Behavioral evidence suggests that Asian elephants (Elephas maximus) strongly rely on their sense of smell in a variety of contexts such as foraging (Santiapillai and Read, 2010) and social communication (Langbauer, 2000; Rasmussen and Krishnamurthy, 2000; Scott and Rasmussen, 2005). Chemical communication in elephants has been thoroughly studied and is considered an important mechanism in regulating the behavior of elephants (Rasmussen 1998; Rasmussen, 1999; Rasmussen and Krishnamurthy, 2000) and the long-term memory of elephants for social odors seems to be excellent (Rasmussen, 1995). In fact, the Asian elephant is one of the few mammal species so far for which a sex pheromone has been chemically identified and functionally verified (Rasmussen et al., 1997, Rasmussen et al., 2005).

The long-term stability and permanence of Asian elephant social groups depends on effective intraspecific communication, operational at both short and long distances (Rasmussen, 1999; Langbauer, 2000). The interactions are facilitated through vocalization (McComb et al., 2000; Nair et al., 2009), social odors (Rasmussen, 1998) and tactile and visual displays (Langbauer, 2000; Sukumar, 2003). However, long-distance communication demands signals that can be emitted and received over a larger distance such as infrasonic vocalization (Langbauer, 2000) and stable chemical signals (Rasmussen, 1998; Rasmussen et al., 2000), where the chemical signals have the advantage of being accessible over both time and space (Schulte et al., 2007). Elephants can perceive these chemical signals via the main olfactory and vomeronasal systems but also via the trigeminal system (Sukumar, 2003; Rasmussen, 2006). Anatomical evidence of well-developed olfactory and vomeronasal systems (Johnson and Rasmussen, 2002; Göbbel et al., 2004; Shoshani et al., 2006) as well as of specialized skin glands (Wheeler et al., 1982; Lamps et al., 2001) further supports the idea that the sense of smell plays a crucial role for elephants.

Of all land animals, elephants have the largest absolute brain size (Cozzi et al., 2001; Hart et al., 2001; Shoshani et al., 2006; Bates et al., 2008b) and accordingly the largest cerebral cortex which is involved in higher-order brain functions. The ratio of brain volume to body mass in Asian elephants is comparable to that of chimpanzees (Shoshani et al., 2006; Hart and Hart, 2007) which suggests that elephants may possess the capacity for complex cognitive processes. The cognitive abilities of elephants are considered extraordinary by some authors (Bates et al., 2008b; Hart et al., 2008; Byrne and Bates, 2009) but most of the evidence is anecdotal, insufficient or inconsistent (Plotnik et al., 2011). Asian elephants have been trained successfully in two-choice visual (Rensch, 1957; Savage et al., 1994; Nissani et al., 2005), auditory (Rensch, 1957; Heffner and Heffner, 1982), and tactile (Dehnhardt et al., 1997) discrimination tasks and were found to readily learn such tasks. However, no studies so far assessed the olfactory discrimination ability in this species, nor the learning speed of elephants with odor stimuli. A comparison of the number of stimulus contacts needed until reaching criterion in different discrimination tasks would offer an opportunity to evaluate which senses the elephants may use more readily when solving a learning problem.

So far, no behavioral test to systematically assess the olfactory capabilities of elephants exists and it was therefore the aim of the present study to develop and apply an olfactory discrimination paradigm for Asian elephants. A second aim was to collect first data on olfactory learning speed, memory and discrimination performance in this species. The behavioral test is based on a voluntary, food-rewarded two-alternative operant conditioning procedure. The animals were taught to sample two odor ports and were food-rewarded when they performed an operant response (putting the trunk at a certain position of the experimental set-up) upon correctly identifying the rewarded odor. Similar operant conditioning procedures to assess olfactory learning, memory and discrimination capabilities have been employed with other mammals such as squirrel monkeys (Laska and Hudson, 1993), spider monkeys (Laska et al., 2003), pigtail macaques (Hübener and Laska, 2001), South African fur seals (Laska et al., 2008), mice (Bodyak and Slotnick, 1999), rats (Slotnick et al., 1991), and dogs (Lubow et al., 1973). This allowed for direct comparisons of the speed of initial task acquisition, the ability to master intramodal stimulus transfer tasks, and olfactory memory performance between species. Also, by using a set of structurally related odorants that has been used with squirrel monkeys (Laska and Freyer, 1997), humans (Laska and Hübener, 2001) and South African fur seals (Laska et al., 2010), the discrimination performance of the elephants for these odors was assessed and compared to that of the other species. The olfactory discrimination paradigm developed and applied in the present study will enable a better understanding of the basic olfactory abilities of Asian elephants and allow for direct comparisons of olfactory discrimination, long-term memory and learning competence between species.
 

The aim of the present study was to train three female Asian elephants to cooperate in an olfactory discrimination paradigm and to collect first data on their olfactory learning speed, olfactory discrimination performance and olfactory memory and to compare these data to those collected in other species.