Behav Ecol Sociobiol (2006) 60: 368–378DOI 10.1007/s00265-006-0174-4

ORIGINAL ARTICLE

Torsten Wronski . Ann Apio . Martin Plath

The communicatory significance of localised defecation sites

in bushbuck (Tragelaphus scriptus)

Received: 2 June 2005 / Revised: 25 November 2005 / Accepted: 9 February 2006 / Published online: 16 March 2006# Springer-Verlag 2006

Abstract Like several other mammals, bushbuck (Trage-laphus scriptus) deposit faeces in specific localised defe-cation sites (LDS). A previous study has ruled out afunction of LDS in the context of parasite avoidance. In thisstudy, we investigated the communicatory significance ofLDS. In a free ranging population, we tested whether LDSserve to demarcate home ranges, and/or if LDS are used forcommunication in a non-territorial context. In both sexes,LDS increased significantly in number towards theperiphery of individual home ranges. However, the distri-bution pattern of LDS, as revealed by a nearest-neighbourmapping technique (nearest distances between LDS), didnot support the idea that LDS serve home range/territory-demarcation because LDS did not follow a pattern ofminimal nearest-neighbour distances along the margins ofhome ranges. We found females to urinate more often inLDS than males. Notably, information transfer was mostfrequent between sending (urinating or defecating) femalesand receiving/responding males (urination or defecation at

places where a female had previously signalled). Ourresults suggest that LDS mainly serve for inter-sexualcommunication in bushbuck.

Keywords Antelopes . Information centres . Inter-sexualcommunication . Territoriality . Uganda

Introduction

Scent marking is a widespread form of communication inmammals (Eisenberg and Kleiman 1972; Johnson 1973;Ewer 1976; Vandenbergh 1983). It can be linked to a widerange of contexts, including kin recognition and sociallearning (Ramsay and Giller 1996), the advertisement ofreproductive status (Walls et al. 1989; Heise and Rozenfeld2002), interactions between predators and prey (Lewis andMurray 1993), foraging (Henry 1977), dispersal anddispersion (Gorman and Stone 1990; Lenti Boero 1995),reproductive suppression (Rylands 1990) and the mainte-nance of dominance hierarchies and internal group-bonds(Gosling and Wright 1994; Gosling et al. 1996). Further-more, scent marking is often related to the occupation andmaintenance of a territory or home range (Gorman 1984;Gosling 1990; Lenti Boero 1995). Urine and faeces of mostmammals contain species-specific, odoriferous substances(pheromones), but not all species use them for marking(Wyatt 2003). Among ungulates, urination and defecation,whether scattered or localised, are perhaps the mostcommon forms of scent marking (Ralls 1971). Thedeposition of excreta bearing scents that identify thedepositor may convey specific information about him orher (Altmann 1969; Ewer 1976). In many mammalianspecies, excreta accumulate in localised defecation sites(LDS; Brown and MacDonald 1985; Smith et al. 1989;Pigozzi 1990; Estes 1991; Sneddon 1991; Hutchings et al.2002; Marassi and Biancardi 2002). Beside a possiblefunction for communication, localised defecation may havea hygienic function in the context of parasite avoidance(Cooper 1997; Ezenwa 2000, 2004; Hutchings et al. 1998,1999; van der Wal et al. 2000).

Communicated by E. Korpimäki

T. WronskiDepartment of Behaviour, Biozentrum Grindel undZoologisches Museum, University of Hamburg,Martin-Luther-King-Platz 3,Hamburg 20146, Germany

A. ApioDepartment of Zoology, Faculty of Science with Education,Mbarara University of Science and Technology,P.O. Box 1410 Mbarara, Uganda

M. Plath (*)Unit of Evolutionary Biology and Systematic Zoology,Institute for Biochemistry and Biology, University of Potsdam,Karl-Liebknecht Street 24-25,Potsdam 14476, Germanye-mail: martin_plath@web.deTel.: +49-331-977-5586Fax: +49-331-977-5070

M. PlathDepartment of Zoology, University of Oklahoma,730 Van Vleet Oval,Norman, OK 73019, USA

For bushbuck (Tragelaphus scriptus, Bovidae: Tragela-phini), we could show that parasite avoidance apparentlyhas a minor or even no importance for the establishmentand maintenance of LDS because the contamination withinfective larvae of several species of gastrointestinal tractnematodes did not significantly differ between pastures in-and outside LDS (Apio et al. 2006). Furthermore,bushbuck are predominantly browsers, which often forageat heights above contamination level (Apio 2003).Bushbuck even increased their foraging rates inside LDS,probably because pastures contain more minerals. Alto-gether, this suggests that LDS serve a social function inbushbuck, namely, communication. In the present study,we therefore focussed on the communicatory significanceof LDS in this species, such as territory-demarcation orinter-sexual communication.

LDS are typically found in species with a high site-fidelity (Pflumm 1989) and territorial organisation(Gosling and Roberts 2001a). This suggests that LDSmay serve to demarcate territories. In many mammalianspecies, dung piles are either found in the approximatecentre of the territory/home range (Mills et al. 1980;Norton 1980; Ono et al. 1988), or along the boundary(Hendrichs and Hendrichs 1971; Dunbar and Dunbar1974; Walther 1978; Ono et al. 1988; Brashares andArcese 1999; Stewart et al. 2001). Often, several in-dividuals use the same LDS, for example in Grant’sgazelle (Gazella granti; Ezenwa 2004) and dikdik(Madoqua kirkii; Hendrichs and Hendrichs 1971;Ezenwa 2004). Numerous studies have suggested afunction of LDS for fending off intruders (Walther 1964;Mykytowycz 1968; Dunbar and Dunbar 1974; Owen-Smith 1977; Gosling 1982; Pigozzi 1990; Zollner et al.1996; Roberts and Lowen 1997; Brashares and Arcese1999). On the other hand, several authors emphasisedthe confidence-enhancing function rather than the re-pellent effects of LDS. The idea that markings provideboth confidence to the resident and intimidate possibleintruders seems plausible and has received circumstan-tial support from field and experimental studies(Mykytowycz and Gambale 1969; von Richter 1972;Joubert 1972). Furthermore, some authors suggested thatcommunal deposition sites should be regarded as centresof information exchange (Eisenberg and Kleiman 1972;Johnson 1973).

Localised defecation in both sexes has been describedfor several ungulates (e.g. dikdik, M. kirkii: Hendrichs andHendrichs 1971; Ono et al. 1988; klippspringer, Oreo-tragus oreotragus: Dunbar and Dunbar 1974; blackrhinoceros, Diceros bicornis: Goddard 1970; white rhinoc-eros, Ceratotherium simum: Owen-Smith 1975). Localiseddefecation in only one sex is known from Grant’s gazelle(G. granti, Estes 1991) and Thomson’s gazelle (Gazellathomsoni, Walther 1978), kongoni (Alcelaphus buselaphuscokei, Gosling 1974) and oribi (Ourebia ourebi, Monfortand Monfort 1974; Brashares and Arcese 1999). In thepresent study, we examined the functions of LDS-utilisation by male and female bushbuck in QueenElizabeth National Park, Uganda. Bushbuck are a solitary

species with high site-fidelity (Allsopp 1971; Waser 1975a,Wronski 2004). Except for bushbuck (Apio et al. 2006),accumulations of faeces have not been described for anyspecies of tragelaphine antelopes (Estes 1991). Formerly,all species within the tribe Tragelaphini were considered toscatter their faeces randomly (Walther 1964), suggestingthat the communicatory function of scent emanating fromexcreta would be less important in this group (Estes 1991).We tested several hypotheses related to the social/communicatory function of dung accumulations in thiswidespread, but poorly known African antelope:

1. We examined the distribution of LDS relative toposition within the home range. We predicted that LDSwould be more frequent at the periphery of a homerange if their major function was communication withindividuals in neighbouring home ranges. Theoreti-cally, LDS might be situated rather in the centre of thehome range, as may be the case in brown hyena,Hyaena brunea (Mills et al. 1980). The shift fromcentral to peripheral marking appears to depend onfactors such as the size of the territory and on energeticand time constraints such as the ability to patrol theborder (Roberts and Lowen 1997; Gosling and Roberts2001a). In relation to body size, bushbuck home rangesare relatively small (Jacobsen 1974; Odendaal andBigalke 1979; Wronski 2005), so that peripheralmarking was most likely.

2. If our first analysis (see above) showed that LDS aresituated at the periphery of home ranges, this wouldgive a first hint that LDS might define territories, butthey might also serve communication between individ-uals in a non-territorial context. We used a furtheranalysis of the spatial distribution of LDS to givefurther insight into a possible territorial function: Thespatial pattern of nearest-neighbour distances betweenperipheral territorial marking sites typically results in apolygon with radially projecting arms (Gosling 1981).This pattern is assumed to be a consequence of theterritorial function of marking sites because it waspredicted that the marks (in this case LDS) form acontinuous line around the perimeter of the territory.Along this line, markings should be distributed atminimum distance from the next marking to enhancethe chance of detection by an intruder, and economydictates that the territory holder should avoid markingexcept along the polygon line (Gosling 1981, 1982;Gosling and Roberts 2001a). We examined thearrangement of LDS within home ranges using thenearest-neighbour mapping technique (Gosling 1981).Following Gosling (1981), we predicted the nearest-neighbour distances to be shifted to shorter distancesthan expected from a random distribution if LDSserved territory-demarcation. Whilst a pattern of LDSdistribution with peripheral arrangement and minimaldistances between LDS would point to a territorialfunction, as a matter of course, one cannot argue inreverse that a negative finding (non-peripheral ar-rangement and/or a pattern of nearest-neighbour

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distances that does not deviate from a random distri-bution) proves the opposite, i.e. that LDS have noterritorial function.

3. Our first two analyses were conducted to give anestimation of whether LDS generally serve commu-nication, and whether a territorial function may bepossible. However, whether LDS are truly used forterritory-demarcation can be determined best byobserving the behaviour of individual bushbuck. Forexample, LDS may also serve for intra- or inter-sexualcommunication. Territoriality is evident only in themale sex, or is at least considerably less pronounced infemales (Wronski 2004, 2005). Therefore, we pre-dicted that males would show more signalling insideLDS, and that the most frequent communication eventwould be that males respond to signals deposited byanother male if LDS truly served territory-demarca-tion. To study this, we tested for sex-specific differ-ences in the frequency of LDS use. Furthermore, wetested for differences in the frequencies of responses(signalling at places where another animal hadpreviously signalled) between the categories ‘malesrespond to females’, ‘females respond to males’,‘females respond to females’ and ‘males respond toother males’.

Methods

Study species

Bushbuck are predominantly browsers and inhabit densebush-land, riverine forests and similar habitats (Jacobsen1974; Simpson 1974; Smiths 1986; MacLeod et al. 1996).Adult males are territorial and their home ranges (mean±SD: 88.05±34.9 ha) encompass several female homeranges (27.43±13.5 ha; Wronski 2004). It is as yetunknown for what period males maintain territories, butour observations indicate that individual males may holdterritories for at least 3 years. Females are organised inmatrilines. Each female shows high site-fidelity, wherebyfemales from different clans show very little home rangeoverlap, but the home ranges of related females (i.e. clanmembers) strongly overlap (Wronski 2004; Wronski andApio 2005). However, this does not mean that clanmembers are constantly forming groups, but even clanmembers are solitary most of their time. Socio-positivebehaviour is typically observed between related females,but is lacking between non-related females, whereaggressive interactions prevail (Wronski 2004; Wronskiand Apio 2005). Sub-adult males form loose, temporarybachelor pools (Wronski 2004, 2005).

Study area and period

We investigated a free-ranging bushbuck population on theMweya peninsula and adjacent areas in Queen ElizabethNational Park, in western Uganda (latitude 0°10′S to 0°12′

S, longitude 29°52′E to 29°54′E). The study area coversapproximately 2.7 km2 and comprises a grassland habitatwith scattered Capparis tomentosa/Euphorbia candelabrathicket clumps and coalesments (Lock 1977; Zandri andViskanic 1992). The altitude of the study area is 940 mabove sea level. The climate is equatorial, with little annualfluctuations in day length and temperature (monthly mean:22–25°C), but with two pronounced wet and dry seasons.During the study period (01.04.99–12.01.02), the meanannual rainfall was 680 mm.

Studied population

Bushbuck on the Mweya peninsula are well-habituated tothe presence of human observers, and many individualsare exceptionally tame. Therefore, several individualscould be observed from close proximity, and the presenceof human observers apparently did not influence thebehaviour of the observed animals. In total, 16 adultmales, 46 adult females and several sub-adult males werepresent in the study area. Because sub-adult males areknown to migrate within a large area, they were notincluded in our investigation. All animals in the study areawere individually known and distinguishable by theircharacteristic coat patterns. Identification was aided by aphotographic file card system. Before this study, nineindividuals (five males and four females) had been radio-collared to help individually track them. To fix radiocollars, animals were chemically immobilised using a dartgun with a 16-g CO2 cylinder. The anaesthesia andsedation drugs were administered intramuscularly using aspecial dart syringe. To restrain adult animals (weighingbetween 28 and 56 kg), either 0.6 to 0.85 ml aceproma-zine or 0.6 to 0.8 ml etorphine HCl (M-99, Immobilon)were used for anaesthesia; 0.6 to 0.85 ml xylazine(Rompun) or 0.8 ml azaperon were used as a sedative.To stimulate the respiration of the animal after it wentdown, doxapram was given intramuscularly or intrave-nously. After the intervention was terminated (after 10–20 min), 1.4 to 2 ml diprenorphin (Revivon) wasadministered as an anti-dote to reverse the effects of theanaesthesia drugs. The recovery time was between 3 and6 min. The immobilisation was done from a car by aveterinarian of the Uganda Wildlife Authority, Dr. L.Siefert (Department of Wild Animal Resource Manage-ment, Faculty of Veterinary Medicine, Makerere Uni-versity, Uganda). The nylon collars used were equippedwith tw-3 tags of BIOTRACK, UK and had a weight of130 g each. Their weight as a percentage of the animals’weight was 3.23±0.83% (mean±SD; 2.15% of the largest,4.38% of the smallest animal). After we had fixed theradio collars, no behavioural differences were recorded,and no case of mortality due to the immobilisationprocedure was observed. We initially collared 11 animals,two of which (18.2%) were caught by predators duringour study period. Among the 99 non-collared animals, 14(14.1%) were caught within the same time; hence,

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collared animals have not suffered increased predationrisk due to our treatment.

Definition and characteristics of localised defecationsites

We defined LDS as areas in which bushbuck faeces hadaccumulated (five or more faecal pellet groups, not morethan 10 m apart; Apio et al. 2006). In a preliminary searchof the study area, 75 LDS could be determined. During thisscreening period, we thoroughly patrolled the whole studyarea several times by foot, thereby including all thicketclumps. Our preliminary study has also shown that LDSwere used by more than one individual and that males andfemales may use the same LDS. The maximum extensionof LDS ranged between 6 and 54 m (mean±SD: 24.9±11.5 m). The variability can be explained in that some LDSwere positioned along thicket fringes so that their shapewas rather oval, not circular like most others. Eleven LDSwere situated inside a thicket, 17 next to a thicket (thicketfringe) and 47 in open grassland. LDS were marked bymarking tapes and labelled with numbers to help re-localisethem. The LDS positions were plotted on a map (1:5,000)and processed as UTM coordinates using a geographicinformation system (Arcview 3.2a in combination withAnimal Movements, Hooge 1998).

Distribution of LDS in relation to home range area

For a spatial analysis of the distribution of LDS withinindividual home ranges, we used two different approaches:In the first step, we asked whether LDS are situated at theperiphery of home ranges. To relate the spatial distributionof LDS to certain home range sections, the home ranges offour males and nine females from three matrilineal clanswere observed. Females were examined both on anindividual level and on the level of matrilineal clansconsisting of related females in neighbouring, overlappinghome ranges (Wronski and Apio 2005). For the latter, weexamined the distribution of LDS relative to the commonhome range of all females of a clan. The calculation ofhome range cores was based on location fixes obtainedover a period of 3 years from haphazardly encounteredanimals and followed procedures described by Wronski(2005). A home range section was defined as the areabetween two home range cores (<15, 15–30, 31–50, 51–70,71–90 and >90%), which were established by using a fixedkernel density estimation (Worton 1989). We determinedthe number of LDS in each home range section. To test fordifferences between sections of decreasing utilisationdensity, we applied a Friedman repeated measuresANOVA on ranks. Generally, we tested for normaldistribution using a Kolmogorov–Smirnov test. In case ofnon-normally distributed data, only non-parametric statis-tics were employed.

Arrangement of LDS within home ranges

We analysed the arrangement of LDS within the homeranges of the same males, females and within the commonhome ranges of groups of related females (matrilines) byusing the nearest-neighbour mapping technique (Gosling1981, 1985). All LDS inside a home range were mapped,and each plot representing LDS was joined by a line to itsnearest neighbour. Both were joined if the nearestneighbours were equidistant. This produced a number ofinternally linked primary clusters, which were again joinedto the nearest neighbouring cluster by a line between thoseLDS closest to each other. Accordingly, secondary clusterswere joined to tertiary clusters etc., until all LDS werelinked together. The mapping technique resulted in anapproximately oval-shaped polygon with a remaining gapat one side (Gosling 1981). The nearest-neighbourdistances between all LDS within a given home rangewere determined, lumped in categories of 10 m intervalsand compared with expected random distributions derivedfrom a Poisson procedure. We tested for differencesbetween expected and observed distribution using a Chi-squared goodness of fit (Dytham 1999).

Frequencies of LDS use

We determined the frequencies of defecation, urination and‘lying out behaviour’ (Walther 1964) inside LDS, and wetested for sex-specific differences. Secretions emanatingfrom inguinal glands can be deposited in LDS during lyingout phases (Kingdon 1982). In a longitudinal samplingstudy, we continuously observed five radio-collared adultmales and four females applying focal animal sampling inconjunction with ad libitum recording of their behaviourinside LDS (Altmann 1974; Martin and Bateson 1985). Werecorded defecation, urination and lying out behaviour ofthe focal animals inside LDS, and LDS visits without oneof these behaviour patterns. If LDS were situated within athicket, they were inspected for fresh urine or faecaldroppings immediately after the focal animal had left.Longitudinal sampling sessions were conducted during 79blocks of observations lasting between 12 and 96 h(1,794 h of non-stop observation in total). Bushbuck showpeak activity at dawn, and they are also active at night(Waser 1975b; Wronski, unpublished data). Therefore, allobservations were carried out equally during day- andnighttime. In total, 29 LDS were used by the focal animalsduring this part of our observations. We calculated thefrequency of urination, defecation, lying out and LDS visitswithout these behaviour categories per hour for both sexes.We tested for sex-specific differences using independent-samples t tests.

Information exchange through LDS

With the attempt to record communication transfer throughLDS, in another approach, we monitored LDS paralleled

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with longitudinal observations of radio-collared focalanimals. We tested for differences in information transferbetween the sexes, i.e. differences between intra- and inter-sexual communication. For this part of our study, fiveradio-collared focal animals (two males and three females)were followed by one observer. Meanwhile, the study areawas patrolled by a second observer to collect data on theactivities, locations and especially LDS visits of otherindividuals present in the home range of the focal animal.Observations were carried out in 16 blocks with a totalobservation time of 848 h. Each observation sequencelasted between 12 and 96 h. We hypothesised that urine,faeces and gland secretions act as signals. We consecu-tively recorded urination, defecation and lying out behav-iour inside LDS, and we noted whether these behaviourpatterns occurred exactly at those places inside LDS whereanother individual had defecated, urinated or shown ‘lyingout’ within the last 24 h. On the other hand, otherindividuals may have ‘responded’ to the signals of the focalanimal. Each of these behaviour patterns were consideredcommunication events if they entailed a response byanother individual within 24 h, or if they followed thesignal of another individual. Beside the direct observationof the focal animal, paralleled by the observation of otherindividuals within its home range, all LDS within the focalanimal’s home range were monitored once a day. Due to anextended study on the gastrointestinal tract parasites ofbushbuck in the study area (Apio 2003), the weight, shapeand size of single faecal pellets could be attributed to thethree sex/age classes ‘adult female’, ‘adult male’ or‘juvenile’. Therefore, some communication events throughfaecal pellets could be recorded even if the sendingindividual (first defecation) or the receiving/respondingindividual (second defection event) was not observeddirectly. However, most communication events wererecorded during the direct observations of the focal animaland other individuals present in its home range. In the latteranalysis, faeces that could not be unambiguously assignedto adult males or adult females were not included in theanalysis. The use of LDS by juveniles was not addressed inour study. Four categories of information exchange weredefined: FF signals send by a female entailing the responseof another female, MF signals send by a male entailing afemale to reply, FM signals send by a female causing amale to respond andMM signals send by a male provokinganother male to respond. We calculated the number ofcommunication events of the four categories per hour. Wetested for differences between the four categories using aFriedman repeated measures ANOVA on ranks.

Results

Distribution of LDS in relation to home range area

The number of LDS in male and female home rangesdiffered significantly between home range sections(Friedman repeated measure ANOVA: males χ2=14.39,

P=0.013, n=4; females χ2=36.63, P<0.001, n=9) and wasincreased in peripheral areas of the home ranges (Fig. 1).A post hoc test revealed significant differences betweenthe <15% section and both the >90% and the 90–71%section of male home ranges (Dunn’s test: P<0.05 in allcases). In female home ranges, all section larger than 70%differed from all sections smaller than 30%, and the >90%section differed from the 50–31% section (Dunn’s test:P<0.05). Regarding the distribution of LDS in female clanhome ranges, the differences in the number of LDS indifferent home range sections were not statisticallysignificant (Friedman repeated measure ANOVA:χ2=8.28, P=0.14, n=3).

Arrangement of LDS within home ranges

The pattern of LDS obtained from the nearest-neighbourmapping method revealed in all cases an irregular,approximately oval-shaped polygon with a number oflinked arms that projected radially outwards. Representa-tively, the pattern of LDS found within the common homerange of one female clan (‘PFG6’) is illustrated andoverlaid with the 90 and 50% kernel home range cores(Fig. 2).

We tested if distances between LDS within home rangesdiverted significantly from a random distribution (Gosling1981). A Chi-squared goodness of fit showed that thecurves describing the frequencies of nearest-neighbourdistances differed significantly from random distributiononly in the male sex (males χ2=23.12, P=0.006, n=4;females χ2=10.85, P=0.21, n=9; female clans χ2=8.19,P=0.42, n=3; Fig. 3). However, even in the male sex, thenearest-neighbour distances were shifted towards longerdistances, not shorter distances as was described forterritorial marking in other species (e.g. Litocraniuswalleri; Gosling 1981).

Frequency of LDS use

Bushbuck visited LDS on an average (mean±SD) of 4.32±1.79 times per day. The rates of LDS visits differedbetween male and female bushbuck: females urinated moreoften than males (independent-samples t test: t7=2.56,P=0.038; Fig. 4). Females also defecated more often inLDS than males, but this difference was statistically notsignificant (t7=2.02, P=0.083). On the other hand, malesshowed more lying out behaviour than females and visitedLDS more often than females without any marking.However, in both cases differences were not statisticallysignificant (lying out t7=1.78, P=0.12; visits withoutmarking t7=0.66, P=0.53; Fig. 4). Males were regularlyobserved extensively sniffing at places where females hadurinated or defecated, whereas this behaviour was muchless frequent in the case of females. However, thisbehaviour was not quantified.

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Information exchange through LDS

Data on information exchange from longitudinal samplingsessions of five adult bushbuck were augmented by datafrom paralleled patrols of other animals present in the focalanimal’s home range and daily monitoring of all LDSknown within its home range. There was a significantdifference between the frequencies of the four categories ofcommunication (Kruskal Wallis test: H=10.95, P=0.012,n=5). To isolate the group or groups that differ from others,we used a post hoc multiple comparison procedure(Student–Newman–Keuls test). The most frequent cate-gory FM differed from all other categories (P<0.05; Fig. 5);hence, the most frequent form of communication throughLDS was that females signalled and males responded.Communication between two males was not observed.

Discussion

In our first analysis we used the distribution pattern of LDSwithin home ranges to test whether LDS generally servecommunication between individuals, either in the contextof territory-demarcation, in a non-territorial context, orboth. Our results showed that in the male as well as in thefemale sex, LDS were more frequent at the periphery ofhome ranges. This result makes a communicatory functionof LDS likely because a peripheral position of LDSincreases the chance to communicate with neighbouringindividuals. Interestingly, the observed distribution patternwas concordant with the pattern found for territorial

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Fig. 1 The distribution of LDS within bushbuck home ranges.Number of LDS in relation to home range sections of increasingkernel utilisation density for males, n=4 (a), females, n=9 (b) andfemale clans, n=3 (c). The >90% section is located at the periphery,the <15% section in the centre of a home range. Box-plots showingthe median (middle line), the inter-quartile range (box) and the 5 and95% values (whiskers). Note that plots a and c do not show whiskersdue to small sample sizes

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marking in another species (O. oreotragus; Roberts andLowen 1997).

In our second analysis using the nearest-neighbourmapping technique, we tested whether the distributionpattern of LDS confirms the idea that LDS serve homerange demarcation. According to Gosling (1981, 1985),territorial species should place their marks in a pattern thatwould result in a high probability of detection by intruders.It was predicted that the marks (in our case LDS) shouldform a continuous line around the perimeter of a territory,or a series of concentric rings, which an intruder has tocross. We found that when connecting all LDS within ahome range using the nearest-neighbour mapping tech-nique, this resulted in typical polygons, but we found noevidence that the nearest-neighbour distances were shifted

towards shorter distances than expected from randomdistribution. Such a shift to shorter distances would haveindicated that bushbuck attempt to minimise the distancesbetween LDS, as would be predicted if LDS served aterritorial function (Gosling 1981). In another study, weexamined the distribution pattern of male ‘horn-rubbing’,whereby males mark twigs and leafs by rubbing their horn-base against them (Wronski et al. 2006). In this case, thenearest-neighbour distances followed the predicted patternwith a shift towards shorter distances than expected from arandom distribution. On the contrary, distances betweenLDS were shifted towards longer distances, at least in themale sex. The ‘negative’ result does not necessarilyexclude the possibility that LDS serve a territorial function;however, the distribution pattern of LDS in male andfemale home ranges does not support this idea. Potentially,the shift to longer distances between LDS than expected byrandom distribution could be due to availability of markingsites or heterogeneous resource or trail distribution(Gosling and Roberts 2001b), but this explanation isinconsistent with our results for horn rubbing (Wronski etal. 2006). Probably, horn rubbing is used for the demar-cation of territories by males, but such a function is notevident for LDS. Similar results were obtained whenanalysing female clan home ranges. Sample sizes were lowin this case, and results for female clans are discussed withcaution. Female clans position more LDS at the margins oftheir common home ranges. Again the nearest-neighbourmapping method did not suggest that LDS are used in aterritorial context, where clans defend common homeranges against other clans.

Territoriality is evident between males (Wronski 2004,2005). Among females, agonistic interactions in thecontext of territory defence are much less frequent evenbetween non-related females (Wronski 2004, Wronski andApio 2005). Hence, if LDS served a territorial function,one would predict males to use LDS more frequently formarking than females. Furthermore, any form of territorialantagonism between the sexes is lacking. Thus, commu-nication via LDS marking should mainly occur betweentwo males and potentially also between two females. Incontrast, our data rather indicated that males defecated andurinated less in LDS than females. In addition, we couldshow that the most frequent form of information exchangethrough LDS was that females signalled (e.g. defecated)and males responded by signalling at the same site. Asignal of a female was rarely followed by excretion ofanother female. We only once observed a communicationevent that was initiated by a male and was answered by afemale. Most notably, communication between two maleswas not found. Based on these findings, we hypothesisethat LDS serve as communication centres for inter-sexualinformation exchange. Future studies will have to examinewhether information transfer between the sexes is morefrequent inside than outside LDS. This would ultimatelyprovide evidence for a function of LDS as informationcentres. Furthermore, future studies will need to examineother forms of information exchange; for example, males

category

FM FF MF MM

inci

denc

es /

h

0,00

0,02

0,04

0,06

0,08

0,10

Fig. 5 The median number of communication events (defecation,urination, lying out) per hour for four categories of informationexchange (FM: a female marks–a male responds, FF: female–female, MF: male–female, MM: male–male). The line drawingshows a defecating female. For box plots, see Fig. 1

0

0,05

0,1

0,15

0,2v

isit

s /

h

urination visits withouts

marking

lying out

*

defecation

Fig. 4 LDS utilisation frequencies (count/h, mean±SD) for males(n=5; shaded bars) and females (n=4; blank bars). The line drawingshows a urinating female. Independent-samples t tests, *P<0.05

375

may partly obtain information without necessarily settingmarks themselves.

One might argue that males may also have responded toolder marks, not only to the most recent mark, which wouldnot have been recoded by our method. However, given thelarge number of observations, we should then haveobserved at least some incidences of ‘a male respondingto another male’. In this scenario, two males would bothhave responded to the same old mark of a female within24 h, which would have been recorded as ‘male–male’communication event in our study. Because we neverobserved this communication category, it seems likely thatmales do not respond to older female signals, or this mustbe at least far less frequent.

Faeces and urine likely provide information concerningfemale receptivity (Blüm 1985). Possibly, females provideinformation concerning their sexual cycle by using LDS tocommunicate to males to avoid sexual harassment(Clutton-Brock and Parker 1995 for a review). If malesreceive information concerning the females’ receptivityinside such information centres, they do not need to visitthe female directly, but the female will be visited by themale and will be mated when she is oestrous. Females alsocommunicated with other females, however much lessfrequently. LDS may serve as information centres also inthis context; e.g. females may gather information concern-ing the relatedness of individuals in adjacent home ranges.The peripheral position of LDS relative to female homerange extensions is best explained in that females attemptto communicate to as many individuals as possible. Forexample, if a female home range overlaps with more thanone male territory, the probability to communicate to bothmales would be highest if she uses peripheral marking.

In summary, we cannot exclude with certainty thepossibility that LDS serve a home range/territory-demar-cation function. However, our data indicate that LDS areprimarily used for inter-sexual communication, wherefemales signal and males appear to patrol LDS to monitorfemales. This is, to our knowledge, the first report that LDShave a more important significance for inter-sexualcommunication than for territory-demarcation in a seden-tary ungulate species.

Acknowledgements The Research Division of the Uganda Wild-life Authority, Kampala, Uganda, and the Uganda National Councilfor Science and Technology gave permission to conduct this researchin Queen Elizabeth National Park. All work conducted was incompliance with the Ugandan law. This study was carried out inaffiliation with the Uganda Institute of Ecology, Mweya, Uganda andthe Mbarara University of Science and Technology, Uganda. Thestudy was supported by a scholarship from the German AcademicExchange Service (DAAD). We are greatly indebted to LudwigSiefert, Department of Wildlife and Animal Resource Management,Makerere University, Kampala for his veterinary assistance in thefield. Our special thanks go to Jonathan Baranga (Mbarara Universityof Science and Technology), Harald Schlieman (University ofHamburg) and Hans Klingel (University of Braunschweig) for theircontinuous support to our project. The collection of a considerablenumber of data was carried out with the help of Solomon Kyabulima,the research assistant of the project, for which we owe him ourgratitude. Lots of thanks to Enzama Modesta and the family of Mr.

and Mrs. Opwonya, especially Joyce Atim. Rüdiger Riesch andMichael Tobler kindly read and helped to improve a previous draft ofthe manuscript. E. Korpimäki, H. Ylonen and an anonymousreviewer provided very helpful comments.

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