2. Tierpsychol., 38,55-69 (1975) @ 1975 Verlag Paul Parey, Berlin und Hamburg TSSN 0044-3573/ ASTM-Coden: ZETIAG
University of Bielefeld, Department o f Ethology, and Serengeti Research Institute‘)
Changes in a Population of Dikdik, Madopa (Rhynchotragus) Qirki (Gunther 1880) By HUBERT HENDRICHS W i t h 3 figures Received: 3 . 5 . 1974
A. Introduction I. The biotope At the northern edge of the Serengeti grass plain, bordering the open acacia woodland, a group of “inselbergs” is spread o u t over a n area of a few square kilometers, called “Massai Kopjes” after their owners till 1959. Such inselbergs consist of granitic outcrops, boulders up to the size of a small house, which are connected and surrounded by tracts of dense woody vegetation, interchanging with patches of shrubs and herbs of a high protein content. For rainfall data, plant and vertebrate species cf. HENDRICHS and HENDRICHS (1971). This bush vegetation is inhabited by Kirk’s Dikdik, Madoqua (Rhynchotragus) k i r k (Giinther ISSO), a browsing dwarf antelope which is independent of water, weighing about 5.5 kgz). The genus Madoqua, about 5 species, is systematically grouped together with 5 o r 6 others as subfamily A’eotraginae of the Bovidae (cf. ANSELL1968). The animals of this subfamily are characterized by their small size and the short spikelike horns of the 68, but very likely d o not form a natural unit. With one exception they have big antorbital glands and with another exception thcy all browse. They seem to live in territories, either singly or in pairs or perhaps in small harems, but very little is known so far about their social and spatial organization. In the acacia woodland t w o othcr Neotraginae, Oreotragus oreotragus (Zimmermann 1783), the Klipspringer, and Raphicerus carnpestris (Thunberg 181 l), the Steenbok, live together with the Dikdik. In the Massai Kopjes the Dikdik is the only dwarf antelope, its main food competitors include t w o hyrax species - the arboreal Heterohyrax syriacus (Schreber 1792) and the semiarboreal Procavia johnstoni Thomas 1894 -, some Murids, Giraffe and occasionnally Rhino and Baboon. For approximate densities of these animals cf. H E N D R I C H S and H E N D R I C (1971). HS
11. Characteristics of the Soit 01 Modison population I n the most northeastern part of the Massai Kopjes the rock boulders are grouped especially close together and the vegetation forms especially extensive thickets. The Massni Contribution No. 188. As Kirk’s Dikdik is the largest of all Dikdik the German names ,,Zwerg-Russel-DikDik” (HALTENORTH and TRENSE 1956) or “Zwergriisselantilope” (DORSTand DANDELOT 1970) are not appropriate, while the name “Kirkdikdik’ (WALTHER 1968) is suitable. 1)
2)
56
HUBERT HENDRICHS
distinguished this area of about 40 ha from the rest and gave it a special name: Soit 01 Modison Kopjes (2’ 30,3’ S, 34’ 52,3’ E). The Dikdik of this area d o of course exchange offspring with those in the rest of the Massai Kopjes and also with those of the woodland from which they are separated by tracts of grassland several kilometers widc, but at the same time they show distinctive characteristics of their own (Tab. 1). It therefore appears appropriatc to consider the Soit 01 Modison Kopjes a demotope (SCHWERDTFEGER 1963) and their Dikdik a deme (GILMOUR and GREGOR1939, cf. SIMPSON1961), a distinct local population.
Tub. 1 : Differences between the Dikdik population of the Soit 01 Modison Kopjes and that of the other Massai Kopjes -~ ~
Soit 01 Modison Kopjes
Rest of Massai Kopjes
bush cover and shrub patches extensive
bush cover scarce ,
marked territorial boundary (‘In total territorial boundary1
>lo
( 3 0 - ) 60 - 80
c 50
of
density (adult Dikdik I k m 2 )
[ 2 0 - ) 25 - 30 ( - 5 0 )
time of activity
also during the day
flight distance (rn) (slowly approaching Landrover)
shrub patches small
- 10
L
territory size (ha)
10 - 30
c 20 at night only
50
-
150
111. The investigations of 1967/69 a. Results Dikdik were observed in the Serengeti region from February 1967 to May 1969. The Soit 01 Modison deme - then 6 pairs with their fawns, i. e. 6 social units, all animals were recognized individually - was observed con1971)9). tinuously from July 1968 to May 1969 (HENDRICHS and HENDRICHS The results were in short: The Serengeti Dikdik live in pairs in territories of 5 to 20 ha. The territorial boundaries are defended by the 8 only who chases off strangers, 8 8 and 99,and sometimes engages in ritualized fights with the neighbours. Strategical points along the boundary are marked by dung areas which are regularly used by the pair or the whole family in a ritualized way. As a very important territorial behaviour the dung ceremony shall be shortly described in detail: The 9 enters the dung place first, lowers the hindquarters and without sniffing or scratching urinates in a full squatting position. She then slightly raises the hindquarters to defaecate. The B waits st$nding outside the dung place behind the 0 . H e may sometimes approach the urinating 9,sniff her anally and then show “Flehmen”. When the 0 leaves the dung place, the CT enters, sniffs the 0’s droppings and may scratch the ground with his forelegs and then will lower the hindquarters and urinate, usually continuing the scratching. H e may interrupt this phase to rise and turn by 180’ before continuing. Finally he will squat and defaecate. Thus the behaviour of the 9 during one dung ceremony usually consists of 5 consecutive units: lowering the hindquarters to the ground; urinating in this squatting position; raising the hindquarter halfway up; defaecating in this half squatting position and finally rising. The B may show up to 16 consecutive units. While carrying out 4 activities (sniffing the droppings [0-2 times per ceremony], scratching [2-41, urinating [ 1-21 and defaecating 3)
The study had been supported by the Max-Plan&-Institut fur Verhaltensphysiologic
Seewiesen.
Changes in n Population of Dikdik, Madoqua (Rhynchotragus) kirki
57
[ 1-21) he changes between the 3 positions (standing, halfsquatting, fullsquatting) in 7 ways: turning by 180’ (0-3 times per ceremony), lowering from standing to half- (1-2) or to fullsquatting (0-I), lower from half- to fullsquatting (0-I), raising to standing from half- (0-1) or fullsquatting (2-2) and raising from full- to halfsquatting (rarely). The 9 usually squats lower urinating than defaecating and always urinatcs firsi. Sometimes she may only urinate or only defaecate. The buck turns and sniffs only standing, he urinates only halfsquatting and defaecates only fullsquatting. H e scratches standing and halfsquatting, in the latter case often urinating a t the same time. Scratching and urinating always occur before defaecating. Although each of these behavioural units could be differentiated further, it will be donc here only for one of them: scratching. Scratching is donc alternating with both front legs 3-5 (rarely 2 or 6-8) scratches per leg, 2-4 (1-6) “legs” per one scratching unit, 1-3 (0-4) scratching units per dung ceremony, 4-8 (0-14) “legs” per dung ceremony, approximately 10-40 (0-100) scratches per dung ceremony. The number of scratches and “legs” appears to change with the cycle of thc biotope, with the rcproductive phase and with the age of the buck, but data are too scarce yet to dctcrminc correlations. In the Soit 01 Modison Kopjes there are two types of boundary: marked boundary lines common with a neighbouring territory and unmarked ones bordcring terrain not occupied by Dikdik. Both the marked and the unmarked parts of the boundary are defended against conspecifics and both are crossed at times. The behaviour differs depending on what boundary type has been crossed. When in a foreign territory the animal takes to rapid flight as soon as it perceives another Dikdik, whether this is the territory holder or not. I n unoccupied terrain a t the sight of another Dikdik the buck o r the pair (a 9 alone will take to flight) f i r s t will freeze and then try to identify the other Dikdik. If it is a neighbour not too far from his territory they tend to avoid it. If it is a stranger or a neighbour far from the territory they tend to approach and chase it off. T o be precise, it is necessary to distinguish between four types of limits: I . dcfended boundary line towards a neighbour, 2. range limit in foreign territory, 3. dcfended boundary line toward terrain not occupied by any Dikdik, 4. range limit i n unoccupied terrain. The dcfended boundaries are always the same for both I3 and 9 of a pair, but the rangc limits vary individually, that of the 8 usually being consideraRy larger than that of the 9. The 9 after a gestation period of 25 weeks gives birth twice a year to a single fawn. The young of both sexes arc expelled from the parental territory a t the age of 7 to 8 months, the male fawn is chased off by the buck, the female fawn possibly by the doe but this could not be ascertained. In the Soit 01 Modison deme there was n o change in mates and none in the territorial boundaries during the 10 months from July 1968 to May 1969. One 9 disappeared in January 1969 and the I3 held the territory alone thereafter.
b. Unanswered questions Although the social and territorial organization of the Dikdik is relatively simple and clcarcut, a number of important questions remained unanswered in the first study.
HUBERT HENDRICHS
58
For example: H o w old do Dikdik get? U p to what a.ge does a pair hold its territory? What is the turnover rate? H o w stable is the pairbond? Is it independent of the territorial bond? H o w stable are the territorial boundaries? D o they change with different holders? Does the 9 have only a pairbond or also a territorial one?
1. 2. 3. 4.
5.
Tab.2: Size and holders of the Soit 01 Modison territories in 1968 and in 1972 (in brackets: the minimum age of the animals, the real age is estimated t o lie between 10 and 5 0 % abovc these figures, cf. T a b 3: the holders of territory VII are not known individually and therefore not considered in the text) territory V
I
held by
size (ha)
1968
1972
1968
1972
10,lL
10,lL
M5 I L )
-
7,a2
M , 16)
- W, 16)
1 3,09 73,93
M, ( 2 )
-
/
6 , ~
University of Bielefeld, Department o f Ethology, and Serengeti Research Institute‘)
Changes in a Population of Dikdik, Madopa (Rhynchotragus) Qirki (Gunther 1880) By HUBERT HENDRICHS W i t h 3 figures Received: 3 . 5 . 1974
A. Introduction I. The biotope At the northern edge of the Serengeti grass plain, bordering the open acacia woodland, a group of “inselbergs” is spread o u t over a n area of a few square kilometers, called “Massai Kopjes” after their owners till 1959. Such inselbergs consist of granitic outcrops, boulders up to the size of a small house, which are connected and surrounded by tracts of dense woody vegetation, interchanging with patches of shrubs and herbs of a high protein content. For rainfall data, plant and vertebrate species cf. HENDRICHS and HENDRICHS (1971). This bush vegetation is inhabited by Kirk’s Dikdik, Madoqua (Rhynchotragus) k i r k (Giinther ISSO), a browsing dwarf antelope which is independent of water, weighing about 5.5 kgz). The genus Madoqua, about 5 species, is systematically grouped together with 5 o r 6 others as subfamily A’eotraginae of the Bovidae (cf. ANSELL1968). The animals of this subfamily are characterized by their small size and the short spikelike horns of the 68, but very likely d o not form a natural unit. With one exception they have big antorbital glands and with another exception thcy all browse. They seem to live in territories, either singly or in pairs or perhaps in small harems, but very little is known so far about their social and spatial organization. In the acacia woodland t w o othcr Neotraginae, Oreotragus oreotragus (Zimmermann 1783), the Klipspringer, and Raphicerus carnpestris (Thunberg 181 l), the Steenbok, live together with the Dikdik. In the Massai Kopjes the Dikdik is the only dwarf antelope, its main food competitors include t w o hyrax species - the arboreal Heterohyrax syriacus (Schreber 1792) and the semiarboreal Procavia johnstoni Thomas 1894 -, some Murids, Giraffe and occasionnally Rhino and Baboon. For approximate densities of these animals cf. H E N D R I C H S and H E N D R I C (1971). HS
11. Characteristics of the Soit 01 Modison population I n the most northeastern part of the Massai Kopjes the rock boulders are grouped especially close together and the vegetation forms especially extensive thickets. The Massni Contribution No. 188. As Kirk’s Dikdik is the largest of all Dikdik the German names ,,Zwerg-Russel-DikDik” (HALTENORTH and TRENSE 1956) or “Zwergriisselantilope” (DORSTand DANDELOT 1970) are not appropriate, while the name “Kirkdikdik’ (WALTHER 1968) is suitable. 1)
2)
56
HUBERT HENDRICHS
distinguished this area of about 40 ha from the rest and gave it a special name: Soit 01 Modison Kopjes (2’ 30,3’ S, 34’ 52,3’ E). The Dikdik of this area d o of course exchange offspring with those in the rest of the Massai Kopjes and also with those of the woodland from which they are separated by tracts of grassland several kilometers widc, but at the same time they show distinctive characteristics of their own (Tab. 1). It therefore appears appropriatc to consider the Soit 01 Modison Kopjes a demotope (SCHWERDTFEGER 1963) and their Dikdik a deme (GILMOUR and GREGOR1939, cf. SIMPSON1961), a distinct local population.
Tub. 1 : Differences between the Dikdik population of the Soit 01 Modison Kopjes and that of the other Massai Kopjes -~ ~
Soit 01 Modison Kopjes
Rest of Massai Kopjes
bush cover and shrub patches extensive
bush cover scarce ,
marked territorial boundary (‘In total territorial boundary1
>lo
( 3 0 - ) 60 - 80
c 50
of
density (adult Dikdik I k m 2 )
[ 2 0 - ) 25 - 30 ( - 5 0 )
time of activity
also during the day
flight distance (rn) (slowly approaching Landrover)
shrub patches small
- 10
L
territory size (ha)
10 - 30
c 20 at night only
50
-
150
111. The investigations of 1967/69 a. Results Dikdik were observed in the Serengeti region from February 1967 to May 1969. The Soit 01 Modison deme - then 6 pairs with their fawns, i. e. 6 social units, all animals were recognized individually - was observed con1971)9). tinuously from July 1968 to May 1969 (HENDRICHS and HENDRICHS The results were in short: The Serengeti Dikdik live in pairs in territories of 5 to 20 ha. The territorial boundaries are defended by the 8 only who chases off strangers, 8 8 and 99,and sometimes engages in ritualized fights with the neighbours. Strategical points along the boundary are marked by dung areas which are regularly used by the pair or the whole family in a ritualized way. As a very important territorial behaviour the dung ceremony shall be shortly described in detail: The 9 enters the dung place first, lowers the hindquarters and without sniffing or scratching urinates in a full squatting position. She then slightly raises the hindquarters to defaecate. The B waits st$nding outside the dung place behind the 0 . H e may sometimes approach the urinating 9,sniff her anally and then show “Flehmen”. When the 0 leaves the dung place, the CT enters, sniffs the 0’s droppings and may scratch the ground with his forelegs and then will lower the hindquarters and urinate, usually continuing the scratching. H e may interrupt this phase to rise and turn by 180’ before continuing. Finally he will squat and defaecate. Thus the behaviour of the 9 during one dung ceremony usually consists of 5 consecutive units: lowering the hindquarters to the ground; urinating in this squatting position; raising the hindquarter halfway up; defaecating in this half squatting position and finally rising. The B may show up to 16 consecutive units. While carrying out 4 activities (sniffing the droppings [0-2 times per ceremony], scratching [2-41, urinating [ 1-21 and defaecating 3)
The study had been supported by the Max-Plan&-Institut fur Verhaltensphysiologic
Seewiesen.
Changes in n Population of Dikdik, Madoqua (Rhynchotragus) kirki
57
[ 1-21) he changes between the 3 positions (standing, halfsquatting, fullsquatting) in 7 ways: turning by 180’ (0-3 times per ceremony), lowering from standing to half- (1-2) or to fullsquatting (0-I), lower from half- to fullsquatting (0-I), raising to standing from half- (0-1) or fullsquatting (2-2) and raising from full- to halfsquatting (rarely). The 9 usually squats lower urinating than defaecating and always urinatcs firsi. Sometimes she may only urinate or only defaecate. The buck turns and sniffs only standing, he urinates only halfsquatting and defaecates only fullsquatting. H e scratches standing and halfsquatting, in the latter case often urinating a t the same time. Scratching and urinating always occur before defaecating. Although each of these behavioural units could be differentiated further, it will be donc here only for one of them: scratching. Scratching is donc alternating with both front legs 3-5 (rarely 2 or 6-8) scratches per leg, 2-4 (1-6) “legs” per one scratching unit, 1-3 (0-4) scratching units per dung ceremony, 4-8 (0-14) “legs” per dung ceremony, approximately 10-40 (0-100) scratches per dung ceremony. The number of scratches and “legs” appears to change with the cycle of thc biotope, with the rcproductive phase and with the age of the buck, but data are too scarce yet to dctcrminc correlations. In the Soit 01 Modison Kopjes there are two types of boundary: marked boundary lines common with a neighbouring territory and unmarked ones bordcring terrain not occupied by Dikdik. Both the marked and the unmarked parts of the boundary are defended against conspecifics and both are crossed at times. The behaviour differs depending on what boundary type has been crossed. When in a foreign territory the animal takes to rapid flight as soon as it perceives another Dikdik, whether this is the territory holder or not. I n unoccupied terrain a t the sight of another Dikdik the buck o r the pair (a 9 alone will take to flight) f i r s t will freeze and then try to identify the other Dikdik. If it is a neighbour not too far from his territory they tend to avoid it. If it is a stranger or a neighbour far from the territory they tend to approach and chase it off. T o be precise, it is necessary to distinguish between four types of limits: I . dcfended boundary line towards a neighbour, 2. range limit in foreign territory, 3. dcfended boundary line toward terrain not occupied by any Dikdik, 4. range limit i n unoccupied terrain. The dcfended boundaries are always the same for both I3 and 9 of a pair, but the rangc limits vary individually, that of the 8 usually being consideraRy larger than that of the 9. The 9 after a gestation period of 25 weeks gives birth twice a year to a single fawn. The young of both sexes arc expelled from the parental territory a t the age of 7 to 8 months, the male fawn is chased off by the buck, the female fawn possibly by the doe but this could not be ascertained. In the Soit 01 Modison deme there was n o change in mates and none in the territorial boundaries during the 10 months from July 1968 to May 1969. One 9 disappeared in January 1969 and the I3 held the territory alone thereafter.
b. Unanswered questions Although the social and territorial organization of the Dikdik is relatively simple and clcarcut, a number of important questions remained unanswered in the first study.
HUBERT HENDRICHS
58
For example: H o w old do Dikdik get? U p to what a.ge does a pair hold its territory? What is the turnover rate? H o w stable is the pairbond? Is it independent of the territorial bond? H o w stable are the territorial boundaries? D o they change with different holders? Does the 9 have only a pairbond or also a territorial one?
1. 2. 3. 4.
5.
Tab.2: Size and holders of the Soit 01 Modison territories in 1968 and in 1972 (in brackets: the minimum age of the animals, the real age is estimated t o lie between 10 and 5 0 % abovc these figures, cf. T a b 3: the holders of territory VII are not known individually and therefore not considered in the text) territory V
I
held by
size (ha)
1968
1972
1968
1972
10,lL
10,lL
M5 I L )
-
7,a2
M , 16)
- W, 16)
1 3,09 73,93
M, ( 2 )
-
/
6 , ~
