Felids are known to strongly rely on olfactory cues for social communication (Stoddart 1980; Gorman and Trowbridge 1989; Wyatt 2014). In addition to faeces and urine some felids, such as the Amur tiger, use the secretions from specialized scent glands located within the urinary tract, for this purpose (Smith et al 1989; Asa 1993; Burger et al 2008). Behavioural studies suggest that these scent-marks may convey information about an individual’s, sex, age, health, reproductive condition, identity and genetic status (van den Brink 1977; Bininda-Emonds et al. 2001; Barja and Javier de Miguel 2010). This variety of information provided through odour signals can be used for a variety of purposes, for example, establishing territorial boundaries, attracting non-related conspecifics as mates, and to avoid inbreeding (Stoddart 1980; Wyatt 2014). Despite the assumed importance of urine and marking fluid odours for behaviours displayed by felids not much is known about the volatiles that make up these complex odour mixtures (Soso et al 2014), and even less is known about if individual chemicals that are components of these odour mixtures may be sufficient to affect intraspecific behaviour (Whittle 1981).

Gas chromatography-mass spectrometry and gas chromatography-olfactometry are methods used to identify which chemicals are the active odour components in a mixture of volatiles. These two powerful methods were recently used to analyse the chemical composition of tiger marking fluid. Two substances were identified as the characteristic odour components of tiger marking fluid: 2-acetyl-1-pyrroline and furfural (Soso and Koziel 2016). Interestingly, 2-acetyl-1-pyrroline is not found in lion marking fluid (Poddar-Sarkar and Brahmachary 2014). However, it is found in the head- and cheek-rubbing markings of both tigers and lions (Soini et al. 2012). Humans have a high olfactory sensitivity for 2-acetyl-1-pyrroline (van Gemert 2011) with detection thresholds below 10 ppt (parts per trillion) and describe it as smelling like popcorn (Schieberle 1991). The second characteristic odour component, furfural, has also been found in the urine of wolf, dog (Wolfram 2013), and African wild dogs (Apps et al 2012), and even in the urine of humans (Wishart et al. 2013). Due to being present in several different species of mammals, furfural is likley to be less species-specific compared to 2-acetyl-1-pyrroline.

Previous studies reported that Amur tigers displayed high interest towards wooden logs that were impregnated with mammalian blood or a blood odour component (Sjöberg 2013; Nilsson et al. 2015). The results from these studies suggest that wooden logs impregnated with behaviourally relevant odours are an effective form of olfactory environmental enrichment for captive tigers. However, it is currently unknown whether the use of conspecific odours instead of prey-related odours is also effective as a form of environmental enrichment in this felid species (Skibiel et al 2007; Szokalski et al 2012).

1) Assess the behavioural responses of captive Amur tigers (Panthera tigris altaica) and African lions (Panthera leo) towards conspecific urine odour and 2-acetyl-1-pyrroline, a volatile component found in tiger marking fluid. But also to 2) compare the behavioural responses towards the conspecific urine odour and the tiger marking fluid component, with the behavioural responses towards two control odours, one plant-derived and one near-odourless. An additional aim was to 3) assess whether conspecific odours presented on wooden logs are a useful form of environmental enrichment for captive tigers and lions.