J. Zool., Lond. (1984) 202,283-297

Age determination and body growth of the Common duiker Sylvicapru grimmiu (Mammalia)

V. J . WILSON*, J. L. SCHMIDT** A N D J . HANKS Institute of Natural Resources, University of Natal, P.O. Box 375, Pietermaritzburg, 3200

Republic of South Africa

(Accepted I4 June 1983)

(With 3 plates and 8 figures in the text)

Age determination in the Common duiker Sylvicapra grimmia was investigated by analysis of tooth eruption and replacement sequence, incremental lines of tooth cementum and tooth wear in a unique collection of 48 known-age skulls, and also by analysis by post-natal body growth in known-age duiker. In both the mandible and maxilla, permanent molariform teeth were fully erupted and in wear by 26 months of age. There was little variation in the age of eruption and replacement of all molariform teeth, making this a particularly useful feature of the duiker for age determination purposes. In contrast, the variability in eruption of the incisiforms, coupled with the difficulty in distinguishing deciduous incisiforms from the permanent counterparts, placed an unexpected limitation on the use of these teeth. Although the apparent linear relationship between tooth attrition and age has potential for further investigation as an age determination technique, the cementum annuli were not correlated with chronological age. Theoretical Von Bertalanfly equations were used to analyse body growth with age. It was concluded that because the asymptote of growth was reached at such an early age, and because there is so much individual variation in growth, body growth, including horn growth, is of very limited value for age determination. Female duiker were significantly larger than males.

Contents

Page Introduction . . .. . . .. . . .. .. .. .. . . 281 Materials and methods . . .. . . .. . . .. .. . . 282 Results .. . . .. . . .. .. .. .. .. . . 284 Discussion . . . . .. . . .. . . .. .. .. .. 290 References . . .. .. . . .. . . .. . . . . .. 294

Introduction The Common duiker (Sylvicupru grimrnia) is one of the more widely distributed of the

African ungulates (Meester & Setzer, 1971). It is typically a savanna species, but also occurs in quite open country, and extends into the alpine zone in mountain areas. Although the species is widespread in Africa, nowhere is it abundant. It is rarely seen in groups larger than two, and usually occurs singly. The Common duiker is mainly nocturnal, and because

*Present address: Chipangali Wildlife Orphanage, P.O. Box 1057, Bulawayo, Zimbabwe. **Present address: Department of Fishery and Wildlife Biology, Colorado State University, Fort Collins, Colorado

80523, U.S.A.

0022-5460/84/020283 + 15 $03.00/0 283

0 1984 The Zoological Society of London

284 V. J . WILSON ET AL

of its non-gregarious and retiring habits, it is a difficult species to study in the field. Thus in spite of its wide distribution, the Common duiker has been the subject of comparatively few investigations, the major studies concentrating on feeding habits (Wilson, 1966a), aspects of reproduction (Child & Mossman, 1965; Symington & Patterson, 1970; Von Ketelhodt, 1977), behaviour (Hopkins, 1966; Dunbar & Dunbar, 1979), blood parasites (Keymer, 1969), predators (Wilson, 1966b), effects of hunting (Child & Wilson, 1964) and drug immobilization (Wilson, 1967). Only two studies have examined techniques for the age determination of the species. Riney & Child (1960) developed nine age classes based on tooth eruption and wear, using four known-age skulls from 1.5 to 21 months to assign chronological ages to the classes. Riney & Child (1964) later investigated horn height as a technique for age determination, but concluded that it was of limited value. No published studies could be found of body growth with age in the Common duiker.

The objectives of this paper are to examine age determination in the duiker based on tooth eruption and replacement sequence, incremental lines of tooth cementum and tooth wear in a unique collection of 48 known-age skulls, to describe and analyse post-natal body growth with age of known-age specimens and to investigate the use of growth data for age determination purposes.

Materials and methods

This study is based on 48 duiker of known-age, ranging from a neonate to 21.5 years of age. All of the animals were raised in captivity in large enclosures in natural to semi-natural conditions, 7 being raised in eastern Zambia, the remainder near Bulawayo in Zimbabwe. Thirty-two duiker were raised naturally by their mothers in enclosure of at least 1000 m2, all of which contained indigenous grasses, shrubs and trees which provided ample food and cover. Sixteen duiker were hand-reared on plain, undiluted cow’s milk to which a small quantity of Terramycin powder was added for the first few days of feeding to prevent stomach disorders. Initially they were fed 4 times a day at approximately 6 hourly intervals. This was gradually reduced to 3 times, twice and once a day until they were weaned at about 4 months of age. Indigenous vegetation was always available to the hand-reared duiker, although they were confined to small cages until they were weaned.

The 48 known-age upper and lower jaws were grouped into age classes based on the sequence of tooth eruption and replacement. X-rays were taken of the mandibles of all specimens with permanent molariform dentition to determine and examine the sequence of the erupting incisiform teeth. The height of the anterior and posterior enamel crown of each of the three fully erupted molars was measured to the nearest 0.1 mm, following the method of Grimsdell (1973) in order to investigate the possible use of tooth attrition as a method of age determination. All fully erupted first, second and third molars in known-age specimens were extracted from one side of the mandible, fixed in 10% buffered formalin and decalcified in 5% nitric acid. The specimens were dehydrated, embedded in paraffin wax, sectioned at 7-15 pm and stained with Haris’ haematoxylin and eosin. The stained sections were examined microscopically with transmitted light for the presence of cementum annuli. Six mandibles from duiker of unknown age collected from various localities in Zambia and Zimbabwe were used to investigate the presence and distribution of tooth cementum annuli in the roots and root pads of the first and third molars using reflected light as described by Morris (1972). Cross-sections and longitudinal sections were taken of each tooth.

Where possible, the known-age duiker were caught each month, weighed to the nearest 0.1 kg and standard body measurements taken as described by Ansell (1965). Horn length was measured along the front surface of both horns, and the mean length calculated and used for subsequent analysis. Five males and 3 females were weighed and measured each month from hi& to death. Theoretical Von

DUIKER AGE DETERMINATION AND BODY GROWTH 285

TABLE I Tooth eruption and replacement in the mandible of the Common duiker

Incisors Canine Premolars Molars

Age Known-age class n (months) 1 2 3 1 2 3 4 1 2 3

1 2 3 4 5 6 I 8 9 10 1 1 12 13

1 4 3 3 2 3 3 5 I 4 I 4 3

0 1-3 2.5-3 4.5 I

8'5-1 0.5 9-10 15-20 11-23 22-25 2648 34-31

60-older

d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d

d/P d/P d/P d P P P P

e e e d d d e d d d E d d d P d d d P e d d d P E d d d P P d d d P P e d d d P P E

d/e d/e d/e P P P P P P P P P P P P P P P P P P P P P

Explanation of symbols: d = deciduous tooth; d/e = deciduous tooth still present, with permanent tooth erupting below; d/P=erupting incisor, I, to I, may be at any stage from d/e to just P; e=permanent tooth just erupting; only cusps or tips visible above bone; E=erupting permanent tooth; all four cusps well above bone but not fully erupted; P= fully erupted permanent tooth.

TABLE I1 Tooth eruption and replacement in the maxilla of the Common duiker

Premolars Molars

Age Known-age class n (months) 2 3 4 1 2 3

1 2 3 4 5 6 I 8 9 10

I 4 2 4 1 3 5 9 3 14

0 1-2.5 34.5 4.5-1 9

8.5-10.5 10-18 18-23 22.5-2 5 26-older

e e e d d d e d d d E d d d P d d d P e d d d P E d d d P P d d d P P e

d/e d/e d/e P P E P P P P P P

Symbols as in Table I.

286 V. J . WILSON E T A L .

Bertalanffy equations to describe growth with age were obtained by calculating the three coefficients in the function by the program of Hanks (1972).

Results Tooth eruption and replacement

Duiker dentition is diphyodont and similar to that of most bovids. There are 20 deciduous teeth and 32 permanent teeth. The complete tooth eruption and replacement sequence in the mandibles of the known-age duiker is shown in Table I, and in the maxilla in Table 11. There was little variation in the age of eruption of the molariform teeth. In both the mandible and the maxilla, all the permanent molariform teeth were fully erupted and in wear by 26 months of age, and there was little overlap between successive age classes leading up to that state of eruption. In the mandible in Class 6, one duiker of 10.5 months had M, still erupting, overlapping with the three duiker of 9, 10 and 10 months in Class 7, where M, was fully erupted. In Class 9, two duiker of 17 and 18 months had a more advanced eruption of M, than the five other animals in that group, overlapping slightly with two animals of 18 and 20 months in Class 8. Class 9 also had one duiker of 23 months in which M, was not fully erupted, which overlapped with Class 10 by one month. In the maxilla, none of the successive age classes overlapped by more than 0.5 month.

Eruption of the permanent incisiform teeth was much more variable in relation to chronological age. The greatest variability occurred in Class 11. X-rays revealed that one 26-month-old duiker was at the same state of tooth development as a 48-month-old animal (Plate I). In both animals, the permanent incisiform teeth were clearly visible beneath the deciduous teeth. The 48-month-old duiker showed a surprising lack of wear on the deciduous incisors and canines (Plate 11) and in this animal and in several others it was impossible to distinguish deciduous incisiforms from the permanent counterparts. The four animals in Class 12 showed various gradations of eruption of the incisors from the state where the deciduous tooth was still present with the permanent tooth erupting below to the state where I, and I, were fully erupted and I, was still deciduous. A further collection of material is required to confirm the sequence of replacement of the incisiforms.

PLATE I. X-ray of the deciduous incisiforms of (a) a 26-month-old duiker and (b) a 48-month-old duiker, illustrating the erupting permanent teeth below the bone.

DUIKER AGE DETERMINATION AND BODY GROWTH 281

PLATE 11. The deciduous incisifoms of a 48-month-old duiker (left) and a 26-month-old duiker (right), the same animals as in Plate I.

288

Age (months)

FIG. 1 . The relationship between molar enamel crown height and age, M, anterior cusp -0; M, anterior cusp. . . 0; M, posterior cusp - - - A. Equations in text.

PLATE 111. The skull and lower jaw ofa 21.5-year-old duiker, the oldest known-age Common duiker on record.

289 DUIKER AGE DETERMINATION AND BODY GROWTH

Tooth attrition

Of the 14 duiker with three fully erupted molars, only four animals were 4 years of age and above (Fig. l), including one animal of 21.5 years (Plate 111), which is the oldest known-age duiker on record. The relationship between age and attrition was investigated, and a linear regression gave the best fit (Fig. 1).

The relationship between molar crown height and age is given by the following equations, where x is age in months, and y is crown height (mm).

M, anterior cusp: y=6.799-0.026x (r=0.812; P<O.OOl) M, anterior cusp: y= 11.479-0.041~ (r=0.865; P<O.OOl)

M, posterior cusp: y= 15.088 -0.049~ (r=0.894; P<O.OOl)

Tooth cementum annuli The reflected light technique demonstrated the presence of cementum annuli in both

the roots and root pads of the first and third molars in duiker of unknown age and this observation stimulated a more detailed analysis of cementum annuli in the molars of duiker of known-age. However, in all cases the lines were very indistinct, and there was a consider- able amount of splitting and joining of lines to the extent that quantification was impossible. Unfortunately, although tooth decalcification, sectioning and staining facilitated both quantitative and qualitative analyis, it was still impossible to correlate cementum annuli with chronological age.

TABLE 111 Von Bertalanfy equations for growth in age in male andfemale Common duiker

Mean size at Age in months Parameter Sex birth+s.E. Von Bertalanffy equation at 'asymptote

Ear length M 76.0kl . l mm t - - 1 19.9 (I-e-O,l53('+6.528)) mm 12 Ear length F 80-1f2.1 mm I I- - 127.4 (I-e-O156('+6W3)) mm 1 1 Shoulder height M 283.6f2.9 mm h t - - 551.3 (l-e-0.147('+4.856))mm 22

Hindfoot length M 184.9f2.3 mm I I- - 300.8 (1-e-@l32('+7.536)) mm 12 Hindfoot length F 183.4f3.3 mm t - - 307.3 (1-e-O201('+4.394)) mm 1 1 Hoof length M 26.0f0.4mm I- - 37.8 (1_e-0.164(t+7.302)) mm 12

Tail length M 69.7+3-1 mm 1 t - - 124.5 (1+-0,224(t+3.216)) mm 10 Tail length F 74.1 f 4 . 3 mm 1 t - - 140.5 (1<-0.198(f+3.683)) mm 10

Weight M 1.51 f 0 . 0 4 kg w, = 18.3 1 (1-e-@l36(k5.416))3 k g 22

Shoulder height F 288.4f4.3 mm h I- - 579.5 (1-e-O-I52('+4506)) mm 16

Hoof length F 26-4fO.6 mm I t - - 39.2 ( 1 - e - o . ~ 3 ~ ( t + 9 . ~ i 3 3 mm 14

Total length M 49 I .5 k 5-7 mm I - - 1061.3 (1+-0.16I(f+4.140)) mm 14 Total length F 496-2+6-9 mm 1 I - - 1105.6 ('-e-O.LSZ(t+4.M4)) mm 14

Weight F 1.64 f 0 . 0 6 kg wf= 18.58 (1+-@179(l+3.g68))3 kg 16

290 V. J . WILSON ET AL.

Body growth

Growth with age in the body parameters measured, together with the mean size at birth and an indication of the age at which the asymptotes are reached, are summarized in Table 111, with growth curves for male shoulder height, tail length, total body length and body weight illustrated in Figs 2-5 respectively. The theoretical Von Bertalanfi equations indicate that males are slightly smaller than females for all the parameters measured, and when all the measurements for each parameter that fell within 5% of the respective asymptotes were compared, the differences between the sexes were significant for ear length, hindfoot length, hoof length and tail length (P<O.Ol), for shoulder height and total length (P<0.05) but not for body weight (0.1 >P>0.05). With the exception of shoulder height and body weight, there was little difference between the sexes in the ages at which the asymptotes were reached (Table 111). The theoretical Von Bertalanfi equations indicate that males reach asymptotic

I . .

520 - T t t 480.

1

E

1 1 I I 1 I I I I 1 I I 1 I l l I I 1

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36

Age (months)

FIG. 2. Theoretical Von Bertalanffy growth curve for shoulder height in male duiker of known-age (range-vertical line; mean-crossbar; standard error-broad ponion of line). The equation is:

h I- - 55 1.3 (I-e-0.147('+4-856)) mm

140 -

40 A A k A Ib ;2 Ib Ik ;8 ;O ;2 ;4 ;6 ;8 ;O 42 ;4 ;6

Age (months)

FIG. 3. Theoretical von Bertalanffy growth curve for tail length in male duiker of known-age (range-vertical line; mean-crossbar; standard error-broad portion of line). The equation is:

/ I - - 124.5 (I+-O224('+3276)) mm

DUIKER AGE DETERMINATION AND BODY GROWTH 29 1

1100- 4A-L-i ' L I ' 1000 - I

- 900- E E

f C 700- 3

- 0

400 d h d h A ;O /2 Ib Ik /8 ;O i2 ;4 ;6 ;8 ;O ;2 ;4 d6

Age (months)

FIG. 4. Theoretical Von Bertalanffjr growth curve for total body length in male duiker of known-age (range- vertical line; mean-crossbar; standard error-broad portion of line). The equation is:

1 t - - 1061.3 (1~-0~161(f+4~140)) mm

20

18

16

14

0 12 c

r - g 10 .-

$ 8

6

4

2

0 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36

Age (months)

FIG. 5. Theoretical von Bertalanffjr growth curve for body weight in male duiker of known-age (range-vertical line; mean-crossbar; standard error-broad portion of line). The equation is:

w - 18.31 (1_e-0.136(~+5.416))3 kg 1-

weight and shoulder height at 22 months, 6 months later than females. This apparent sexual dimorphism in growth rate is confirmed by Figs 6 and 7, which also illustrate the extent of the individual variation in growth with age. The drop in weight of 2-4 kg by all three females (Fig. 7) was unrelated to season or reproductive status. The three duiker were not reared simultaneously, and there was no record of any environmental or stress factors which could have caused the drop.

Horn growth with age was not amenable to analysis by the Von Bertalanffy equation. Although horns were first visible externally as points of keratinization at three months of

292 V. J. WILSON E T A L .

L Q x

0

.- a

Age (months)

FIG. 6. Growth in body weight with age in five male known-age duiker.

weight and shoulder height at 22 months, 6 months later than females. This apparent sexual dimorphism in growth rate is confirmed by Figs 6 and 7, which also illustrate the extent of the individual variation in growth with age. The drop in weight of 2-4 kg by all three females (Fig. 7) was unrelated to season or reproductive status. The three duiker were not reared simultaneously, and there was no record of any environmental or stress factors which could have caused the drop.

Discussion Tooth eruption and replacement

There is little variation in the age of eruption and replacement of the molariform teeth (Tables I and II), making this a particularly useful feature of the duiker for age determination purposes. The variability in eruption of the incisiform teeth (Table I), coupled with the difficulty in distinguishing deciduous incisiforms from the permanent counterparts, reduced the overall viability of this method of age determination, as serious errors in age allocation may occur if the incisiform teeth are examined in isolation. However, if incisiform teeth are examined together with the molariforms, tooth eruption and replacement is undoubtedly the most useful technique for age determination of the duiker up to the age when full permanent dentition is reached. Based on Tables I and 11, Table I V summarizes the conclusions on the recommended allocation of chronological ages to each of the age classes. Although Class

DUIKER AGE DETERMINATION AND BODY GROWTH

100

80 c

E E - 60- f

? 40-

2 0 -

0, c

293

-

-

t , +f I 1 I

20

18 - I6 -

-

L 0)

Y 4 14- 0) -

12- w- I c 2 10-

.p 8

e

- E

3 -

- 2 6 -

I I I I 1 I I I I I I I I

2 4 6 8 10 12 14 16 18 20 22 24

Age (months) FIG. 7. Growth in body weight with age in three female known-age duiker.

26

Age (months) FIG. 8. Growth in horn length with age in duiker of known-age (range-vertical line; mean-crossbar; standard

error-broad position of line).

294 V. J . WILSON ET AL

TABLE IV Summary of conclusions on recommended allocation of chronological ages to age classes in the Common

duiker

Mandible Maxilla

Age Age Age Age class (months) class (months)

1 2 3 4 5 6 7 8 9

10 1 1 12 13

0 1.5 3.0 4.5 7.0 9.0

10.0 17.5 20.0 24.0 30.0 35.0

+ 60.0

1 2 3 4 5 6 I 8 9

10

0 2.0 4.0 6.0 8.5

10.0 15.0 21.0 24.0

f26.0

13 is shown as +60 months, full permanent dentition in the mandible could be attained at least 10 months earlier. Further known-age material is required to confirm the sequence of eruption of the incisiforms, and also the age at which the deciduous incisiforms are replaced by their permanent counterparts. The fact that one duiker of 48 months still had deciduous incisiforms shows how variable this event can be in this particular species, in contrast to the Impala (Aepyceros melampus) (Roettcher & Hofmann, 1970), Greater kudu (Tragelaphus strepsiceros) (Simpson, 1966) and Blesbok (Damaliscus dorcas phillipsi) (Ludbrook & Ludbrook, 1981) where variability in eruption of the incisiforms was less than 1 year. In contrast, Grobler (1980) reported that in Sable (Hippotrugus niger) I, erupts at 18-24 months, I, at 22-28 months, I, at 28-34 months and C, at 34-40 months, a range of 18-40 months. Attwell (1 980) found a similar progression for the Blue wildebeest (Connochaetes taurinus) although in this species it extended from 12 to 48 months.

Only one other study (Riney & Child, 1960) had examined the use of tooth eruption and replacement for age determination of the Common duiker, and that study was based on only four known-age specimens. The unique collection of 48 known-age duiker described in this study has enabled us to expand and modify Riney & Child’s original age classes and assigned chronological ages.

Tooth attrition and cementum annuli

The relationship between age and attrition described in Fig. 1 must be regarded as pro- visional at this stage until more known-age duiker from 4 to 21 years of age are available. Furthermore, considerable caution must be exercised in using the attrition pattern from

DUIKER AGE DETERMINATION AND BODY GROWTH 295

animals from Zambia and Zimbabwe raised in captivity (even though they were in natural to semi-natural conditions) to extrapolate to other populations or areas in Africa, as the rate of attrition will vary significantly according to diet quality, hardness of teeth, genetic variability, etc. It was therefore disappointing to find so much variability in the quantity and quality of the cementum annuli when correlated with chronological age, as this potentially most useful technique had to be rejected in this species from the collection areas. It is probable that the duiker used for this investigation did not experience the required growth checks that are necessary to produce regular cementum annuli. It is now accepted that when environmental conditions deteriorate and/or food quality declines, the growth of the ostein matrix in the tooth is checked. However, mineralization continues at a uniform rate, thus forming a line of greater density when the growth of the matrix slows up, the regions of active growth appearing in the tooth as broad translucent bands (Spinage, 1973, 1976). Thus, in those areas where animals are subjected to pronounced seasonal variations in climate and hence physiological condition, pronounced growth checks will occur that in turn will be reflected in the development of clear cementum annuli (e.g. Red deer (Cervus eluphus) (Mitchell, 1967); Eland (Taurotrugus oryx) (Jeffrey & Hanks, 198 1)). In contrast, where there are small seasonal changes in climate and physiological condition, cementum annuli are far less well-defined (e.g. White-tailed deer (Odocoileus virgianus) (Sohn, 1967; Lockard, 1972); Mule deer (Odocoileus hemionus) (Connolly et ul., 1969)).

Body growth Wilson & Clarke (1 962) reported that female duiker were slightly heavier than males, and

they suggested that this may be a consequence of pregnancy in the female. This study has shown that female Common duiker are significantly larger than males in all parameters measured with the exception of body weight. As a method for age determination, body growth is of limited value, except in animals less than 12 months old, because the asymptote of growth is reached at such an early age (Table 111). Furthermore, there is so much individual variation in growth (Figs 2-7) that even in animals less than 12 months old serious errors can occur. For example, Fig. 6 shows that at 10 months of age, the weights of five known-age male duiker ranged from 9.6 to 14.5 kg, and that a body weight of 10 kg was reached for the first time in one individual at 4.0 months and in another 12 months. It is interesting to note that in all the parameters measured, individual variability was reduced as the asymptote was reached (Figs 2-7). Even horn growth (Fig. 8) was far too variable to be of any real use for age determination purposes. For example, a horn length of 70cm was recorded in known-age individuals ranging from 10 to 19 months, confirming that it is virtually impossible to distinguish sub-adult from adult duiker in the field. The statement by Riney & Child ( 1 964) that when the horns were about half the length of adult horns the animals were probably less than five months of age was not confirmed by this study. If an approximate asymptote of horn length is taken as 100 mm, half that length is reached at 9-10 months (Fig. 8).

We would like to thank Dr J. J. R. Grimsdell and Professor D. E. van Dijk for helpful advice in the analysis of cementum annuli and tooth eruption. Technical assistance was provided by Dr C. A. M. Attwell, Messrs R. Haynes, L. Raw, B. L. P. Wilson, K. V. J. Wilson, Mrs A. Ludbrook, Mrs B. Poggenpoel, and Mrs P. Wilson which is gratefully acknowledged. We would also like to thank Mr

296 V. J. WILSON E T A L

T. Allen-Rowlandson for allowing us to use his unpublished data on horn growth, and Mrs J. Hancock for typing the manuscript. Financial assistance for field work on the project was provided by the Department of National Parks and Wildlife Management (Zimbabwej.

REFERENCES

Ansell, W. F. H. (1965). Standardisation of field data on mammals. Zoologica A f . 1: 97-1 13. Atwell, C. A. M. (1980). Age determination of the blue wildebeest Connochaetes taurinus in Zululand. S. A f . J.

Child, G. & Mossman, A. S. (1965). Right horn implantation in the Common duiker. Science, N. Y. 149:

Child, G. & Wilson, V. (1964). Delayed effects of tseste control hunting on a Ehuiker population. J. Wildl. Mgmt

Connolly, G. E., Dudzinski, M. L. & Longhurst, W. M. (1969). An improved a g e - l a weight regression for black-

Dunbar, R. I. M. & Dunbar, E. P. (1979). Observations on the social organization of common duiker in Ethiopia.

Grimsdell, J. J. R. (1973). Age determination of the African buffalo, Syncerus cafler Sparrman. E. Afi. Wildl. J.

Grobler, J. H. (1980). Body growth and age determination of the sable Hippotragus niger niger (Hams, 1838).

Hanks, J. (1972). Growth of the African elephant (Loxodonta aficana). E. Af . Wildl. J. 10: 251-272. Hopkins, J. M. (1966). Observations on the rearing and behaviour of young duikers in captivity. Niger. Fld 31:

Jeffrey, R. C. V. & Hanks, J. (1981). Age determination of eland Taurotragus oryx (Pallas, 1766) in the Natal

Keymer, I. F. (1969). Investigations of the duiker (Sylvicapra grimmia) and its blood protozoa in Central Africa.

Lockard, G. R. (1972). Furthei studies of dental annuli for aging white-tailed deer. J. Wildl. Mgmt 36: 46-55. Ludbrook, J. V. & Ludbrook, A. L. (1981). Tooth eruption and replacement sequence in blesbok in Natal.

Meester, J. & Setzer, H. W. (1971). The mammals ofAfiica. An identifrcation manual. Washington: Smithsonian

Mitchell, B. (1967). Growth layers in dental cementum for determining the age of Red deer (Cervus eluphus L).

Morris, P. (1972). A review of mammalian age determination methods. Mammal Rev. 2: 69-104. Riney, T. & Child, G. (1960). Breeding season and the ageing criteria for the common duiker (Sylvicapra grimmia).

Riney, T. & Child, G. F. T. (1964). Limitations of horn height as an index to ageing the Common duiker (Sylvicapra

Roettcher, D. & Hofmann, R. R. (1970). The ageing of impala from a population in the Kenya Rift Valley. E.

Simpson, C. D. (1966). Tooth eruption, growth and ageing criteria in greater kudu-Tragelaphus strepsiceros Pallas.

Sohn, A. J. (1967). An evaluation of the dental annuli technique for determining age of White-tailed deer in Iowa.

Spinage, C. A. (1973). A review of the age determination of mammals by means of teeth, with special reference

Spinage, C. A. (1976). Incremental cementum lines in the teeth of tropical African mammals. J. Zool., Lond. 178:

Symington, R. B. & Patterson, N. J. (1970). A preliminary report on the phenomenon of unilateral implantation

Von Ketelhodt, H. F. (1977). Observations on the lambing interval of the Grey duiker (Sylvicapra grimmia

ZOOI. 15: 121-130.

1265-1 266.

28: 866-868.

tailed deer and mule deer. J. Wildl. Mgmt 33: 701-704.

A f . J. E c o ~ ~ 249-252.

11: 31-53.

Koedoe 23: 13 1-1 56.

118-131.

Highveld. S. AS. J. Zool. 16: I 13-122.

Phil. Trans. R. SOC. 255: 33-108.

Lammergeyer 31: 38-42.

Institution Press.

J. Anim. Ecol. 36: 279-293.

Proc. Fedn Sci. Congr. (Salisbury, S. Rhodesia, May, 1960) 1: 291-299.

grimmia). Arnoldia Rhod. 1 ( I ) : 1-5.

A f . WiIdl. J. 8: 3742.

Arnoldia Rhod. 2 (21): 1-12.

Proc. Iowa Acad. Sci. 74: 72-77.

to Africa. E. A/?. Wildl. J . 11: 165-187.

117-131.

in the right uterine horn of the Common duiker, Sylvicapra grimmia. Arnoldia Rhod. 4 (32): 1-5.

grimmia). Zoologica A f . 12: 232-233.

DUIKER AGE DETERMINATION AND BODY GROWTH 297

Wilson, V. J. (1966~). Notes on the food and feeding habits of the Common duiker Sylvicupru grirnmiu, in eastern

Wilson, V. J. (1966b). Predators of the Common duiker Sylvicupru grirnrniu, in eastern Zambia. Arnoldiu Rhod.

Wilson, V. J. (1967). The use of oripavine hydrochloride (M.99) in the drug-immobilization of duiker (Sylvicupru

Wilson, V. J. & Clarke, J. E. (1962). Observations on the Common duiker (Sylvicupru grirnmiu) based on material

Zambia. Arnoldiu Rhod. 2 (14): 1-19.

2 (28): 1-8.

grimmiu). Arnoldiu Rhod. 3 (20): 1-6.

collected from a tsetse control game elimination scheme. Proc. zool. SOC. Lond. 138: 487497.