Much ado about bonobos: Ten years of management and research at

Planckendael Wild Animal Park, Belgium Jeroen Stevens

1,2, Hilde Vervaecke

1,2, Ward Melens

3, Marleen Huyghe

3, Peter De

Ridder1 & Linda Van Elsacker

1,2,3

1University of Antwerp, Universiteitsplein 26, B-2610 Wilrijk, Belgium

2Centre for Research and Conservation, Royal Zoological Society of Antwerp, K.

Astridplein 26, B-2018 Antwerp Belgium 3Planckendael Wild Animal Park, Royal Zoological Society of Antwerp,

Mechelsesteenweg 26, B 2812 Muizen-Mechelen

Abstract This paper consists of two parts. In the first, we review the history of the bonobo

group at Planckendael since 1993, describing group history, enclosure design and the

different research topics of past and present. The second part consists of a case study

of the utilisation of the outdoor enclosure throughout the past ten years. In 1993 only

a few bonobos ventured outside. In 1997 all animals spent more than 50 percent of

their time outdoors and this trend had stabilised by 2001. Interestingly the spread of

participation indices decreased between 1997 and 2001, showing that the bonobos

used the island more equally in 2001. Finally we compiled a list of 80 plant species

that could be found on the island in 1997, and found evidence that bonobos ate at least

16 of these species. We show that applied ethology also has been part of our

objectives and this will be more so in the future.

Introduction

The Bonobo Project at Planckendael Wild Animal Park (Belgium) of the Royal

Zoological Society of Antwerp (RZSA) started in 1992. Its original aim was the

fundamental study of the species in the zoo and in the wild, combined with in- and ex-

situ conservation efforts. For this purpose, a new bonobo housing facility was

designed, and in 1993 an adjacent outdoor island was completed. A special

publication about the founding of the colony (‘Bonobo Tidings’, 1993) was edited in

which some preliminary findings and some first events were described. In the current

paper, we elaborate on what happened in the colony in the ten years that followed. We

focus on group history, management and research programmes and show, by means of

a case study on enclosure utilisation how the latter two have interacted.

Group History The Royal Zoological Society of Antwerp has kept bonobos in its collection since the

1940s. They were kept in pairs or small groups until 1986, when a first attempt was

made to create a single group (Beyens, 1987). Due to construction works on the

Antwerp ape house, this group was then split up temporarily in 1987 again. The

breeding pair, Desmond and Dzeeta, was moved to Planckendael Wild Animal Park

and was reunited with the two females Hermien and Hortense in 1989 (Hol & Van

Elsacker, 1990). This resulted in both Hermien and Hortense each giving birth to a

son in 1990. Since both females had no experience with rearing offspring, a

successful training program was set up to stimulate maternal behaviour (Van Elsacker

& Struyf, 1990). Despite the original

success, Hermien’s son Riddle died at 18-months in 1991. The remaining five

bonobos were moved to the newly built enclosure in 1992 and were joined by three

young males Joey, Kidogo and Ludwig (Van Elsacker, 1997). At this point the whole

original group that had been formed in 1986 was reunited. The addition of Joey

proved to be difficult however, and it was decided not to integrate him in the group.

The two other males integrated well.

In 1993 the first birth occurred in this group, when Hermien gave birth to a daughter

Unga (Van Elsacker et al., 1993). Four more births followed in 1994, 1998 and 2003.

No infants were hand-reared. The mothers were not separated at the time of birth and

all these bonobos were born in the presence of all group-members, including several

adult males. See Table 1.

Table 1. Overview of group membership between 1989 and 2003

Name Sex Year of Birth

(estimate)

In Group

since Removal/Death

Desmond Male (1970) 11/12/1987 11/02/2000 (Death)

Kidogo Male 28/02/1983 04/03/1992

Dzeeta Female (1971) 11/12/1987 17/10/2002 (Death)

→ Joey Male 13/12/1982 04/03/1992 07/08/1992 (to Antwerp)

→ Ludwig Male 26/08/1984 04/03/1992 20/05/1999 (to Frankfurt)

Hermien Female (1978) 06/06/1989

→ Riddle Male 08/04/1990 08/04/1990 12/10/1991 (Death)

→ Unga Female 02/02/1993 02/02/1993 11/09/2001 (to Columbus)

→ Zomi Female 28/01/1998 29/01/1998

Hortense Female (1978) 06/06/1989

→ Redy Male 24/11/1990 24/11/1990

→ Vifijo Male 23/07/1994 23/07/1994

→ Zamba Male 16/04/1998 16/04/1998

→ E… Male 27/04/2003 27/04/2003 27/06/2003

Kosana Female (1980) 21/06/1999 11/09/2001 (to Milwaukee)

Djanoa Female 27/03/1995 01/09/2002

Apart from births, the group demography has known a few deaths and some

migrations. Since the start of the project, four animals have died. Hermien’s first-born

infant, Riddle, died at 18 months of age due to vitamin D deficiency. Since then,

artificial UV radiation is routinely provided to all newborns on days when they cannot

go out. In 1999 Desmond, the oldest male, died at 29 years of age and in 2002 Dzeeta,

the long time alpha female, died at 31 years of age. Very recently, in 2003, the last

born infant of Hortense died too, of yet unknown cause.

Apart from births and deaths a number of migrations have taken place. All of these

transfers were part of the international breeding programme for bonobos, co-ordinated

by Antwerp Zoo and Milwaukee Zoo. Studies in the field have shown that females

migrate at adolescence while sons remain within their natal group throughout life

(Kano, 1992). As a consequence, in the wild, females are less related to each other

than males are (Hashimoto et al., 1996; Gerloff et al., 1999), although some male

bonobos do transfer occasionally too (Hohmann, 2001). SSP and EEP members have

agreed to mimic these natural migration patterns and in captivity, females are

transferred at adolescence. Males normally remain in their birth group and are

transferred only exceptionally. For example, in 1999, it was decided to remove the

adult male Ludwig from the Planckendael group. He had been hand-reared and

seemingly did not recognize Dzeeta as his mother. Copulations between the two were

observed and to prevent inbreeding, Ludwig was moved to Frankfurt Zoo. Later that

same year an adult female, Kosana arrived from Leipzig Zoo. She was introduced to

all animals within one day. No problems occurred during this process, despite

Kosana’s limited experience with adult female bonobos. As far as is known, she had

spent the major part of her life with only one up to a few males. In September 2001

Kosana and the adolescent Unga, daughter of Hermien, moved to the USA. In

September 2002 Djanoa, a young female from Berlin Zoo, arrived. Once again the

introduction was completed within one day and no problems occurred.

The Enclosure The enclosure consists of a main hall, five smaller off-exhibit cages and an outdoor

island (For details see Van Elsacker et al., 1993). The bonobos are housed together

for most of the day and night. The group always has access to the 600m³ hall and no

animal is separated from the others, except in case of serious illness. In the morning,

this hall is cleaned and the bonobos are temporarily kept off exhibit in five cages.

After each bonobo has received an individual portion of food (milk and fruit), the

group returns to the hall where the rest of their meal (a variety of fruit and vegetables)

has been spread out. In the late afternoon the bonobos are called back in the cages

again, where each of them receives an individual portion of food, before they all

return to the main hall where again the rest of their food is spread out. When

temperatures are too low for the bonobos to go on the outdoor island, they receive an

extra ‘snack’ (mostly nuts, sliced vegetables and fruit or browse) at noon.

The bonobos are given access to the 3000m² island, as soon as temperatures rise

above 12°C,. The group always has the choice to remain inside and is never locked

out.

The island is surrounded by a moat that consists of several parts (see Van Elsacker et

al. 1993). First there is a shallow area, then a steeper slope, fenced by electric wire

and finally a deep ditch. Bonobos have a reputation for not being afraid of water and

it had been suggested that keeping them on an island would be impossible (de Waal,

1989). In Planckendael, the bonobos do not shun the water yet sometimes play in it or

wade in it. The major reason for them to enter the moat is to obtain food, thrown to

them by visitors (which is discouraged) or to collect vegetation growing there

naturally (see below). Most often they enter the moat bipedally and enter the water up

to waist-level. There have been no incidents of drowning, in contrast to chimpanzees,

where drowning was reported

occasionally in similar exhibits (Angus, 1971; Adang et al., 1984). No attempts to

escape by jumping across the moat have been made either. The electric fence seems to

be an adequate extra barrier that keeps the bonobos from entering too deep or from

trying to cross the moat.

In 1993, before the bonobos could go out on the island, they were given experience

with an electric fence in a temporary outdoor cage (see Van Elsacker et al., 1993).

The electric fence was marked with brightly coloured ribbons. If the apes touch the

wire, they experience a mild electric shock and learn to avoid it. When the apes went

on the island for the first time, the same brightly coloured ribbons were attached to all

wires around the island, to indicate the presence of electric fences to the apes. This

procedure has been repeated each time a new bonobo entered the group.

During the first years after the island was opened, vegetation was settling and electric

fencing were used to protect most plants too. The next summer the fences were

removed and bonobos had access to most plants on the island. A large weeping

willow and a maple tree were accessible to the bonobos too. The old weeping willow

has died and fell down in 1998. The maple tree has had to be protected again with

electric wire since 1999, as the bonobos stripped the bark and the tree was damaged.

Research

Research on bonobo behaviour was one of the prerogatives when the building was

designed. Therefore a special observation area was constructed from which the apes

can be observed in both the inside and outside enclosures. The research team consists

of zoo staff and students, from different universities in Belgium as well as from

several other countries, such as Japan, Austria and Germany. The different research

topics that have been or are currently under study can be roughly divided in four

categories. First, there is an interest in cognition, such as social learning, laterality,

mirror recognition and tool-use (Walraven et al., 1993; Walraven et al., 1995; de

Vleeschouwer et al., 1995; Takeshita & Walraven, 1996). Second, mother infant

relations are being studied (De Lathouwers et al., 2000). Third, social relationships

have been studied extensively (Vervaecke, 1999; Vervaecke et al., 2000a, 2000b,

2000c) often using a multidisciplinary approach in which data on behaviour are

combined with endocrinological data (Heistermann et al., 1996; Vervaecke et al.,

1993; Vervaecke et al., 1999; Shimizu et al., 2003; Sannen et al., 2003). Finally the

species’ locomotion is being studied (Aerts et al., 2000; D’Aout et al., 2001; D’aout

et al., 2002).

Case Study of Applied Research and Management: Utilisation of the Island

Methodology

When the bonobos were given access to the island in 1993, only a few of them

ventured out. It was therefore decided to start a long-term follow up study of how the

bonobos utilised the island. Here we present some results of this study. Data were

collected during three summer seasons, at four-year intervals: April – October 1993,

September 1997 and April - July 2001. In 1993, when the island was first opened, we

only scored whether bonobos were inside the hall or out on the island by using

instantaneous scan sampling

(Altmann, 1974). In 1997 and 2001 this was repeated, but now the specific location of

each individual was noted as well. For this purpose, a grid of 70 squares of

approximately 6,5 metre by 6,5 metre each was superimposed on the island map (see

Figure 1). This allowed us to evaluate utilisation of the island by means of a Spread of

Participation Index (Dickens, 1955). This index has been used to evaluate utilisation

of captive habitats in various species (Hedeen, 1983; Sheperdson et al., 1993;

Traylor-Holzen & Fritz, 1985). The index ranges from 0 to 1. The maximum value of

1 indicates individuals make minimum use of the enclosure, spending all time in one

quadrant. When the index approaches 0, the individuals utilise the full range of the

island, using all quadrants equally.

Figure 1. A map of the island with superimposed grid

Indoors versus outdoors

Figure 2 shows the proportion of time the bonobos spent on the island for 1993 versus

1997 and for 1997 versus 2001. In 1993 most bonobos spent most of their time in the

inside enclosure. Only the oldest female Dzeeta, and Kidogo, a sub-adult male, spent

up to 60% of their time outdoors. All the others initially preferred the inside enclosure

and spent for more than 50% of their time inside. There was a significant increase for

the whole group in 1997 compared to 1993 (Wilcoxon matched pair test: n=7, z=

2,20, p<0.05). This is mainly due to Hermien, Hortense and Desmond, and to a lesser

extent to Redy and Ludwig. There was little or no increase for Dzeeta and Kidogo.

Interestingly, by 2001 this trend had stabilised. Although there is a slight decrease for

Hermien and her daughter Unga, there was no significant difference between 1997

and 2001 (Wilcoxon matched pair test: n=7, z=1,18; p>0,05).

Figure 2. Percentage of time spent outdoors in 1993, 1997 and 2001

% o f t i m e s p e n t o u t d o o r s 1 9 9 3 v e r s u s

1 9 9 7

0 , 0 0

2 0 , 0 0

4 0 , 0 0

6 0 , 0 0

8 0 , 0 0

1 0 0 , 0 0

Dze

eta

He

rmie

n

Hort

ense

De

sm

ond

Kid

ogo

Lu

dw

ig

Red

y

i n d i v i d u a l s

% o

f ti

me s

pen

t o

utd

oo

rs

1 9 9 3

1 9 9 7

% of time spent outdoors in 1997 versus 2001

0

20

40

60

80

100

Dzeeta

Herm

ien

Hort

ense

Unga

Kid

ogo

Redy

Vifijo

individuals

% o

f ti

me

sp

en

t

ou

tdo

ors

1997

2001

SPI indices

Figure 3 shows the SPI indices for individual bonobos in 1997 compared with 2001.

In 1997 the SPI indices ranged from 0.64 to 0.78, indicating that the bonobos

systematically used only a small part of the island. By 2001 however, the SPI had

dropped significantly (Wilcoxon matched pair test: n=7, z=2.37, p<0.05) and ranged

between 0,27 and 0,42. This may be partially due to growing independence of

immature individuals Vifijo and Unga, but is also very remarkable for the adults.

Even Kidogo and Dzeeta, who were often outside from the opening of the island (see

figure 2), had a high SPI index in 1997, which had lowered by 2001.

Figure 3. SPI indices for 1997 and 2001

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

Dze

eta

Herm

ien

Horte

nse

Unga

Kidog

o

Redy

Vifijo

SPI 1997

SPI 2001

(Wilcoxon matched pair test n=7, z=2.37 p<0.05)

Plant consumption

In 1997 we compiled a list of 80 plant species, belonging to 35 different families that

could be found on the island (see Appendix I 2). These included both vegetation that

was originally planted on the island in 1992 (P), as well as plants that colonised the

island by themselves in the subsequent years(C). Sixteen species of these plants

(belonging to ten families) were eaten regularly by the bonobos during a two-week

period in September 1997. This list is not exhaustive, as some plants flower or bear

fruit during months that were not sampled here.

Discussion It is clear that the bonobos were very cautious of going out on the island in 1993.

Only two individuals spent more than 50% of their time outside. By 1997 most

individuals spent about 60% of their time out on the island, and this remained so in

2001. The spread of participation indices show that, while in 1997 the bonobos only

used certain areas of the island, they used the island more extensively in 2001. We

explored this difference visually by calculating for each quadrant the average how

often it had been visited by the different individuals in 1997 and in 2001 (see Figure

4).

Figure 4. Mean frequency of visit per quadrant in 1997 and 2001

A

BC

DE

FG

HI

JK

L

-1

0

1

2

3

4

5

6

7

8

0

0,05

0,1

0,15

AB

CD

EF

GH

IJ

KL

-1

0

1

2

3

4

5

6

7

8

0

0,05

0,1

0,15

1997 2001

Black bars represent areas visited most frequently by bonobos, grey bars show

frequency for the other areas

Apparently, in 1997, bonobos preferred the area around the inside enclosure near a

large climbing structure and, to a lesser extent, the nearby visitors area. Although on

average the bonobos used more quadrants in 2001, there still is a preference for the

area around the main building. The climbing structure had been renewed and this site

was still very popular. We now also see a new pattern arising. The bonobos preferred

an area on the south-western side of the island. We suspect this may be due to public

feeding. Although the public is not allowed to feed the animals, zoo visitors

frequently do so. In 1997 this happened mostly on the visitor’s site near the main

building and the bonobos developed the habit of begging for food. Therefore in 1998

we started playing a sound message, pointing out in four languages to the visitors in

this area that feeding the apes is strictly forbidden. This was partially effective, in that

feeding on this side of the island decreased. But visitors started to feed the bonobos

more frequently on the opposite side of the island, which may correspond with the

‘sudden interest’ of the bonobos for this spot. The effects of public feeding and the

presence of visitors in general, may be a fruitful research topic in the future. We also

suspect that shade is a very important factor that decides which sites are preferred by

the bonobos. This opens the potential for experimental set ups, creating places of

shades at places where the public can more easily observe the apes. This might also

decrease the visitors’ urge to feed the bonobos to lure them closer by.

Acknowledgements

We thank the bonobo keepers, Ludo van Mirlo, Harry De Gruyter, Joris Jacobs and

Stéphane Dawance for the fruitful co-operation throughout the years. Valery and

Donald Sibley were so kind to correct the English spelling. Thanks to all students for

gathering data in 1993 and to Maarten De Rouck for collecting the data in 2001. We

thank the Flemish Government for structural support to the CRC. The first author

received a grant from the Institute for Promotion of Innovation by Science and

Technology in Flanders (IWT: grant number 3340).

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Appendix I. List of identified plant species on the Planckendael bonobo island

Family Species - Latin name Species - English name planted Eaten

Alismataceae Saggitaria saggitifolia Arrowhead P N

Heracleum sphondylium Hogweed C N Apiaceae

Daucus carota Wild carrot C N

Eupatorium cannabinum Hemp-agrimony C N

Erigeron canadensis Horseweed C N

Achillea millefolium Yarrow C N

Matricaria recutita Scented Mayweed C N

Tanacetum vulgare Common tansy C N

Artemisia vulgaris Wormwood C N

Tussilago farfara Colt's-foot C N

Senecio jacobea Common ragworth C N

Cirsium vulgare Spear thistle C N

Hypochaeris radicata Cat's ear C N

Taraxacum officinale Dandelion C Y

Sonchus asper Prickly Son-thistle C Y

Crepis biennis Rough Hawk's beard C Y

Petasites hybridus Butterbur P N

Asteraceae

Petasites japonicus Japanese butterbur P N

Betulaceae Alnus glutinosa Alder P Y

Symphytum officinale Common comfrey C Y Boraginaceae

Myosotis palustris Water Forget-me-not C N

Cannabaceae Humulus lupulus Golden hop C N

Caprifoliaceae Sambucus nigra Common elder P N

Ceratophyllaceae Ceratophyllum demersum Hornwort P N

Convolvulaceae Calystegia sepium Bindweed C N

Cyperaceae Scirpus lacustris Common club-rush P N

Dryopteridaceae Dryopteris filix-mas Male fern C N

Elatinaceae Hypericum perforatum Perforate St.John's-wort C N

Equisetaceae Equisetum arvense Field Horsetail C N

Amorpha fruticosa False Indigo Bush C Y

Cytisus scoparius Broom C N

Vicia cracca Tufted Vetch C N

Lathyrus pratensis Meadow Vetchling C N

Melilotus officinalis Ribbed Melilot C N

Medicago lupulina Black Medick C N

Trifolium repens White clover C Y

Trifolium rubens Red Trefoil C N

Fabaceae

Lotus corniculatus Common Bird's-foot-trefoil C N

Appendix I Continued…

Family Species - Latin name Species - English name planted Eaten

Geranium rotundifolium Round-leaved Crane's-bill C N Geraniaceae

Geranium robertianum Herb-robert C N

Grossulariceae Ribes spp Currant P N

Iridaceae Iris pseudacoris Yellow flag P Y

Juncaceae Juncus effusus Soft rush C Y

Lycopus europaeus Gipsywort C N

Mentha aquatica Watermint C N

Glechoma hederacea Ground-ivy C N

Lamium purpureum Red Dead-nettle C N

Lamiaceae

Prunella vulgaris Selfheal C N

Menyanthaceae Menyantes trifoliata Buckbean C N

Nympaeceae Nymphea alba White water-lily P Y

Oleaceae Fraxinus excelsior Ash P N

Onagraceae Lythrum salicaria Purple loosestrife C N

Osmundaceae Osmunda regalis European royal fern P N

Plantaginaceae Plantago major Greater Plantain P N

Glyceria maxima Glyceria C N

Phragmites australis Common reed P N

Poaceae

Poa sp. Grass P Y

Rumex hydrolaphatum Water Dock P N

Rumex conglomeratus Clustered Dock C Y

Polygonaceae

Polygonum persicaria Ladysthumb C Y

Pontederiaceae Pontederia cordata Pickerel weed C N

Ranunculis lingua Greater Spearwort C N Ranunculaceae

Ranunculus acris Meadow buttercup C N

Sorbaria sorbifolia Sorbaria (tree spiraea) P N

Rubus caesius Dewberry C N

Potentilla anserina Silverweed C N

Rosaceae

Alchemilla spp Lady's mantle C N

Salix caprea Goat willow P Y

Salix pendrata Bay willow P Y

Salix cinerea Grey willow P Y

Salix acutifolia Siberian Violet-willow P Y

Salicaceae

Salix repens creeping willow P Y

Sparganiaceae Sparganium erectum Bur-reed P N

Acer platanoides Norway maple P Y

Acer sacharinum Silver maple P Y

Acer campestre Field maple P Y

Staphyleaceae

Acer capillipes Jap. stripped-bark maple P Y

Typhaceae Typha latifolia Common cattail P N

Urticaceae Urtica dioica Common nettle C N

P: Plants were put on the island

C: Plants “colonised” the island by themselves

N: Bonobos were not seen consuming these plant species (in September 1997)

Y: Bonobos were seen consuming these plant species (in September 1997)