Hubert, Bernard

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Made in United States of America 
Reprinted frolli BULLETIN OF C A R N E G I E  MusEuhf OF NATUXAL H I S T O R Y  
No. 6, 1978 
@ 1978 by the Trustees of Carnegie Institute, all rights reserved 
MODERN RODENT FAUNA OF THE LOWER OMO VALLEY, ETHIOPIA 
BERNARD HUBERT 
Laboratoire de Zoologie Appliquee, O.R.S.T.O.M., B.P. 1386, Dakar, Senegal 
Y ABSTRACT 
I One hundred and seventy rodents, comprising 15 species of 
nine genera and five families (Sciuridae, Gerbillidae, Criceto- 
myidae, Muridae, and Gliridae), have been captured in the lower 
Omo Valley. These represent a good sampling of the modern 
rodent population of the several biotopes of the areas-Sahelian 
savanna, arid zones (paleontological beds), and forested blocks 
comprising a continuous stratum of large trees and associated 
bushes and shrubs. 
.P ' 
INTRODUCTION 
One hundred and seventy rodents, comprising 15 
species of nine genera and five families, were cap- 
tured in the lower Omo Valley in the summer of 
1973 during the paleontological expedition orga- 
nized by Yves Coppens. These represent a good 
sampling of the modern rodent population of the 
several biotopes of the areas. 
The specific designation of certain species men- 
tioned here cannot always be regarded as definitive, 
because systematic revisions may be required. 
However, their ecological characteristics are well- 
defined. A future study, based on karyotypes, will 
permit the systematics of species to be more firmly 
established. 
Animals have been captured in various ways- 
through excavation of their burrows; by hand at 
night with the aid of a light; by traps set at burrows 
or in lines and baited with peanut butter; or by large 
metal cans sunk half to three-quarters of a m into 
the ground. 
/ 
I RESULTS 
Species List 
Sciuridae 
Heliosciurus gambianus omensis (Thomas, 1909)* 
Xerus rutilus (Cretzschmar, 1826) 
Tatera nigricauda (Peters, 1878) 
Tatera initzuscula Osgood, 1936 
Taterillus harringtoni (Thomas, 1906) 
Gerbilhs pulvinatus Rhoads, 1896 
Gerbillus pusillm Peters, 1878 
Saccostonzus mearnsi Heller, 1910 
Mastomys erythroleucus (Temminck, 1853) 
Arvicantlzis niloticus (Desmarest, 1822) 
Arvicanthis somalicus Thomas, 1902 
Acomys percevali Dollman, 1911 
Acomys wilsoni Thomas, 1892 
Thamnomys dolichurus (Thomas and Wrough- 
Gerbillidae 
Cricetomyidae 
Muridae 
ton, 1908)"" 
Gliridae 
' 
seum, Nairobi, in 1967). 
Graphiurus nzurinus Desmarest, 1822 
*Captured by A. Duff-Mackay (National Mu- 
**Captured by F. Rhodain and R. Houin. 
The presence of at least two other species is in- 
directly documented. An immense network of bur- 
rows, 3 to 5 cm in diameter, situated at a depth of 
about a meter, occurs on the surface of the Kibish 
Formation sediments, and may well testify to the 
presence of a bathyergid mole-rat. Some nests, 
filled with dry leaves, and unlike those of Graphiu- 
rus or of Thanznonzys, were found situated either in 
hollow limbs or in the empty trunks of certain trees 
in the gallery forest and could well belong to a spe- 
cies of Thallornys, a genus already documented 
elsewhere in Ethiopia (Petter, 1973). 
DISCUSSION 
Geographic Distribution 
Some species are widely distributed throughout 
sub-Saharan Africa (Arvicanthis niloticus, Masto- 
mys erythroleucus, Thamnomys dolichurus, Gra- 
phiurits murinus). Others are restricted to eastern 
Africa (Xerus rutilus, Tatera nigricauda, Taterillus 
109 
110 BULLETIN CARNEGIE MUSEUM OF NATURAL HISTORY NO. 6 
Table 1 .-Number of rodents collected in the five ecological zones of the trapped area in the Omo Valley, Ethiopia. The number of 
trap-nights is indicated for each zone, but is not signijkant because sonte species were collected by digging their burrows or by sunken 
can-traps. 
Riverine areas Arid zones 
Without trees, 
With trees with grass J 
Species captured & shrubs & thickets Slopes Bottom Plateau 
Xerus rutilus 
Tatera nigricauda 
Tatera minuscula 
Taterillus harringtoni 
Gerbillus pulvinatus 
Gerbillus pusillus 
Saccostomus mearnsi 
Mastontys erythroleucus 
Arvicanthis niloticus 
Arvicanthis somalicus 
Acomys percevali 
Acomys wilsoni 
Total specimens 
Number of trap-nights 
4 
2 
11 
2 
11 
1 
9 
3 
2 
7 
4 
16 
19 53 
640 1,880 
5 
3 16 
3 31 
290 630 
5 
8 
1 
3 
27 
6 
3 
9 
62 
1,711 
harringtoni, Saccostomus mearnsi, Arvicanthis so- 
malicus, Acomys wilsoni). Others appear to be 
more or less endemic and limited in distribution to 
southern Ethiopia and northern Kenya (Heliosciu- 
rus gambianus omensis, Tatera minuscula, Gerbil- 
lus pulvinatus, Gerbillus pusillus, Acomys percev- 
ali). 1 
Ecological Aspects 
These taxa differ in their biology. Certain species 
dig burrows and are active nocturnally (Mastomys 
erythroleucus) or diurnally (Xerus rutilus). Others 
are active both day and night and construct nests 
of dry vegetation at the foot of bushes or in high 
grasses (Arvicanthis spp.). Still others are arboreal 
and active during the day (Heliosciurus gambianus 
omensis) or the night, and construct nests of dry 
leaves in hollow limbs (Graphiurus murinus) or at- 
tach them to bushes or lianas (Thamnomys dolichu- 
rus). Their nests do not seem to be occupied 
throughout the year. 
Three major habitats may be usefully distin- 
guished (see Table 1). The riverine area has two 
aspects-with trees and shrubs (including Trichilia 
roka, Tapura Jischeri, Ficus sycomorus, Celtis in- 
tegrifolia, Ziziphus rubescens, Cordia gharuf) 
forming a continuous canopy, and with lianas (Sis- 
sus, Sabia) present. This zone appears to have a 
poor rodent fauna; only Heliosciurus gambianus 
omensis, Graphiurus murinus, and Thamnomys 
dolichuriis have been captured. Native villages sit- 
uated here harbor Arvicanthis niloticus and Mas- 
tomys erythroleiicus. There is also the riverine 
zone, largely without trees, but with grasses and 
very dense thicket. Here Mastomys erythroleucus, 
Saccostomus mearnsi, Acomys wilsoni, and Tatera 
nigricauda occur. The soils of this zone are heavy 
and clay-like and often appear as vertisols. The lat- 
er zone is flooded at more or less regular intervals 
in keeping with the Omo flood regime. 
The Shungura Formation exposures may be con- 
sidered separately and to have three aspects. The 
slopes of the exposures are comprised of detritus 
and eroded Plio-Pleistocene sediments. This very 
arid facies, practically without vegetation, harbors 
Acomys percevali. The cuestas of these exposures, 
which are covered with tuffs, and the bottoms, 
which separate them and contain recently eroded 
sediments, still have a very arid vegetation com- 
prised of open shrubs (Euphorbias, Adenium obe- 
sum, Cissus rotundifolin, Dasysphiera prostrata, 
Commiphora africana, Adenia venenata, Carallu- 
ma russelliana, Sesamothamniis brisseanus, and 
Maerua crassifolia) and rare herbaceous plants (In- 
digofera sp., some Cyperaceae). In these situations 
Gerbillus pusillus, Taterillus harringtoni, Tatera 
minuscula, Arvicanthis somalicus, and Xerus riiti- 
lus occur. 
Finally, the plateau has several soil types, more 
or less rich in clay, and these have a considerable 
V 
Reproduction 
Observations made during the summer of 1973 
broadly confirm the conclusions of previous work- 
ers (Dieterlen, 1967; Happold, 1966; Poulet, 1972; 
Hubert, 1977) on the reproduction of tropical ro- 
dents in sub-Saharan Africa. Reproduction occurs 
some weeks after onset of the rainy season. The 
onset of rains in early July 1973, in the north Shun- 
gura area, saw active reproduction of the principal 
rodent species represented there. In August, 80% 
of the trapped females were sexually active-either 
in estrous, gestating, or lactating. Farther south, on 
the other hand, in the Kalam area, where rain was 
lacking, there was no evidence of reproductive ac- 
tivity among those rodent populations. 
1978 HUBERT-RODENTS FROM OMO VALLEY, ETHIOPIA 111 
influence on the local composition of the vegeta- 
tion, generally that of a more or less open shrub or 
bush savanna (Acacia paolii, A. refcieizs, A .  hor- 
rida, Grewia terias, Cadaba glaizdulosa, C. gilletti, 
Sciatula Izortacarztha, Serriconiopsis pallida) with 
herbs (Blepharis persica, Polygala erioptera, Ipo- 
mea belpharosepala) as well as numerous grasses 
(Aristida, Cerzclzrus, Chloris, Dactylocterziuni, and 
others). The plateau rodents are Xerus rutilus, Aco- 
mys wilsoni, and Arvicaritlzis somalicus, which oc- 
cur everywhere, and Gerbillus pusillus and G. pul- 
vinatus which occupy areas of lighter, more sandy 
soil than those where Taterillus Izarrirzgtorii and Ta- 
tera nigricauda are found. 
The distribution of these various rodent species, 
which utilize the part of the environment which best 
agrees with their ecological preferences, is further 
affected by another limiting factor-dryness- 
which is more or less strongly pronounced accord- 
ing to the year and the season. Except for the gal- 
lery forest species, the rodent fauna is rather char- 
acteristic of dry, and even arid zones. The low 
incidence of species in the gallery forest is a result 
of recurrent dry periods that prevent the occurrence 
of species that are linked to a permanently moist 
environment and in addition the occasional flooding 
of the entire area, thereby restricting immigration 
by burrowing or purely terrestrial species. 
Taxonomic Comnzents 
The modern rodent fauna of the Lower Omo Val- 
ley is typical for this area in Africa, where different 
types of habitat are represented-Sahelian savanna, 
arid zones, and forested blocks comprising a con- 
tinuous stratum of large trees and associated bush 
and shrubs. 
There are two squirrels, one arboreal (H.  g. 
ornensis, described from this place) and one fos- 
sorial (X. rutilus). Two species of Tatera are pres- 
ent, one widely distributed in eastern Africa (T. izi- 
gricauda), and a very small one, endemic to this 
area, T. rninuscula (which was described by Osgood 
in 1936 from specimens collected in a nearby area, 
the Webbi Shebelli in southeastern Ethiopia, and 
was never officially collected since that time). Ta- 
terillus harrirzgtoni occurs in all this part of eastern 
Africa (Robbins, 1975) where it lives together in the 
Sahelian savanna with two species of gerbils, a me- 
dium-sized hairy-footed species, G. pulvinatus (Hu- 
bert, 1978; Schlitter, personal communica- 
tion) and a small one with naked sole, subgenus 
Hendecapleura, Gerbillus pusillus (Roche, 1976). 
Saccostonzus rnearnsi is the northern form of this 
genus, occuring in Ethiopia, Uganda, Kenya, and 
Tanzania (Hubert, 1978). The Mastonzys seems to 
be referable to Mastorrzys erythroleucus, a large 
species characterized by a light gray belly, a brown- 
yellowish back, and a karyotype of 38 chromo- 
somes, occurring in western and central Africa (Pet- 
ter, 1957 and 1978). Two species of Arvicaizthis are 
represented-A. riiloticrts, a large species, which is 
found in wet areas in the savannas over all Africa, 
and A. sornalicus, a smaller one with a paler fur, 
from the arid zones of eastern Africa. The two spe- 
cies of Acornys were reported from this area by 
Matthey (1968). 
CONCLUSIONS 
It is worth noting that four of the nine rodent 
genera present in the lower Omo basin are repre- 
sented each by two species adapted to slightly dif- 
ferent habitats. Here is an adaptative evolutionary 
process of some plasticity frequently found in var- 
ious animal species. It permits maximum utilization 
of the heterogeneity of the environment, in space 
and in time. This strategy, reflected in more or less 
marked specialization of different species, adapted 
to particular conditions, contrasts with that of spe- 
cies substantially less strict in' their ecological re- 
quirements. However, those latter species are ca- 
112 BULLETIN CARNEGIE MUSEUM OF NATURAL HISTORY NO. 6 
pable of very rapid occupation of various habitats 
given some favorable change of a seasonal or other 
unusual nature. 
Thus, the modern rodent fauna of the Loweí- 
Omo basin is rich, reflecting the different habitats 
present, which is characteristic of the African tropi- 
cal zones, even the dry zones. 
LITERATURE CITED 
DIETERLEN, F. 1967. Jahreszeiten und Fortpflanzungsperioden 
bei den Muriden des Kiuusee-Gebietes (Congo). Ein Beitrag 
zum Problem des Populationdynamik in den Tropen. Teil 1. 
Zeit. Saugetierkunde, 21:1-44. 
HAPPOLD, D. C. D. 1966. Breeding periods of rodents in the 
northern Sudan. Revue Zool. Bot. Afr., 74:357-363. 
HUBERT, B. 1977. Ecologie des populations de rongeurs de Ban- 
dia (Senegal) en zone sahelo-soudanienne. Terre et  Vie, 
31:33-100. 
-. 1978. Revision of the genus Saccostorizus (Rodentia, 
Cricetomyinae), with new morphological and chromosomal 
data from specimens from the Lower Omo Valley, Ethiopia. 
Bull. Carnegie Mus. Nat. Hist., 6:48-52. 
. 1978. Caryotype de Gerbillus pulviizatus Rhoads, 1896 
(Rongeurs, Gerbillidés) de la vallée de l’Omo (Ethiopie). 
Mammalia, 42:225-228. 
MATTHEY, R. 1968. Cytogénétique et taxonomie du genre 
. 
Aconzys. A .  percevali Dollman et A .  wilsoni Thomas, 
especes d’Abyssinie. Mammalia, 32:621-627. 
PETTER, F. 1957. Remarques sur la systématique des Rattus af- 
ricains et  description d’une forme nouvelle de l’Air. Mam- 
malia, 21:124-132. 
. 1973. Capture de Tlzalloitys paedulcus scotti en Ethio- 
pie. Mammalia, 37:360-361. 
. 1978. Les rats a mamelles multiples d’Afrique occiden- 
tale et centrale: Mustomys erythroleiicus (Temminck, 1953) 
et M .  huberti (Wroughton, 1908). Mammalia, 41:441-444. 
POULET, A. 1972. Recherches ecologiques sur une savane sah- 
elienne du Ferlo septentrional (Senegal). Les Mammiferes. 
Terre et Vie, 26:440472. 
ROCHE, J. 1976. A propos des petites gerbilles a soles plantaires 
nues (sous-genre Hendecapleura) de l’est africain. Monit. 
Zool. Ital., n.s., Suppl. 6, 13:263-268 (for 1975). 
i. 


Modern rodent fauna of the lower Omo Valley, Ethiopia

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