Food odour preference behaviour in three Australian Pteropus species (Chiroptera: Pteropodidae)
Date
1996
Authors
Oldfield, Anthony Charles
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This thesis reports an investigation into the olfactory preferences of three Australian Megachiropteran species, Pteropus poliocephalus, P. scapulatus and P. alecto, for a variety of plant-derived odours. Methodologies were devised for investigating odour preference behaviour, involving equipment design, development of new applications for existing statistical techniques for the analysis of preference data, and analysis of odorous headspace in test mixtures and from flowers in the field. Initially, preliminary behavioural observations (Section II) indicated that all three bat species exhibited positive approach behaviours in response to fruit-derived odours and that they responded both within and between species to different quantities of test odour, 0.5mL of test odour distillate at a decision distance of 125mm producing the optimal responses in P. poliocephalus and P. scapulatus, with P. alecto responding with equal intensity to all odour quantities. A common behavioural ethogram was devised for Pteropus, and applied to more detailed analyses of preference responses. These revealed that within each species, bats expressed different degrees of preference for different odours under controlled conditions. When odour preferences within a species were ranked on a decision axis, odour pairs with low separation values were more likely to change in rank position than those further apart. Not only then was each species able to detect fruit odours, but also they could discriminate between different odour types. Patterns of preference for the same test odour stimuli were not the same when compared across species. P. poliocephalus and P. scapulatus preference hierarchies had distinct regions of clustering of odours where the outcomes of pair-wise choices were variable. In contrast, odour comparisons on P. alecto ranks produce more definitive outcomes, with the most significant agreement in preference patterns across individual bats. The existence of preference intransitivity in all three species indicated that these bats employ a comparative method of odour evaluation as opposed to an absolute utility method often described for foragers with transitive preferences. Thus for these bats the 'value' of odours is dependent upon the context within which the odour comparisons are made. Those odours with low levels of separation on the preference hierarchies were more frequently associated with preference intransistivity. Furthermore, the more generalist feeder P. alecto appeared to have the highest sensitivity to variation in odour concentrations, suggesting that dietary specialisation does not necessarily coincide with olfactory acuity. These bats did not select odours on the basis of absolute concentration or intensity, but on qualitative characteristics. The potential for the development of odour-active agents to interfere with bats' odour preference behaviour, in relation to reducing bat damage is substantial. The continuation of Gas Chromatographic - Olfactometric (GCO) investigation of odours involved with high incidences of preference intransitivity is strongly recommended, as is further study of bat-flower volatile interactions. Until now it has not been possible to state with absolute confidence that non-echolocating Megachiropterans are capable of detecting and discriminating between food-related odours. The speculation regarding Pteropus using their sense of smell to locate food odours, and the potential for developing odour deterrents can now end. Further studies on these topics are now warranted and feasible with the use of the techniques here developed.
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