Olfaction in chicken (Gallus gallus): A neglected mode of social communication?

Avian olfaction has been neglected for a long time, although pioneering work has been conducted from the 1960th on (Wenzel, 1968, 1971a,b; Bang, 1960; Bang and Cobb, 1968; see also Nevitt and Hagelin, 2009). However, much of this research focused on odour perception in general or on the use of olfactory cues in non-social contexts, e.g. for navigation (Papi et al., 1974; Grubb, 1974; Wallraff, 1979; Gagliardo, 2013) or foraging (e.g. Grubb, 1972; Hutchinson and Wenzel, 1980). In addition, this research focused on few avian taxa, in which the olfactory sense was regarded to be important due to large relative olfactory bulbs (Bang and Cobb, 1968). These taxa included, for example, the kiwi (Apteryx australia), which has a relative olfactory bulb size of 34% (ratio of the bulb to the hemisphere), the Procellariiformes, i.e. tube-nosed marine birds, with a mean ratio of 29%, and few other species and taxa (Bang and Cobb, 1968). Within the last decade the use of olfactory cues in the above mentioned topics and avian taxa has been further explored (Nevitt and Bonadonna, 2005; Gagliardo et al., 2011; Amo et al., 2013; Gagliardo 2013) and, in addition, the social olfactory communication has attracted the interest of research (e.g. Hagelin and Jones, 2007; Caro and Balthazart, 2010; Caspers and Krause, 2013; Caro et al., 2014). Thus, the potential not only of olfactory cues (i.e. information that has not designed for the purpose of communication by natural selection (Danchin et al., 2008)) but also of olfactory signals (i.e. information/trait with adaptive function that alter the behaviour of receivers (Danchin et al., 2008)) became apparent also in avian taxa with smaller relative olfactory bulbs. Olfactory cues have been shown to play roles in inter-specific interactions such as for species recognition (Zhang et al., 2009; Mardon et al., 2010; Krause et al., 2014) or as chemical defences against predatory species (e.g. Parejo et al., 2013). Olfactory signals are important in intra-specific communication. Offspring related odours (de Leon et al., 2003; Caspers and Krause, 2011; Amo et al., 2014; Golüke et al., 2016) and the reproductive partners’ scent (Bonadonna and Nevitt, 2004) can be recognized. The sex of an individual (Whittaker et al., 2010; Amo et al., 2012a) and kinship (Coffin et al., 2011; Krause et al., 2012; Bonadonna and Sanz-Aguilar, 2012) can be encoded in the scent. Olfactory signals are used for mate choice decisions (Amo et al., 2012b; Whittaker et al., 2013; Caspers et al., 2015) and provide information about the MHC (Strandh et al., 2012; Leclaire et al., 2014).