January 2008 vol. 15 African Bat Conservation News
West African forests are usually grouped into two blocks:
Upper Guinea (Guinea and Sierra Leone to Ghana; "Western
Region" according to GRUBB, 1978) and Lower Guinea
(Nigeria and eastward; "West Central Region" according to
GRUBB, 1978). The West African rainforest region is
characterized by a large number of species that are either
endemic to Upper or Lower Guinea or both of them (BAKARR
et al. 2004, KÜPER et al. 2004). The hiatus dividing both
blocks is called Dahomey Gap (Fig. 1), i.e. a stretch of
savanna reaching southward to the coast of the Gulf of
Guinea (Dahomey was the former name of Bénin). However, it
is still disputed whether this savanna-like vegetation exists
because of a climatic anomaly or due to anthropogenic land-
cover changes. DUPONT and WEINELT (1996) suggested
that it was caused by both factors. ROBBINS (1978)
considered human land use concentrated on the rich alluvial
soils between Lomé, Togo, and Lagos, Nigeria, as the main
driver of vegetation patterns (rather than climate) and
therefore a relatively recent impact. AKOEGNINOU (1998),
who investigated isolated forest stands within the savannas of
southern Bénin, assumed that the present rainfall is still
sufficient to allow the establishment of a dense semi-
evergreen forest, which would therefore represent the natural
vegetation of this region without anthropogenic influence. On
the contrary, SALZMANN and HOELZMANN (2005) reported
that the palaeorecord from Lac Sélé, situated about 60 km
northeast of Niaouli, suggests that the role of humans in
shaping the West African savannas has been overestimated.
Nowadays, this area is largely dominated by farms, fallows
and grasslands intermingled with small fragments of semi-
deciduous forest (ADOMOU, 2005). BOOTH (1958) also
indicated that at certain periods the Dahomey Gap had been
much wider than at present.
BOOTH (1954, 1958) considered the savanna vegetation
of the Dahomey Gap to be an important faunal barrier for
forest-dependent species, leading over evolutionary time to
endemic taxa on both sides of the Dahomey Gap. This view
was challenged by ROBBINS (1978), who demonstrated that
several forest-dependent mammal species can be found in
forest patches within the Dahomey Gap. In the course of
ongoing bat inventories throughout Bénin (BIOTA-project), we
sampled one of these areas falling within the gap, the Niaouli
Forest, to assess the composition of forest- vs. savanna-
dependent bat species and to evaluate the importance of
these forest fragments as stepping-stones connecting
populations on both sides of the Dahomey Gap.
Material and Methods
Niaouli Forest (6°44’N, 2°08’E) is located about 50 km
north of Cotonou and covers ca. 220 ha. Nowadays, only 65.5
ha of remnant dense forest remains that represent relatively
undisturbed forest. Part of this forest is classified as “forêt du
bas fond” and comprises 24.2 ha, which is intersected by the
Ava River (Fig. 2). The majority of this forest type is
permanently flooded. A second portion (41.3 ha) is located on
a plateau (“forêt du plateau”), which is surrounded by
We sampled bats in Niaouli Forest for 3 nights (5th, 6th and
7th of August) in 2003 with 2 mist nets (26 mist net-hours) and
1 night (1st of Jun) in 2007 with 5 mist nets (32.5 mist net-
hours). Mist nets employed measured 12 x 2.8 m (16 mm
mesh; 2 x 70 d netting), with 5 shelves. Nets were erected
between poles near ground level or slightly elevated above
the surrounding vegetation (herb layer). Mist nets were open
INVENTORY OF BAT SPECIES OF NIAOULI FOREST, BÉNIN,
AND ITS BEARING ON THE SIGNIFICANCE OF THE DAHOMEY
GAP AS A ZOOGEOGRAPHIC BARRIER
By: Bruno A. Djossa1,2; Brice A. Sinsin1; Elisabeth K.V. Kalko2,3 and Jakob Fahr2
1 Laboratoire d’Ecologie Appliquée-FSA/UAC/Bénin. 2 Institute of Experimental Ecology, University of
Ulm, Germany. 3Smithsonian Tropical Research Institute, Balboa, Panama
Figure 1: Potential extent of the forest biome in West Africa (OLSON et al. 2001), showing the Dahomey Gap (encircled), which
separates Upper and Lower Guinea. The point indicates the location of Niaouli Forest.
January 2008 vol. 15 African Bat Conservation News
between 19:15 and 20:00 until 00:00 hrs during the first half of
the night and re-opened in the early morning from 4:00 to 6:30
hrs. Sites were selected in both “forêt du plateau” and “forêt
du bas fond”. Species were identified with keys of HAYMAN
and HILL (1971) and BERGMANS (2002) as well as the
reference collection recently established at the University of
Abomey-Calavi. To identify Epomops spp., we mainly relied
on forearm length, body mass, and the pattern of the third
palatal ridge to distinguish between E. buettikoferi (Matschie,
1899) and E. franqueti (Tomes, 1860). Two specimens of
Hypsignathus montrosus H. Allen, 1862 (1 ♂, field number [F-
N°] 1850; 1 ♀, F-N° 11b) and one specimen of Hipposideros
cyclops (Temminck, 1855) (♂, F-N° 1867) were collected and
deposited in the reference collection at the University of
Abomey-Calavi, all other bats were released.
We captured 55 bats in total (34 in 2003 and 21 in 2007)
comprising six species (Table 1). Records of Hypsignathus
monstrosus and Megaloglossus woermanni Pagenstecher,
1885 constitute the first published records for Bénin. Based on
their general distribution patterns, habitat preferences of
species recorded during the present survey can be
characterized as follows. Epomophorus gambianus (Ogilby,
1835) is a savanna species that invades the forest zone
where rainforest has been converted to farmbush
(BERGMANS, 1988; FAHR and EBIGBO, 2003). In West
Africa, Epomops franqueti is mostly confined to rainforest
(BERGMANS, 1989). Hypsignathus monstrosus is mainly
found in the forest zone, but extends into savannas along
gallery forests and forest islands (BERGMANS, 1989; FAHR
et al. 2006). Megaloglossus woermanni is mostly confined to
rainforest (BERGMANS, 1997; FAHR and EBIGBO, 2003).
Eidolon helvum is a migratory species, which, depending on
season, is found both in rainforest and savanna habitats
(BERGMANS, 1991). Hipposideros cyclops (Fig. 3) is mostly
found in the rainforest zone but extends into the forest-
savanna mosaic along gallery forests and forest islands
(DECHER and FAHR, 2005). Overall, four species (H.
monstrosus, E. franqueti, M. woermanni and H. cyclops) or
67% of the species total are those that are mainly found within
the forest zone.
Epomops, Hypsignathus and Megaloglossus were listed by
BOOTH (1954) as genera occurring in rainforest east and
west of the Dahomey Gap, and BERGMANS (1997) mapped
the Dahomey Gap as a barrier for Hypsignathus and
Megaloglossus. These conclusions are not supported by our
data as they were found to occur within the Dahomey Gap.
Figure 2: Two different views of the flooded part (“forêt du bas
fond”) of Niaouli Forest and Ava River.
x ± SD
Body mass (g)
x ± SD
Epomophorus gambianus ♂♂ (n =3) 88.3±1.2 (87.0-89.2) 117.3±16.4 (105-136)
♀♀ (n =10) 81.6±3.5 (75.2-86.0) 83.4±9.3 (74-103)
Epomops franqueti ♂♂ (n =3) 89.7±3.4 (86.8-93.5) 111.0±9.6 (100-118)
♀♀ (n = 4) 80.3±3.5 (75.2-82.7) 83.5±11.3 (73-99)
Hypsignathus monstrosus ♂ (n =1)
subadult 109.7 161
♀♀ (n= 2) 111.1 (110.5-111.7) 212.5 (201-224)
Megaloglossus woermanni ♂♂ (n = 9) 40.5±0.8 (38.6-41.5) 13.0±0.7 (12-14)
♀♀ (n= 4) 40.2±0.6 (39.7-41.0) 12.8±1.5 (11-14)
Eidolon helvum ♂♂ (n =3) 116.8±1.4 (116.0-118.5) 218.0±14.1 (205-233)
♀ (n =1)
subadult 100.7 107
Hipposideros cyclops ♂ (n =1) 68.2 34
Table 1: Bat species recorded during this study from Niaouli Forest, southern Bénin. Measurements include only adult specimens
(n=39) except for two subadult specimens as indicated.
BEKKER and EKOUÉ (2004), who also reported
Epomophorus gambianus from Niaouli Forest, additionally
found Nanonycteris veldkampii (Jentink, 1888) (a migratory
species occurring in both forest and savanna habitats) as well
as Hipposideros caffer (Sundevall, 1846) (a species found
both in forest and savanna habitats). Both E. franqueti and H.
cyclops were previously recorded from Kpodave (ROBBINS,
1980), which is located about 40 km west of Niaouli. Epomops
franqueti, M. woermanni and H. cyclops were also captured in
Lama Forest (VOGLOZIN, 2005; WEBER, 2005), another
fragment situated about 25 km north of Niaouli. These
different collections from several forest remnants within the
Dahomey Gap confirm the presence of forest-dependent bat
species in the Dahomey Gap as already reported by
January 2008 vol. 15 African Bat Conservation News
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Submitted: 30 August 2007
Accepted: 16 November 2007
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ROBBINS (1978). We therefore agree with ROBBINS (1978)
that the presence of forest-dependent mammals within the
Dahomey Gap necessitates a re-evaluation of its importance
as a zoogeographic barrier, and in particular for mobile
mammals like bats.
We appreciate funding by the German Ministry of Education and
Science through the BIOLOG-program (BMBF; project W09 BIOTA-
West, 01 LC 0411). We thank the authorities of Niaouli Forest for
granting the permit to conduct this survey.