Endangered West African Chimpanzees Pan troglodytes verus (Schwarz, 1934) (Primates: Hominidae) in
Senegal prefer Pterocarpus
erinaceus, a threatened tree species, to build their nests: implications for their
conservation
Papa Ibnou Ndiaye 1, Anh Galat-Luong 2, Gérard Galat 3 &
Georges Nizinski 4
1 UCAD, Université
Cheikh Anta Diop, Département de Biologie animale, B.P 5005, Dakar-Fann,
Senegal
2,3 UCAD - IRD, Université Cheikh Anta Diop - Institut de Recherche pour le Développement,
Département Ressources vivantes, and IUCN Species Survival Commission, Route des Pères Maristes, Dakar, Senegal
4 IRD, Institut de Recherche pour le
Développement, UMR 211 Bioemco, 5 rue du Carbone, 45072 Orléans cedex 2, France
1 ibnou.ndiaye@ucad.edu.sn (corrosponding
author), 2 anh.luong@ird.fr, 3 gerard.galat@ird.fr, 4 georges.nizinski@ird.fr
Abstract: The West African Chimpanzee Pan troglodytes verus is Endangered(A4cd ver 3.1) in Senegal (Humle et al. 2008), mainly due
to habitat fragmentation and destruction. We gathered
qualitative and quantitative data on thetree species preferences of the West African Chimpanzee for nest
building in order to gain insight into habitat
dependence. Between March 1998 and
Febrary 2000 we identified tree species in which a sample of 1790 chimpanzee nests had been built, and ranked
species in preference order. We
compared this sample to the relative abundance of tree species in the
chimpanzee habitat to determine whether particular species
were chosen for nesting. We observed that about a quarter (25.42%) of nests were built in Pterocarpus erinaceus, which is considerably greater than would be expected from the abundance of this species in the habitat (6.35%), indicating a strong preference by
chimpanzees. We examined the physical traits of the most-used tree species and
concluded that height and wood hardness may be key choice features. P.
erinaceus is threatened in Senegal due to extensive
cutting, which may endanger chimpanzees living outside the boundaries of
protected areas. In the current anthropogenic setting our results provide
conservation managers with information on how to protect a key aspect of the
chimpanzee natural environment.
Keywords:Chimpanzee, conservation, Pan troglodytes verus,
Pterocarpus erinaceus, nest building.
doi: http://dx.doi.org/10.11609/JoTT.o3603.5266-72 | ZooBank: urn:lsid:zoobank.org:pub:6948B88F-F433-4D34-AB50-9D6D9B4BF7B1
Editor: Jill Pruetz, Iowa State
University, Ames, USA Dateof publication: 26 December 2013 (online & print)
Manuscript details: Ms # o3603
| Received 30 April 2013 | Final received 11 November 2013 | Finally accepted
28 November 2013
Citation: Ndiaye, P.I., A. Galat-Luong, G. Galat & G.
Nizinski(2013). Endangered West
African Chimpanzees Pantroglodytes verus (Schwarz, 1934) (Primates:
Hominidae) in Senegal prefer Pterocarpus
erinaceus, a threatened tree species, to build their nests:
implications for their conservation. Journal of Threatened Taxa5(17): 5266–5272; http://dx.doi.org/10.11609/JoTT.o3603.5266-72
Copyright: © Ndiaye et al. 2013. Creative
Commons Attribution 3.0 Unported License. JoTT allows unrestricted use
of this article in any medium, reproduction and distribution by providing
adequate credit to the authors and the source of publication.
Funding: This study was carried out and funded within the
framework of the ‘IPMO’ and ‘ BIOEMCO’
research programs of
the French Institut de Recherche pour le Développement (IRD) and the
University of Cheikh
Anta Diop (Dakar, Sénégal).
Competing Interest: The
authors declare no competing interests. Funding sources had no role in study
design, data collection, results interpretation and manuscript writing.
Acknowledgements: We would like to thank the directors, senior staff and
agents of the Senegalese National Parks and Forestry for their kind
collaboration, and we are also grateful to the inhabitants of Kédougou
department for their warm welcome. We thank Yérémakan Keita, forestry
technician at IRD, and local experienced rangers for help in plant species
identification. Authors wish to thank also the anonymous reviewers and the
Online Access to Research in the Environment (OARE) for facilitating
literature.
For figures, images, tables -- click here
Common Chimpanzee (Pan troglodytes Blumenbach, 1799) nest
building behaviour has been reported by Nissen (1931), Bernstein (1962, 1967,
1969), Goodall (1962), Sabater Pi (1985), Wrogeman (1992), Barnett et al. (1994,
1996), Kortlandt (1996), Plumptre & Reynolds (1997), Brownlow et al. (2001), and Basabose & Yamagiva (2002) and more recently by Furnichi &
Hashimoto (2004), Hernandez (2006), Ogawa et al. (2007), Koops et al.(2007, 2012) and Stanfort & O’Malley (2008). In Senegal, little data is published
concerning the nest building behaviour of the West African Chimpanzee (Pan
troglodytes verus Schwarz, 1934). Baldwin et al. (1981) collected information on nest heights, nest
grouping, the number of nests per nest tree, the minimum distance between nests
and nest tree trunk diameters in the Niokolo Koba National Park. At Fongoli, approximately 50km southeast
of Niokolo Koba National Park in southeastern Senegal, Stewart et al. (2007)
studied the comfort of chimpanzee nests on the basis of their physical
features; Stewart & Pruetz (2013) describe the anti-predator function of
the nest. Pruetz et al. (2008)
studied chimpanzees around Fongoli in comparison to those in the protected
Niokolo Koba National Park to assess the anti-predator role of chimpanzee
arboreal nest building behaviour, while also carefully detailing habitat
structure and arboreal nest heights. However, there have been no published studies in which the plant species
that chimpanzees use to build their nests were analysed.
The West African chimpanzee (Image 1) is listed as Endangered (A4cd ver 3.1) by IUCN (Humle
et al. 2008). In
Senegal, the main threats are habitat fragmentation/destruction (Galat-Luong et al.
1999–2000; Carter et al. 2003; Humle et al. 2008) and competition with humans
(Pruetz 2002). Additionally, some tree species used for woodworking, such as Pterocarpus
erinaceus, are becoming hard to find outside of national parks (Brunken
et al. 2008; author pers. obs.).
Galat-Luong et al. (1999–2000, 2009),Pruetz (2002), Pruetz et al. (2002), Carter
et al. (2003) and Ndiaye et al. (2013) showed that
chimpanzees still roam outside of their main refuge in Senegal, Niokolo Koba
National Park. In this study we went outside
of protected areas to gather and analyse the first qualitative and
quantitative data on the West African Chimpanzee’s tree
species preferences for nest building in Senegal. Furthermore, we related these preferences to the availability of
suitable trees in their habitat and to the features of preferred trees. These data are needed to provide
conservation managers with information on the
extent of habitat dependency of this ape in Senegal and what consequences it
may have in the anthropogenic setting currently characterizing this country.
Methods
Study Area: This study was carried out in Kédougou Region (12033’N &
12011W) in southeastern Senegal (Fig. 1), in West Africa. See Pruetz et al. (2002, 2008)
and Stewart
& Pruetz (2013) for detailed descriptions of the habitat
vegetation types. We
surveyed the entire region for chimpanzee habitats based on the presence of
their nests. Annual rainfall in
Kedougou over the 1995–1998 period ranged from 1000–1600 mm, with
one dry season from October to May and one rainy season from June to September (Baldensperger 1965), which is typical of a Sudano-Guinean climate as defined by Aubreville
(1949). The mean annual temperature
was around 28.60C
(21.9–35.2 0C) (Galat et al. 2009). Further details on the climate and its
changes during this period and the impact on large faunaincluding chimpanzee behaviour were reported by Galat
et al. (2009) and Galat-Luong et al. (2009).
Sudano-Guinean wooded savanna vegetation, as described by Aubreville
(1949), prevails in this area. The
tree densities vary, and open dry forests are sometimes found. Typically, Guinean tree species grow in
gallery forests, which could be relicts of a former denser forest cover that
diminished as a result of increasing dryness (Mühlenberg et al. 1990). Almost all trees shed their leaves
during the long dry season, except for evergreens in gallery forests. The leaves usually re-emerge just prior
to the first rains.
Nest trees: In a previous study (Galat-Luong et al. 1999–2000), in a 15,000km survey carried out in a vehicle, we first identified chimpanzee nesting sites in southeastern Senegal. The present study spanned over 80 days
between March 1998 and February 2000, and we covered about 380km outside
protected zones on foot and recorded the number of chimpanzee nests on
different species.
We identified plant species on the basis of the works of Berhaut (1967), Berhaut (1971–1979), Ferry
et al. (1974), Maydell (1990), Choudens
et al. (1995) and Ba et al. (1997), and with the contribution of a forestry
technician from the French Institut de Recherche pour le Dévelopement, Dakar, and local experienced rangers.
Abundance of available trees in the habitat: We also
sampled the availability in the habitat of tree species (and attached vines) that could potentially host chimpanzee nests by
recording them along 927 sampling transects set up perpendicularly to the
gallery forests along five rivers where chimpanzee nests had been recorded (Diaguiri River: 598
transects; Dimboli River: 130; Dialabatama River: 37; Djigoumato River: 56; and
Linguékoto River: 106).
Species preferences for nest building: In
order to assess tree species preferences for nest building, we compared the number of
nests hosted by the different tree species to the abundance of the trees in the
habitat using Fisher’s exact test (two tailed).
Results
Nest trees: We sampled chimpanzee nests (N=1794) and found that only four had been
built on the ground, while 1790 were built in trees. We identified the tree species bearing the
nests (Table 1). Chimpanzees had
built nests for resting in 34 different tree species.
Abundance of available trees in the habitat: We identified 834 trees and vines
belonging to 44 different species (Table 1).
Species preferences for nest building: Some
species were chosen proportionally to their abundance, whereas others were
preferred or less preferred (Fisher’s exact test p-value significant to
extremely significant; Table 1). Pterocarpus erinaceus, Parkia biglobosa,
Anogeissus leiocarpus, Cola cordifolia, Erythrophylum guineensis, Ficus
gnaphalocarpa, Lannea acida, Piliostigma reticulatum, and Dalbergia
sissoo were used to a greater extent than their
availability in the habitat would suggest.
Other tree species, including Syzygium guineense, Cordyla africana, Mitragyna inermis, Saba
senegalensis, Dialium guineense, Bombax costatum, Terminalia macroptera, Grewia
bicolor, Borassus aethiopium, Crateva religiosa, Nauclea latifolia, Acacia
seyal, Bauhinia rufescens, Pterocarpus santalinoides, Daniellia oliveri,
Lonchocarpus laxiflorus, Detarium microcarpum, Afrormosia laxiflora, Ziziphus
mauritiana, andFicus thonningii, were used less than expected for
nesting. We did not find any
statistical difference between nest use and availability in the habitat for the
other tree species.
Discussion
Our results showed that chimpanzees in Senegal were highly selective when choosing trees in the environment to
build their nests. Pterocarpus erinaceus was the most used by far: 25.42% of the nests were built in this species. This is four times more than expected by chance, given its relative abundance among trees in the habitat (6.35%, p<0.0001). In Issa, Ugalla, western
Tanzania, chimpanzees also built their nests in a Pterocarpusspecies (P. tinctorius Welw.)
more often (184 of 1504 nests = 12%) than would be expected considering the availability of this species in
transect samples (8 of 211 trees = 4%; Hernandez 2006). The second most used species, Diospyros
mespiliformis, was chosen proportionally to its abundance. Chimpanzees
feed on fruits of this tree, but ripe fruits were not always available (Ndiaye et al. unpub. data). Together with P. erinaceus, more than a third (36.82%) of all nests
were built in one of these two species. The three other species used most frequently, i.e., Parkia biglobosa (11.17% of the nests), Anogeissus
leiocarpus (9.22%), and Cola cordifolia (7.60%), were all
highly selected (p<0.0001). Nearly half (47.99%) of all nests were
recorded in the three most used species, i.e., Pterocarpus erinaceus, D. mespiliformis and Parkia biglobosa.
Different authors have described selection of some tree species for nest
building by chimpanzees, including Wrogemann (1992), Brownlow et al. (2001),
Basabose & Yamagiwa (2002), Hernandez (2006), Stewart et al. (2007) and Ogawa et al. (2007). According to Stanford & O’Malley (2008), out of 163 tree species
present in Bwindi National Park, Uganda, only four
harboured 72.1% of all sampled chimpanzee nests. These authors noted the type of nest
tree is influenced especially by the extent of food availability, safety and
comfort (Stanford & O’Malley 2008). Furnichi
& Hashimoto (2004) analysed different factors influencing nesting-site
selection by chimpanzees in Kalinzu Forest, Uganda, where only four of seven
preferred species provided edible fruit, and one of four less preferred species
provided both edible fruit and leaves, the preference for certain species may
not be explained by the availability of edible fruit or leaves in the preferred
trees. Table
2 describes the physiognomic features common to the six most used tree species,
which hosted 70% of all nests. These features, especially the wood hardness (which explains why they
are regularly used by woodworkers), seemed to be associated with the
chimpanzees’ preferences. The sixth species, Syzygium guineense, though
also hard, may have been less preferred (5.36% of the nests versus 9.35% in the habitat, p=0.0002)because it was the smallest species.
Two other large tree species, which could be considered as being good
‘nest hosts’ due to their height, i.e., Butyrospermum parkii (syn. Vitellaria paradoxa, “Karité”, “Shea”) and Adansonia
digitata, were not used more than expected (0.06% and
0.34%, respectively) given their abundance in the new habitat (0.36% and
0.12%, respectively, with no statistical significance). The
common feature between these two tree species is their very soft and relatively
poor quality wood. This also
suggests that wood quality may be a chimpanzee nest tree selection criterion.
In this study, we noted a chimpanzee nest in an Elaeis guineensis Jacq tree on the edge of a gallery forest. Neither preference nor avoidance
was significant (p=0.0977). The nest was made of a single E. guineensis palm leaf even
though several other tall trees, including Diospyros mespiliformis, were
growing nearby. Gippoliti
& Dell’Omo (1995) also reported observing chimpanzee nests in E. guineensistrees in Guinea-Bissau. Moreover, Barnett et al. (1994) and Prangley & Barnett (1994)observed a similar phenomenon on Mount Nimba in
Guinea. Kortlandt (1996) reported
observing chimpanzee nests in this species since 1965 in Guinea. All of these authors considered that
nest building in E. guineensis trees is a typical behaviour of
chimpanzees inhabiting West African degraded savanna forests, where the canopy
is generally not closed. Two
authors (A.G.L. & G.G.) also observed that in Senegal E. guineensis trees
were used as sleeping trees by Guinea baboons (Papio papio Desmarest 1820) along the Gambia River.
The high extent to which Pterocarpus erinaceus trees were used by
chimpanzees for nest building should be emphasized. In West Africa and Senegal, this tree
species is commonly used for fuel, woodworking and medicinal purposes (Lykke
2000; Karon et al. 2003; Brunken et al. 2008). As it is a highly valued fodder tree,
pruning is a serious threat (Bonkoungou et al. 2001), and the species is
declining and disappearing (Diallo 1997; Koita 1998). Furthermore, as the stumps generate few
offshoots, regrowth is low and therefore regression is accelerated (Fournier et al. 2001). In addition, fallow shortening will lead
to its extinction (Camara 1997). In Senegal, the species became so rare
that logging, sawmills and woodworking companies had to stop exploiting this
resource (P.I.N., pers. obs. and pers. com. of sawmill and woodworking company
owners). As a result, though P.
erinaceus is not registered on the IUCN Red List (but quantitative
scientific data are lacking) as are the closely related species P.
angolensis D.C.
and P. brenanii L. Barb. & Torre,(IUCN 2010), it is apparently threatened in Senegal.
In conclusion, chimpanzees were found to show preferences when choosing
trees to build their nests. Pterocarpus erinaceus, a tree that is
threatened in Senegal outside national parks due to abusive cutting and
pruning, was found to be the tree species that chimpanzees most preferred for
nest building, though its numbers have been drastically decreased. This choice is likely related to the
hardness of its wood. There is a high risk that abusive cutting of P.
erinaceus could endanger chimpanzees outside of protected areas where most
of the population of Senegal’s chimpanzees live. Consequently, chimpanzee conservation
outside of such areas seems to be partly dependent on the preservation of this
tree species. Moreover, in
the habitat destruction and global climate change setting, chimpanzees will
have to cope with increased flora changes. The results of the present work will provide conservation managers with
information on how to protect the species’ natural environment and to make
appropriate management decisions.
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