mate with food, the

chirps are usually chee or chee-chee and grade into

caroling notes.

Postures and Movements

Figures 2D, J illustrate basic or "standard" postures (Willis, 1967:16) for the Ocellated Antbird.

The long tail is rather down and the head nestled

far back, giving a humble or puffed look compared

to the posture in Bicolored Antbirds. Perhaps Ocellateds bring the large head and bill over the center

of gravity by retracting them "humbly."

Like Bicolored and Spotted Antbirds, Ocellateds

cling easily to slender vertical perches (Figures

FICURE 2.-Foraging Ocellated Antbirds, from field sketches: A, subordinate bird keeps low and

watches dominant ones while foraging; B, the body often forms a parallelogram in side view;

c, slightly alarmed bird flicks or jerks the tail upward now and then; D, normal or standard

posture; E, alert dominant bird forages busily; F, very "humble" posture of female waiting for

me to lead her to ants; c, swinging on a liana; H, dissecting prey on the ground; i, hopping on

the ground after prey ran under leaves; j , standard posture from the rear.
NUMBER 144

TABLE 2.—Perches used by foraging Ocellated Ant birds (foraging over swarms of army ants, Barro

Colorado Island, 1 October 1960 to 30 September 1961, only)

Height

height

in

meters

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

2.0

3.0

4.0

5.0

6.0

Total

of perch

no.

records

292

708

750

400

194

62

28

32

6

5

27

4

4

0

1

2513

percent

11.6

28.2

29.8

15.9

7.7

2.5

1.1

1J

0.2

0.2

1.1

02

02

0.0

0.0

angle

in

degrees

20

40

60

80

100

120

Angle of perch

no.

records

560

314

272

137

892

8

2T8S

percent

25.6

14.4

12.5

6.3

40.8

0.4

diameter

in cm

1

2

3

4

5

6

7

8

10

15

25

log

buttress

Diameter of perch

no.

records

218

451

212

84

36

10

2

5

2

9

1

1

3

IOST

percent

21.0

45.6

20.5

8.1

3.5

1.0

02

05

02

0.9

0.1

0.1

0.3

2A, E; Table 2). In all three species, toes III and IV

of the lower foot stay together in locknut fashion;

presumably this prevents rotation of the foot on

slippery surfaces, such as wet saplings. The toes

spread in three directions, which probably aids stability. The ability to cling permits all these antbirds to stay perched near the ground over army

ants even in the dark undergrowth of tropical forests, where nearly all perches are vertical lightseeking trunks. When on a horizontal perch, an

Ocellated stands rather far back and must flutter a

little to get the feet over the perch in moving

forward; however, the toes can dangle and need

not be tightly clasped.

Ocellateds do not cling well to thick trunks and

normally use perches 1-2 cm in diameter (Table 2).

I have seen birds slip and flutter when trying to

perch on buttresses only 6 cm in diameter. As has

been suggested for Spotted Antbirds (Willis, 1972a),

using slender perches probably allows clear views

of predators and prey as well as being more suitable for the claws and feet of these birds. Also,

TABLE 3.—Records of foraging techniques of Ocellated Antbirds (5 October 1960 to 4 October 1961,

over swarms of army ants, Barro Colorado Island, only; figures in parentheses are records from 5

October 1961 to 2 September 1970)

Place of capture

Motion for capture

sally lunge toss leaves total

ground, rock, root

log

fallen debris

trunk, buttress

liana, stem

limb

twig, petiole

leaves

air

?

Total

3393 (1517)

5

1

23 (6)

24 (4)

3

1

22 (3)

9

0 (9)

3481 (1539)

210 (56)

4 (1)

4

12 (2)

36 (11)

1 (1)

11 (4)

35 (5)

26 (3)

0 (1)

339 (84)

63 (8) 12

63 (8) 12

3678

9

5

35

60

4

12

57

35

0

3895

(1581)

(1)

(8)

(15)

(1)

(4)

(8)

(3)

(10)

(1631)
10 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

army ants rarely climb or attack up slender stems.

However, stems under 1 cm in diameter bend with

the weight of the heavy Ocellateds and tend to be

avoided more than such stems are avoided by

smaller birds.

The claws, toes, and legs of Ocellated Antbirds

are very thick and strong. The curved claws easily

break human skin when one holds a bird. This is

the largest bird I know that regularly clings across

rather than along a vertical surface. Allometric

increases in leg size with larger body size perhaps

would make a larger clinging bird almost a monstrosity. Ocellated Antbirds cling less often than

do Bicolored Antbirds (Table 2, angle of perch),

suggesting that the former are slightly too large to

cling easily.

Like Bicolored and Spotted Antbirds, Ocellated

Antbirds pitch or swing around vertical or other

perches quickly and easily. Reversing direction on

a perch involves little more than footwork and a

slight upHirt of the tail.

An Ocellated hops and bounds between perches

close together and flutters short distances too. The

bird about to fly often faint-sings, then points the

body in the direction of flight (Figure 3A). Flight

is rather slow, fluttery, and direct; on longer flights

the bird glides briefly now and then (Figure 3B).

About the only time a bird misses a beat is when it

passes between saplings close together. The long

tail seems to beat up and down or to drag slightly

and comes down for alighting (Figure 3c). Perhaps

it is used for braking this heavy bird, especially in

sallying for prey (see later); but it also flicks conspicuously during alarm and thus may have communicatory functions as well. The wings often

spread widely on alighting, but flight usually starts

with a jump rather than with wide spreading of

the wings. Consequently, the first part of flight may

be an arc or the descending segment of one. Flight

is not fast or maneuverable, so that pugnacious

Buff-throated Woodcreepers (Xiphorhynchus guU

tatus) sometimes chase Ocellateds in the air, even

though the large antbirds easily supplant these

woodcreepers on perches. An Ocellated Antbird

maneuvers in and out of tangled undergrowth well

enough and sometimes flies 20 to 30 m, but ordinarily it stops on a perch, peers ahead, and flies 10

to 20 m at the most to a suitable new perch as it

travels.

Wandering

Ocellated Antbirds seen or heard away from ants

are almost always traveling to or from ant swarms

or are searching for them. Mostly Ocellateds keep

low in forest undergrowth, usually about 1-2 m up,

faint-sing to each other or loud-sing periodically

and travel rapidly from one perch to the next. If

they see a human, they chirr. They seldom cross open

areas, but I have seen them cross an open stream

(Rio Agua Salud) 10 m across; these birds moved

up to 3-6 m above the ground and flutter-glided

across like chachalacas (Ortalis spp.). I have seen

Ocellateds follow ants out of the forest into grass

and brush at the edge of a back yard (Cerro

Campana), but I have never seen them enter the

laboratory clearing on Barro Colorado.

FICUIE 3.—Ocellated Antbird traveling: A, the bird points and lowers the front of the body; B,

an occasional brief glide interrupts the flight; c, the bird alights with feet high, wings and tail

spread.
NUMBER 144 11

Ocellateds do not join the wandering mixed

flocks of antwrens (Johnson, 1954; Willis, 1972a)

but sometimes accompany or are followed by antfollowing birds, especially Bicolored Antbirds. On

days when a colony of ants is not swarming one

often sees groups of Bicolored and Ocellated Antbirds wandering low through the undergrowth, as

a front or in leapfrog fashion. At times other antfollowing birds, such as Barred and Plain-brown

Woodcreepers (Dendrocolaptes certhia, Dendrocincla fuliginosa) and Gray-headed Tanagers (Eucometis penicillata), wander at 5-10 m above the

two antbirds. Infrequently Spotted Antbirds join

the motley traveling group. At times an Ocellated

Antbird goes to or follows a Spotted Antbird, which

is another species that commonly follows ants. Once

a single song from a Spotted Antbird was enough

to bring in an Ocellated.

To find a new bivouac of the "nomadic" colony

of army ants in the early morning, Ocellated and

other antbirds commonly search along the path of

the raid of the previous day; sometimes they miss

the new bivouac. Then they wander widely, join

any bird that sings, and look around it. A female

and her young female got so used to me at a colony

that one morning they veered off to me (Figure 2F)

and thus missed the ant bivouac they soon would

have hit. Ocellated Antbirds wander along the ant

trails and toward songs of other Ocellateds if the

ants "fold" their swarm late in the day. Playing

tape-recorded songs of Bicolored Antbirds near such

folded swarms brought Ocellateds in on five occasions; playing Ocellated songs quickly brings in

Ocellateds.

Johnson (1954:47) theorized that chirrs of Ocellated and other antbirds attract other birds to ants.

Since chirring is normally only a response to the

observer or ground predators, it is rare for undisturbed antbirds to chirr. I observed Ocellateds arriving at swarms on several occasions, and few

chirred more than a few times at me before starting to forage silently. More often, the arriving bird

was silent or faint-sang. Chirring does not seem to

be used as an attractant or clue, although it could

accidentally be a clue.

Ocellated Antbirds that cannot find an active

nomadic raid of the army ant Eciton burchelli

sometimes visit the tree where a statary colony they

previously followed is hiding. They circle the base

of the tree and follow any line of ants to the distant swarm. Once the above-mentioned female and

her young female encountered a line of ants; the

adult turned correctly toward the ant swarm (which,

as any ant-follower should know, is in the direction

from which the ants carry food!), but the young

bird turned toward the ant bivouac.

If there is no line of ants or swarm, Ocellateds

sometimes wander about or wait in cover nearby,

preening and faint-singing, for up to several hours

at a time. At other times they move off and check

another statary colony. They sometimes move from

one colony of ants to another during the course of

a day or move back and forth between colonies

every day or two, even colonies a kilometer apart.

Probably each bird knows of the general whereabouts of a few other colonies even when it is

primarily following only one nomadic colony.

Foraging

When waiting for food over army ants (Figures

2, 4), the Ocellated Antbird looks about with quick

movements at its low perch, turning its head 30

or so degrees each time and occasionally cocking

the head. Usually it is hunched with head retracted

and tail down. If no prey appears, or if ants attack

up its perch, the bird hops or flutters a short distance. Usually birds face the rear of the swarm of

ants from just behind the foremost ants, and a

bird that moves ahead to keep over the ants must

turn around each time it stops to forage. Often,

before moving, the bird faint-sings a few times.

Dominant or lone birds often move low, at normal foraging heights. A subordinate bird may move

up to a meter or two off the ground to look around

before traveling or dropping to a new site. Birds

FIGURE 4.—Ocellated Antbirds foraging: A, mated pain often

forage together, though one bird or both often ruff the

throat; B, a peck at the ground.
12 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

disturbed by a human or ground predator often

move to 1-2 m up, too.

Since a swarm front of Eciton burchelli moves

about 15 m per hour (Willis, 1967:6), the birds

have to move occasionally to keep over the active

part of the swarm. At times a bird moves laterally

on the swarm front, right or left, to a more active

part of the front. If the ants stop activity on this

front the bird begins to faint-sing, wander, and

check other small groups of ants. Finally it moves,

faint-singing, back toward the ant bivouac or in

the direction the ants are retreating. Often it finds

the ants flowing to the attack on some other branch

raid, but if the ants are just returning to the

bivouac the bird wanders back and forth along the

ant trail, around the raid and bivouac at the two

ends of the ant trial, and then leaves faint-singing

or loud-singing for another ant colony.

At times a foraging Ocellated clings so low over

the ants that its tail or lower wing touches the leaf

litter, but more often the bird is about 0.2-0.3 m

above the advancing hordes (Table 2). Ocellateds

sometimes stand on lianas or roots, but seldom

stand long on the ground itself. Logs are seldom

used, but a bird may hop under a log as the ants

pass.

Ocellateds usually dart down to catch food just

flushed by the ants, then bound back up to a perch

so fast that the army ants have little chance to

counterattack (Table 3). The bird about to chase

prey holds the head up alertly, then lowers it and

points the bill rapidly as if at an erratically moving

prey, and leaps. The tail goes up briefly as a brake

as the bird hits the ground and often is spread as

the bird grabs the prey and returns to the perch.

A brief jerk of the tail follows a successful swallow,

and the bird turns to look for more prey. Over 75

percent of such sallies to the ground are within

0.5 m of the perch, less than 1 percent over 2 m

(Table 4); distances are almost exactly like those

for Bicolored Antbirds (Willis, 1967:30).

Sometimes an Ocellated, tail up, hops, bounds,

and spins nimbly among the ants if prey escapes

the first peck in a sally to the ground. The longer

hops^ are twice the length of the body. Ocellateds

are not really terrestrial and do not walk on the

ground the way Black-faced Antthrushes do; but

Ocellateds hop on the ground more readily than

do Bicolored Antbirds. Ones that are hopping keep

TABLE 4.—Heights of attempts at prey for Ocellated

Antbirds (Barro Colorado Island, over swarms of

army ants; records within parentheses=5 October

1961 to 2 September 1970; records outside=5 October 1960 to 4 October 1961)

Height in meters

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

2

3

4

Total

.Vumbers of records

3643 (1583)

18 (5)

15 (3)

6 (3)

8 (2)

3 (1)

2 (8)

5 (2)

5 (0)

1 (0)

10 (4)

6 (1)

2 (0)

3726 (1612)

Percent

97.84 (98.2)

0.48

0.40

0.16

0J2I

0.08

0.05

0.13

0.1S

0.03

0.27

0.16

0.05

the tail somewhat raised; standing birds have tails

down (Figures 2, 4).

At times an Ocellated tosses dead leaves by swiping at them with the bill or pecking them and

tossing them. Occasionally the bird stamps the feet

as it twists about, shoving leaves out of the way

with its body. Less often, the antbird sallies clumsily and flutteringly to snap prey out of the air or

off above the ground. Prey on or above the ground

is likely to be pecked off (Figure 4B) after the bird

hops to a nearby stable perch. Occasionally an

Ocellated flies to vegetation 3 or 4 m up, cranes

the head at moving prey, and gets it or not before

returning near the ground. Once a female peered

up with one eye and then the other, hopped upward, and suddenly did a sally to the ground and

got a grasshopper that had dropped past her from

2 m up. In wetter forests than on Barro Colorado

Island, such as at El Tigre (Colombia) and the Rio

Medio (Panama Canal Zone), dense vegetation

grows up the trunks of trees and is sometimes used

by Ocellated Antbirds; I have seen them wander

briefly up to 8 m above the ground in epiphytes and

vines on slanting tree trunks. Most prey, however,

comes from the ground (Table 5).

Once a young female Ocellated, resting, stole

booty from an army ant. Thievery is more common

in subordinate antbirds, especially Bicolored Antbirds (Willis, 1967:30).
NUMBER 144 15

TABLE 5.—Distances of sallying to the ground for

Ocellated An thirds (foraging over swarms of army

ants, Barro Colorado Island, 4 October 1960 to 2

September 1970)

Distance

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

2

3

4

5

6

Total

No. of records

184

235

158

120

122

52

29

61

8

25

85

4

3

1

1

1088

Percent

16.9

21.6

14.5

11.0

11.2

4.8

2.7

5.6

0.7

2.3

7.8

0.4

0.3

0.1

0.1

100.0

The stereotypy of foraging is not matched by

sterotypy of prey (Table 6). Prey from scorpions

and spiders to roaches and katydids are snapped up

eagerly. Millipedes and sowbugs, however, are common in the leaf litter, but are not taken often.

Caterpillars and other items that seldom occur in

the leaf litter are also rare in Ocellated diets. The

commonest items were orthopterans (sensu lato)

and spiders. Only large items could be identified in

the field; many beetles probably are among the unidentified small insects.

Birds foraging away from competitors and uninterruptedly at good sites over the ants darted for

food at intervals of 3 to 258 seconds (average =

38.5; median = 24). This is about the same rate

as in Spotted and Bicolored Antbirds foraging uninterruptedly.

Prey is mostly the length of the exposed bill

("1 B" or exposed bill length = 18.2 mm) or less;

but some larger items are taken, much as in Bicolored Antbirds. Tiny items are swallowed so rapidly that they can seldom be identified. Prey items

over 10 mm in length sometimes require chewing,

shaking, and gulping. The bird often holds its bill

up and chews such an item conspicuously. Large

items may be dissected, much as in Bicolored Antbirds (Willis, 1967:31); the prey is carried away

from ants, each leg is shaken until the body falls

TABLE

Kind of prey

sowbugs

scorpion

whip scorpion .

spider

millipede

centipede

stick insect

roach

cricket

grasshopper

katydid

caterpillar .

ants

hymenopteran

lizard

insect

arthropod

leaf

?

Total

>.—Food items taken

T 0-5

9

1

(1)

10(18)

1

1

4(4) 1

(1)

4

(4)

1

14 1

2

2

5 (6) 89 (6)

52 (34) 91 (6)

10

7

3

3

(1)

1

1

76(12)

91(13)

by Ocellated Antbirds

15

9(4)

14(10)

1

8

1

23(5)

56(19)

20

1

40(18)

(2)

33 (10)

7(11)

29(4)

1

(1)

(1)

Ml)

41 (26)

153 (74)

Length

25

2

6(6)

3(1)

2(6)

4(2)

(2)

(2)

17(19)

(see explanation

in mm

30 35

1 1

5(2)

5(1)

(2)

5

1

4(2)

21 (7) 1

40

2

2

3

1

2

1

1(1)

12(1)

in Table

45

1

(1)

(1)

2

3(2)

50

2

(1)

(1)

1

1

4(2)

4)

55

(1)

(1)

2

1

3(2)

Total

9

9(1)

1(2)

77 (49)

1

3(3)

1

67 (26)

10(21)

53(7)

4(2)

2

(6)

2

3(1)

18

3(1)

241 (60)

504 (179)
14

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

off, then the head and thorax are chewed off, and

the abdomen is eaten last. The dissecting bird holds

its head low and hunches the body (Figure 2H). It

jerks its tail up briefly now and then. The legs are

splayed, the rear toes pointing inward (reverse

pigeon-toed).

After dissecting prey or chewing juicy prey, Ocellated Antbirds often wipe the bill repeatedly in the

usual fashion, base to tip on alternate sides with

quick strokes. At times a foraging bird gapes repeatedly and regurgitates a few exoskeletons of

prey, but a slight raising of the tail to drop white

excreta is much more common.

Ocellated Antbirds sometimes drink water from

the "drip-tips" of leaves but seldom drink at other

times. Their prey are so juicy that they probably

need little free water.

During medium or heavy rains Ocellateds faintsing or loud-sing and move to cover. Light rains,

which do not interfere with ant foraging much, do

not stop Ocellated foraging either.

FORAGING COMPETITION AND GRUNTING

Ocellated Antbirds dominate most other ant-following birds and as a result occupy the central and

best foraging zones over antswarms. Smaller birds

and some larger ones are "supplanted" (driven

from their perches) with loud snapping of the bill

and a whirr of wings on an arrowlike attack. As a

consequence, many competitors move away as soon

as the antbird approaches ("displacings"). Some

must watch until the antbird leaves, then move in

and forage where it was ("returns"). Supplantings,

displacings, and returns are listed in Table 7.

Bicolored Antbirds, abundant competitors over

the ants, draw most of the attacks of Ocellated Antbirds. Even pointing the bill at a Bicolor and jerking the tail a few times will sometimes send Bicolors

away. The Bicolors persistently infiltrate the ranks

of Ocellated Antbirds, even though the latter grunt

and try to keep the central and best zone free of

these competitors, thus relegating them to the outer

TABLE 7.—Antagonistic foraging interactions of Ocellated Antbirds (5 October

1960 to 21 January 1971, Barro Colorado Island, birds foraging over swarms of

army ants)

Species A

Antagonistic interactions (losses/wins by species

A to Ocellated Antbirds)

supplantings displacings returns fighting

Intraspecific

Ocellated Antbird

Interspecific

Bicolored Antbird

Gray-headed Tanager

Plain-brown Woodcreeper

Spotted Antbird

Buff- throated Woodcreeper

Slaty Ant&hrike

Swainson's Thrush

Chestnut-backed Antbird .

Wood Thrush

White-whiskered Puffbird

Kentucky Warbler

Canada Warbler

Thrush species

Anolis frenatus (lizard) ....

Gray cheeked Thrush

Broad-billed Motmot

Black-striped Woodcreeper

Rufous Motmot

Squirrel Cuckoo

Barred Woodcreeper

1033

2360/3

186/1

76

64

11/3

5/3

7

7

3

1/1

1

1

1

1

/2

/3

/6

/8

/13

459

465

49/1

40

65

5

/

/17

/5

11

35

8

10

4
NUMBER 144 15

concentric "zone" around the ants. When a subordinate Ocellated Antbird is getting little food, it

usually heads for the nearest Bicolored Antbird and

supplants it, especially if the Bicolor tries for food

one or two times. Probably this is an efficient technique, for the Bicolor is likely to be in the best

place that is not occupied by dominant Ocellateds.

Twice a very subordinate female Ocellated, badgered by other Ocellateds, was supplanted from behind by a Bicolor; and once a very irate Bicolor

chasing other Bicolors managed to supplant an

Ocellated. This Bicolor tried again, but the Ocellated just ignored his lunge the second time. Bicolors are much smaller than Ocellated Antbirds

(30-36 v. 45-55 g) but differ less in bill length

(culmen of 113 east-Panamanian Bicolors, x =

20.8 mm; culmen of 71 Panamanian Ocellateds,

x = 24.1 mm). Thus, Bicolors probably take many

arthropods that are of interest to Ocellateds.

Gray-headed Tanagers and Plain-brown Woodcreepers persistently move down to the ants but are

chased up by the grunting or attacks of Ocellated

Antbirds (Willis, 1966, comments on the woodcreepers). An Ocellated pounced on and pecked

one young Tanager that foraged low; it then foraged high. Once an Ocellated beat a Tanager to

prey because the Tanager started from 4 m up, the

Ocellated from 0.3 m up. Spotted Antbirds evade

the Ocellated Antbirds in many ways—by going

high or peripherally, behind bushes, etc.; they seldom are attacked because they wander in the concentric zone outside the Bicolor zone rather than in

the zone next to Ocellated Antbirds (Willis, 1972a).

Many other species are attacked if they come near

the Ocellateds, but most species do not come close.

In dense cover there is less fighting and less grunting at competitors. Perhaps there are more prey

in such situations, but the main reason more birds

can be peacefully accommodated is that they can

stay somewhat out of sight of each other.

Repeated grunting keeps many possible competitors away from Ocellateds. An Ocellated starts

or speeds up its grunting as a small competitor

appears or approaches, or even if a distant small

bird catches an insect. When the small bird moves

off or behind cover, the grunting stops as if switched

off. Once the rapid grunts at a Bicolored Antbird

became a rattling cha-a-a-i-in-in-imp-imp-imp series,

rather like chittering or growling. The Ocellated

may grunt even if preening, but it is usually foraging busily when it grunts.

Grunting is never given at larger birds, even

nearby Barred Woodcreepers or White-whiskered

Puffbirds (Malacoptila panamensis). (Once an

Ocellated spread its throat feathers and extended

its head toward a Puffbird, which ignored it.) Even

grunting at other Ocellateds is very rare; I recorded

only two cases in which dominant males grunted at

subordinate females, and one case in which a female grunted at her grown son as he wandered past.

Other sounds, noted under "agonistic behavior,"

are used when Ocellateds forage together and no

small species are present. However, I specifically

recorded grunting at approaching Bicolored Antbirds on Barro Colorado Island 381 times, at

Spotted Antbirds 44, at Gray-headed Tanagers 22,

at Plain-brown Woodcreepers 20, at Chestnutbacked Antbirds (Myrmeciza exsut) 7, Slaty Antshrikes (Thamnophilus punctatus) 3, Buff-throated

Woodcreeper 1, and Golden-collared Manakin

(Manacus vitellinus) 1. I noted grunting at combinations of small competitors and in situations

where other Ocellateds were present with small

competitors on many other occasions. I recorded

grunting at Bicolors also at the Madden Forest Reserve, Limbo Hunt Camp, Rio Agua Salud, Rio

Medio, Cerro Campana, and £1 Tigre, and at

Spotteds at the Limbo Hunt Camp.

Grunting even displaces scolding chirrs at the observer at times; an Ocellated disturbed by me and

seeing a Bicolored Antbird move in over the ants

often stopped mobbing and started frantic foraging and grunting, by a kind of "social facilitation";

however, I once noted that grunts stopped as a

snake (Pseustes poecilonota, a nest robber) glided

past and resumed after it was gone.

A few species dominate Ocellated Antbirds. A

pair of Slaty Antshrikes supplanted an Ocellated

Antbird three times near their young, and Buffthroated Woodcreepers sometimes harass the slowerflying antbird, but usually the antbird dominates

these two species. An aggressive Black-striped

Woodcreeper (Xiphorhynchus lachrymosus) chased

three Ocellateds one day, but these woodcreepers

usually forage high above ants. When motmots fly

down to capture prey, they scare out Ocellateds;

the Rufous Motmot (Baryphthengus ruficapillus)

sometimes hogs a horizontal perch low over the cen-
16 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

ter of a swarm for several minutes, but gives the

ants up to the circling antbirds when the ants

move away from the horizontal perch. Ocellateds

sometimes have their crests raised when working

near motmots. Squirrel Cuckoos (Piaya cayana)

are more agile than motmots and can flutter down

and scare out antbirds in chases for prey or just

take a perch from them. Cuckoos are like motmots,

however, in preferring horizontal perches, which

seldom are available near the ground.

The only effective competitor of Ocellated Antbirds on Barro Colorado was the Barred Woodcreeper. This large woodcreeper usually ignores

the antbirds, which circle it rather boldly. They

tend to avoid the open places and large trunks it

favors, so there is little overlap; however, it supplants them vigorously at times.

Presumably the big ant-following Rufous-vented

Ground Cuckoo (Neomorphus geoffroyi), once

present on Barro Colorado Island, dominates Ocellated Antbirds. Black-crowned Antpittas (Pittasoma michleri) and Rufous-crowned Antpittas

(Pittasoma rufopileatum) do so, the former at the

Limbo Hunt Club (Panama) and the latter at El

Tigre (Colombia). Black-chested Jays (Cyanocorax

affinis) scared one Ocellated down from 8 m up at

El Tigre.

Off Barro Colorado Island, I recorded Ocellated

Antbirds supplanting Bare-crowned Antbirds

(Gymnocichla nudiceps) at Tucura and Cano Remolina in Colombia, Immaculate Antbirds (Myrmeciza immaculata) at El Tigre, Ruddy Woodcreepers

(Dendrocincia homochroa) at Cerro Campana

(Panama), and Red-throated Ant Tanagers (Habia

fuscicauda) on the Bohio Peninsula (Panama). The

general rule in all these supplantings, as on Barro

Colorado, is that large birds supplant small ones.

Maintenance Behavior

As befits relatively dominant members of a community, Ocellated Antbirds spend their extra leisure time preening or resting in cover near but

seldom over the ants. Females fed by their mates,

and females low on the intraspecific peck order,

often rest and preen for long periods. Preening

perches are generally under clumps of the palm

Oenocarpus panamensis, in dense treefalls or vine

tangles, or in similarly safe places. The perches

are usually horizontal (Table 8). Resting probably

saves energy and reduces danger from predators;

preening probably guards against small things that

might harm a bird, such as cold and rain and parasites.

PREENING, STRETCHING, RESTING

Preening has not been analyzed in detail but is

generally similar to that of Bicolored Antbirds

(Willis, 1967:35-36). In two bouts of preening,

about five minutes apart, a male Ocellated started

with the upper and under surfaces of the wing,

followed by the scapulars and around the wing

base, then the upper breast, then the flanks and

the edges of the abdominal apterium. Finally, he

preened around the tail after scratching the head

and preening the upper back. Feathers, particularly of the tail, are preened from base to tip.

Ocellated Antbirds scratched over the wing (30

times), seldom under the wing (7 times).

After bouts of preening, or when a bird stops

foraging and is about to move to cover for preening, common stretching motions are toe-standing,

right and left stretches, and double-wing or "half"

flexes.

The resting bird (Figure 5A) sits with head retracted, tail somewhat down, and body feathers

fluffed. At times one extends its toes briefly or lets

them dangle. Females being fed by their mates

spend most of the day preening and resting, and

TABLE 8.—Perches of preening and resting birds

(PB=preening birds; FR=females resting, waiting

for mates to feed them)

Height in meters

height

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

2

Total

records

PB

3

15

24

34

25

9

14

7

6

5

20

762

FR

4

8

8

8

8

8

3

7

2

4

5

65

Angles in degrees

Angle

20°

40°

60°

80°

100°

records

PB

67

40

12

3

2

FR

39

12

2

1

1

55

Diameter in

centimeters

diameter records

1

2

3

4

5

6

7

15

PB

10

58

25

9

6

-

-

1

K)9

FR

5

26

7

3

9

1

2

-

53
NUMBER 144 17

at such times use horizontal perches about 2 cm in

diameter and 0.4 m up, just as do preening birds

(Table 8).

Mutual grooming has not been observed, except

perhaps for one young female that seemed to pick

spider webs off her mother's head. Since young

often nibble or gape at parents, this perhaps was

not actual grooming.

BATHING

Ocellated Antbirds occasionally bathe in small

creeks, once in a pool of water atop a shelf fungus.

Baths may be at any hour of the day, for I have

recorded them from 7:55 A.M. to 6:15 P.M. At times

several Ocellateds bathe, sometimes with Bicolored

Antbirds. The Ocellated hops down toward the

water, looks at it and around, stands in the water,

quickly dips the breast, and throws water over the

neck and head by fluttering the wings in a spray

of water. Except for these brief fluttering dips, the

head remains up and the bird keeps a wary lookout.

The tail may be partly spread and rest on or in the

water. The back is sometimes fluffed to show the

grayish bases of the interscapular feathers. Then

the bird hops or flies to nearby perches, shakes the

rear end vigorously, and preens the tail and other

feathers from base to tip. At times the bird hops

in and out of the water, alternating bouts of bathing with brief alert periods or sessions of preening.

Then it retires to cover to preen energetically.

ANTING

Occasionally Ocellated Antbirds capture a small

prey, hold it in the tip of the bill, chew it (Figure

5B), and brush it through the primaries or undertail coverts in typical "anting" (Whitaker, 1957).

In 24 instances of anting, 10 items were finally

eaten and 2 thrown away. In the other 12 cases, I

did not see what happened to the prey. Possibly

anting is a foraging behavior, brushing off distasteful secretions of prey on wings and under the tail,

as I have suggested for other ant-following species

(Willis, 1967:32-33). At times Bicolored and Ocellated Antbirds anted actively near each other with

similar items, apparently aitfs or other social insects flushed by the army ants. In Bicolored Antbirds, most anting is by subordinate and presumably

hungry birds; but in Ocellated Antbirds 8 cases of

anting were by subordinates, 1 by a dominant bird,

and 13 by birds that were not competing with other

Ocellated Antbirds (most were competing with Bicolored Antbirds).

Anting may also soothe skin irritated by molt,

as Potter (1970) suggests, for in 1961 all my records were from July to November, the main months

of molting in this species. In later years I have

had several records for May and June, months in

which molting is uncommon; but I have no records for a few visits in January and February,

months in which there is little molt.

Male Ocellated Antbirds anted on 18 occasions,

females on 6. Probably the tendency of females to

rest while males feed them leads to this disparity of

observed numbers.

REACTIONS TO ARMY ANTS AND OTHER INSECTS

Ocellated Antbirds are dominant to most other

birds and thus can usurp the perches low over

army ants. As a result, they are exposed to the attacks of army ants more often than are other species that follow ants. Ants often turn back on

FIGURE 5.—Maintenance hehavior: A, resting; B, anting; c, bird on the ground jiggles the leg at

attacking army ants.
18 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

encountering the foot of a bird, unless ants in the

main body of the swarm push them up. Occasionally, however, ants bite or sting the antbird.

Typical reactions of Ocellated Antbirds to attacking ants include stamping or quivering (Figure

5c) the foot that ants are attacking, pecking at the

offending ants and tossing them into the air, jiggling or jittering back and forth from one foot to

the other, dancing about as if on hot coals (mostly

when getting prey on the ground), and finally fleeing to a new perch if the ants persist. The body

is usually high on the legs, which are extended.

The tail sometimes jerks or flicks upward a few

times as ants attack. At times the Ocellated champs

the bill (mandibulates) before hopping off. At one

ant bite, a bird jumped 0.3 m in the air like a

Blue-black Grassquit (Volatinia jacarina). Ant attacks probably discourage use of the ground and

other broad perches, such as logs and fallen limbs.

At times an Ocellated Antbird loses all or part of

its prey to the ants. One female Ocellated watched

the ants pour over a dropped leg of a grasshopper

and champed a few times. Others chirred faintly

on similar occasions.

Mosquitoes flying by occasionally elicit a peck.

Antipredator Behavior

Ocellated Antbirds are probably prey as well as

predators, for there was a rather high disappearance rate on Barro Colorado Island in 1960—1970

(Willis, MS). I never saw any hawks or other predators attack Ocellateds, but they become alarmed

very easily. As in Bicolored Antbirds, the three

major kinds of alarm displays other than reactions

to insects are freezing with keening, panicking with

chipping, and mobbing with chirring. Screaming

(as in the hand), flight to cover, and tameness and

investigating are less common reactions to predators.

FREEZING

At distant danger, such as a large bird flying

past or a bird giving an alarm call, Ocellated Antbirds often freeze (Figure 6A, E) and keen briefly.

The head extends (as in Willis, 1967:17, "extending" means opening the angle between the part

cited and the main part of the body, and "flexing"

means closing the angle between the part cited and

the main part of the body) as the bird ducks or

FIGURE 6.—Antipredator behavior: A, freezing at keening from another bird; B, chirring and

tail jerking at distant thunder; c, alert watching; D, investigating me (at El Tigre) ; E, a freezing pose kept for 12 minutes.
NUMBER 144 19

inclines the front part of the body downward.

Probably the femora are flexed to produce the lowering ol the front of the body, for the bird often

crouches. The tail remains closed and is not flicked.

The body is sleeked. Birds may freeze, as at the

stroke of a wand, then resume foraging as if suddenly released from a spell. Ongoing grunts at

competitors also halt during the freezing and resume suddenly at its end.

Freezing, or keening and freezing, were 15 times

reactions to alarm calls (Plain-brown Woodcreeper,

5; keening Bicolored Antbirds, 3; Barred Woodcreeper, 3; Collared Aracaris, Pteroglossus torquatus, 1; Black-striped Woodcreepers, 1; chipping

Ocellated Antbirds, 1; Slate-colored Seedeater,

Sporophila schislacea, 1) and 6 times reactions to

large birds (Double-toothed Kite, Harpagus bidentatus, 2; Crested Owl, Lophostrix cristata, 1; Tiny

Hawk, Accipiter superciliosus, 1 at Limbo Hunt

Camp; Barred Forest-Falcon, Micrastur ruficollis, 1

at Boca del Rio Verde; Ramphastos toucans, 1).

Keening by other Ocellateds also caused freezing.

Once one froze as a helicopter passed over, and

another ducked as a Squirrel Cuckoo flew over.

PANICKING

At close danger, Ocellated Antbirds chip and

flee for low tangles or other cover, where they flick

their long tails actively and chip sharply. They

crouch low on their legs. The display is often social, with several birds chipping and flicking in

irregular alternation. At times there is a long

period of hysteria, with paroxysms or outbursts of

chipping and tail-jerking. If danger is not so pressing, the antbirds chip and flick irregularly during

foraging. They move quickly, darting for prey as

if being attacked, and turn the head sharply as

they look about alertly. As the panic abates, the

chipping becomes muffled "chut-ut" sounds and

often grades into muffled chirring. The flicking

continues and gradually dies out, with many short

bouts later.

The flicking of the tail is somewhat different

from that of Bicolored Antbirds, which flick the

spread tail upward and then lower it gently for the

next flick. Ocellated Antbirds spread the tail less

often, and lower it quickly after each sudden upward jerk. Moreover, the tail often goes above the

line of the body in its upward movement, rather

than stopping at the line of the body as in Bicolored Antbirds. During active flicking, the Ocellated tail is in a downward or resting position

between flicks, while the Bicolored tail is always

moving and seldom is in the up (resting) position.

The tail seems to serve as a signal of excitability or

alarm in both species. Possibly the long tail of

Ocellated Antbirds compensates somewhat in display conspicuousness for the fact that it does not

spread widely. However, the long tail may be more

necessary for balance in flight or for spreading in

aggressive displays, as described below. It may also

be needed as a brake for the large body in sallying

to the ground, as described earlier.

The alarm calls of Plain-brown Woodcreepers

and Spotted Antbirds often (5-}- records each)

cause chipping, panicking, flight, or intention

movements of flight, such as reversing on the perch

or jerking the tail, in Ocellated Antbirds. Alarm

calls of several other birds sometimes cause panicking, such as Black-breasted Puffbirds, Notharchus

pectoralis, 1; Buff-throated Woodcreeper, 1; Slaty

Antshrike, 1; Black-throated Trogon, Trogon rufus,

1; and Bicolored Antbird, 1. Wings overhead, 2;

and flying large birds often cause panic (Wood

Owl, Ciccaba virgata, 1; Semiplumbeous Hawk,

Leucopternis semiplumbea, 1; White Hawk, Leucopternis albicollis, 1; Double-toothed Kite, 1;

Hook-billed Kite, Chondrohierax uncinatus, 1; toucan, 1; Collared Aracari, 1; Chuck-will's Widow,

Caprimulgus carolinensis, 1; Rufous Motmot, 3;

Barred Forest-Falcon, 1 at Boca del Rio Verde).

An agouti (Dasyprocta punctata) dashing through

a swarm caused panic once; but usually slow-moving agoutis are ignored or only force the bird to

fly up to 1 or 2 m above the ground briefly. My

waving a hat and (twice) standing near young birds

caused panic in tame Ocellateds; and humans often

cause muffled chipping.

MOBBING

The usual reaction to large ground animals, especially humans, is mobbing with chirring. Probably

both activities normally disturb and drive away

predatory mammals, which could not catch prey

well if some small bird were giving the alarm and

fluttering nearby. Chirring calls, as I have noted

elsewhere (Willis, 1967), probably mimic the growls

of carnivores and drive away nonpredatory but in-
20 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

terfering mammals. Chirring calls and muffled

intermediates between chirring and chipping calls

often alternate, for mobbing often grades into panicking or vice versa. If moderately tame birds are

mixing panicking with mobbing, however, an observer can quickly turn their chipping and muffled

chirring to pure chirring and mobbing by walking

toward the birds a few steps. Birds usually chinwhen they first see an observer, then gradually begin muffled noises. Finally they either warily return to foraging or start faint-songs, loud-sing, and

leave the swarm.

In mobbing, the bird jerks the spread tail upward frequently (Figure 6B). At times each flick

of the tail coincides with a chirr, the cheee part

on the upstroke and the terminal yuk part on the

downstroke. The bare and bright blue face is often

turned toward the observer, but it is restricted in

area by the fact that the crown feathers are slightly

spread, thus covering the bare area almost down to

the eye. The throat feathers are also ruffled but

tend to spread down from the bare face and thus

expose more of it below the eye. Often the mobbing bird swings around and around a vertical

perch, seemingly showing off the blue face and

dark eye as a possibly frightening "eyespot" design

(Willis, 1969:378). By contrast to sleek-bodied

freezing and panicking birds, mobbing birds are

either inflated or fluffed out. Probably the ocellated pattern is displayed by this fluffing.

Mobbing is usually a social activity, necessarily

so in many cases because these birds are so social.

Once the chirrs of a bird in the net brought up

two distant others to chirr at me. When local Ocellateds were tame and had stopped chirring at me,

the persistent chirrs of a distrustful newcomer were

often enough to start the tame birds chirring. It

thus is often mobbing in the strict sense, that of

mob attack.

Often a bird terminating mobbing, or a moderately tame one that is jerking the tail a little but

is not excited enough to chirr, does "toe-looking"

(Figure 7). The bill points down at the feet, and

one face and then the other is turned to the observer as if the bird were a human bashfully looking at his feet but keeping an eye on another human

at the same time. This may also display the "eyespot" design of the face, possibly in a somewhat

threatening way. Once a female toe-looked as her

FIGURE 7.—Toe-looking.

mate chased an intruder, suggesting that toe-looking may be thwarted attack. Once a female chirred

and toe-looked when her grown young female

preened near me. At times a tame bird grunts at

the approaching observer, as if he were a little antbird. Champing the bill, tail-flicking, and other

displacement activities often accompany toe-looking

or grunting. One tame female near me champed

her beak as three people photographed noisily at

some distance from us.

Many chirring reactions were to mammals: 7

times to passing humans, even when the birds were

ignoring me; 7 to tayras {Eira barbara); 5 to coatimundis (Nasua narica), especially ones dashing

through; 4 to white-faced monkeys (Cebus capucinus), especially ones on the ground or ones grunting at me; 2 to squirrels (Sciurus granatensis); 2 to

collared peccaries (Tayassu tajacu); 1 to a squawking, running agouti; 1 to a passing four-eyed opossum {Philander opossum). As noted later, even

tame antbirds chirred if I stood near their young

or held them in the hand, and chirring was the

normal reaction of antbirds to me unless they were

tame. Snakes gliding by twice caused chirrs; once

it was the nest-robbing snake Pseustes poecilonota.

Sitting hawks also elicit chirrs, plus at times chipping: Ornate Hawk-Eagles, Spizaetus ornatus, 2;

White Hawk, 1; Gray-headed Kite, Leptodon cayanensis, 1; Common Black Hawk, Buteogallus

anthracinus, 1, in the Madden Forest Reserve. A

Squirrel Cuckoo gliding in once caused chirrs; as

noted earlier, this cuckoo often supplants and thus

competes with Ocellated Antbirds. Alarm calls of

other small birds, especially the buzzing ones of

reactions to sitting predators, caused chirrs several

times: chipping and chirring of Bicolored and
NUMBER 144 21

Spotted Antbirds, the chirrs of other Ocellated Antbirds, the ah'rrrrrr and cah-cah of Slaty Antshrikes,

the stieking of Plain-brown Woodcreepers, 6, the

ivh'kurr of growling alarm of a Barred Woodcreeper, the peer-peer-peer-peer! alarm of a Buffthroated Woodcreeper.

Other uses of chirrs seemed to express mild alarm

or irritation: at the start of thunder or rains (Figure 6B); when an insect that had run under leaves

could not be found even by tossing the leaves;

when a juicy part of an insect dropped into ants;

before a clumsy sally up at an insect from an exposed perch 2 m above the ground; at the crash of

a falling log. One female chirred when her mate

supplanted their daughter.

REACTIONS WHEN CAPTURED

Ocellated Antbirds kick and chip when captured

in mist nets. Often they chip or chirr when the

first panicky attempts to escape fail. In the hand,

tame birds are likely to give a few vehement chirrs.

Naive birds, unaccustomed to humans, are more

likely to squeal violently or to attempt a kick-fluttering escape now and then than to chirr and ruff

their throats at one. Their faces become pallid

rather than the bright blue of chirring birds. Many

birds chirr or chip as they flee upon release. Often

birds peck at one's finger, holding and twisting it

in the hooked tip of the bill with painful effects.

FLIGHT, TAMENESS, AND CURIOSITY

Silent flight to cover or intention movements of

flight, such as turning away from a passing big

bird, are common. Usually panicking or freezing

movements accompany the flight. The loud alarm

calls of Plain-brown Woodcreepers and other birds

sometimes provoke simple flight to cover. Simple

flight often involves hiding behind tree trunks or

low cover, out of the sight of the observer. Such

birds become alarmed if they see the observer or

his eye through a hole in the vegetation, but otherwise they can be watched through such holes.

Ocellated Antbirds on Barro Colorado Island are

less tame to humans than are Bicolored Antbirds,

and hence far less tame than Spotted Antbirds. The

larger the bird in this series, the less tame it is

initially. Ocellated Antbirds join in the general

mobbing and chirring of all three species when

one first approaches a swarm of ants. The Ocellated

Antbirds commonly move up to 1 or 2 m above

the ground, stare and toe-look at one, and finally

flee for low cover with chipping notes. From cover,

there is a pandemonium of muffled chirrs, chips,

and faint-songs. One sees long black tails jerking

vigorously in the dark cover. Then faint-songs begin, and finally loud-songs as the Ocellateds desert

for another swarm of ants or hide for long periods

in distant cover.

Over the course of a few hours, if birds stay near

the ants and one is careful to stay well behind the

ants, the Ocellated Antbirds gradually become less

agitated. They sneak in to the ants whenever they

can do so behind low cover. They flush with chirrs

if one approaches, but then return if one retreats a

little. Eventually they only faint-sing and move a

little if one tries to see them in the low cover.

Finally they stay, looking about warily and foraging cautiously (Figure 6c). Over the course of a

few days, some birds habituate to one or become

fairly tame. They never approach one's feet the

way tame Bicolored Antbirds do, but they do forage

and carry on their other activities fairly normally.

They are especially likely to become bold if tame

Bicolored and other antbirds lead the way. However, an Ocellated Antbird often avoids the end of

a swarm near the observer even after one has known

the bird for several years. Birds that one meets

again after an absence of several months chirr, but

soon become fairly tame. It takes persistent watching of individuals to get close enough for filming

(3—5 m), however, and even in tame birds natural

behavior patterns are fully expressed only when

one is 10 m or more away.

Crippled birds are unusually wary and hide in

cover or panic even when the observer is no stranger

to them. One male with a broken wing chirred

and hopped to 7 or 8 m up a liana as I passed.

In some areas, Ocellated Antbirds are tamer than

the ones on Barro Colorado Island. On the Rio

Agua Salud and Navy Pipeline Road, not far from

Barro Colorado Island, they seem much tamer. Perhaps this is because hunting of mammals in these

areas has removed most mammalian predators, so

that the birds are less threatened by mammals than

they are in a game reserve like Barro Colorado.

Possibly the low palms and other undergrowth in

less mature forests protect them better too. In one
22 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

forest with dense undergrowth, that of El Tigre in

Colombia, Ocellateds did tail-flicking much less

than they did on Barro Colorado.

In the mature forests on Barro Colorado, there

are large areas of very open undergrowth in which

Ocellated Antbirds are very shy, periodically jerking their tails and looking about alertly as they

forage. Instead of mobbing, they usually flee one's

approach. When tame birds work such open undergrowth, they are very quiet, alert, and quick to flee

for cover. They get little prey in such areas, for

they are too busy looking around rather than down

at the ants. Most of their foraging comes in areas

near or in cover. Large groups of birds are more

active in foraging in open undergrowth, probably

because an individual can afford to leave some of

its alertness to the many other eyes of the group

and concentrate more on foraging.

Common mammals, such as agoutis and peccaries, usually disturb Ocellateds very little. The

birds fly up to 0.8 m or so above the ground and

drop back down after the mammal passes.

In no locality are Ocellated Antbirds very curious. Even young birds seldom approach the observer to look him over the way young Bicolored

Antbirds do. A few birds peer at one during breaks

in chirring (Figure 6D), at least in places with

plenty of cover. Perhaps the dominance of Ocellated Antbirds makes it possible for them to find

food without investigating every nook and cranny,

so that they are not investigative in general. Usually they do not have to forage near the observer,

the way subordinate and young Bicolored Antbirds

must do when Ocellated or dominant Bicolored

Antbirds take the other areas of ant swarms.

Agonistic Behavior

Agonistic behavior, as in earlier papers (Willis,

1967, 1972a), will here be considered competitive

reactions to animals of more or less the same size

as the behaving animal. Those kinds of attack and

escape that have to do with attacking prey or escaping from predators or parasites are discussed above.

The agonistic behavior of Ocellated Antbirds includes submissive display, flight, aggressive displays,

attack, and fighting. Interspecific agonistic behavior, mostly simple attack and fleeing, has been

discussed under Foraging Competition.

SUBMISSIVE DISPLAYS

Ocellated Antbirds, the dominant birds over

swarms of ants, have more submissive displays and

perform them far more often than they do aggressive ones. They have more submissive behavior

than does the subdominant Bicolored Antbird

(Willis, 1967:45-48) and far more than does the

subordinate Spotted Antbird (Willis, 1972a). As is

usually the case in antbirds, the submissive behavior is displayed mainly to dominant members of

the species rather than to other species.

Although the Ocellated Antbird has many submissive displays, they intergrade and do not form

distinctive clusters or what Morris (1957) has called

displays of "typical intensity." For purposes of description, the spectrum of submissive displays may

be divided into five groups: cringing, wing-waving,

pleading, bunching, and nibbling.

Subordinate Ocellated Antbirds quickly take a

humble pose when dominant ones come near. These

birds always look somewhat humble, because of

their habit of foraging with low tails and retracted

heads, but the cringing subordinate lowers its head

and tail still more. When the dominant bird

alights above it, the cringing bird sometimes seems

to drape itself like a wet rag (Figure 8D). The

angle between head and neck is extended, keeping

the head almost level even when it is lowered,

nearly to the ground. At times the bird bobs the

head, emphasizing the low pose. Usually the whole

head seems sleeked and snakelike, but at times the

throat feathers are ruffled. Throat spreading is

often associated with bill wiping or with successful

retreat from a dominant, suggesting that it may be

aggressive behavior conflictingly present in the submissive display.

The bare blue face is pallid, and the area is restricted by crown and throat feathers, which close

like an iris diaphragm around it. Plate XI in Meyer

de Schauensee (1964) shows this effect. (The pallid

face and closed facial area in this painting actually

result from using specimens as models, but the pose

illustrated is accidentally rather close to cringing.1

The head faces ahead rather rigidly, but the eyes

1

 The bird pictured in Howell (1957) is naturally blue in

the face but has an unusually closed facial area; perhaps the

artist, Don Eckelben*y, saw a mobbing or alarmed bird but

used specimens for the final picture.
NUMBER 144 23

diverge and move actively, and the body moves

from side to side so that the frozen head can still

look about.

The body often seems fluffed, but a fleeing bird

often sleeks. The bird seems to shrink in place, for

it crouches or clings close to the perch; however,

the toes are loose rather than clamped. The lowered tail seems to jiggle slightly at times; usually

the cause is "chittering," a faint rattling sound

that is used mainly during cringing. The bird

seems to freeze or be inhibited about foraging; the

dominant bird is likely to supplant it if it goes for

prey. Often the chittering leads to chittering faintsongs as the subordinate bird bounds or flutters

away from its opponent. Often the bird goes downward in moving away from the opponent, even to

the extent of hopping away along the ground. If

the dominant bird follows, the cringing bird slinks

about with chitters and snakelike motions.

If the bird had been grunting at another species

before cringing, it stops abruptly as it begins to

cringe. Even a dominant Ocellated moving nearby

may cause the subordinate to stop grunting. However, a cringing bird pressed but not attacked by

another sometimes prolongs the grunting; the notes

become long and scratchy "whines" mixed with

chittering noises. Often the whining bird begins

"wing-waving." The tips of the wings flick out

more and more often, until the bird is fluttering

spastically (Figure 8B). The wings are sometimes

waved very widely, often in jerky alternation with

disjointed upward flicks of the closed tail (Figure

8G). The head may be snaked forward and back

and often is jerked back as the tail jerks up, so the

bird seems spastic or compressed by the closing of

an invisible box. The whining noises extend at

times into squealing ones, mixed with chittering

and with chittering faint-songs. Wing-waving and

whining are typical displays when young birds or

adult females are crowded by aggressively displaying other adults. The wing-waving bird may face

toward or away from the dominant opponent, or

even hop toward it with gaping (Figure 8B).

Often the wing-waving grades into or alternates

with an even more assertive display, "pleading."

The wing-waving or other bird hops up to the silent

aggressor and, tongue up, gapes or even screams in

its ear (Figure 8H). The gaping pleader holds the

rear of the head low, for the head is hyperextended

on the neck. It gapes almost as if to swallow the

head of the aggressor, which may send it fluttering

away with a swift peck or, nonplused by the vigov

of the screaming and pleading, hop away for the

moment. At times birds gape at each other in brief

quarrels over a single food item. The pleading bird

may continue to chitter, whine, squeal, wing-wave,

and tail-jerk. The body is fluffed, the tail somewhat

spread, but down (even on the ground). The bird

may even push the dominant bird about bodily.

"Bunching" is a social kind of submissive behavior. The birds of a family crowd close together,

the subordinate members of the group following

like shadows and alighting within a few centimeters of the dominant male each time he alights

(Figures 8E, F and 9). At other times the male

goes to the female as the menacing other birds approach. I often felt afflicted by double, triple, or

even quadruple vision, for the birds of each group

sometimes alight in a row on a vertical or other

perch and display at the opposing group like monkeys of the "see no evil, hear no evil, speak no

evil" type. F. Gary Stiles and I have seen Groovebilled Anis (Crotophaga sulcirostris) in western

Mexico give even more effective aggressive team

displays, the shoulder-to-shoulder birds of two different groups rushing back and forth at each other

on the ground like opposing teams in football; and

DeVore and Hall (1965) report that male baboons

(Papio anubis) group effectively to meet a dominance challenge; but the bunching of Ocellated

Antbirds contrasts with these in being mostly restricted to subordinate pairs or families.

Occasionally a bunched pair or family does manage to supplant the dominant opponent; once I

saw two birds of a family alight to either side of

the opposing male and squeeze him out like a seed

from a grape. Moreover, the upper or dominant

bird of a team may be challenging weakly (Figure

8E), or all birds may do so. Usually the weakest

members of a family crowd close to the dominant

one of their family as if inciting him not to retreat

from the dominant bird of the other family.

Often a pair or family crowds close together to

forage during intervals in the dispute (Figure 9A).

They may gape or nibble at each other, especially

the female and young birds (Figure 9B). At times

both opposing groups bunch at each other, for the

female of a family is small and likely to be ousted
24

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

FIGURE 8.—Submissive behavior: \, subordinate bird, below, pleads with challenging dominant

one, above; B, screaming and wing-waving bird pleads as it pesters a dominant bird; c, subordinate bird rests at the periphery of a swarm until dominant birds leave; D, cringing bird takes

very low pose; F, female (in front) bunches with her weakly challenging mate (note ruffling

of crown as a submissive movement) and nibbles at him; F, bunching pair watch dominant

birds take over the ants; c, pleading and wing-waving by a female on the ground; n, pleading

female yells in the ear of dominant bird.

even if her mate is dominant. The dominant male,

however, more often challenges alone and his female follows him at a distance or forages; the subordinate pair or family bunches. The dominant

male often ignores his mate, even when she bunches

with him and "nibbles" up at him, while the subordinate male nibbles and/or pecks down at his

mate.

During bunching, the female or young bird nibbles up now and then to the downward-pointed

beak of the challenging male of the family. If the

female or young is above him, he tosses his beak up

at times to meet its downward nibbling, then returns to beak-down challenging. Often caroling accompanies the nibbling, and then both the visual

and auditory parts of the display resemble courtship feeding. In some cases, the male did caroling

and the female stopped her screaming and wingwaving; perhaps caroling tends to stop such displays. The female, however, is sometimes the bird

that carols during nibbling. To some extent the

mutual nibbling causes the male to go into a more

upright and hence more challenging pose; its effect

is to incite him to attack or face the other pair

more strongly than before. The process reminds

one of "inciting" in ducks.
NUMBER 144 25

FIGURE 9.—Social submissive behavior: A, both of a pair cringe together; B, young female and

mother nibble at each other when ousted by another pair; c, mother takes submissive pose

near her slightly aggressive grown son.

If the subordinate bird is attacked despite its

cringing, pleading, wing-waving, bunching, or nibbling, it usually gives a few screams or squawks

and hops away with head low. At times a strained

chirr emerges among the screams. Then it recovers

and starts chirping to itself or grunting at Bicolored

Antbirds or other competitors at some far corner

of the ant swarm. At times it chirrs at the distant

approach of the dominant competitor. Occasionally

a subordinate male or family goes off with faintsongs, then loud-songs, and either finds another ant

colony or returns to the same swarm later still

evasively or cringingly subordinate.

AGGRESSIVE DISPLAYS

Ocellated Antbirds completely lack aggressive

calls, except for an occasional chirr or chip, but

have a distinct silent display. It may be called

"challenging," although it is only moderately like

that display in Bicolored Antbirds (Willis, 1967:49).

The challenging Ocellated Antbird (Figure 10A)

B

FIGURE 10.—Aggressive behavior: A, challenging; B, wings spread in pecking attack of bird that

would not flee.
26 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

spreads the tail, stands high and upright with legs

splayed, and periodically points the bill down at

its chest (flexes the head toward the neck).

The toes are clamped on the perch; only insubordinate birds have the toes loose. The shoulders

may come out slightly (Figure 11B). The body is

spread, seemingly inflated rather than fluffed (Figure 1 IF). The throat feathers are ruffled, but this

shows mainly at lower intensities when the bill is

not strongly down. The face is bright blue, and

its size is maximum because the feathers of the

crown are sleeked back from it while the throat

feathers are ruffled away from it.

When in this upright pose, the bird periodically

lifts its bill to the horizontal with a jerky and

ratchetlike motion, and lowers it again. It also

turns its head from side to side. The whole display, especially these movements, probably shows

the blue faces and dark eyes as giant "eye-spots"

against the black bib. Meanwhile, the rusty nape

feathers part from the feathers of the neck to

give a hammerheaded appearance. The face and

hammerhead are displayed when the bird turns its

head from one side to the other, so that rusty, black,

and blue parts of the head are conspicuously displayed in challenging. The gray crown does not

seem to be used, except perhaps as a "facelike"

gray field separating the blue "eyespot" facial areas.

The black bib is outlined by rusty on the breast.

Black ocellations spot the rusty belly below this

(Figure 10A). The black tail is shiny and conspicuous and is another plumage character that is

mainly displayed in challenging. The scaled pattern on the back, however, does not seem to be

used in this or any other display and may be concealing coloration against the leaves of the forest

floor.

The tips of the wings are sometimes spread a

little (Figures 11A, B), but ordinarily the wings are

not fully spread for challenging. Once, however,

FICURE 11.-Behavior of dominant birds: A, alert staring at an opponent (low intensity challenging; B, challenging over the shoulder at an opponent (note that the facial disks become

giant eyespots); c, challenging at medium intensity, as female follows in bunching action; D,

pointing at opponent of another or the same species before a supplanting attack; E, challenging

from the front; F, low-intensity challenging (note expanded belly region).
NUMBER 144

two birds went for one prey and the two spread

their wings up, gaped, and the larger bird grabbed

the prey. Once, too, a dominant bird that failed

to supplant another did a wing-spread (Figure 10B)

as it then pecked the other off its perch.

Adult, settled males use challenging more often

than do females or young males. Females and

young males, when dominant, are more likely to

ruff the throat, spread the tail, and supplant the

opponent (Figure 11D). Challenging is best developed in confident, dominant birds; but the male of

a bunched subordinate family may be recruited to

challenge for a time by the nibbling and following

of his mate or young (Figure 8E). Occasionally

pairs challenge persistently and circle each other

warily for several minutes.

After challenging and following a subordinate

or insubordinate bird about for a few minutes, the

silent dominant bird is likely to fly at or over it

with an audible whirr of wings (normal flight is

silent) and a ferocious series of bill-snapping, thus

supplanting it. Usually the intruder squawks,

whines, wing-waves, and flees; or it flees with loudsongs. If it does not flee, the dominant bird pecks

at it from nearby and supplants it again. However, there were seldom the vigorous "gantlets" or

series of supplantings seen among excited Bicolored

An thirds.

Occasionally, in 9 of 1500 encounters (Table 7),

there was a brief screaming fight. This rate of

fights is about 0.6 percent, or 2.4 times the rate for

fights among Bicolored Antbirds (Willis, 1967:53).

Ocellated Antbirds, however, have fewer intraspecific supplanting attempts than do Bicolored Antbirds; indeed, Table 6 shows that Ocellated

Antbirds supplant or displace Bicolored Antbirds

more often than Ocellated Antbirds supplant each

other. Supplantings and fights are probably uncommon in Ocellated Antbirds because the welldeveloped system of submission usually keeps

competitive situations from escalating into violence.

Fights are generally short but vicious, involving

pecking and clawing but not much wing-beating.

Perhaps the wings are too weak to be very useful.

The defeated bird may scream loudly as it flees.

One fight ended with the two females glaring at

each other, heads sleeked but bodies and tails

spread.

Dominant birds, at least well-fed ones, sometimes

give in for a time to the wing-waving, pleading,

27

and pecks of subordinate birds; this also reduces the

incidence of fighting. The dominant bird gives a

deep chirr and sputtering faint-songs as it is badgered by the frantic subordinate, then hops away.

The next minute, however, it is likely to supplant

the subordinate and take the position it vacated.

It may also refuse to give in and may peck at the

bird screaming in its ear, sending it hopping away.

If the subordinate birds team up to oust a dominant one for a time, the dominant one may forage

away from them for some hours; it is then difficult

to say which bird is dominant. Later encounters

tend to be more definite, however, in that one bird

consistently challenges and chases the others about

even when they bunch or plead.

OTHER AGONISTIC BEHAVIOR

Toe-looking (Figure 7) is often used by feuding

Ocellated Antbirds; it is frequently associated with

low-intensity challenging, and like challenging involves "arching" the head (flexing it toward the

neck). Jerking the tail, bill-wiping, supplanting

nearby Bicolored Antbirds instead of the opponent

("redirection activity"?) are often part of agonistic

activity. A challenging bird loses its upright posture

when it forages, but a cringing or wing-waving bird

may flit the wings, flick the tail, bound about with

head low, and chitter or whine even as it forages

near the dominant bird. The subordinate may grunt

at Bicolored Antbirds, but its grunts are very

scratchy and quickly grade into whines if the dominant bird comes closer. Feuding Ocellated Antbirds

sometimes chirr, chip, and sing during a series of

chases or supplantings.

Many of these seem displacement activities, combinations of behavior patterns, or conflicting behavior patterns. Probably mixtures of any two

patterns described in this report are possible, and

in some other species such mixed patterns are important (Tinbergen, 1953). However, the mixed

patterns of Ocellated Antbirds are variable and

infrequent compared to the unmixed patterns.

Loud-singing (Figure I 2A) is sometimes related

to agonistic behavior. The dominant male at a

swarm loud-sings more loudly than other males at

the swarm when a distant bird loud-sings, and he

may look that way (Figure 12B), or go off to meet

the intruder. If I played recorded loud-songs, the
28 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

FIGURE 12.—Loud-singing male (left) gets a stare from a

distant male (right) over the ants.

dominant male quickly came up loud-singing and

circled me and the tape recorder. When two pairs

are rather equally matched and a "bunching" battle

with much challenging ends indecisively, one pair

may leave with loud-songs and the other pair loudsing back. The agonistic nature of loud-singing in

these circumstances is somewhat uncertain, however, for birds frightened from a swarm of ants by

the observer or departing it after the ants stop

raiding often loud-sing, too. Possibly the dominant

male may only be saying "come closer" when he

loud-sings. Loud-singing seems primarily an attracting call in Ocellated Antbirds, as is described

below. As Thielcke (1970:228) points out, only

the reproductively stimulatory function of song has

yet been proved; theories that songs ward off intruders need observational or experimental backing,

although muted Red-winged Blackbirds have been

shown to lose territories (Peek, 1971).

Reproductive Behavior

Ocellated Antbirds are monogamous and pair for

life. I have no records of divorces among definitely

mated birds, although a bird that loses its mate

usually gets another one within a year or two. One

young female did switch from one young male to

another, but I was not sure if she had been with

the first male long. Courtship involves three major

activities: loud-singing, courtship feeding, and

traveling with the mate.

LOUD-SINGING

A male that has lost his mate loud-sings (Figure

12A) repeatedly at the swarm of ants he is following or at a short distance from it. If the female

answers, his songs become faint-songs or serpentinesongs; but if the female has disappeared he continues loud-singing for several minutes at a time.

Such periods of loud-singing may occur at any time

of day, but are more frequent in the early morning

and late afternoon. Departure of a male from a

swarm of ants to loud-sing persistently is almost a

sure sign that the mate has disappeared; when she

is merely off incubating he loud-sings only to answer distant loud-songs. The male loud-sings near

presumed roosting areas, in the last light of evening, when he has lost his mate. Young males that

have never had a mate do not perform such loudsinging, so far as I have been able to determine.

Loud-singing brings in any other birds in the vicinity, and the male courts any female that appears.

COURTSHIP FEEDING AND COPULATION

As in many other antbirds, courtship feeding is

the main courtship activity of Ocellated Antbirds.

The male eats the legs off prey, chews the prey,

looks about as if thinking, faint-sings or wanders

with faint-songs (Figure 13B), and flies to the watching female. At times a lone male wanders with food,

as if hoping a female will appear. The lone male

may carol now and then as he carries food and

end loud-songs with serpentine-songs.

From an initially rather upright and overbearing

pose that may somewhat resemble challenging (the

tail is spread, the legs splayed, the body upright

and inflated, the stiff neck and throat ruffled, and

the bill down), the male that finds a female carols

and pokes the food down at her (Figure 14A). If

she takes the food he loses the upright pose and

becomes less puffed out, as was seen most clearly

once when the two tugged back and forth at an

insect for more than a second. She often crouches

or is in a low pose (but her body and tail may

be spread), her head low and extended on the neck

so her bill points up.

If he holds back with the food, she carols a bit

Perhaps caroling overcomes agonistic tendencies. If

he eats the food, she champs her beak, but usually

he swipes it past her beak again. At times they

seem to be fencing back and forth. She grabs the

food and hops away quickly; he stands upright a

moment, then champs or wipes his bill or not, and

returns to foraging.
NUMBER 144 29

B

FIGURE IS.—Courtship feeding: A, female screams at mate (right), which bobs the head ritually;

B, male faint-sings with food in bill; c, male feeds resting female; D, female takes low posture

as she eats the food; K, female pecks at male bill when he stays and bobs the head after a courtship feeding.

After repeated feedings, the female stays on her

perch, takes the food quickly (Figure 13c), and

champs her beak as the male departs. At this time,

there is little evidence of agonistic behavior and

little caroling; the transfer of food is quick and

simple. If the male stays near the female, she may

give faint chee or chee-chee chirps and peck at him

lightly (Figure 13E) as if still hungry; he usually

returns to foraging as soon as she starts chirping.

If he preens instead, she chirps now and then. At

times a series of caroling and chirping notes follows

a feeding as if the pair are talking to each other.

Rapid courtship feeding marks the early courtship process. One widower fed the mate of an incubating neighbor every minute or two with loud

caroling and overbearing poses. The cringing female avoided the widower, however, except to grab

his offerings of food. I have not directly observed

the formation of a pair bond, except for a young

female that met an eligible male a day at most before I found him feeding her busily (she had been

at a distant ant colony until two days before).

Probably the pair bond can be formed rapidly, for

thereafter this young female stayed with that male.
30 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

FIGURE 14.—Pre- and post-copulatory poses: A, courtship feeding with swiping the prey past the

female bill; B, post-copulatory aggressive sidling to female; c, post-copulatory pose, rather like

challenging.

During the subsequent months of the pair bond,

courtship feeding is irregular, usually less frequent.

Before each nesting, however, the male begins to

feed the female regularly. She preens and rests in

cover as much as 50 m behind the ants, and he

ferries all her food. When the ants move too far

ahead of her, he begins to serpentine-sing (Figure

15) as he returns to the ants after feeding her; often

she moves with him to a new patch of cover closer

to the ants.

After repeated feedings (Figure 14A) he tries to

hop onto her back as soon as she lowers her head

to eat the food. Usually she hops or flutters away,

FIGURE 15.—Male (left) serpentine-singing for female (right)

to bring her to new resting site closer to ants.

tail-jerks, and chirps back at him. One male pecked

at his mate when she did so, but fed her again

after getting the food she dropped as a result. Another male toe-looked when his female hopped

away. Finally, after many courtship feedings, the

female stays for copulation.

In copulation, the male flutters the wings as he

perches on the back of the female. His crown is

sleeked, his throat ruffed, and he is somewhat

puffed out as if aggressive. His bill is horizontal

and his tail is closed as he tries to push it down

on one or the other side of the female's tail. The

caroling notes often continue during copulation

and become low-pitched or hissing cheahh or

chwohh notes from one bird. The female slips out

from under after a second or two, or he flies off;

he stands puffed out, spread-tailed, and ruffthroated (Figure 14c) on her or another perch,

then preens briefly or returns to foraging. She carries off and eats his food, perhaps after ritually

ducking her head his way a few times (Figure 14B).

The male sometimes feeds the female so frequently that she refuses to take his food. He carols

as he swipes it past her bill several times, as if tantalizing her with the aroma. She may growl as she

turns her head away. At times she takes the food

and swipes it past his beak repeatedly; one bird
NUMBER 144 SI

carols each time. Often she is in a somewhat challenging pose (upright, with body and tail spread,

throat spread, and head somewhat arched on the

neck). He spreads his tail and sleeks his head as he

carols each time he tries to feed her; his posture

becomes more challenging. If she takes and drops

the food repeatedly, he flies down, picks it up, and

returns to feed her repeatedly. He may chew the

prey even more between attempts to feed her or

take it to the ground for dissection. Finally he eats

it himself or leaves her with it still in her or his

bill. She may drop it and look down lazily, or

gulp heroically. He probably eats any food he carries away, for he does not return from his foraging

for a long time.

If the male does not feed the female often, she

stretches and faint-sings, then moves to the ants and

forages near him. She may give brief chee or cb.ee

chee chirps, or carol briefly, as he dissects food or

carol or whine as she hops up to him. Often her

caroling is a simple chee chee chee, without a drop

in pitch. He may carol back, with a drop in pitch.

Often he lowers the head and bobs it (Figure 13A).

He resumes feeding her again. In the dry season, I

have seen a female gape and whine at her mate

repeatedly without his feeding her or giving way

to her. Although, I have seen courtship feeding at

every month of the year, there is less often feeding

and more often female begging in the dry season.

Male to male pair bonds develop and sometimes

persist for several years when no female is available. The two try to feed each other and often

pass food back and forth several times. Neither

accepts food the way a female would, which is

probably one reason that the appearance of a nubile female breaks up the fragile male-to-male bond.

There is much caroling, and many overbearing

poses, when two males pair. Often the other bird

is a son of the male involved, and the sporadic

feedings are probably possible because some sons

associate with fathers for several years. Occasionally such sons feed and attempt copulation with

their mothers.

TRAVELING WITH THE MATE

Pairs of Ocellated Antbirds stay together. They

preen or forage from the same perch less than the

width of a body apart at times. The tail of one

may rest on the body of the other. Foraging birds

hardly seem to notice each other even when they

are almost touching (Figure 4A). Once I saw two

bird: cling with their feet alternating on the perch.

Once a male nibbled the toe of a female above

him and she moved up.

When other birds are present, the pair may carol

or gape and nibble at each other's heads as if nervous. Often, too, they carol or chirp faintly (possibly

agonistic?) as they come close together. The female

sometimes has to whine and gape (plead) or wingflutter to her own mate, especially if he is fighting

with other Ocellateds. Occasionally he pecks back

gently. When they go for the same prey together,

the large male is likely to snap at the female and

end up with the prey; but then he may feed most

of it to the female. One male did steal food from

his female and she pecked at him; later he supplanted her. This was in the dry season, however,

and the pair were subordinate to another pair. In

the dry season, there is much whining and caroling

as the two come together, and they seem generally

slightly agonistic; but they still stay close together.

There are occasional supplantings, the female by

gaping and pleading at her mate (who may chirr)

and the male by simply supplanting her. When

mates challenge each other on meeting, usually one

nibbles toward the beak of the other, which nibbles

back and loses its challenging pose too.

When a pair of Ocellated Antbirds moves, the

two faint-sing back and forth. Faint-songs or serpentine-songs of the male often induce the female

to leave her patch of cover or desert the swarm

with him if a human comes near. Longer and

louder songs bring them together if they get out

of sight of each other for some reason. If the male

finds a good antswarm or branch of the swarm, he

often serpentine-sings repeatedly (Figure 15). The

female quickly follows. If the male hesitates because other Ocellateds dominant to him are at the

swarm, his mate may serpentine-sing and lead him

in to a side branch of ants. Once, when a male was

crippled, his mate loud-sang and led him in to the

ants by going back to him repeatedly. In traveling,

the male is more likely to be in the lead and to give

inflected faint-songs or fragmented serpentine-songs.

When the pair arrives at a tape recorder after playback of songs of Bicolored Antbirds, they chirp or

carol briefly to each other as they look about.

About the only time a pair separates is when one

bird is on the nest.
32 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

SEARCHING (FOR NEST SITES?)

Occasionally a timid pair of Ocellated Antbirds

wanders through the forest away from or near a

swarm of ants and behaves most peculiarly. The

male alights low on buttresses of trees, peers down

between them, and serpentine-sings on and on even

though no ants are there. The female flies up and

takes his place, then looks down at the space between the buttresses. Often one or both disappear

between the buttresses before moving on warily to

new buttresses. The female visits some buttresses

and serpentine-sings, too, attracting the male.

Once I was able to see what happened, for the

birds performed this activity at a swarm of ants.

Male XG serpentine-sang repeatedly on a buttress

of a small tree, flew 2 m toward his mate (MBRM),

then returned to the buttress and serpentine-sang

again. Then he hopped down onto the leaf litter

between two buttresses and stopped calling as his

mate flew 1.5 m away and looked at him. He sat

very low, his bill inward toward one buttress (Figure 16A) for nearly a minute. The female wandered off and he broke the pose; he returned to

foraging near her.

THE NEST

The nest of Ocellated Antbirds is not certainly

known. Neal G. Smith (pers. corara.) saw an Ocellated near a nest behind loose bark of a log on the

Navy Pipeline Road in 1964; the two eggs went to

Charles Sibley for egg-white protein analysis. The

nest site, however, sounds like that known (Y.

Oniki, pers. comm.) for Wing-banded Antbirds

(Myrmornis torquata), which occur regularly on

the Pipeline Road (Karr, 1971). Moreover, Skutch

(1946) warns that antbirds often seem to be curious

about nests that are not their own, so that only

continued watching could have determined what

species made this nest.

On 7 May 1961, I found a nest sunk in the

ground between buttresses of a tree of Quararibea

asterolepis on Barro Colorado Island, southwest of

Balboa 3. The nest was partly protected by lianas

across the buttresses and was a neat open cup of

slender strands. One heavily speckled egg, larger

than the egg of a Bicolored Antbird, was in the

nest. Unfortunately, I saw no bird go to the nest

(an antswarm with several Ocellated Antbirds was

near the nest when it was found), and the egg disappeared from the nest a day or two later. On 13

June 1967,1 found an empty nest in a similar place,

northeast of Balboa 5.6, while watching a pair of

Ocellateds searching for a nest site. The evidence

that these were indeed Ocellated nests must rest

on the facts that Ocellateds search for nest sites in

such places, and that no other bird on Barro Colorado has such a nest and an egg that size. The

FICURE 16.-Male (A) crouches in leaf litter between buttresses, probably searching for nest

site. Small figure below gives top view. Fledgling (B) about three weeks out of the nest waits

on tree buttress, a frequent hiding place.
NUMBER 144 33

nests of all other antbirds, ovenbirds, and woodcreepers on the island are known; no tanager or

treetop bird is likely to nest in such sites.

INCUBATION AND BROODING

It may seem presumptuous to talk about incubation and brooding when the nest is unknown, but

watching pairs of Ocellated Antbirds at swarms of

army ants shows that they are much like Bicolored

Antbirds in these respects. Male and female Ocellateds both have brood patches when nesting.

Since one or two young eventually arrive at

swarms of ants, we can presume that the clutch is

two as in most antbirds, possibly one at times. Incubation is marked by the disappearance of the

male for nearly all morning, as in Bicolored Antbirds. Presumably the female incubates all night

and he incubates all morning without feeding at

the swarm of ants. In one case, however, a male

briefly visited the ants before going to the nest about

8:00 AM. Between about 11:00 AM and 12:00 M,

loud-songs in the distance elicit loud-songs from

the female at the ant swarm. She flicks her tail,

looks about, flies his way, and returns with grunts

and loud-songs. The male sweeps in with a few

chirrs at the observer and much caroling as he

meets the female and she nibbles at him. Then he

moves in over the ants and forages rapidly, as if

famished. He preens quickly between rapid sallies

for prey. The female rests, watches him and prey,

and preens; but she does not forage much. The

pair are together at the swarm for an hour or two

about noon. The female departs with a few faintsongs. The male hardly looks her way. She arrives

again in late afternoon, and he disappears. The

afternoon periods are irregular in .length, and the

female sometimes leaves (probably for incubation)

well before dark. Thus, the male has at least two

incubation periods per day and the female at least

two (including the night period).

During early brooding, the visits of male and

female alternate, with the female foraging at the

ants early in the morning. Presumably she broods

all night, as do other female antbirds, and the male

takes over in the early morning. Both sexes probably brood young, as in most antbirds. Each parent

stays at the swarm of ants an hour or two at a

time, then dissects a large prey item, eats projecting legs, and faint-sings as it looks about with the

body or abdomen of the prey in the beak. It moves

off in a straight line, faint-singing and looking

around at each stop. It may stop and point the bill

upward to rechew the prey. The mate arrives from

that direction within half an hour, and forages

vigorously. Occasionally the mate loud-sings in that

direction and the foraging bird at the swarm answers, the mate moves in, there is a meeting with

loud caroling, and the pair forage together for a

time. As the young grow older they are brooded

less, for both parents are at the ant swarm much

of the time.

CARE OF THE FLEDGLINGS

Bob-tailed fledglings eventually appear near

swarms of ants. The small young hide on the

ground between buttresses of trees, and later low

in dense treefalls, and are difficult to flush. From

their labored but not weak flight, from the lengths

of their tails, and feathering of their bodies, and

comparison of these characters with young of known

age in other antbirds, I estimate that young Ocellateds are between two and three weeks old (age

since hatching) before they arrive at swarms. I do

not know whether they stay at the nest until this

age or, as is more likely, move out of the nest at

an age of about two weeks and are gradually moved

toward the ant colony. I have not found parents

and small young away from ants.

Parents ferry food to the hidden young much as

before fledging. The parent's faint-songs, looking

about, and movement directly toward the young

allow the observer to approach it. The parent then

chirrs violently, flies around, and the young freezes.

One may flush it accidentally, at which the parent

chirrs frantically. A few faint-songs or serpentine-songs, however, start the young one peeping

and moving toward the parent. If the observer is

nearby, the peeping of the young gets a loud chip

or chirr from the parent, at which the young

abruptly stops calling and freezes. Chased young

fly well, high into liana tangles or other cover, and

can be caught with mist nets but not by hand. The

young follows the parent to a distant tangle, and

waits there. I have not seen distraction displays.

The young peeps loudly before feedings and

squeaks as it is fed. It sits, even in the leaves of

the forest floor, and beats its wings downward. The

parent may carol faintly as it feeds the gaping,
34 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

flutter-winged fledgling. If it gapes too violently,

the parent turns the nape of the neck to it and resumes the feeding when it settles down. A chirr

in its face sometimes shuts it up if it peeps loudly

after the feeding.

As in Bicolored and Spotted Antbirds, if there

are two young, each parent takes one. Once when

a male was crippled, however, the female fed both

young birds. If there is only one, the male parent

usually helps or is helped by the female in feeding

the young, but he is likely to start feeding the female again. She passes his food on to the young

bird much of the time. At times a female with her

young bird is at a swarm of ants a kilometer or so

from the male with his young bird, but the family

soon rejoins. The family normally is together over

the ants.

GROWTH OF THE FLEDGLINGS

The smallest young seen had tails about 10-20

mm long, with vanes for 60 percent of that length.

The legs were bare except for a circlet of pinfeathers at the "heels," and the undersides of the wings

were bare back to the sheaths of the remiges. The

body was fairly well feathered, but the head was

rather bare. Black throat feathers and gray-tipped

blackish crown feathers were just coming out. The

face was dull and blackish, the gape angles and

gape apd tongue bright pale yellow. The base of

the lower mandible was pale. In the hand, the

young pecked and snapped, jerked the tail, struggled, and sometimes screamed.

By an estimated week out of the nest, the young

bird has a tail half the adult length. The grizzled

crown is sometimes fairly well feathered and sometimes bare anteriorly, and the young bird is nearly

adult weight. By two weeks out of the nest, the

tail is three-quarters the adult length. Some new

adult feathers are on the chest. The tail is full

length only at about three weeks out of the nest.

New gray feathers of the adult plumage are appearing at the front of the crown, but the change

to adult plumage is then very slow. Even at 12

weeks out of the nest the grizzled juvenal feathers

still cover the rear crown. The face is turning blue

by then, but it is still mottled with dusky and with

whitish areas. The gape angles are still pale, but

the bill is nearly completely dark.

By 18 weeks out of the nest there are often still

some dark or pale areas on the blue face, and the

gape angles are still pale, but the young bird is

gray-crowned and has nearly completed body molt

into adult plumage. The tail feathers are finishing

molt, and specimens in various museums show that

wing molt is also finishing as the last juvenal feathers disappear from the crown. The molt from

juvenal to adult plumage is thus complete, rather

than restricted to body feathers. By 21 weeks (five

months) out of the nest it is difficult to tell young

from adult. The process is thus much slower than

in Bicolored and Spotted Antbirds, which molt into

adult plumage in about five weeks after leaving the

nest (Willis, 1967, 1972a) but do not go through

wing or tail molt until the following year. Perhaps a dominant species can support an early wing

and tail molt and give the young a better chance

to survive the first year; survival of juveniles is better in Ocellateds than in the two other species

(Willis, MS).

The young Ocellated Antbirds start feeding

themselves as fast or faster than do young Spotted

and Bicolored Antbirds. Young Ocellated Antbirds

with tails half the adult length spend much time

over the ants when the birds are undisturbed by

competing Ocellated Antbirds or by predators. The

young peer at the ants or peck clumsily now and

then. By the time the young have tails three-quarters the adult length, they occasionally sally clumsily for their own prey. Sometimes they get only a

bit of leaf or a twig and chew it briefly before

dropping it. They tend to stand on the ground

and hop or whirl in the middle of the ants rather

than do neat sallies to the ants and back up, but

they definitely get some tiny prey items. By four

weeks out of the nest, even earlier than in Bicolored and Spotted Antbirds, the young Ocellateds

are getting much of their own food. Their parents

seldom feed them after this time. Perhaps their

simple foraging method and dominant status make

it possible for them to get much of their own

food at an early age, while the variety of methods

smaller and less dominant ant-following birds must

use makes for slower maturation or learning of

foraging techniques.

Young birds that are still being fed by their parents wait near them over the ants, gape and squeak

whaiaiaih at the parents periodically, and sometimes carol and flutter the wings at them. The
NUMBER 144 35

parents gape and extend the head at them, turn

the head away from the young each time it pleads,

or retreat and champ the bill before the importuning young. When one young is fed, the other

may come up and gape, turning the body back and

forth as it lowers the head and tail in a rather

submissive way. One young female dropped her

food but was too naive to pick it up; the mother

supplanted her with a vigorous snap! of the beak

but then flew down, picked up the food, and fed

the young female.

As noted earlier, parents commonly lure young

away from a human observer by serpentine-singing

or faint-singing, at least until the young are no

longer being fed. The parent chirrs at the observer. Later, the young often follow the songs one

parent is using for attracting the other. Young

come up and beg when the father feeds the mother,

and sometimes even beg from strange males on their

way to feed their mates.

Young Ocellated Antbirds loud-peep frequently,

and their peeping is beginning to change into faintsongs and loud-songs when they are four weeks out

of the nest. The notes are a series of quavering

peeps, however, when the parent is feeding the

young occasionally. Young chirr and chip infrequently, and these notes are rather weak and falsetto until they are three or four weeks out of the

nest. However, they crouch and hide readily at the

chirrs or chips of adults. Grunting notes at other

species are still falsetto at 4-12 weeks out of the

nest. Loud squeaking notes of feedings tend to

grade into whining and chittering as the parents

start to reject the young birds.

Older young, foraging for themselves, occasionally gape and flutter to the parent. More often,

however, they gape and nibble with the parent or

whine, chitter, or plead with it to keep a good

foraging site or bump the parent (even bodily!)

off its perch. At times the young bird chirps or

carols, chee chee. The older young hop about cringing or whining at times. Challenging is rare before

the young are foraging for themselves. After this,

young males sometimes gape and snap or challenge

at their mothers (Figure 9c), who are subordinate

to all males unless protected by their mates. Females usually tolerate their grown young, however,

except for gaping and nibbling. Possibly the wingfluttering and pleading of adult birds develop directly out of techniques used by young birds that

stay near their parents. The male parent often

supplants or even pounces on the young bird if it

gets in the way of his foraging, but the chirrs of the

female at the screeching of the young may stop his

attacks short.

CLAN FORMATION

Young Ocellated Antbirds continue to associate

with their parents after the parents are no longer

feeding them, and even after the young birds get

completely adult plumage. This leads to the formation of one of the most complex familial societies yet reported for any bird. These are far

more complex societies than those of Bicolored Antbirds, in which parents drive their young away as

they get adult plumage. In Ocellated Antbirds,

patrilineal "clans" develop around a successful pair,

forming families in which young males and the

mates they bring home are tolerated in and outside

of breeding seasons for several years, in assemblages

that can separate or come together as food supplies

dictate. Four such families were observed over several years on Barro Colorado: around males XR,

YX, XRYG, and YBXB (Figures 19-25).

The young female commonly stays with her parents for six to eight months, until the next breeding

season after her hatching. Then she mates outside

the clan (in the few cases known) and does not

associate further with her parents. She has been

wandering to swarms away from her parents occasionally since she was a few weeks old, but she

readily rejoins them, with a little chittering and

gaping at their heads to ward off occasional pecks,

until she gets a mate of her own. She then becomes

a member of his clan, unless he is a solitary male

that has not stayed with his clan. Her adopted

clan now tolerates her as a member of the loose

family; however, she often has to display submissively when other males of the clan are nearby,

in a way that her mate need not do. Also, she tends

to stay close to her mate and bunch with him if

other clan members become aggressive.

Young males occasionally wander off as solitary

males, but often associate with their parents periodically for a year or more. Some submissive

behavior is necessary, especially low-intensity chittering, cringing, gaping at the head of the adult

male, and whining. At times the young male dis-
36 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

places his subordinate mother; however, usually

the parents tolerate or ignore the young bird.

Brothers and sisters also tolerate each other, even

foraging a few cm apart. Sometimes they bob the

head and gape at each other, then one retreats.

Occasionally the adult male feeds a year-old young

male, probably mistaking it for a female. Occasionally the young male feeds new fledglings of his

parents, probably mistaking them for nubile females; however, his activity is altruistic in its results. Young born in different years tolerate each

other, but older ones bob the head (Figure 17) or

gape at young of the year in some encounters.

Wing-fluttering is not often used, and bunching is

done with the parents or siblings rather than

against them. In other words, one can get groups

of several birds bunching together against a neighboring clan. The bunching becomes unstable with

more birds, so that clans of grandparents, parents,

and several broods of young do not join closely.

Ocellated Antbirds are not very successful at nesting, and pairs that belong to a clan tend to wander

off from it, but occasionally one can see eight or so

birds of a clan at one good ant swarm. Typically

the largest part of a clan present on any one day

consists of two grandparents, one or two males of

the previous year or two with a bride or two, and

perhaps three young of the current year as offspring

of the grandparents and of one of the young pairs.

Other members of the clan may be at another ant

colony. The clans are often more inclusive than

one can see at any one swarm, for a few days later

there may appear another young male of the previous year and his family, while one or more of the

original group is at another ant colony for the time

being.

Eventually, apparently, such clans break down

into separate units as the "grandparents" isolate

themselves more and more from related grandparents or siblings. Probably most of the birds of

Barro Colorado Island are related to each other,

but even among the SO or so birds in my study

area there seemed to be three major clans and one

minor one. Probably, had I known the complete

genealogies of the various birds, some peculiar spatial organizations of pair home ranges (see below)

might have become more understandable. It seems

that as the birds age, however, they tend to isolate

themselves and to become the "grandparents" of

separate clans. Normal attrition, in a bird that has

a short life cycle (Willis, MS) and high predation

on nests, probably insures that the loose clans must

break apart as parents and siblings die off.

The development of these clans has not progressed to the degree of regularity one sees in family

flocks of various birds, such as the Australian Bell

Magpie, Gymnorhina tibicen (Carrick, 1963), or in

Anis, Crotophaga ani (Davis, 1942). Possibly the

group territories of these species evolved through

a stage like that in Ocellated Antbirds. The lability

of the clans of Ocellated Antbirds, however, makes

them in some senses more social than flocks that

keep together. Communication, particularly submissive behavior, is certainly more complex than in

flock-forming jays (Brown, 1963). An assemblage

in which the various members can split apart and

come back together again, such as this one, seems

to require greater individual recognition and social

FIGURE 17.-One-year-old uncle (left) of two young birds bobs (threatening?) at one of them,

which gapes and nibbles, while the other (right) wing-waves and tail-flicks as if expecting food

(or submissive?).
NUMBER 144 37

interaction than an assemblage in which the members are constantly together or accept any new

members. Brereton (1971) has noted a similar phenomenon in Australian parrots: birds of wet areas

are territorial, birds of dry areas flock, and birds of

intermediate habitats have intermediate spacing

systems but more complex vocalizations than do

birds of either extreme.

The clan of Ocellated Antbirds is a patrilineal

one, in which exogamy is created by importation

of females from outside the clan. Many mammals

(Red Deer, Cervus elaphus, Fraser Darling, 1937;

baboons, Papio anubis, DeVore and Hall, 1965)

have matrilineal clans, in which males move from

clan to clan and females stay with the clan of their

birth. Perhaps female movement is favored if the

pairs are to be monogamous, as in antbirds, while

male movement is favored if polygamy or promiscuity is possible.

The clans of Ocellated Antbirds are rather like

the loosely social clans in chimpanzees (LawickGoodall, 1968), which also unite and separate according to changes in food supply—fruiting trees

in the case of chimpanzees.

NEST SURVIVAL, RENESTING, AND BREEDING SEASONS

Even though no nest has been found, knowledge

of incubation routine shows that nest success is low

and that individual pairs renest repeatedly throughout the rainy season (April to December) on Barro

Colorado Island (Figure 18). We can estimate that

incubation probably takes about 16 days and the

nestling period 14 days, as in related antbirds; with

building, a complete nesting probably requires some

37-40 days. Young are fed for some four weeks

after they leave the nest, and then the parents nest

again. The young of the first brood still are with

the parents. Indeed, one young female accompanied her mother away from the swarm and came

back with the father, in a pair that were feeding

young in the nest. At times a pair will have two

broods of dark-faced young, as the pair that had

r/ XG

9 PXRP

0* BRGM

9 MBRM

(f XRYG

9 BGMG

0" YBXB

9 RXRY

0* XBGR

9 GXYR

<f YX

9 XY

0* XR

9 URGM

(f YRGX

9 -X

0* RBYX

9 XYRG

"i 1 1 1 ' 1 1 1 1 1 1 1 1 1 1 1 1 1

jllill N

["I"

II II I III II

ill - NO REPRODUCTIVE ACTIVITY

| - COURTSHIP FEEDING

A - COPULATION

^ - INCUBATE | - NESTLINGS

Q - FLEDGLING N - NEST UKELY

10 20 30 10 20 30 9 19 29 9 19 29 8 18 28 7 17 27 7 17 27 6 16

APRIL MAY JUNE JULY AUGUST SEPTEMBER OCTOBER NOVEMBER

FIGURE 18.—Nesting of nine pairs of Ocellated Antbirds on Barro Colorado in 1961. Fledged

young stay with parents during later nestings. Times of nests, not located, are estimated from

the behavior of birds at ant swarms.
38 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

young 2 days and about 12 weeks out of the nest

on 7 August 1965.

Young birds out of the nest are still being fed in

January in some years, so that nesting certainly extends into December. The earliest young seen were

ones about three weeks out of the nest on 2 June

1967. These young probably came from a nest in

which eggs were laid about 5 April. With the long

breeding season, it should be possible for pairs to

rear three or even four broods in one year. Specimens of young birds from eastern Panama and

western Colombia, where rains last all year, indicate nesting in January and February. In these

regions, nesting may go on all year.

The poor success of nesting, as in many birds of

tropical forests, means that few pairs actually raise

more than one or two broods per year. From the

nine pairs in Figure 18, 27 of 31 detected nestings,

or 87 percent, were unsuccessful; there must also

have been undetected nestings, such as ones in

which eggs were destroyed within a day or two of

laying. Willis (MS) estimates nest survival as 4.2

percent. (Detection of a nesting by watching parents away from the nest requires incubation at that

nest for one or more days.) Since the four successful nestings produced only one young each, and

the clutch size is likely to be two, only 4 eggs out

of 50-60, or 7-8 percent, produced fledglings. Since

none of these nests was visited by the observer, the

possibility that the observer causes the high nest

destruction often seen in tropical nests is eliminated; that is, nest destruction is not an artifact

of observation.

Spatial Behavior

SPATIAL DISTRIBUTION: TERRITORIALITY,

SUPERIMPOSED PAIRS, AND SUPERIMPOSED CLANS

As is the case for Bicolored Antbirds (Willis,

1967:93), two to four Ocellated Antbird pairs may

be found at the same swarm of ants even during

the months of breeding (Table 9). Coexistence once

was thought to indicate nonterritoriality, but in

Bicolored Antbirds coexisting pairs are still territorial (Willis, 1967:102). The pair on its own territory dominates others, which upon analysis turns

out to be the only relevant criterion for territoriality—a territory is a space in which one animal or

TABLE 9.—Records of pairs of Ocellated Antbirds

at swarms of Eciton burchelli on Barro Colorado

Island

Month

November 1960

December

January 1961

February

March

April

May

June

July

August

September

October

November

Total

Wandering

birds, no

pairs

ft i

-

-

10

8

2

2

-

_

-

-

-

9

-

SI

Number

1

6

6

1

14

17

19

22

23

34

18

37

29

30

256

of pairs

2

-

6

6

6

11

8

12

7

14

18

6

8

3

To?

of antbirds

3

-

3

9

1

_

8

10

_

4

15

-

2

-

52

4

-

-

1

-

-

3

_

-

-

-

-

-

4

group dominates others that become dominant elsewhere.

Ocellated Antbirds, at low densities, show much

the same type of territoriality as do Bicolored Antbirds. Figures 19 to 23 show maps of home ranges

of several such males and their mates over the

years. These ranges are much larger than in Bicolored Antbirds—about 1500 m across (area, 1.75

sq km) rather than 750 m across (area, 0.44 km2).

The ranges of Ocellated Antbirds overlap extensively. When one pair near the edge of its range

meets another pair well within its range, the latter

pair dominates. When the same two pairs meet

well within the range of the former pair, the former

pair dominates. There have been several cases of

these space-centered reversals of dominance, but not

as many cases as I recorded for Bicolored Antbirds.

Ocellated Antbird pairs tend to show flight or submissive behavior rather than attack and challenge,

and the "main" territorial pairs thus tend to avoid

each other. Moreover, the ranges and dominance

"cores" or territories within those ranges are so

large and diffuse that some main pairs never moved

far enough peripherally to be subordinate.

When one of the main pairs disappears, a neighboring pair may move into its region as if it had

earlier been prevented from doing so. Figure 21

shows that male MOPS and his mate moved into

the region of male XRYG and his mate after the
NUMBER 144 39

latter pair disappeared between 1968 and 1969.

The pair MOPS was moving from a region of low

density of Ocellated Antbirds to the "escarpment"

zone of higher density (see below), suggesting that

they got a better habitat by the move.

The main pair of a region is usually the pair

that comes up if one plays recorded loud-songs of

Ocellated Antbirds in the forest. The male does

not show signs of challenging, but he does loudsing vigorously and look about as he sweeps past

rapidly. The following female may echo his loudsongs. Then the pair moves away rapidly, unless

there is a swarm of ants. (If one plays loud-songs

of Bicolored Antbirds, by contrast, any pair of

Ocellated Antbirds in the area is likely to move

in without loud-singing, chirr at the observer, and

stand about as if waiting for ants.) Loud-singing is

not used regularly as a territorial call by Ocellated

Antbirds, although they respond to loud-songs.

More often, as noted earlier, the loud-songs are

signals between mates or are used when a pair is

scared away from ants or hunting a new colony of

ants. (Since the main pair of a vicinity respond

to wandering pairs by loud-singing, the latter often

Home Range of <?YBXB

and his mate

FICURE 19.-Sites where male YBXB and his mate (1960-1963, RXRY; 1964-1968, GOBW) were

seen at swarms of army arm. Location of a possible nest in 1961 is indicated by a triangle.
40

home on them. This might discourage use of loudsinging in territoriality, since neighbors would

move in and compete.)

So far the Ocellated Antbirds are not very different from Bicolored Antbirds. However, Ocellated Antbirds in areas of high densities have, in

addition to "main" pairs, what one can call "superimposed" pairs. The simplest class of superimposed pairs is that of a male young bird and his

mate, which often occupy the territory of the father

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

and mother as the nucleus of a clan. Figure 23

shows how young male RSWR stayed in the range

of his father and mother, XR and XGBR. He was

mated and had young in the area in 1964 and early

1965, as did his parents, thus forming a very large

clan. XR did not chase him, and indeed RSWR

helped XR in many disputes with neighboring pairs

and clans. In late 1965, XR had disappeared and

RSWR was mated with his mother, XGBR. The

next few years he had other mates.

\

> I • -'5 ?.'•'. • -T^ r ' X 54 y5 |4

 6

,

^*^-I 3 a ^ V 7 4 *46

T

\

Home Range of b*XR/G

and his mafe

1961-1968=1-8

FIGURE 2O.-Sites where male XRYG and his mate (1961-1963, BGMG; 1964-1965, PWBM;

1968, ZYOS) were at swarms of ants.
NUMBER 144 41

More often the superimposed young pairs of a

clan fight a little with the father of the clan, but

not as strongly as they fight with outsiders. When

the young male loses his mate, he sometimes rejoins

his parents as a threesome (see the section, "A Day

at a Swarm of Ants"). Eventually he gets another

mate and wanders more and more apart from his

parents. Perhaps this leads to the second class of

superimposed pairs, which are rarely dominant

pairs that wander over the areas of main pairs or

between the cores of home ranges of main pairs.

Figures 24 and 25 show two such pairs, which

tended to wander in slightly different areas from

surrounding pairs but which can scarcely be said

to have had separate dominance or territorial centers of their own. Male XBGR and mate unfortunately disappeared in late 1961; they seemed to

dominate over other pairs in the canyon areas between Wheeler 20 and Balboa 10 and may have had

a territorial center there; if so, however, they had

to forage out of their territory much of the time in

1960-1961. Male YX and his mate, however, definitely centered almost on the same ranges as males

XBGR and XR (Figure 25). Male YX tended to

dominate XBGR when both were far southwest or

northwest, but dominated male XR only on a few

brief occasions when both were in a zone approximately 200 m southwest of Drayton 5.

The situation became more rather than less complex after XBGR disappeared, for YX in 1961 had

a son (SS) which by 1963 got a mate and joined

his parents to form a superimposed clanl Half the

area of this superimposed clan was the northeastern

half of the area of the clan based on XR and his

many descendants, and half was the southeastern

half of the home range of the developing clan of

YBXB and his descendants. The result was that,

from 1960 to 1967 or 1968, there was a high-density

9 9

Range of (fMOPS

1965-1971 = 5-1

 5

300

FICUBE 21.-Sites where male MOPS and his mate (1965-1969, SUSP) were at swarms of ants.
42 SMITHSONIAN CONTRIBUTIONS TO ZOOLOG

Home Range of

and his mate

1960-1969=0-9

FICURE 22.-Sites where male XG and his mate (1961, PXRP; 1963-1968, MBRM) were at

swarms of ants.
NUMBER 144 43

zone for Ocellated Antbirds along the escarpment

from about 400 m west of Drayton 10 to the area

southeast of Wheeler 10. In this zone, there were

clearly main pairs plus superimposed pairs, and

some of both groups formed loose clans.

Superimposed pairs rarely occur in Bicolored

Antbirds, except when a young pair has no territory during the first dry season they are together.

In that species, each young "superimposed" pair

manages to carve out a dominance area, perhaps a

small one, by the first nesting season. In Ocellated

Antbirds, however, locally high densities of nesting

pairs were permitted by having pairs with little

dominance (or dominance only over other superimposed pairs or over peripherally wandering main

pairs) managing to coexist with pairs of normal

(locally supreme) dominance.

ROLE OF FEMALES IN CLANS AND TERRITORIES.—

Female Ocellated Antbirds, as has been noted, are

smaller than males. Females play little part in territorial or agonistic encounters and are subordinate

even to trespassing males unless their mates are

there to bunch with. Females, especially ones whose

mates are incubating, must cringe and whine and

wing-wave to stay at a swarm of ants if males not

of their clans are present.

A female dominates other females present if she

is near her own area, or if her mate has established

dominance over the mates of the other females.

A subordinate female often can, of course, rush for

the protection of her own mate or sidle cautiously

near her son if a dominant female or male presses

her.

The females usually stay near their mates or

older sons, if these are present, and as a result

have more or less the status of their mates or older

sons. Young females are usually with their parents

and take more or less the status of their parents.

Other birds supplant very young females right under the noses of their parents at times, but then

Home Range of oX

and his mofe / /

f

/

3

Home Range of o'RSWR

and his mote // » Mi--

100 200 300 400500

meter!

FIGURE 2S.-Left, sites where male XR and his mate (1961, URGM; 1962-1965, XBGR) were

at swarms of ants. Right, sites where male RSWR (the son of XR and XGBR, in 1962) and

his mate (1963, RUOB; 1964-1965, GPMO; September 1965, XGBR; 1966-1967. SPYD; 1968,

OWYS) were at swarms of ants.
44

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

\

Home Range of d* XBGR

and 9GXYR

1960-1961=0-1

0 300 J I

METERS

FIGURE 24.—Sites where male XBGR and female GXYR were at swarms of army ants until both

disappeared, late in 1961. Note that this area overlaps that for males XR, YBXB, XG, and YX.
NUMBER 144 45

flee as the parent attacks. Later the young females mation thus helps protect both young and old femay dominate the other birds, as long as the par- males from competing antbirds, even when the

ents of the young females are not far away. Older female has to cringe to her son. Possibly this helps

young females, in adult plumage but still with female survival, which is much poorer than male

their parents, often dominate neighboring females

when the neighboring males are away. Clan forsurvival (see legends for Figures 19-25).

Home Range of 6 YX

FIGURE 25.—Sites where male YX and female XY were at swarms of army ants until 1966. The

area is almost the same as that for male XBGR, and overlaps that for males XR, RSWR,

YBXB, XB, and several males not mapped herein.
46 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

SPATIAL DISTRIBUTION: ESCARPMENT ZONES

VERSUS FLAT AREAS

On Barro Colorado, Ocellated Antbirds concentrated over the years and formed clans mainly in

regions of hilly terrain and toward the center of

the island. The successful clans developed mainly

in the escarpment region near the top of the island,

in a zone Woodring (1958) shows as hard and

slope-forming Bohio conglomerate. The flat top of

the island, a basalt cap, has occasional pairs from

the nearby escarpment zones but is not really good

for Ocellated Antbirds. The flat Barbour Peninsula, which additionally is low woodland rather

than tall forest, seems not to have the species.

When ant colonies move that way or onto the

peninsulas of Gigante Bay, the following Ocellated

Antbirds soon return to colonies closer to the center of the island. Low woodland as such, however,

is occupied if it occurs on varied terrain: the areas

along Wheeler, Balboa, and Lathrop Trails on

Barro Colorado Island; numerous areas on the Rio

Agua Salud and the Navy Pipeline Road.

It so happens that most of the escarpment regions

are toward the center of the island, so it is difficult

to know if Ocellated Antbirds avoid peripheral

zones and peninsulas or avoid flat areas. A slight

tendency to avoid the flat basaltic cap at the center

of the island and occasional following in steep

zones right down to Wheeler Estero or to the laboratory clearing, however, suggest that the birds are

not avoiding the edges of the island as much as

they avoid terrain of low relief.

I am not sure if relief as such is important, except perhaps in providing a variety of habitats.

Perhaps landslides and tree-fall zones along gullies,

rapid release of minerals by erosion, and other

aspects make an area of moderate relief more productive than a flat one (except a river floodplain,

where deposits of eroded materials and periodic

floods should also do so?). It seems to be a commonplace observation in tropical America that bird

species diversities are higher in foothill zones than

on the tropical plains. Ant-following birds reach

their highest diversities in foothill zones, both in

Panama and in the Colombian-Peruvian foothills

of the Andes.

Even on small Barro Colorado Island there was

a diversity gradient in professional ant followers

between the escarpment zones and the flats. On

the flats were mostly four generalized species—

Plain-brown Woodcreepers, Spotted Antbirds,

Bicolored Antbirds, and Gray-headed Tanagers—

which also occurred (some in reduced numbers)

in escarpment zones. On the escarpment, two large

and dominant species—Ocellated Antbirds and

Barred Woodcreepers—were added. In escarpment

zones elsewhere in the Canal Zone, one adds also a

very large species—Black-crowned A«tpitta—and

possibly three or four other species—Ruddy Woodcreepers, Rufous-vented Ground-Cuckoos, Barecrowned Antbirds, Immaculate Antbirds. The

actual distributions of the last four species, however, require closer study.

The northern escarpment zones on Barro Colorado are mostly off my study area, but occasional

visits to this zone suggest that only along Pearson

Trail and southwest to the start of Standley Trail

has there been a fairly high density of Ocellated

Antbirds at times. The area never seems to have

had as high a density of Ocellateds as the southern

escarpment zone.

POPULATION DENSITIES.—Since there is a variable

distribution of Ocellated Antbirds along the escarpment zones on Barro Colorado Island, it is difficult

to calculate home ranges and population densities

in any meaningful way. In the main study area,

which included much of the flat basaltic cap of

the island, the centers of home ranges of main

pairs in 1961 were about 500 m apart. This would

give about 250 hectares per main pair. Including

birds of the previous year but not young of the

year, there were in August of 1961 some 18 birds

on the study area, or 7 per square kilometer. This

is about 0.35 g per hectare, less than the 3 g per

hectare of Bicolored Antbirds or the 7 g per hectare of Spotted Antbirds. In addition, Ocellated

Antbirds are almost absent in the many flat areas

off my study area, so that the total population on

Barro Colorado Island in August, 1961, was probably only 45 birds (3 per square kilometer, or 0.15

g per hectare). By 1971 the population had decreased to 5 males and 1 female (Willis, MS), all

in the escarpment zones; the species seems on its

way to extinction on Barro Colorado Island.

DETAILED SPATIAL RELATIONSHIPS—

A DAY AT A SWARM OF ANTS

The "macrospatial" relationships of geographic
NUMBER 144 47

range, of habitat and niche, and of territoriality

are reflected in but give only a frame for the picture of detailed relationships of distribution over

swarms of ants, antagonistic or other interactions

there, and of individual distances and the roles of

males, females, and young birds competing with

each other and with other species. Perhaps a description of part of a day at a swarm of ants will

give a better picture of how the Ocellated Antbirds manage the complex spatial relationships of

their lives:

The day is 23 August 1963, and a large nomadic

colony of army ants is moving northward up the

escarpment in tall forest just west of Drayton 4,

an area so much in the center of Ocellated activity

that I thought of it as "Ocellated Alley." It is a

blue-and-white morning, with cumulus sailing

through polygons of blue sky in the green ceiling

of the canopy. It is still cool, but sunbeams probe

downward from the polygons, for I am arriving

late (8:56 AM) after an unsuccessful search for a

lost colony of ants far to the northwest.

Loud stick! alarm calls of a Plain-brown Woodcreeper mix with stet and chip alarms of a Grayheaded Tanager pair, then chirrs and chip-ip! of

an Ocellated Antbird. The cause of the alarm is

an agile little Semiplumbeous Hawk, bright white

bel6w, which flies from near the ants with a lizard

(Ameiva leptophrys) in its talons.

Tame Bicolored Antbirds and Spotted Antbirds

move out of my way with musical notes as I approach the ants, but the Ocellateds are still in a

panic of chipping and tail-jerking. They hide well

behind practically no ground vegetation except big

trunks. The Ocellateds and other birds are long

since used to me, for they scarcely chirred as I

approached. A few weeks before my approach

would have brought a storm of remonstrative chirring, but I have been following this colony for

several weeks now.

As some seven Bicolored Antbirds move back in

over the ants, a few of the Ocellateds present appear as if by magic. Male XR, the venerable boss

of the clan, jerks his tail a little over the ants as

his son of 1962, RSWR, faint-sings and wanders at

the left end of the raid. Earlier this summer

RSWR briefly had a mate, but she moved over

to another male; he will not have another mate

until next summer, when his first offspring will

make this a three-generation clan. His mother,

XGBR the mate of XR, is now near him at the

left end. There are several other birds in the clan,

probably other 1962 offspring of XR and XGBR,

but most of them have not been around for several

days. They must have found another colony of

ants in the wide home range of the clan . The baby

female of the clan, GOBW, is present but not evident at the moment; perhaps she is hiding in a

tangle nearby. The daughter of XR and XGBR,

she is now fed by them and by the amorous RSWR,

who occasionally feeds his mother as well. However, GOBW will next year become the mate of

YBXB, in the home range to the northeast, and

over the next four years help him develop his clan;

she will not associate with her parental clan again.

The Bicolored Antbirds occupy my attention for

a long time, for the pair to the north is gradually

becoming dominant over the pair to the south as

the ants move north on two forks (Willis, 1967:98).

I am only vaguely aware of the quietly foraging

Ocellateds, mainly because they take the other fork

of the swarm and force all the Bicoloreds to my

fork and into disputes with each other.

Here comes female Ocellated XY, her head low

and her whole posture humble, faint-singing. Her

mate, YX, must be incubating this morning. Probably the clan of XR has chased her from the other

fork of the swarm, for XY and her mate are subordinate. Three weeks ago, when the ant colony

was statary off to the southwest, there were a few

hours when it looked as if YX were dominant. He

took silent and upright challenging poses, and XR

and RSWR both moved out of the way humbly.

The son of YX and his daughter-in-law were present then, for YX is the head of a superimposed

clan. However, YX's glory did not last long; perhaps he was only dominant briefly because XR and

his clan had been away the preceding few days.

The son and daughter-in-law of YX were having

troubles; the son challenged but his mate was

bunching up to and nibbling at him, as they faced

but gradually retreated before even the young

members of the other clan. This forced them next

to YX, who was none too friendly; his son had to

cringe and whine a little, and even so moved out

of YX's way. RSWR came up and supplanted YX's

son, who moved near YX again; RSWR challenged

a little and moved off. Fifteen minutes later RSWR
48 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

was back, supplanting YX's daughter-in-law. Then

XR joined RSWR in challenges to YX and his

cringing son. YX's challenging was weak, and he

faced XR rather than pointing the beak at him;

XR supplanted him. YX could not even displace

his own son a minute later; his son gaped, almost

swallowing his head, and YX chirred in annoyance

before flying off. A rain started YX and his mate

to wandering, loud-singing, as the other clan took

the few active sites of the ants. YX and XY took

a left fork of the swarm, supplanting the female of

yet another pair (10 Ocellateds were present in

all). The next day YX was dominant again, but

XR and RSWR took over again late in the day.

The following day YX's son and daughter-in-law

disappeared, and have not been around since.

Probably they are at another ant colony, for in

1964 the mateless son will turn up with YX and

his mate, and the three will clash with XR's clan

much as they are doing this year.

For the last several days, YX and XY have been

subordinate. YX can supplant most of the young

males of the other clan, except RSWR when backed

up by XR. The young males of the other clan,

other than RSWR, however, deserted this colony

a week or two ago. YX can supplant the female

and young female of the other clan, and XY can

supplant the young female, but this seldom helps

much because the opposing females immediately

bunch together with the males of their clan. So,

today, XY moves near me and supplants a Bi

colored Antbird, taking the center of this fork of

the swarm. Other Bicolors quickly spiral in, however, and female XY has to grunt frantically and

point her beak repeatedly to keep the barbarian

horde out of her foraging zone. Perhaps hearing

the sounds, in comes male RSWR and supplants

her with a ferocious whirr of wings and snapping

of the beak. She slinks off, in a very low cringing

posture. XR and the baby female GOBW arrive.

The baby is peeping persistently as she follows her

father. He supplants XY again, and then feeds his

own mate despite the frantic begging of the baby.

RSWR feeds his mother. The four birds of the

clan take a circle 2 m in diameter over the ants,

and female XY wanders peripherally. RSWR displaces her once, but she mostly stays more than

2 m from the active clan. XR ignores her, as he

usually does. Is she perhaps a daughter of his? I

banded her, him, and YX together in one net

nearly three years ago. But perhaps they have just

seen each other often over the years.

The Ocellateds of the clan grunt at a brave male

Spotted Antbird that briefly infiltrates their ranks,

snaps up a small insect, and flees. All ignore an

agouti wandering through. The alarm notes of a

Black-chested Puffbird cause crouching and keening among the circling ring of Bicolored Antbirds,

and a Rufous Motmot over the assemblage freezes

bolt upright. There are occasional sounds of the

large Barred Woodcreepers high near the Puffbird;

the only two pairs of Barreds on Barro Colorado

are feeding at this swarm today, but are working

high probes of ants rather than coming low and

ousting the Ocellateds and Bicolors as they sometimes do. The Gray-headed Tanagers are not challenging the five Ocellateds and seven Bicolors

either, and like the two Plain-brown Woodcreepers

are staying high. By the end of observations at

2:23 PM, I will have seen 29 birds of 9 species at

this swarm, including a Slaty Antshrike briefly

present. The Puffbird continues alarm notes. Is

the Semiplumbeous Hawk back? With faint-songs,

one of the Ocellateds lures the baby female into a

thicket off left. I have not seen her fed today, but

she is at the stage when she is still fed most of her

food.

It is 10:00 AM, and male XR preens over the

ants even as he grunts at the circling and bickering

Bicolors. He flies over and feeds his mate, caroling

briefly, then returns to the ants. She preens. They

are probably getting ready to nest again. The Tanagers give up and leave; perhaps there are too

many Bicolors and Ocellateds near the ground,

and too few ant probes up trees. A Plain-brown

Woodcreeper works the left fork, but its stiek!

calls on my approach cause keening among the

Bicolors and chipping from the Ocellateds, which

vanish into cover. I watch Bicolor disputes for 30

minutes. When a band of white-faced monkeys on

the ground ahead races up into the trees, an Ocellated chirrs loudly. It is sitting, resting, but jerks

its tail upward. I watch a dispute between the

Barred Woodcreepers overhead. The Tanagers left

too early, for Plain-brown and Barred Woodcreepers are at an active ant probe up a tree trunk now.

The Barreds supplant Plain-browns now and then

as the battle moves back and forth. Rains inter-
NUMBER 144 49

rupt observations for an hour. I watch Bicolors

after a stiek! outburst of Plain-browns sends the

Ocellated clan to a thicket ahead, where four birds

a meter apart panic in concert—tails are jerking

up, stuttering chips and occasional chirrs burst out,

and birds turn their heads sharply.

At 12:00 M here is male Ocellated YX with his

mate. Rains interfere with my observations, but

he seems to be foraging as busily as he can to

make up for a morning of no food. His female

disappears soon, probably to the nest. He supplants several Bicolors, seeming to head for them

right away as if he knows a Bicolor will be in the

best available position for foraging. He is at the

right fork of the ant swarm, alone except for fighting Barreds and Bicolors. I check the left fork

before I leave and find the other Ocellated group

there. The female is resting in a vine tangle ahead

of the ants as her son and husband work. The

baby female is not visible. There is no sign of

birds when I return at 5:30 PM to check the ant colony, but everybody except male YX is present the

next morning at 8:20.

It was not an unusually exciting day for Ocellateds over the ants; in fact, most of my notes for

the day had to do with the fights among Bicolors

and Barreds. There were only five Ocellateds present much of the time, and only two pairs. However, several kinds of spatial distribution can be

seen from the account: the main clan ousting the

lone female of a superimposed clan; the later separation of the lone female and her mate at another

fork of the ants; the aggressive role of the young

male of the clan, and his probably sexual feeding

of his mother and of his baby sister; the slowing of

feeding after about 10:00 AM for members of the

dominant clan, etc. It is a complex society, but

knowledge of individual life histories explains

many of the spatial arrangements one sees at a

given ant colony.

Discussion

The life of the dominant antbirds at swarms of

army ants on Barro Colorado Island is plainly not

simple, but neither is it a bed of thorns. Ocellated

ability to supplant most small antbirds keeps them

out of competition, even if they are a constant

nuisance—especially the abundant and persistent

Bicolored Antbirds. Most large birds, such as motmots, Squirrel Cuckoos, and Barred Woodcreepers,

are not suited for foraging on vertical perches near

the ground like an antbird and are only sporadically troublesome to Ocellated Antbirds. As noted

earlier (Willis, 1972a), the Ocellated Antbirds are

usually able to take the front, low, and central

zones where ants flush most prey and relegate Bicolored and Spotted Antbirds to concentric or

peripheral zones. In the central zone, Ocellateds

forage mostly in one simple way (sallying to the

ground) that requires little maturation or practice—young birds soon forage for themselves.

The problems for foraging Ocellated Antbirds

seem to come with intraspecific interactions and

with other environmental restrictions. While there

were a few pairs of Ocellateds in many parts of

Barro Colorado, the birds concentrate mainly over

the largest ant raids in the central escarpment

zone—"Ocellated Alley." In this region, there were

not only pairs or clans, but superimposed pairs

and clans. As many as 10 or 12 birds were at some

swarms of ants, and three pairs were commonly

represented at a good ant colony even though four

pairs rarely coexisted. Such concentrations have

been noted rather often elsewhere in Panama and

Colombia and probably have the same social organization.

At such swarms, intraspecific dominance hierarchies come into effect and seem to force out lowranking birds—both in clans and outside clans.

These low-ranking birds then must move to distant

colonies, probably at some personal risk both from

waiting predators and of loss of time and food.

When a swarm varies in flushing power from day

to day, the low-ranking birds probably have to

move away from and to it repeatedly.

Probably the complicated social structure and

submissive behavior of Ocellated Antbirds allow

them to avoid some of the risks when subordinate

birds have to move while yet insuring that they

do move if a given swarm gets too crowded. The

clan formation clearly could act as "kin selection,"

in the sense of Hamilton (1963), by favoring the

offspring of a dominant pair. Instead of young

being tossed out of the parental sphere to fend for

themselves, they are tolerated for years (a bit

churlishly if competition is rough). Young males

stay with the parents and sometimes are waiting

to take over that area when the old male dies.
50 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

They are far higher in the local hierarchy than

they would be outside the protective influence of

their fathers; even when he is subordinate they

can stay near him and yell in his ear if he gets

churlish. Of course, they often drop out and go

to another swarm if the local competition gets

really strong. In a few cases, the young males actually feed young birds of later broods.

Young females stay with their parents much of

the time and are thus protected for several months

after they begin to forage for themselves, rather

than being at the bottom of peck orders for these

months as in Bicolored and Spotted Antbirds. Survivorship of young female Ocellateds is higher

(about 60 percent) than for young female Spotteds

and Bicolors (40-45 percent—Willis, MS). The

time between a young female's leaving her parents

and her finding a suitable mate to protect her may

be very short—a few days in the one case observed.

In 1961, there was not the surplus of unmated

male Ocellateds there has been in subsequent years;

one female (XGBR) that lost her mate actually

waited until January, 1962, to get a new one after

the disappearance of his female. However, even

under such circumstances a young female could

probably stay with her parents for long periods.

She could wander out periodically to check for

males or to listen for the persistent loud-singing of

one that had lost his mate.

Ocellated Antbirds have a complex submissive

behavior and a simple aggressive one; Bicolored

Antbirds tend the other way but have much aggression. Spotted Antbirds have practically no submissive behavior and have well developed and

distinctive aggressive displays that they seldom

need to use, for they drive out most intruders.

Since Spotted Antbirds are less adapted to ant

following and close meeting of individual birds

than are Bicolored Antbirds, and the latter less

well adapted to following and social life than Ocellated Antbirds, it is possible that this is an evolutionary sequence. The sequence starts with

territorial birds that have aggressive behavior well

developed; the aggression increases spectacularly as

birds crowd together over ants; but more crowded

birds replace aggression with submissive hierarchies. In other words, increased crowding beyond

a point leads not to increased aggression but to the

increased submission seen in Ocellated Antbirds.

Southwick (1970:5) notes similar increases and

then decreases in aggression with mice and rats

under increasing crowding; but in mice and rats

the very overcrowded animals seem to become

passive rather than react with increased submissive behavior. Perhaps passivity is not desirable

for Ocellated Antbirds, which still have dominance

hierarchies and a fair amount of aggressive behavior. Unlike fed rodents in cages, the Ocellateds

must still forage for their own food near domineering other individuals.

Another way to describe the change is in terms

of "overpopulation," which increases in the sequence from Spotted to Bicolored to Ocellated

Antbirds. It may seem odd to talk about overpopulation for a bird that is so rare in tropical

forests as the Ocellated Antbird; but it may tend

toward overpopulation in concentrating over an

extremely limited food resource. The evolutionary

result of overpopulation and high interaction rates

of competing individuals over army ants is at first

increased aggression, as in Bicolored Antbirds.

Later, the agonistic interactions decrease or become

submissive ones. The possible evolutionary sequence, and even more the experimental one in

rats and mice, suggest that overpopulated humans

could go this way too: territorial, then highly aggressive, and finally submissive or passive to their

local dictators or "main pairs." This might be

especially likely where there are space limitations,

as over army ants. Other types of social organizations, such as herds or flocks, seem not to develop

such systems; or perhaps such organizations are the

stage beyond the Ocellated stage.

The great development of submissive behavior

in Ocellated Antbirds, and the slight development

of aggressive behavior, probably facilitates clan formation as well as aggregation of unrelated birds.

As a member of a dominant species, dependent on

rich front and center places at ant swarms, the

dominant individual Ocellated Antbird probably

does not need very much intraspecific aggression to

keep the small place it needs, at the center. However, the center is a small area, and the subordinate bird that stays nearby must confront the

dominant one quite closely. In these circumstances, submissive behavior would be quite valuable—hence its hypertrophy. The hypertrophy

would especially favor related animals, ones that
NUMBER 144 51

stay close to the dominant individual. The kin

selection made possible by this is actually an advantage to the dominant individual, since his relatives are more likely to succeed.

Submissive behavior is also useful to female

Ocellated Antbirds. They are smaller than males

and never win direct contests. By bunching up

with their sons or mates or parents, they can avoid

extreme defeat. If no protecting bird is around,

they can whine and be submissive and stay until

the mate arrives from his tour of duty on the nest.

Females, in contrast to young males, seldom deserted a swarm due to competition unless their

mates or clans also did so.

It is difficult to know why female Ocellated Antbirds should be smaller and less dominant than

males, unless this keeps them out of disputes or

helps population control in the way suggested by

Wynne-Edwards (1962). Female survival is poorer

than male survival (Willis, MS). Perhaps the low

status of females in peck orders insures that any

excess females without mates will tend to die off

rapidly and not use up food supplies. It may be

better in a monogamous species to have a small

surplus of males rather than of females, for a female that is not breeding is gaining only a little

foraging experience while a male that is not breeding may be gaining status as well. Perhaps, however, the small female is better when the male has

to feed her, using up less food. It may also be

that the females use slightly smaller food than do

males; but males and females often went for the

same prey, and bill lengths seem similar. Could

the male recognize the female by her small size,

as Jehl (1970) suggested for sandpipers? In the

declining populations of 1966 to 1971, males sometimes fed other males as if they did not recognize

sex; recognition of sex seemed to be based on the

fact that females accept food readily as adults,

while males do so only as young birds. Male-male

feedings were confused, for the fed male tried to

give the food back.

The overlapping of home ranges in Ocellated

Antbirds, and the presence of superimposed pairs

and clans, is an overpopulation problem that goes

beyond kin selection and clan formation. It seems

that it was better for pairs of Ocellateds to stay

in the escarpment zone on Barro Colorado, even

though this meant they often had to compete with

dominant pairs or clans not closely related to them.

(Of course, all the 45 or fewer Ocellateds on Barro

Colorado must have had many genes in common.)

They did this rather than move onto flat areas

like Barbour Point, where students and I saw many

ant swarms but never saw Ocellated Antbirds.

Given that a pair needs a wide foraging area to be

certain of having a swarm of ants to follow each

day, this makes it necessary to have superimposed

pairs or else a system of dominance like that in

Bicolored Antbirds (Willis, 1967:110) in order to

get more than a few pairs of Ocellateds in the small

escarpment zone on Barro Colorado. The dominance system of Bicolored Antbirds requires a great

expenditure of aggressive energy, which may be

too difficult when a territory would have to be four

times as large as that of Bicolored Antbirds. Thus,

given a habitat restriction and the need for a very

large foraging range, it uses much less energy to

be subordinate more or less everywhere (i.e., be a

superimposed pair) rather than try to keep up a

dominance area that may not have any ants on it

much of the time.

The basic question then becomes, why are Ocellated Antbirds restricted to escarpment zones when

the ants go all over Barro Colorado Island? MacArthur, Recher, and Cody (1966) speculated that

restriction of birds to certain patches in seemingly

homogeneous habitat, or rather the subdividing of

a habitat into suitable patches on the basis of very

small differences, is likely to be common in the

species-rich tropical avifaunas; however, many antbirds do not show this pattern. Neither Bicolored

nor Spotted Antbirds show this pattern to any great

extent, except for some avoidance of precipitous

slopes in the canyon west of Balboa Trail. Ocellated Antbirds, however, do show this pattern.

They are almost as tied to certain areas on Barro

Colorado as are motmots (Electron platyrinchum

and Baryphthengus ruficapillus), which nest only

in steep-sided gullies and hence are mostly in regions of gullies.

Are Ocellated Antbirds restricted by their nest

sites? Since the nest has not been definitely di*

covered, there is a slight possibility that they may

nest deep within motmot burrows or in fallen logs

across gullies. However, I have never seen a mudstained Ocellated, nor seen them show any interest

in old logs. The two likely nests, and the pattern
52 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

of nest-searching, suggest that they nest between

tree buttresses where lianas cross to give some protection. These sites are most common in areas of

moderate slopes, since buttresses tend to protect

trees against windthrow where the soil is shallow

or wet (as by springs, which emerge on slopes) and

where trees are exposed to the wind. Cativoespav£ forests (Prioria copaifera—Anacardium excelsum), such as the flats near Armour 10 and the

flats near Wheeler 25, have few buttressed trees and

seldom attract Ocellated Antbirds. Moreover, trees

do not often fall in these areas and bring down

lianas across the bases of other trees; the forest has

a tall and virgin aspect compared to the rather

sloppy and undisciplined look of forests in Ocellated Alley.

There are certainly some buttressed trees and

liana crossings, however, even in flat areas of Barro

Colorado Island. Moreover, small numbers of

Ocellated Antbirds do use most such areas. I have

noted the "undisciplined look" of forests in Ocellated Alley. These zones on Barro Colorado are

very diverse, with patches of windthrown trees, of

old forests and young, of rotting logs, of diverse

slopes and rapid erosion, of springs and seepages,

and a wide variety of other microhabitats one does

not find in the rather monotonous flat zones. Is

the very diversity of such zones, or some other

factor, leading to greater food supplies or cover for

Ocellateds in these zones?

At the moment, I can only suggest some differences that may be important to foraging Ocellated

Antbirds between the regions where they are common and the regions where they are not. The zones

where they are uncommon tend to be peninsular,

peripheral, flat, and young forest; these forests

have a strong dry season, abrupt leaf fall, and little

leaf litter in the rainy season; diese forests have

few fallen trees and hence relatively open undergrowth; and these forests may have less light and

release of soil nutrients than do slope forests.

Peninsulas should impede the free movement of

army ant raids, which tend to reflect back and forth

within a small peninsula and to repeatedly rework

areas already passed over. I followed one ant colony for several months in the peninsulas of Gigante

Bay, and found Ocellated Antbirds at the colony

only at the start of its odyssey there. Although a

pair of Ocellateds worked the base of the peninsula on Lathrop Trail and others worked the base

of the Barbour Peninsula, we never found Ocellateds far out these peninsulas.

Simpson (1964) pointed out the "peninsula effect" for faunas of mammals, and it is well known

for birds. This is the lowering of numbers of land

species breeding in such areas as Florida, and is a

subset related to the "island effect" of isolating a

fauna or flora on an island—the smaller the island,

the fewer the species that survive there (Preston,

1962). A peninsula or island is somewhat or completely isolated, and hence gets new animals of

some species too slowly to keep up with total losses,

especially if there are periodic habitat changes that

prevent the animals from surviving on the peninsula or island indefinitely. Florida thus lacks tropical birds that it would have if it were connected

to Central America, for periodic cold waves or effects of glaciation have eliminated many tropical

species with little or slow replacement. Some introduced tropical species, such as Red-whiskered

Bulbuls (Pycnonotus jocosus), Blue-gray Tanagers

(Thraupis episcopus), and Spotted-breasted Orioles

(Icterus pectoralis), are doing well and increasing

the diversity.

In the context of Barro Colorado, the impeding

of movement of army ants and the possibility that

very long periods may be without ants—followed

by periods of overworking when colonies do happen to enter the peninsula—may represent a

"peninsula effect" like that of south Florida.

Spotted Antbirds are on the peninsulas, but can

forage away from army ants for long periods if

necessary (Willis, 1972a). Bicolored Antbirds are

also on the peninsulas occasionally (Willis, 1967),

but have smaller foraging ranges than do Ocellated

Antbirds and presumably can survive on smallei

ant colonies or on ones that flush little food.

Ocellated Antbirds, however, live on the rather

narrow Bohio Peninsula near Barro Colorado.

Moreover, the eastern part of Barro Colorado, out

to Barbour Point, forms a huge peninsula that is

wide enough to support several pairs of Ocellated

Antbirds. That it does not suggests that there are

other things wrong with the peripheral areas on

Barro Colorado than simple impediments to ant

movement. Peripherality as such does not seem

likely to cause problems, except perhaps for lakebreeding mosquitoes and for the fact that isolated
NUMBER 144 53

points on Barro Colorado are swept by the drying

northeast trade winds in the dry season.

Mosquitoes carried fowl pox and avian malaria

to Hawaiian birds, virtually eliminating them in

the lowlands and leaving them only in the uplands

(Warner, 1968). The mosquito Anopheles albimanus has become a real pest along the borders of

the lake on Barro Colorado in the years 1965-1971,

probably because the lake since 1964 has been stabilized rather than low in the dry season, which

has permitted an explosive growth of the water

weeds (Hydrella species) in which the mosquito

breeds. The decrease in Ocellated Antbirds has

mainly come in the 1965 to 1971 period. The loss

has been characterized by high losses of females,

which incubate long periods at night and afternoon rains, and probably do so between tree buttresses. I have found A. albimanus unusually

common in such sites during rains and even at

other times. These events, however, may be coincidental. Ocellated Antbirds have not shown signs

of bird pox, except for occasional loss of the tips

of toes, nor have I seen any listless as if malariainfected or arbovirus-infected. They should have

defenses against these diseases and against mosquitoes, probably including sleeping with the head in

the fluffed back feathers as do other antbirds. Antbirds are probably not like the Hawaiian birds,

which had never encountered mosquitoes before

Culex pipiens fatigans was introduced in 1826, and

hence had no behavioral or immunological defenses. Moreover, Ocellated Antbirds occur just

across Gatun Lake on the Rio Agua Salud, where

there should be many Anopheles albimanus (there

certainly are plenty at nearby Frijoles). Thus,

mosquitoes and diseases along the lake shore seem

possible but unproved as reasons for the tendency

of Ocellateds to favor upland zones on Barro Colorado Island.

The effect of the trade winds seems a possible

reason for the seeming tendency of Ocellateds to

concentrate on the south side of the island's hills,

particularly in the sheltered upper parts of southfacing ravines from Shannon Trail across Drayton

Trail. Although some birds were in the corresponding north-facing escarpment over the years, it was

never an Ocellated Alley like the southeast side of

the hill. The trade winds strike isolated points,

such as the tips of Barbour Point, the tops of

ridges, and northeast slopes of the island, with

more vigor than one would suppose on reading

how little wind there supposedly is in the tropical

forest undergrowth. The most obvious effect is to

dry out and crack the soil and leaves of the leaf

litter, but there are probably effects on tree types

and deciduousness as well. Such periodically dry

zones perhaps produce fewer prey items for the ants

and birds than do more protected zones. Sunlight

and occasional wind would have the same effects

on nearly all shores of the island, but especially

on the northeast side.

The trade winds may also eliminate trees that

are not resistant to being blown over, and thus

eliminate one source of diversity in tree species and

in undergrowth patchiness. Periodically, windstorms come up from the southeast and topple

trees right and left on that side of the island. On

1 October 1961 a storm did so and created many

treefall tangles that are just now growing up. Dennis Knight (pers. comm.) talked to an old resident

of Barro Colorado who says that many of the

trees of Barbour Point were leveled in a windstorm

about 1919. Certainly Barbour Point is rather low

forest today, and this may be one reason that Ocellated Antbirds do not occur there.

Ocellateds, however, seem to do well in equally

low forest on Balboa Trail and across Shannon

Trail. It seems doubtful that Ocellated Antbirds

are restricted to tall forest. Much of the eastern

half of the island is low forest and much of the

western is tall forest (Bennett, 1963); but Ocellated

Alley cuts almost perpendicularly across the boundary between tall and low forest. In the Pipeline

Road Reservation, Ocellateds do well in low forest

as well as high.

Low forest, however, may exacerbate problems of

trade winds and dry seasons. I sampled leaf litter

for insects from February to November, 1961, and

found that areas of low forest tend to drop their

leaves rapidly in the dry season, have a spectacular

bloom of leaf-litter feeders as soon as the rainy season moistens the dry litter, then be rather barefloored much of the rest of the rainy reason

(Willis, MS). Taller forests, especially on protected

southern slopes, tend to drop their leaves more

evenly through the year and to have arthropods

more evenly throughout the year. Low forests are

certainly "lighter forests" (Eisenmann, 1952) much
54 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

of the dry season, for they tend to lose more leaves

and to be hot, dry, and light underneath. Unfortunately, I did not check leaf-litter insects in low

forests on the side of Barro Colorado away from

the trade winds to see whether such forests have

less periodicity in leaf fall than do the exposed

low forests I did check.

Low forest, especially in trade-wind zones, has

other characteristics that may disturb Ocellated

Antbirds. (Low forest on Barro Colorado Island

is 50 to 100 years old and is 20-30 m in height, I

hasten to add.) This forest tends to be very open

underneath, with new fallen trees or tangles around

former fallen trees. There is little cover, and Ocellated Antbirds seem very nervous when working

in such areas. There is little ground cover from

small seedlings or saplings, and only large patches

of wild pineapples (Ananas magdalenae) where

there is impeded drainage. Areas of impeded drainage and seeps occur, naturally, farther up toward

escarpments in the areas where local landslides

and windthrow also cause clutter in the undergrowth. Flat areas tend not to have this clutter.

The clutter, besides providing cover for Ocellated

Antbirds, may provide their prey with more food.

So, the Ocellateds may have several reasons to

avoid a flat, windswept, low-forested peninsula like

Barbour Point.

Among other possible reasons for Ocellated Alley, drainage and soil and erosion may play a part.

Flat areas tend to get sheets of water during extended rainstorms, and such sheets may carry off

the leaf litter or drown some arthropods in it. The

army ants are also interrupted or drowned. The

sheet erosion probably carries off soil nutrients,

too. Areas of greater slope tend to have crossing

roots, buttresses, logs, and other clutter that keep

the particulate matter back while allowing the

water to run off quickly in natural gullies. Perhaps

the impeded runoff and spring-emergent erosion

one gets on slopes also releases nutrients to plants

more quickly than in flat areas, resulting in greater

productivity. (Flat areas along rivers are almost

lacking on Barro Colorado; it is just a hilltop. The

eroded materials go to fill up Gatun Lake only.)

One also has to keep in mind that the steeper

slopes on Barro Colorado are mostly Bohio conglomerate, while the flat basaltic cap and the flat

peninsula of Barbour Point have different and

perhaps better weathering and mineral characteristics. However, Ocellated Antbirds do not seem

to do well in Bohio conglomerate on the lowforested, hilly, and narrow peninsulas of the northeast and windy side of the island.

In conclusion, likely reasons for high abundance

of Ocellated Antbirds in the southeast escarpment

zone on Barro Colorado are the absence there of

drying effects of northeast trade winds on the leaf

litter, the moderate clutter of the undergrowth in

a steep and rarely windswept zone, and perhaps

greater productivity of plants, leaf litter arthropods, and army ant colonies in a complex but not

peninsular or isolated region. Mosquitoes from

the lake may keep Ocellateds from peripheral areas,

too.

That Ocellated Antbirds, dominant birds at the

swarms, are so much more restricted to the "best"

zones on Barro Colorado than are birds low on

the interspecific peck order over ants, like Bicolored

and Spotted Antbirds, is perhaps not surprising.

Ocellateds are specialists, which because of their

dominance never have to forage away from the central and best zones over army ants or forage in

many different ways. They are not generalists and

probably cannot take even a moderate deviation

from optimum foraging conditions. Bicolored and

Spotted Antbirds can use optimum foraging conditions, but most use less optimum conditions

whenever Ocellated Antbirds are present. Bicolored and Spotted antbirds are probably able to use

zones in which not another species but an unfavorable environment creates the suboptimum

conditions.

Moreover, Ocellated Antbirds are large birds

that require more food per unit time than do small

birds, much as large Zebras (Equus hemionus) on

the African plains (Bell, 1971) require more

abundant foods than do small Thompson's Gazelles

(Gazella thomsoni). Probably the Ocellateds must

stay in zones where the ants flush food consistently

rapidly, while Bicolors and Spotteds can persist

even when ants flush little food. Size, while it gives

dominance, probably forces animals like Zebras

and Ocellated Antbirds to occur in low densities or

stay in zones where food is very abundant. If there

is indeed more food in Ocellated Alley, it would

support large birds, and this would explain why

the largest ant followers on Barro Colorado—
NUMBER 144 55

Barred Woodcreepers and Ocellated Antbirds—

persisted on the alley into the 1960s. The

disappearance of large species of ant-following

birds during the 1960s and before (in the case of

Rufous-vented Ground-Cuckoos) suggests that

either the food supply of the escarpment is no

longer sufficient or that predation is too severe

(Willis, MS). In either case, dominance and specialization clearly carry risks as well as advantages,

for the large and dominant ant-following birds

have been the first to disappear.

Dominance over other species and the moderate

demands of an environment that fluctuates considerably seem possible reasons why Ocellated Antbirds have developed a social system like that of

chimpanzees. Dominant species can group without

attracting dominant competitors. If they are occasionally in an environment that makes grouping

valuable, such as a group of fruiting trees for

chimpanzees or a good ant colony for the antbirds,

they will develop grouping tendencies. If, however, the environment forces the animals apart at

other times, they will form loose or facultative

groups. Mexican Jays (Brown, 1963) probably can

form regular groups because the environment never

gets bad enough to force birds off their territories,

even though groups are necessary so that a large

enough area can be occupied to include suitable

winter as well as summer habitats. If the environmental fluctuations are slightly greater than for

Mexican Jays, the Ocellated or chimpanzee social

structure preserves some kin advantage while permitting grouping. If even greater animal movement is needed, in a more fluctuating environment,

it becomes valuable to separate up or to join huge

herds, as in Hamadryas baboons (Crook, 1970) or

budgerigars (Brereton, 1971). Such anonymous

flocks (Lorenz, 1963) are social in terms of numbers but lack rich communication and internal

structure. Thus, an occasionally rich environment

seems to lead to the mixture of kinship groupings

and isolated movement in chimpanzees and Ocellated Antbirds.

Ocellated Antbirds resemble chimpanzees in

having a highly developed system of calls and displays, with an emphasis on submissive behavior.

It may be that the complex communication developed in a loose clan system was a starting point

for human language. Anthropologists have until

recently assumed that humans developed mainly as

group-territorial animals like baboons. However,

baboons (DeVore and Hall, 1965) and gorillas

(Schaller, 1963), seem relatively uncommunicative

in their groups; one wonders why language would

develop in such a system. Struhsaker's (1967) list

of the number of calls for various primates suggests that forest and savannah species, mostly

grouping or territorial species, have fewer calls

than do the less tightly knit groups of the forest

edge (chimpanzees, vervets, Macaco fuscata); opencountry species have especially few calls. Brereton

(1971) reports similar trends for Australian parrots. It may be that the grouping species have

more mimicry or graded calls, and hence have a

more complex communicatory system than their

low number of discrete calls would suggest. However, graded calls occur among the clan-forming

species as well; the songs and the submissive calls

of Ocellated Antbirds are examples of graded calls.

If human language arose from graded calls (Marler, 1965), more study of open-country animals is

needed to see if their vocal repertoires include

more graded calls and more complex ones than are

found in such animals as chimpanzees. Since humans probably started hunting in forest-edge situations rather than in direct competition with the

hyenas, lions, and hunting dogs of open country,

a chimpanzee-like social structure seems more likely

than a troop structure; the lack of vocal communication of open-living groups is another argument

in favor of clans. Possibly human language arose

as submissive or socially facilitory calls, rather than

as aggressive calls or play calls as had been suggested by earlier primatological work.

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