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Small mammals of arid savanna and montane sites in northern Kenya
JournalofArid Environments (1986) 11, 173-180
Small mammals of arid savanna and montane sites in northern Kenya G. H. G. Martin* Accepted 11 February 1985 Small mammal populations were studied in the Mt Kulal region of northern Kenya. Six rodent and one insectivorous species were recorded from eight arid sites and an additional two species of rodents and a shrew were found at sites on Mt Kulal. Estimates of rodent densities were made and were generally found to be low. The montane grassiand had a higher rodent population than those recorded from arid sites around the mountain.
Introduction A large part of northern Kenya is arid land merging into semi-desert. It thus falls into ecoclimatic zones V and VI as described by Pratt and Gwynne (1977). The region is of particular importance as it is a zone of increasing desertification and is a study area of the UNEP-MAB Integrated Project in Arid Lands (IPAL). Little is known about small mammals in the various habitats in the area and the present study examines the distribution of small mammals in some of the mosaic of habitats found in northern Kenya. In each habitat, an attempt was made to estimate the density of small mammal populations. This paper is based on the results obtained from four visits made to the area in 1979, 1980 and 1981. The study area lies between the south-eastern shore of Lake Turkana and Marsabit mountain in northern Kenya. Most of the area consists of a large desert plain surrounded by hills of volcanic origin; Mt Kulal (2295 m) in the west, Mt Marsabit (1930 m) in the east, the Hurri Hills (1310 m) to the north and the Nyiru and Ndoto mountains to the south. Soils are derived from two parent materials, pre-Cambrian basement rocks or recent volcanics. Rainfall is usually low, highly variable and of short duration. The main rains occur in two seasons, March - May and October - November. Most of the area has less than 200 mm of rain a year, (Edwards, Field et al. 1979; Bake, 1983). At higher altitudes, rainfall amount and duration increases while variability decreases. At Gatab, on Mt Kulal rainfall is about 600 mm a year and higher up it exceeds 900 mm. Potential evaporation over most of the region is high and has been estimated at 2620 mm per annum FAO (1971). Herlocker (1979) has prepared the most detailed study of the vegetation of the region where the primary physiognomy ranges from annual grassland to evergreen mountain forest.
* Departmentof Zoology, KenyattaUniversity, Nairobi, Kenya. © 1986 Academic PressInc. (London)Limited
0140-1963/86/050173+ 08 $03.0010
174
G. H. G. MARTIN
Study sites
Arid habitats (a) Balesa-Kulal (July 1979) altitude 600 m; 2° 32'N 37° 04'E. (i) Riverine Acacia; (ii) Acacia reficiens shrubland; (iii) old lava flow. (b) Kargi (August 1979) altitude 533 m; 2° 29°N 37°36'E. (i) Degraded lava flow; (ii) Low sand dunes; (iii) lava outcrop. (c) 01 Torot (July 1980; May and December 1981) altitude 660 m; 2° 33°N 37°02'E.
(i) DuospennalSolanum shrubland; (ii) DuospermallndigophoralSalsola shrubland.
Montane Habitats, altitude 2000 m; 2° 38'N 37° 02'E. Mount Kulal (July 1980. (i) Perennial grassland; (ii) evergreen forest.
Methods Metal snap traps and Sherman live traps were used to trap the small mammals. Normally a square grid of live traps was set out at each site and between 49 and 81 traps were used on a grid. Trapping was carried out for between 5-7 consecutive days. Trap days were sometimes lost due to traps being disturbed by animals. The trap interval at Bulesa Kulal and Kargi was 30 m for all sites. For the DuospermalSolanum grid the interval was 15 m and for the DuospermallndigophoralSalsola site and both montane sites 10 m. At all sites an effective trapping area was calculated by adding a boundary strip half a trap interval wide to the area of the grid. The snap traps were laid in a line in areas adjacent to, but not less than 150 m from, all the live trap grids. In addition, in 1980, snap traps were set in aboveground situations in the forest and also in 1980and December 1981on the Duosperma/lndigophoralSalsola site. All traps were inspected twice a day between 0615 hours and 0800 hours and between 1730hours and 1830hours. The principal bait used was peanut butter. Results All the eight arid sites are examples of some of the mosaic of habitats found in the arid savanna area of the south-west Marsabit District and are therefore considered together. The results from the two montane sites are examined separately.
Arid habitats Seven species of small mammals were trapped during the course of the study, six rodent species, Tatera nigricauda Peters, Graphiurus (Claviglis) murinus Desmarest, Gerbillus gerbil/us Oliver, Arvicanthis niloticus Desmarest, Acomys subspinosus Waterhouse and Xerus rutilus Cretschmar, and one insectivore, Elephantulus rufescens Peters. Trap success rates varied considerably in the eight arid habitats; for snap traps the rate ranged from 0 per cent at the 01 Torot DuospermallndigophoralSalsola site in 1980 and 1981 (December) to 17 per cent at the lava outcrop at Kargi, whilst for live traps the range was from 0 per cent on the sand dunes at Kargi and 01 Torot 1981 (December), to 4'6 per cent at the lava outcrop at Kargi (Table 1). In a total of 4126 trap days in arid areas, 104 animals were caught, an overall trap success rate of 2·5 per cent; in 1979 the rate was 4'1 per cent, 0·9 in 1980 and 0·2 in 1981 (May) and 0 per cent (December). The low numbers
SMALL MAMMALS OF ARID SAVANNA
175
Table 1. Trapping success in aridand montane areas of northern Kenya
Habitat
Trap days
Number of animals caught
Trap success (%)
Snap Live Total
Snap Live Total
Snap Live Total
Balesa Kulal (1979)
120
282
402
20
6
26
16'7
2·1
6·5
Riverine Acacia Lava Kargi (1979) Degraded lava Lava outcrop Sand dune 01 Torot 1980
120 118
282 282
402 400
15 8
5 6
20 14
12·5 6'8
1·8 2'1
5·0 3'5
106 88 99
282 282 282
388 370 311
3 15 2
2 13 0
5 28 2
2'8 0'7 17·0 4'6 2'0 0'0
1'3 7'6 0·5
160
320
480
4
5
0·3
1-30
1'0
125 149
320
445 149
0 2
3
3 2
0 1'3
0'90
0'7 1-3
253 256 192
253 359 246 50
0 1 0 0
0 0 0
0 1 0 0
0 0 1·0 0 0 0 0
0 0·3 0 0
100
240
340
0
13
13
0
5'4
3·8
150 149
486
596 149
2 7
1'3 4·7
0'2
0·5 4'7
Acaciareficiens
Duospermalsolanum Duospermal.Indigophora/ Salsola
Bushes (above ground) 01 Torot 1981 Duosperma/Solanum (May)
Duospermal.I ndigophora/(May) Salsola (December)
Bushes (above ground) Mount Kulal (1980) Grassland Forest (ground) (above ground)
102 54 50
3 7
of individuals of the different species caught in the eight habitats studied make it difficult to draw reliable conclusions about species distribution (Table 2). For example, there was no obvious reason why Tatera and Xerus should not be found in the riverine area at BalesaKulal. Elephantulus was only found in the Acacia rejiciens area at Balesa-Kulal. Gerbillus was the only species recorded from the sand dune area at Kargi. Xerus was the most widespread species, and was trapped or observed in six of the eight sites. During 125 traps days in aboveground traps near the Duosperma/lndigophora/Salsola grid, two specimens of G. (Claviglis) murinus were captured in 1980. No animals were captured in 1981at this site in 50 trap days. The degraded lava and sand dune sites at Kargi and the 01 Torot sites were the poorest areas for small mammals. The relatively high success rate and large number of individuals recorded at the lava outcrop south of Kargi is almost entirely due to the farge number of specimens of one species, Acomys, caught at this site - 23 out of a total of 26 individuals captured. Generally, the habitats at Balesa-Kulal appeared to be more favourable for small mammals than the other arid sites studied. The results of morning and evening catches are presented in Table 3. The data are insufficient to draw conclusions about Elephantulus, but the morning and evening catches are statistically significant in the other species. Xerus is diurnal whereas Tatera, Gerbillus, Arvicanthis and Acomys are nocturnal or crepuscular species. Minimum estimates of small mammal populations excluding Xerus can be made using numbers of individuals trapped on a grid. Such estimates would range from Olha at the 01 Torot sites (1981) and on the Kargi sand dunes (1979) (the latter is a known underestimate as two Gerbillus were caught by snap traps in the area), to 3'11ha on the Duosperma/lndigophora/Salsola site (1980). The average figure for arid sites was 1'01ha (Table 4). So few individuals were recaptured that no valid estimate could be made of home range or range length. The recapture distances of those individuals which were recaptured are given in Table 5.
Live Snap Live Snap Live Snap
Snap Live Snap Live Snap
Snap Live Snap Live Snap Live
Snap Live Snap Live Snap Live
type
Trap
(Above ground)
Forest (ground)
KulaI1980 Grassland
Bushes (above ground)
(December)
Duosperma/IndigophoraJ Salsola (May)
Snap Live Snap Live Snap
Duosperma/Solanum (May) Snap
01 Torot 1981
Bushes (above ground)
Duosperma/lndigophoraJ Salsola
01 Torot 1980 Duosperma/Solanum
Sand dune
Lava outcrop
Kargi1979 Degraded lava
Lava
Riverine Acacia
Acaciareficiens
Balesa-KulaIl979
Habitat
0 2 0 0 0
0 0 0 0 0 0
0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
0 8 2 0 0
0 0 0 0 0 0
0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 3
0 0 0 0 0 0
0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 1 4
0 0 0 0 0 0
0 0 0 0 2
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0
0 0 0 0 0 0
I 1 0 I 0
0 0 0 0 0 0
10 2 0 0 5 I
0 0 0 0 0
0 0 0 0 0 0
0 0 0 1 0
0 0 0 0 2 0
2 1 12 3 0 0
0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0
I 2 0 0 0 0
0 0 3 I 0 2
0 0 0 0 0
0 0 0 0 0 0
0 2 0 0 0
0 0 13 9 0 0
0 0 0 0 0 0
0 0 0 0 0
0 1 0 0 0 0
0 0 0 0 0
2 0 2 0 0 0
4 0 0 0 3 0
0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0
0 0 0 0 0 0
4 1 0 0 0 0
0 10 2 1 7
0 1 0 0 0 0
3 0 2 2
11
3 2 15 9 2 0
20 4 15 4 8 3
Crocidura Myomyscus Grammomys Claviglis Tatera Gerbillus Arvicanthis Acomys Xerus Elephantulus Total
Table 2. Numbers ofindividuals of each species caught in each habitat
;z:
Z
-
> ~
~
p
P
-J
0-
-
SMALL MAMMALS OF ARID SAVANNA
177
Table 3. Dailyactivity patterns based oncatches Morning catch (nocturnal/crepuscular)
Tatera Gerbillus Arvicanthis Acomys Xerus Elephantulus
Evening catch (diurnal activity)
4*
18
22
0*
2*
9
26
0*
o
13*
2
* Significant at p =
0'05
4
cl test)
Table 4. Density estimate of small mammal populations inarid andmontane
habitats in northern Kenya
Density (No./ha)
Site Bulesa Kulal (July 1979)
Acacia reficiens Riverine Acacia
1·0 1·0 0'75
Lava
Kargi (August 1979) Degraded lava Lava outcrop Sand dune
o
01 Torot Duosperma/Solanum (July 1980) Duosperma/Solanum (May 1981) Duosperma/lndigophora/Salsola (July 1980) Duosperma/lndigophora/Salsola (May 1981) Duosperma/Indigophora/Salsola (December 1981)
o 3'1 o o
0'5
2'25
Kulal (July 1980) Grassland Forest
2'1
25·0 1'25
Table 5. Recapture distances of species caught in arid andmontane habitats Average recapture distance (m) Arid habitats
Tatera Gerbil/us Arvicanthis Acomys Elephantulus
120 120
100
55 60
Comments Two individuals each recaptured once One individual recaptured once Two individuals each recaptured once Four individuals each recaptured once One individual recaptured once.
Av. 84 Montane grassland
Myomyscus
16
Three individuals each recaptured once
178
G. H. G. MARTIN
Montane habitats-Mt Kulal A total of three species of rodents, Praomys (Myomyseus) fumatus Peters, Thamnomys (Grammomys) doliehuris Smuts and G. (Claviglis) murinus Desmarest and the shrew, Crocidura bieolor Bocage were trapped at the Mt Kulal sites (Table 2). The grassland site
had a live trap success rate of 5'4 per cent, but no animals were caught in the snap traps (Table 1). In the forest, the live trap grid had only a single trap success in 446 trap days. In 150trap days of snap trapping on the ground, two animals were caught whilst in the aboveground snap traps seven animals were caught in 149trap days (Table 1). Thus, the success rates in the forest were 0·2 per cent for live traps, 1'3 per cent for ground snap traps and 4'7 per cent for aboveground snap traps. Myomyseus was the only rodent caught in the meadow. The capture of two individuals in the forest was possibly due to the close proximity of the trap line in which they were caught to the grassland area. A single Claviglis was caught in a live trap on the forest floor, but all other specimens of both Claviglis and Grammomys were caught in aboveground situations, in bushes, trees or on a cliffface in the forest (Table 2). The only shrews caught were found in the grassland area. No animals were caught during the day in either the forest or grassland sites. Three Myomyseus were each recaptured once at an average distance of 16 m (Table 5). Estimates of small mammal densities for ground dwelling species were 1·28/ha in the forest, and 25/ha in the grassland (Table 4). Discussion The list of species recorded during the current studies is similar to that recorded during the Royal Geographical Society Expeditions to South Turkana, (Coe, 1972). The Royal Geographical Society area lies in the same ecoclimatic zone as the arid sites of the present study but was close to the Kerio River. G. doliehurus and the gerbils Taterillus nubilus and Gerbillus pusillus mentioned in the RGS report were not recorded from arid sites in 1979, 1980 and 1981, nor was the shrew C. bieolor. However, the small numbers of animals caught in the arid areas in the Kulal area make it quite likely that some species have been missed. It is worth noting that the records of Grammomys and Claviglis of the RGS expeditions were each based on single specimens recorded in the 3 years. Tatera robusta reported from the Kerio Valley was not found around Mt Kulal but T. nigricauda was. However, comments by Davis in Meester & Setzer (1977) indicate that the differences between some races of these two species are slight. Although G. dolichurus and C. bicolor were not caught in the arid sites, they were trapped on Mt Kulal and their range might be expected to extend to suitable sites at lower altitudes. Two other species of rodent were trapped at an altitude of about 2000 m on Mt Kulal, Myomyscus fumatus was recorded in the grassland and C. murinus in the forest. Myomyscus was not recorded from the Kerio Valley by Coe (1972). The three specimens of Grammomys caught from forest sites are interesting because two of them had ears with a distinct white sub-auricular tuft. The presence of this feature has been used to distinguish G. cometes from G. dolichurus by Misonne in Meester & Setzer (1977). The skull and head and body measurements for all three specimens were less than the range indicated for G. cometes; the specimens have therefore been provisionally retained as G. dolichurus. It appears that the sub-auricular tuft may be a variable feature and, in consequence, it must be used with caution in identification. Four specimens of Claviglis were trapped in the forest and were all similar in size and appearance: dark grey above and dark grey patchily washed with buff below. This description contrasts markedly with that of two Claviglis caught at 01 Torot which were
SMALL MAMMALS OF ARID SAVANNA
179
smaller, light smoky grey above and light grey with buff below, becoming cream on the throat and chin. The average body measurements for available specimens from the two sites are given in Appendix I. An examination of material from intermediate sites as well as more from forest and arid areas could prove interesting. Delany (1966) trapped mammals on Mt Moroto in northern Uganda. Like Kulal, Mt Moroto is an isolated mountain with montane forest and grass savanna, but it differs in being wetter. From trapping sites on Mt Moroto at about 2300 m, three species of rodent but no shrews were recorded. Praomys morio, Lophuromys sikapusi, in the forest and Otomys irroratus and L. sikapusi from the grassland. The two mountains, although they have some vegetational similarities, appear to have no small rodent species in common, although both appear to have few species present. Appendix I. Body measurements ofGraphiurus (Claviglis) sp. caught in (a) forest and (b) aridsavanna Habitat
n
Weight (g)
Head and body (mm)
Tail (mm)
Hind foot (mm)
Forest
4
Arid savanna
1*
25'1 (20'5-33'0) 12
88'4 (82-95) 72'5
79'0 (72-89) 76·0
17'6 (16'5-18'0) 14·0
Ear (mm) 16'0 (15'0-17'6) 13·8
n = number in sample; figures in brackets indicate the range.
* The second specimen was taken by a crow before measurements could be taken but was very similar in size and appearance to the first. Generally, the habitats in which the various species were found and their daily activity patterns were in agreement with those recorded by other workers as summarized by Delany (1975), Delany & Happold (1979) and Kingdon (1974). Where there is good vegetation cover some species such as Arvicanthis, Elephantulus and Tatera occur, whereas species such as Gerbil/us can survive in more arid, sparsely vegetated sites. Xerus was observed in a wide range of habitats but not in the driest areas such as the sand dune site at Kargi. The large number of Acomys caught amongst the lava outcrops at Kargi parallels the high Acomys catch in a very similar site from south of Lake Turkana (Coe, 1972). The only species that appeared strictly diurnal wasXerus. Six Elephantulus were captured, four during the day and two at night, which agrees with other records of the day and night activity of this species (Kingdon, 1974). The low trapping success rates in the arid areas near Mt Kulal were very similar to those reported by Coe (1972) in the Kerio Valley, where rates ranged from less than 1'0 per cent to 4·3 per cent. Elsewhere in arid areas of Africa reported trapping rates have been higher, for example Nel & Rautenbach (1975) working in the Kalahari Gemsbok National Park had rates averaging about 10per cent. Trapping rates were also low in the Kulal forest with ground traps success varying from O'2 per cent for live traps to 1·3 per cent for snap traps and an overall trap success of 0·6 per cent. This compares with a rate of 25 per cent from Mt Moroto forest where a combination of live and snap traps were used (Delany, 1966). The density estimates were made using a boundary strip of half a trap interval in width to calculate the effective trapping areas of the grids. However, the effective trapping areas thus calculated may be low estimates because Fleming (1971) suggested that the average distance between successive captures gave a more realistic estimate for the width of the boundary strip. This method was not used in this study as too few recaptures were made to give reliable estimates of average distance. If the average distances were close to the figures given in Table 5, then of course density estimates would be reduced particularly where small grids were used.
180
G. H. G. MARTIN
The average distance figures for northern Kenyan rodents are extremely tentative but interestingly the figure of 16 m for Myomyscus of the montane grassland is close to distances recorded for rodent species from grasslands in Uganda, 22-35 m (Cheeseman & Delany, 1979), and south Central Kenya, 6-21 m (Delany & Roberts, 1978) and 16-28 m (Martin, in prep.). The large average distances from the arid sites may indicate that greater distances have to be travelled in search of food or some other resource. One would expect the populations of animals to be lower in arid areas compared to habitats where food resources are more plentiful. The apparent low population density encountered in the montane forest is more difficult to explain. Superficially, resources appear to be much more abundant than those in the arid habitats of the plain below. The almost year-round night cloud mists ensure that the pronounced seasonal differences in vegetation growth of the arid habitats are not experienced. A seasonal fluctuation in food supply may occur but the wide variation in availability between dry and wet season on the plains seems less likely. For both arid and montane habitats it is necessary that studies over the entire annual climatic cycle are carried out before faunal lists can be completed and the role of rodents in the ecosystems of northern Kenya be realistically assessed. I am extremely grateful to all the IPAL staff at Gatab, Balesa-Kulal and 01 Torot who were so helpful. Particular thanks is given to O. O. Opiyo for material collected in 1979 and to Piers Simpkin for his help and good company in 1980. This work was carried out while I was receiving a research grant from Kenyatta University.
References Bake, G. (1983). Analysis of climatological data from the Marsabit District of Northern Kenya. IPAL Technical Report B-3 UNESCO-MAB Integrated Project in Arid Lands. Nairobi. 89 pp. Cheeseman, C. L. & Delany, M. J. (1979). The population dynamics of small rodents in a tropical African grassland. Journal of Zoology, 188: 451-475. Coe, M. J. (1972). The South Turkana expedition, Scientific paper IX. Ecological studies of the Small Mammals of South Turkana. GeographicalJournal, 138: 316-338. Delany, M. J. (1966). Small rodents from the higher altitude of Mt Moroto, Uganda. RevueZoologie etBotanie Afrique, 73: 339-344. Delany, M. J. (1975). Rodents of Uganda. London: British Museum (Natural History). 165 pp. Delany, M. J. & Happold, D. C. D. (1979). Ecology of African Mammals. London: Longman. 434 pp. Delany, M. J. & Roberts, C. J. (1978). Seasonal population changes in rodents in the Kenya Rift Valley. Bulletin of theCarnegie Museum of Natural History, 6: 92-108. Edwards, K. A. Field, C. R. & Hogg, T. G. G. (1979). A preliminary analysis of climatological data from the Marsabit District of Northern Kenya. IPAL-Technical report B-1, UNEP-MAB Integrated project in Arid Lands, Nairobi. 44 pp. Fleming, T. H. (1971). Population ecology of three species of neotropical rodents. Miscellaneous Publications of Museum of Zooloy, University of Michigan, 143: 1-77. Herlocker, D. (1979). Vegetation of Southwestern Marsabit District, Kenya. IPAL Technical Report D-1, UNEP-MAB Integrated Project in AridLands, Nairobi. 68 pp. Kingdon, J. (1974). East African Mammals Vol. IIB Hares & Rodents. London: Academic Press. 758 pp. Meester, J. & Setzer, H. W. (Eds) (1977). The Mammals of Africa An Identification Manual. Washington: Smithsonian Institution. Nel, J. A. ]. & Rautenbach, I. L. (1975). Habitat use and community, structure of rodents in the southern Kalahari, Mammalia, 39: 9-29. Pratt, D. J. & Gwynne, M. D. (1977). Rangeland Management andEcology in EastAfrica. London: Hodder & Stoughton. 310 pp.
Small mammals of arid savanna and montane sites in northern Kenya G. H. G. Martin* Accepted 11 February 1985 Small mammal populations were studied in the Mt Kulal region of northern Kenya. Six rodent and one insectivorous species were recorded from eight arid sites and an additional two species of rodents and a shrew were found at sites on Mt Kulal. Estimates of rodent densities were made and were generally found to be low. The montane grassiand had a higher rodent population than those recorded from arid sites around the mountain.
Introduction A large part of northern Kenya is arid land merging into semi-desert. It thus falls into ecoclimatic zones V and VI as described by Pratt and Gwynne (1977). The region is of particular importance as it is a zone of increasing desertification and is a study area of the UNEP-MAB Integrated Project in Arid Lands (IPAL). Little is known about small mammals in the various habitats in the area and the present study examines the distribution of small mammals in some of the mosaic of habitats found in northern Kenya. In each habitat, an attempt was made to estimate the density of small mammal populations. This paper is based on the results obtained from four visits made to the area in 1979, 1980 and 1981. The study area lies between the south-eastern shore of Lake Turkana and Marsabit mountain in northern Kenya. Most of the area consists of a large desert plain surrounded by hills of volcanic origin; Mt Kulal (2295 m) in the west, Mt Marsabit (1930 m) in the east, the Hurri Hills (1310 m) to the north and the Nyiru and Ndoto mountains to the south. Soils are derived from two parent materials, pre-Cambrian basement rocks or recent volcanics. Rainfall is usually low, highly variable and of short duration. The main rains occur in two seasons, March - May and October - November. Most of the area has less than 200 mm of rain a year, (Edwards, Field et al. 1979; Bake, 1983). At higher altitudes, rainfall amount and duration increases while variability decreases. At Gatab, on Mt Kulal rainfall is about 600 mm a year and higher up it exceeds 900 mm. Potential evaporation over most of the region is high and has been estimated at 2620 mm per annum FAO (1971). Herlocker (1979) has prepared the most detailed study of the vegetation of the region where the primary physiognomy ranges from annual grassland to evergreen mountain forest.
* Departmentof Zoology, KenyattaUniversity, Nairobi, Kenya. © 1986 Academic PressInc. (London)Limited
0140-1963/86/050173+ 08 $03.0010
174
G. H. G. MARTIN
Study sites
Arid habitats (a) Balesa-Kulal (July 1979) altitude 600 m; 2° 32'N 37° 04'E. (i) Riverine Acacia; (ii) Acacia reficiens shrubland; (iii) old lava flow. (b) Kargi (August 1979) altitude 533 m; 2° 29°N 37°36'E. (i) Degraded lava flow; (ii) Low sand dunes; (iii) lava outcrop. (c) 01 Torot (July 1980; May and December 1981) altitude 660 m; 2° 33°N 37°02'E.
(i) DuospennalSolanum shrubland; (ii) DuospermallndigophoralSalsola shrubland.
Montane Habitats, altitude 2000 m; 2° 38'N 37° 02'E. Mount Kulal (July 1980. (i) Perennial grassland; (ii) evergreen forest.
Methods Metal snap traps and Sherman live traps were used to trap the small mammals. Normally a square grid of live traps was set out at each site and between 49 and 81 traps were used on a grid. Trapping was carried out for between 5-7 consecutive days. Trap days were sometimes lost due to traps being disturbed by animals. The trap interval at Bulesa Kulal and Kargi was 30 m for all sites. For the DuospermalSolanum grid the interval was 15 m and for the DuospermallndigophoralSalsola site and both montane sites 10 m. At all sites an effective trapping area was calculated by adding a boundary strip half a trap interval wide to the area of the grid. The snap traps were laid in a line in areas adjacent to, but not less than 150 m from, all the live trap grids. In addition, in 1980, snap traps were set in aboveground situations in the forest and also in 1980and December 1981on the Duosperma/lndigophoralSalsola site. All traps were inspected twice a day between 0615 hours and 0800 hours and between 1730hours and 1830hours. The principal bait used was peanut butter. Results All the eight arid sites are examples of some of the mosaic of habitats found in the arid savanna area of the south-west Marsabit District and are therefore considered together. The results from the two montane sites are examined separately.
Arid habitats Seven species of small mammals were trapped during the course of the study, six rodent species, Tatera nigricauda Peters, Graphiurus (Claviglis) murinus Desmarest, Gerbillus gerbil/us Oliver, Arvicanthis niloticus Desmarest, Acomys subspinosus Waterhouse and Xerus rutilus Cretschmar, and one insectivore, Elephantulus rufescens Peters. Trap success rates varied considerably in the eight arid habitats; for snap traps the rate ranged from 0 per cent at the 01 Torot DuospermallndigophoralSalsola site in 1980 and 1981 (December) to 17 per cent at the lava outcrop at Kargi, whilst for live traps the range was from 0 per cent on the sand dunes at Kargi and 01 Torot 1981 (December), to 4'6 per cent at the lava outcrop at Kargi (Table 1). In a total of 4126 trap days in arid areas, 104 animals were caught, an overall trap success rate of 2·5 per cent; in 1979 the rate was 4'1 per cent, 0·9 in 1980 and 0·2 in 1981 (May) and 0 per cent (December). The low numbers
SMALL MAMMALS OF ARID SAVANNA
175
Table 1. Trapping success in aridand montane areas of northern Kenya
Habitat
Trap days
Number of animals caught
Trap success (%)
Snap Live Total
Snap Live Total
Snap Live Total
Balesa Kulal (1979)
120
282
402
20
6
26
16'7
2·1
6·5
Riverine Acacia Lava Kargi (1979) Degraded lava Lava outcrop Sand dune 01 Torot 1980
120 118
282 282
402 400
15 8
5 6
20 14
12·5 6'8
1·8 2'1
5·0 3'5
106 88 99
282 282 282
388 370 311
3 15 2
2 13 0
5 28 2
2'8 0'7 17·0 4'6 2'0 0'0
1'3 7'6 0·5
160
320
480
4
5
0·3
1-30
1'0
125 149
320
445 149
0 2
3
3 2
0 1'3
0'90
0'7 1-3
253 256 192
253 359 246 50
0 1 0 0
0 0 0
0 1 0 0
0 0 1·0 0 0 0 0
0 0·3 0 0
100
240
340
0
13
13
0
5'4
3·8
150 149
486
596 149
2 7
1'3 4·7
0'2
0·5 4'7
Acaciareficiens
Duospermalsolanum Duospermal.Indigophora/ Salsola
Bushes (above ground) 01 Torot 1981 Duosperma/Solanum (May)
Duospermal.I ndigophora/(May) Salsola (December)
Bushes (above ground) Mount Kulal (1980) Grassland Forest (ground) (above ground)
102 54 50
3 7
of individuals of the different species caught in the eight habitats studied make it difficult to draw reliable conclusions about species distribution (Table 2). For example, there was no obvious reason why Tatera and Xerus should not be found in the riverine area at BalesaKulal. Elephantulus was only found in the Acacia rejiciens area at Balesa-Kulal. Gerbillus was the only species recorded from the sand dune area at Kargi. Xerus was the most widespread species, and was trapped or observed in six of the eight sites. During 125 traps days in aboveground traps near the Duosperma/lndigophora/Salsola grid, two specimens of G. (Claviglis) murinus were captured in 1980. No animals were captured in 1981at this site in 50 trap days. The degraded lava and sand dune sites at Kargi and the 01 Torot sites were the poorest areas for small mammals. The relatively high success rate and large number of individuals recorded at the lava outcrop south of Kargi is almost entirely due to the farge number of specimens of one species, Acomys, caught at this site - 23 out of a total of 26 individuals captured. Generally, the habitats at Balesa-Kulal appeared to be more favourable for small mammals than the other arid sites studied. The results of morning and evening catches are presented in Table 3. The data are insufficient to draw conclusions about Elephantulus, but the morning and evening catches are statistically significant in the other species. Xerus is diurnal whereas Tatera, Gerbillus, Arvicanthis and Acomys are nocturnal or crepuscular species. Minimum estimates of small mammal populations excluding Xerus can be made using numbers of individuals trapped on a grid. Such estimates would range from Olha at the 01 Torot sites (1981) and on the Kargi sand dunes (1979) (the latter is a known underestimate as two Gerbillus were caught by snap traps in the area), to 3'11ha on the Duosperma/lndigophora/Salsola site (1980). The average figure for arid sites was 1'01ha (Table 4). So few individuals were recaptured that no valid estimate could be made of home range or range length. The recapture distances of those individuals which were recaptured are given in Table 5.
Live Snap Live Snap Live Snap
Snap Live Snap Live Snap
Snap Live Snap Live Snap Live
Snap Live Snap Live Snap Live
type
Trap
(Above ground)
Forest (ground)
KulaI1980 Grassland
Bushes (above ground)
(December)
Duosperma/IndigophoraJ Salsola (May)
Snap Live Snap Live Snap
Duosperma/Solanum (May) Snap
01 Torot 1981
Bushes (above ground)
Duosperma/lndigophoraJ Salsola
01 Torot 1980 Duosperma/Solanum
Sand dune
Lava outcrop
Kargi1979 Degraded lava
Lava
Riverine Acacia
Acaciareficiens
Balesa-KulaIl979
Habitat
0 2 0 0 0
0 0 0 0 0 0
0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
0 8 2 0 0
0 0 0 0 0 0
0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 3
0 0 0 0 0 0
0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 1 4
0 0 0 0 0 0
0 0 0 0 2
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0
0 0 0 0 0 0
I 1 0 I 0
0 0 0 0 0 0
10 2 0 0 5 I
0 0 0 0 0
0 0 0 0 0 0
0 0 0 1 0
0 0 0 0 2 0
2 1 12 3 0 0
0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0
I 2 0 0 0 0
0 0 3 I 0 2
0 0 0 0 0
0 0 0 0 0 0
0 2 0 0 0
0 0 13 9 0 0
0 0 0 0 0 0
0 0 0 0 0
0 1 0 0 0 0
0 0 0 0 0
2 0 2 0 0 0
4 0 0 0 3 0
0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0
0 0 0 0 0 0
4 1 0 0 0 0
0 10 2 1 7
0 1 0 0 0 0
3 0 2 2
11
3 2 15 9 2 0
20 4 15 4 8 3
Crocidura Myomyscus Grammomys Claviglis Tatera Gerbillus Arvicanthis Acomys Xerus Elephantulus Total
Table 2. Numbers ofindividuals of each species caught in each habitat
;z:
Z
-
> ~
~
p
P
-J
0-
-
SMALL MAMMALS OF ARID SAVANNA
177
Table 3. Dailyactivity patterns based oncatches Morning catch (nocturnal/crepuscular)
Tatera Gerbillus Arvicanthis Acomys Xerus Elephantulus
Evening catch (diurnal activity)
4*
18
22
0*
2*
9
26
0*
o
13*
2
* Significant at p =
0'05
4
cl test)
Table 4. Density estimate of small mammal populations inarid andmontane
habitats in northern Kenya
Density (No./ha)
Site Bulesa Kulal (July 1979)
Acacia reficiens Riverine Acacia
1·0 1·0 0'75
Lava
Kargi (August 1979) Degraded lava Lava outcrop Sand dune
o
01 Torot Duosperma/Solanum (July 1980) Duosperma/Solanum (May 1981) Duosperma/lndigophora/Salsola (July 1980) Duosperma/lndigophora/Salsola (May 1981) Duosperma/Indigophora/Salsola (December 1981)
o 3'1 o o
0'5
2'25
Kulal (July 1980) Grassland Forest
2'1
25·0 1'25
Table 5. Recapture distances of species caught in arid andmontane habitats Average recapture distance (m) Arid habitats
Tatera Gerbil/us Arvicanthis Acomys Elephantulus
120 120
100
55 60
Comments Two individuals each recaptured once One individual recaptured once Two individuals each recaptured once Four individuals each recaptured once One individual recaptured once.
Av. 84 Montane grassland
Myomyscus
16
Three individuals each recaptured once
178
G. H. G. MARTIN
Montane habitats-Mt Kulal A total of three species of rodents, Praomys (Myomyseus) fumatus Peters, Thamnomys (Grammomys) doliehuris Smuts and G. (Claviglis) murinus Desmarest and the shrew, Crocidura bieolor Bocage were trapped at the Mt Kulal sites (Table 2). The grassland site
had a live trap success rate of 5'4 per cent, but no animals were caught in the snap traps (Table 1). In the forest, the live trap grid had only a single trap success in 446 trap days. In 150trap days of snap trapping on the ground, two animals were caught whilst in the aboveground snap traps seven animals were caught in 149trap days (Table 1). Thus, the success rates in the forest were 0·2 per cent for live traps, 1'3 per cent for ground snap traps and 4'7 per cent for aboveground snap traps. Myomyseus was the only rodent caught in the meadow. The capture of two individuals in the forest was possibly due to the close proximity of the trap line in which they were caught to the grassland area. A single Claviglis was caught in a live trap on the forest floor, but all other specimens of both Claviglis and Grammomys were caught in aboveground situations, in bushes, trees or on a cliffface in the forest (Table 2). The only shrews caught were found in the grassland area. No animals were caught during the day in either the forest or grassland sites. Three Myomyseus were each recaptured once at an average distance of 16 m (Table 5). Estimates of small mammal densities for ground dwelling species were 1·28/ha in the forest, and 25/ha in the grassland (Table 4). Discussion The list of species recorded during the current studies is similar to that recorded during the Royal Geographical Society Expeditions to South Turkana, (Coe, 1972). The Royal Geographical Society area lies in the same ecoclimatic zone as the arid sites of the present study but was close to the Kerio River. G. doliehurus and the gerbils Taterillus nubilus and Gerbillus pusillus mentioned in the RGS report were not recorded from arid sites in 1979, 1980 and 1981, nor was the shrew C. bieolor. However, the small numbers of animals caught in the arid areas in the Kulal area make it quite likely that some species have been missed. It is worth noting that the records of Grammomys and Claviglis of the RGS expeditions were each based on single specimens recorded in the 3 years. Tatera robusta reported from the Kerio Valley was not found around Mt Kulal but T. nigricauda was. However, comments by Davis in Meester & Setzer (1977) indicate that the differences between some races of these two species are slight. Although G. dolichurus and C. bicolor were not caught in the arid sites, they were trapped on Mt Kulal and their range might be expected to extend to suitable sites at lower altitudes. Two other species of rodent were trapped at an altitude of about 2000 m on Mt Kulal, Myomyscus fumatus was recorded in the grassland and C. murinus in the forest. Myomyscus was not recorded from the Kerio Valley by Coe (1972). The three specimens of Grammomys caught from forest sites are interesting because two of them had ears with a distinct white sub-auricular tuft. The presence of this feature has been used to distinguish G. cometes from G. dolichurus by Misonne in Meester & Setzer (1977). The skull and head and body measurements for all three specimens were less than the range indicated for G. cometes; the specimens have therefore been provisionally retained as G. dolichurus. It appears that the sub-auricular tuft may be a variable feature and, in consequence, it must be used with caution in identification. Four specimens of Claviglis were trapped in the forest and were all similar in size and appearance: dark grey above and dark grey patchily washed with buff below. This description contrasts markedly with that of two Claviglis caught at 01 Torot which were
SMALL MAMMALS OF ARID SAVANNA
179
smaller, light smoky grey above and light grey with buff below, becoming cream on the throat and chin. The average body measurements for available specimens from the two sites are given in Appendix I. An examination of material from intermediate sites as well as more from forest and arid areas could prove interesting. Delany (1966) trapped mammals on Mt Moroto in northern Uganda. Like Kulal, Mt Moroto is an isolated mountain with montane forest and grass savanna, but it differs in being wetter. From trapping sites on Mt Moroto at about 2300 m, three species of rodent but no shrews were recorded. Praomys morio, Lophuromys sikapusi, in the forest and Otomys irroratus and L. sikapusi from the grassland. The two mountains, although they have some vegetational similarities, appear to have no small rodent species in common, although both appear to have few species present. Appendix I. Body measurements ofGraphiurus (Claviglis) sp. caught in (a) forest and (b) aridsavanna Habitat
n
Weight (g)
Head and body (mm)
Tail (mm)
Hind foot (mm)
Forest
4
Arid savanna
1*
25'1 (20'5-33'0) 12
88'4 (82-95) 72'5
79'0 (72-89) 76·0
17'6 (16'5-18'0) 14·0
Ear (mm) 16'0 (15'0-17'6) 13·8
n = number in sample; figures in brackets indicate the range.
* The second specimen was taken by a crow before measurements could be taken but was very similar in size and appearance to the first. Generally, the habitats in which the various species were found and their daily activity patterns were in agreement with those recorded by other workers as summarized by Delany (1975), Delany & Happold (1979) and Kingdon (1974). Where there is good vegetation cover some species such as Arvicanthis, Elephantulus and Tatera occur, whereas species such as Gerbil/us can survive in more arid, sparsely vegetated sites. Xerus was observed in a wide range of habitats but not in the driest areas such as the sand dune site at Kargi. The large number of Acomys caught amongst the lava outcrops at Kargi parallels the high Acomys catch in a very similar site from south of Lake Turkana (Coe, 1972). The only species that appeared strictly diurnal wasXerus. Six Elephantulus were captured, four during the day and two at night, which agrees with other records of the day and night activity of this species (Kingdon, 1974). The low trapping success rates in the arid areas near Mt Kulal were very similar to those reported by Coe (1972) in the Kerio Valley, where rates ranged from less than 1'0 per cent to 4·3 per cent. Elsewhere in arid areas of Africa reported trapping rates have been higher, for example Nel & Rautenbach (1975) working in the Kalahari Gemsbok National Park had rates averaging about 10per cent. Trapping rates were also low in the Kulal forest with ground traps success varying from O'2 per cent for live traps to 1·3 per cent for snap traps and an overall trap success of 0·6 per cent. This compares with a rate of 25 per cent from Mt Moroto forest where a combination of live and snap traps were used (Delany, 1966). The density estimates were made using a boundary strip of half a trap interval in width to calculate the effective trapping areas of the grids. However, the effective trapping areas thus calculated may be low estimates because Fleming (1971) suggested that the average distance between successive captures gave a more realistic estimate for the width of the boundary strip. This method was not used in this study as too few recaptures were made to give reliable estimates of average distance. If the average distances were close to the figures given in Table 5, then of course density estimates would be reduced particularly where small grids were used.
180
G. H. G. MARTIN
The average distance figures for northern Kenyan rodents are extremely tentative but interestingly the figure of 16 m for Myomyscus of the montane grassland is close to distances recorded for rodent species from grasslands in Uganda, 22-35 m (Cheeseman & Delany, 1979), and south Central Kenya, 6-21 m (Delany & Roberts, 1978) and 16-28 m (Martin, in prep.). The large average distances from the arid sites may indicate that greater distances have to be travelled in search of food or some other resource. One would expect the populations of animals to be lower in arid areas compared to habitats where food resources are more plentiful. The apparent low population density encountered in the montane forest is more difficult to explain. Superficially, resources appear to be much more abundant than those in the arid habitats of the plain below. The almost year-round night cloud mists ensure that the pronounced seasonal differences in vegetation growth of the arid habitats are not experienced. A seasonal fluctuation in food supply may occur but the wide variation in availability between dry and wet season on the plains seems less likely. For both arid and montane habitats it is necessary that studies over the entire annual climatic cycle are carried out before faunal lists can be completed and the role of rodents in the ecosystems of northern Kenya be realistically assessed. I am extremely grateful to all the IPAL staff at Gatab, Balesa-Kulal and 01 Torot who were so helpful. Particular thanks is given to O. O. Opiyo for material collected in 1979 and to Piers Simpkin for his help and good company in 1980. This work was carried out while I was receiving a research grant from Kenyatta University.
References Bake, G. (1983). Analysis of climatological data from the Marsabit District of Northern Kenya. IPAL Technical Report B-3 UNESCO-MAB Integrated Project in Arid Lands. Nairobi. 89 pp. Cheeseman, C. L. & Delany, M. J. (1979). The population dynamics of small rodents in a tropical African grassland. Journal of Zoology, 188: 451-475. Coe, M. J. (1972). The South Turkana expedition, Scientific paper IX. Ecological studies of the Small Mammals of South Turkana. GeographicalJournal, 138: 316-338. Delany, M. J. (1966). Small rodents from the higher altitude of Mt Moroto, Uganda. RevueZoologie etBotanie Afrique, 73: 339-344. Delany, M. J. (1975). Rodents of Uganda. London: British Museum (Natural History). 165 pp. Delany, M. J. & Happold, D. C. D. (1979). Ecology of African Mammals. London: Longman. 434 pp. Delany, M. J. & Roberts, C. J. (1978). Seasonal population changes in rodents in the Kenya Rift Valley. Bulletin of theCarnegie Museum of Natural History, 6: 92-108. Edwards, K. A. Field, C. R. & Hogg, T. G. G. (1979). A preliminary analysis of climatological data from the Marsabit District of Northern Kenya. IPAL-Technical report B-1, UNEP-MAB Integrated project in Arid Lands, Nairobi. 44 pp. Fleming, T. H. (1971). Population ecology of three species of neotropical rodents. Miscellaneous Publications of Museum of Zooloy, University of Michigan, 143: 1-77. Herlocker, D. (1979). Vegetation of Southwestern Marsabit District, Kenya. IPAL Technical Report D-1, UNEP-MAB Integrated Project in AridLands, Nairobi. 68 pp. Kingdon, J. (1974). East African Mammals Vol. IIB Hares & Rodents. London: Academic Press. 758 pp. Meester, J. & Setzer, H. W. (Eds) (1977). The Mammals of Africa An Identification Manual. Washington: Smithsonian Institution. Nel, J. A. ]. & Rautenbach, I. L. (1975). Habitat use and community, structure of rodents in the southern Kalahari, Mammalia, 39: 9-29. Pratt, D. J. & Gwynne, M. D. (1977). Rangeland Management andEcology in EastAfrica. London: Hodder & Stoughton. 310 pp.