Olfactory communication and hunting behaviour of Eurasian lynx Lynx lynx in the Northwestern Swiss Alps

Chemical signalling in the form of scent-marking with urine, faeces or gland secretions is widespread in mammals and its role in territoriality, competition or mate choice is widely recognised for many species. Mammals regularly check and renew their scent-marks and place their own scent-marks on top of those left by others. Such over-marking is essential for communication with neighbouring territory holders or group members and high scent-marking rates increase reproductive success. However, chemical signals are not only perceived by the intended receivers but can be intercepted and exploited by competitors, predators or parasites (eavesdropping). In wild felids, the occurrence of scent-marking behaviour and the chemical compositions of different scent sources have been described for an increasing number of species. However, the role of over-marking in social organisation of wild felid populations, the factors influencing spatial and temporal distribution of scent-marks in territories (e.g. eavesdropping by prey), and the information content of scent-marks have not yet been studied extensively in wild felids. The aim of my thesis was to explore the possible functions of scent-marking in felid social organisation using the Eurasian lynx Lynx lynx as a model species and focusing on the above-mentioned research topics.
In my first study (chapter 1), I investigated scent-marking behaviour and its role in communication among resident and non-resident Eurasian lynx using infrared camera traps. I could show that communal marking sites play an important role in communication between male and female lynx and in competition between males. I demonstrated that lynx were able to discriminate between self and non-self and that over-marking does not mask the underlying scent-mark. These results support the function of communal marking sites as “chemical bulletin boards”.
In chapter 2, we describe a robust method for identifying kill sites from movement patterns by analysing GPS location clusters (GLCs) generated by GPS-collared lynx. We were able to find large as well as small prey items and could show that the majority of the kills (92%) were found in GLCs lasting ≥ 9h. The method was then used in the next chapter to relate lynx scent-marking rates to hunting behaviour.
In my third study (chapter 3), I followed tracks of GPS-collared lynx in the snow and recorded scent-marks and evidence of hunting behaviour along these tracks. I was able to show that overall scent-marking rate was lower when lynx were hunting but that hunting lynx increased scent-marking rates in places, where there was a high chance of detection by conspecifics (along forest roads). Lynx also increased scent-marking rates during mating season but only when they were not hunting. My results suggest that lynx face a trade-off between enhancing the detection probability of scent-marks by conspecifics and avoiding eavesdropping by prey.
Finally, in my last study (chapter 4), I collected urine from captive and wild Eurasian lynx and analysed volatile constituents of urine by means of solid phase microextraction and gas chromatography-mass spectrometry. I identified several carboxylic acids, aldehydes, ketones, and esters, as well as high amounts of cyclic octaatomic sulphur. I could show that lynx urine contains sex-specific information on reproductive state, as well as individual identity cues. Relative sulphur content in urine samples decreased with age of the urine sample and could serve as an indicator for the freshness of a scent-mark.
The patterns of scent-marking I observed during my studies suggest that urine marking plays an important role in communication between potential mates and rivals and, hence, in social and spatial organisation of Eurasian lynx populations. I was also able to chemically analyse the information content of lynx urine and show that urine marks are well-suited to fulfil the suggested functions in the wild. As such, my work contributes to a better understanding of the functions and constraints of chemical signalling in wide-ranging solitary predators.