Social associations with conspecifics can expedite animals’ acclimation to novel environments. However, the benefits gained from sociality may change as the habitat becomes familiar. Furthermore, the particular individuals with whom animals associate upon arrival at a new place, familiar conspecifics or knowledgeable unfamiliar residents, may influence the type of information they acquire about their new home. To examine animals’ social dynamics in novel habitats, we studied the social behaviour of African elephants (Loxodonta africana) translocated into a novel environment. We found that the translocated elephants’ association with conspecifics decreased over time supporting our hypothesis that sociality provides added benefits in novel environments. In addition, we found a positive correlation between body condition and social association, suggesting that elephants gain direct benefits from sociality. Furthermore, the translocated elephants associated significantly less than expected with the local residents and more than expected with familiar, but not necessarily genetically related, translocated elephants. The social segregation between the translocated and resident elephants declined over time, suggesting that elephants can integrate into an existing social setting. Knowledge of the relationship between sociality and habitat familiarity is highly important in our constantly changing world to both conservation practice and our understanding of animals’ behaviour in novel environments.
Keywords: African elephant; association; conservation; novel environment; social behaviour; translocation
Animals often encounter novel environments, both naturally and owing to human activities. Dispersing individuals encounter novel habitats while searching for a place in which to settle (Stenseth & Lidicker 1992), and migrating animals locate novel habitats periodically (Mettke-Hofmann& Gwinner 2004). Furthermore, animals encounter novel places owing to human modifications to the environment, e.g. habitat loss (Sutherland & Dolman 1994), and fragmentation (Ewers & Didham 2006), or owing to wildlife management activities such as translocations and reintroductions (Griffith et al. 1989; Fischer & Lindenmayer 2000). In both natural and unnatural encounters with novel habitats, animals lack vital information regarding suitable forage, hiding locations, mating opportunities and predators. Social interactions with conspecifics can expedite animals’ acclimation to a novel environment.
Despite the extensive work on the adaptive significance of sociality (Slobodchikoff 1988), very little is known about its importance when animals face novel environments. Several benefits may be gained from interacting with conspecifics in a novel habitat. For example, social learning and cueing are important mechanisms for rapidly gaining knowledge about a new environment (see reviews in Danchin et al. (2004) and Bonnie & Earley (2007)) and the presence of conspecifics is known to facilitate learning novel tasks (Moscovice & Snowdon 2006). Associating with conspecifics in a novel environment may provide protection against unknown predators (Isbell et al. 1990) and unfamiliar aggressive conspecifics (Cheney & Seyfarth 1983; Jack & Fedigan 2004). However, associating with conspecifics in a novel environment can also entail costs owing to resource competition (Koenig 2002) and agonistic interactions during territory acquisition (Stamps 1994).
We suggest two hypotheses regarding the relationship between sociality and animals’ familiarity with a habitat. Our first hypothesis ‘beneficial sociality in novel environments’ (BSNE) states that animals gain added benefits from associating with conspecifics in a novel environment (e.g. through social learning), but these added benefits diminish as the habitat becomes familiar. BSNE predicts a decrease in the number of conspecifics an animal associates with over time. Our alternative hypothesis, ‘costly sociality in novel environments’ (CSNE) states that social associations in a novel habitat incur added costs (e.g. owing to territorial disputes), but these costs are outweighed by the benefits of sociality as the habitat becomes familiar. CSNE predicts an increase in the number of conspecifics an animal associates with over time. To our knowledge, no study has thus far investigated this relationship between sociality and habitat familiarity.
Another important question about animal sociality in novel environments is as follows: who are the particular individuals that animals associate with? Animals can associate with either unfamiliar local residents or familiar conspecifics that arrived with them to the new location. Associating with familiar conspecifics has several advantages, including protection during encounters with aggressive unfamiliar conspecifics (Cheney & Seyfarth 1983; Jack & Fedigan 2004), inclusive fitness benefits (Ward & Hart 2003) and reducing neophobia (Coleman & Mellgren 1994). Furthermore, associating with unfamiliar conspecifics can be costly. For example, unfamiliar individuals may carry unknown diseases (Loehle 1995) or be aggressive (Goossens et al. 2005), and learning about unfamiliar conspecifics may come at the expense of learning about the new habitat (Burman & Mendl 1999). However, in a novel setting, there is an asymmetry in the knowledge about the new habitat: the local, unfamiliar residents have information about the new habitat that familiar conspecifics might not have (Forsman et al. 2007). Thus, there may be a great advantage to associating with unfamiliar residents in a novel environment.
African elephants’ (Loxodonta africana) social dynamics provide an excellent opportunity for studying sociality in novel environments. Elephants live in fission–fusion societies in which core family groups (second tier units) occasionally form bond groups (third tier social structures) (Moss & Poole 1983; Wittemyer et al. 2005). Elephants’ social dynamics are governed by ecological factors (Wittemyer et al. 2005) and the formation of bond groups is thought to be important for gathering both social (Moss & Poole 1983) and ecological (Foley 2002) information. Furthermore, elephants are highly intelligent mammals (Hart et al. 2008) that are capable of distinguishing between the vocal signatures of familiar and unfamiliar conspecifics (McComb et al. 2000, 2003).
Recently, management of elephant populations has included translocating them from familiar to novel environments (Dublin & Niskanen 2003), providing opportunities for examining their social dynamics in novel environments. First, to distinguish between our BSNE and CSNE hypotheses, we examined the change over time in association between the translocated elephants and conspecifics (familiar and unfamiliar). Based on the African elephants’ social learning abilities and their lack of territorial behaviour, we predicted to find evidence supporting the BSNE hypothesis. Second, we examined whether the translocated elephants formed bond groups with familiar or unfamiliar conspecifics, predicting that they will associate with knowledgeable unfamiliar conspecifics to learn about their new home. Finally, we explored possible explanations for the social patterns found.
2. MATERIAL AND METHODS
(a) Translocation and sightings
During September 2005, 150 African elephants were translocated from Shimba Hills National Reserve on the coast of Kenya (4.08 °S to 4.38 °S and 39.58 °E to 39.38 °E) to Tsavo East National Park (2.08S to 3.78°S and 38.18°E to 39.38 °E), a distance of 160 km. This translocation was part of the Kenya Wildlife Service (KWS) effort to decrease human–elephant conflict in the vicinity of Shimba Hills. Twenty elephant groups comprising adult females, juveniles and calves (average group size 6.8) and 20 independent adult males were moved over the course of 32 days. The release site differs ecologically from the source site and is separated from it by dense human population, providing a unique opportunity for examining the social behaviour of the elephants in a novel environment.
During the translocation, all the elephants were tagged with yellow zip ties on their tails to distinguish them from the local Tsavo elephant population. Unique white numbers painted on the translocated elephants’ backs, natural ear marks and tusk shapes were used for individual identification of the translocated elephants (Moss 1996). Elephants’ ages were estimated based on Moss (1996).
The locations, their time and the identities of the translocated and local Tsavo elephants were recorded in Tsavo East for a year post-translocation using a Geko 201 GPS unit (Garmin Ltd., USA). Road transects were conducted using a vehicle four to five times a week, alternating between four routes of similar length (50–70 km) on the existing roads within Tsavo East National Park. A total of 3371 elephant sightings were recorded, of which 386 and 2985 were the translocated and local elephants, respectively. Of the 150 elephants translocated, data on 83 were obtained, and are presented here. Because males leave the social unit in which they were born at the age of 15, and because the social behaviour of these independent males differs from that of females and their young offspring (Moss & Poole 1983), such translocated males were excluded from our analyses.
(b) Social association
Elephants were defined as associating with one another if they were sighted within 500 m from one another within a 2 hour time period, based on McComb et al. (2000, 2003). They showed that elephants can individually recognize conspecifics’ vocalizations over great distances (1 km). Therefore, the definition of social association used here includes not only direct interactions but also recognizes the communicative capabilities of elephants to acquire information about the number and identities (translocated or local) of vocalizing conspecifics (McComb et al. 2000, 2003). Thus, the definition of social association used here allows for the acquisition of inadvertent social information about the new environment (Danchin et al. 2004).
To test whether the number of conspecifics (translocated and local) with whom a translocated elephant is associated changed over time, we counted the number of conspecifics in association with each translocated elephant for each of its sightings (using the above definition for association) and analysed it using a random effects-mixed model. Time was a fixed effect in the model, elephant identity was included as a random effect to control for repeated measures of the same translocated individual and season (wet or dry) was included as a fixed effect in the model to account for the seasonal effects on social association.
To examine whether associating with conspecifics provided direct adaptive benefits, we examined the relationship between body condition (see the definition in the electronic supplementary material) and association with conspecifics using a random effects-mixed model. The number of conspecifics (translocated and local) in association with the translocated elephants and time were fixed effects in the model, and elephant identity was a random effect in the model. Since none of the interactions among the effects was significant, they were not included in the final statistical model (Engqvist 2005).
To quantify the association among the translocated elephants, we computed an association matrix using the simple ratio association index (AI; Ginsberg & Young 1992), which is often used in the studies of elephant social behaviour (McComb et al. 2000, 2001; Wittemyer et al. 2005; details in the electronic supplementary material).
To quantify the association of each translocated individual with all other translocated elephants, weighted degree (WD), a measure from social network theory (also referred to as vertex strength in Barrat et al. (2004)) was calculated using UCINET (Borgatti et al. 2002). WD is calculated for each translocated individual as the sum of its association indices with all other translocated elephants: WDiZPnj Z1 AIij where i is a certain translocated elephant; j is any other translocated elephant; and n is the number of translocated elephants. WD was calculated only for the translocated elephants older than 5 years (excluding independent adult males). Calves (younger than 5 years) seldom leave their mothers (Wittemyer et al. 2005), and including them would have disproportionately increased the WD of females with calves.
To examine the association between the translocated and local elephants, their association with one another (AL) was calculated as the proportion of sightings the translocated elephants were observed in association with the local elephants: ALiZðniL=ni Þ where niL is the number of times the translocated elephant i was in association with any local elephant (see the association definition above) and ni is the total number of times the elephant i was seen. AL was calculated only for the elephants older than 5 years and excluding adult males. Since calves’ activities are strongly associated with their mothers’ (Wittemyer et al. 2005), their AL would have been the same as their mothers’, and including them would have biased the average AL towards that of females with calves. The relationship betweenWDand AL was examined using a Pearson correlation coefficient test.
(c) Bond group formation
To evaluate whether the translocated elephant family groups formed bond groups with other translocated (familiar) elephants or with local (unfamiliar) conspecifics, the individual sightings were grouped into core family groups (also known as second tier units; Wittemyer et al. 2005). The translocated elephants captured together, as a cohesive group, were considered to be a family group (see relatedness results below to support this grouping method). The local elephant family groups were assigned based on spatial proximity, since no genetic data were available for them. Local elephants within five elephant body lengths of one another when first sighted were considered to be a family unit. The number of group associations, using the association definition above, was summed for each of the following categories: TT, two translocated groups captured separately associating with one another; LL, two local groups associating with one another; TL, translocated group and local group associating with one another; and T, translocated or L, local groups alone.
To determine whether the observed association between groups differed froman expected association rate, a c2 was used to compare the observed values with an expected distribution, created using a permutation model (see the electronic supplementary material for permutation model details).