Journal of Mammalogy, 84(3):1019±1030, 2003 AGE ESTIMATION AND DISPERSAL IN THE SPOTTED HYENA (CROCUTA CROCUTA) RUSSELL C. VAN HORN,* TERESA L. MCELHINNY, AND KAY E. HOLEKAMP Department of Zoology, Michigan State University, 203 Natural Science Building, East Lansing, MI 48824, USA Downloaded from https://academic.oup.com/jmammal/article/84/3/1019/903732 by guest on 30 September 2021 We used observations of known-age, free-ranging spotted hyenas (Crocuta crocuta) from a large social group to develop age-estimation models. A model based on tooth-eruption data estimates the ages of animals 10.0±15.5 (61.1 SD) months old. We used tooth-wear data to estimate the ages of adult males 64.9 months and ages of females 622.6 months. Analysis of known and estimated ages shows that males usually disperse from their natal group when 24±60 months of age. Eight of 20 males whose fates were known lived in 3 groups over time, and at least 7 of 41 resident immigrant males appeared to arrive in the study group years after leaving their birthplaces. Thus, males of this species often engage in multiple dispersal events. Key words: age estimation, Crocuta crocuta, dispersal, spotted hyenas Age in¯uences many aspects of mam- mation of annuli may be irregular in C. cro- malian biology, including physiology cuta (Lindeque and Skinner 1984) and oth- (Blom et al. 1994), epidemiology (Mills et er carnivores inhabiting constant environ- al. 1999), and behavior (Bernstein and ments, as is often the case in equatorial re- Ehardt 1985). Because anthropogenic dis- gions. Also, this method requires tooth turbances may alter age-speci®c mortality extraction, which may reduce future feed- and population structure (e.g., Hofer et al. ing ef®ciency of the subject (Van Valken- 1993), the ability to estimate the ages of burgh 1988). animals can facilitate their conservation. In Tooth-wear data represent another poten- addition, age data can enhance understand- tial basis for age estimation in live African ing of mammalian evolution because age it- carnivores (Smuts et al. 1978; Stander self may be an important parameter in evo- 1997). Such data can be collected less in- lutionary processes such as sexual selection trusively than data on annuli, although both (Brooks and Kemp 2001). require immobilization of subjects. Kruuk Counts of dental annuli are frequently (1972), in his seminal work on spotted hy- used to estimate the ages of mammals, in- ena behavior and ecology, had no data from cluding carnivores (Driscoll et al. 1985; known-age animals but assigned individu- Fandos et al. 1993; Landon et al. 1998; als to 1 of 5 relative age classes based on Spinage 1973). Annuli were used by van wear of p3. Lindeque and Skinner (1984) Jaarsveld et al. (1987) to estimate the ages later used the surface area of p3 to distin- of spotted hyenas (Crocuta crocuta) living guish 7 relative age classes among South at relatively high latitudes in southern Af- African C. crocuta. Relationships between rica. These age estimates have been used in dental morphology and age in captive spot- analyses of growth and development (van ted hyenas were described by Binder and Jaarsveld et al. 1987, 1988). However, for- Van Valkenburgh (2000), but the diet of * Correspondent: [email protected] captive animals is softer and probably more 1019 1020 JOURNAL OF MAMMALOGY Vol. 84, No. 3 nutritious than that of free-living C. crocuta Our 1st goal was to develop and validate (Berger et al. 1992), so these relationships age-estimation models for C. crocuta using may differ in the wild. Tooth-wear criteria data from known-age wild individuals. Our may overestimate the ages of young ani- 2nd goal was to test the hypothesis that sec- mals and underestimate the ages of older ondary dispersal occurs in spotted hyenas animals (Spinage 1973), so model valida- and thus that not all interclan transfer is pri- tion is particularly important. Known-age mary dispersal. To accomplish this, we data from free-ranging C. crocuta have not compared the ages of immigrating and em- been used to build or validate any age-es- igrating males to determine what proportion timation models, although such validation might be secondary dispersers. Downloaded from https://academic.oup.com/jmammal/article/84/3/1019/903732 by guest on 30 September 2021 is desirable (e.g., Gipson et al. 2000; Harris et al. 1992; Oosthuizen and Bester 1997). MATERIALS AND METHODS The ability to estimate absolute age of spot- We focused on 1 clan of C. crocuta inhabiting ted hyenas would facilitate the investigation the Talek region (18409S, 358509E) of the Masai of biological phenomena dependent on mat- Mara National Reserve, Kenya, in open grass- uration, such as dispersal. land (Frank 1986). From June 1988 through Natal or primary dispersal is the com- June 2001 this clan was observed for 23±31 plete and permanent departure of an indi- days per month, except for April 1991 when hy- vidual from its birthplace (Greenwood enas were monitored for only 14 days. All in- 1980). Secondary dispersal is any dispersal dividuals in the study clan could be recognized movement occurring after natal dispersal by their unique spot patterns. Spotted hyenas are strongly monomorphic in size and appearance (Pusey and Packer 1987) and is relatively (Hamilton et al. 1986), but we were able to sex common among small mammals (reviewed animals in this study by the dimorphic mor- as `transfer' dispersal in Cockburn 1992) phology of their erect phalluses (Frank et al. and some primates (reviewed in van Noord- 1990). Ages of cubs when 1st observed were wijk and van Schaik 2001). However, it is estimated to 67 days based on pelage, size, and considered uncommon among large mam- behavior (Holekamp and Smale 1998). mals (Sinclair 1992), and the extent to Hyenas were anesthetized with Telazol (W. A. which it occurs among carnivores is cur- Butler Company, Brighton, Michigan; 2.5 mg/kg) rently unknown. administered in a dart using a CO2-powered ri¯e Female spotted hyenas rarely disperse (Telinject Inc., Saugus, California). Most hyenas from the clan, which includes adult natal (76.8%, n 5 151) were darted only once; but to accomplish other research objectives, some hye- females and their offspring and 1 to several nas were darted repeatedly. Cubs typically were adult immigrant males (Holekamp et al. darted when 8±12 months of age (n 5 63). Natal 1993). However, nearly every male even- males also were darted when $24 months of age tually emigrates and assumes a low rank in (n 5 14), and natal females were darted again another clan (East and Hofer 2001; Hen- when we believed them to be pregnant (n 5 36). schel and Skinner 1987; Holekamp and Immigrant males were considered resident if they Smale 1998; Smale et al. 1997) after pu- stayed in the clan $6 months (n 5 58), and most berty at about 24 months of age (Matthews resident males (70.7%) were darted. Nonresident 1939). Natal dispersal appears necessary for immigrant males (i.e., those that stayed in the males to achieve reproductive success clan #6 months) were excluded from all analy- (Engh et al. 2002). Before both primary and ses. Eighteen resident immigrant males and 13 natal males were radiocollared. Those natal males secondary dispersal, males use the range of known from radiotelemetry data to establish res- their current clan as a secure base from idency in 1 clan (i.e., remained in a non-Talek which to explore (Smale et al. 1997; E. E. clan for $6 months) before moving to a 2nd clan Boydston, in litt.), then transfer directly into were classed as secondary dispersers, as were ra- a new clan; they do not become nomads (E. diocollared resident Talek immigrant males that E. Boydston, in litt.). subsequently established residency in another August 2003 VAN HORN ET AL.ÐAGE ESTIMATION AND DISPERSAL IN CROCUTA 1021 clan. Smale et al. (1997) used radiotelemetry to appreciable effect on model performance and so demonstrate that dispersing male hyenas usually were retained for model validation. take exploratory forays outside their natal home Multicollinearity among predictor variables range before emigrating. Therefore, adult natal and low ratios of sample size to predictor vari- males without radiocollars were considered dis- ables can produce spurious regressions (Neter et persers only if they had engaged in such excur- al. 1996). We conducted principal components sions before their disappearance from the clan, if analyses (PCA) on the correlation matrix of each they were in good health when last seen, and if model-building data set (Morrison 1990) to re- they were last seen in the Talek area when $24 duce iteratively the collinearity and dimension- months of age. If these conditions were met, the ality of the data while retaining the maximum estimated age of primary dispersal (n 5 26) was amount of information. Multiple linear regres- Downloaded from https://academic.oup.com/jmammal/article/84/3/1019/903732 by guest on 30 September 2021 the age of the male when he was last seen in the sion models were built with the remaining pre- Talek territory before his 1st absence of $6 dictor variables (Appendix I). Various transfor- months. mations (e.g., log, ln) of predictor and response Thirty-one morphological measurements (15 data (i.e., age in months) were examined. No dental, 4 cranial, and 12 postcranial; Appendix I) variable-selection method will automatically were collected from immobilized hyenas (n 5 ®nd the most appropriate predictor variables 228 dartings of 165 animals) and those found (Neter et al. 1996). Therefore, we chose the ®nal dead (i.e., n 5 33 necropsies, including 25 ani- predictors based on congruence of forward, re- mals not darted).