EXPLOITING INTERSPECIFIC OLFACTORY COMMUNICATION TO MONITOR PREDATORS

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Initial detection

Stoats first became active 2 to 180 minutes (mean = 67.08 minutes ± SE 10.07) after the trial began. Stoats moved freely throughout the arena: both pen 1 (mean = 12.65 minutes ± SE 6.56) and 3 (mean = 15.21 minutes ± SE 5.58) (Figure 3.1) were entered within the first hour by 16 of the 18 stoats and 90% of the foraging units were also visited within the first hour. Time until first approach was influenced by treatment as stoats approached and inspected foraging units containing predator odour more expediently than control units, with ferret odour provoking the most pronounced behavioural response (Table 3.2, Figure 3.2a).

Prey survival

Stoats consumed 94% (203/216) of the food presented based on prey remaining at the end of the night. There was no significant relationship between treatment and food remaining (mean = 0.36 prey ± SE 0.18) at the end of a trial night (Fisher’s exact test, P = 0.89). Time when food eaten was significantly shorter at foraging units with ferret odour, while other treatments were similar to the controls (Table 3.2, Figure 3.2b).

Encounter

Stoats spent significantly more time at foraging units containing the scent of known sympatric predators (ferret or cat) than with odour of the novel predator (wild dog) or either of the controls (Table 3.2, Figure 3.3), which is consistent with inspection behaviour. Ferret odour incited the most prolonged initial investigation (mean = 141.44 seconds ± SE 23.22) followed by cat odour (mean = 103.76 seconds ± SE 20.72).

Risk assessment

Risk assessment behaviours were only exhibited during the initial approach to the treatment. A cautious approach, characterised by slow careful movements or standing on hind legs, was most often observed with ferret odour (Appendix II: S3), less often with cat odour (Appendix II: S4), occasionally with wild dog odour, and never with non-odour or pungent controls (Figure 3.4a). The difference from the non-odour controls was significant for both cat (Fisher’s exact test P=0.031) and ferret odour (Fisher’s exact p<0.0001), but not for wild dog odour (Fisher’s exact test P=0.4706). Ferret odour was detected by some stoats at a distance of >2 m, based on sudden changes in behaviour and the initiation of a cautious approach.
Significant increases in scanning were observed when stoats investigated cat odour (Fisher’s exact test P=0.0072), but not ferret (Fisher’s exact test P=0.10), wild dog (Fisher’s exact test P= 0.23), or pungent (Fisher’s exact test P= 1.00) foraging units (Figure 3.4b).

Discussion

Odour provoked clear behavioural responses in a subordinate carnivore, with sympatric dominant predator scent eliciting the greatest deviation from the baseline measure (non-odour control). Stoats did not avoid treated foraging areas (Prediction 1), but instead were attracted to the kairomones, carefully inspecting (Prediction 7) the odour source. Ferret odour provoked the most pronounced behavioural changes, with stoats approaching three times faster than to the second most alluring odour. This was reflected in shorter survival times of prey (Prediction 2), again in contrast to our prediction. The time spent at foraging units was positively correlated with the cautious approach response variable, and the results for this variable indicate that, contrary to Prediction 3, stoats spent more time in close proximity to odour from sympatric predators than odour from a non-sympatric predator or the pungent odour or non-odour controls. Visits to foraging units were brief, rarely more than two minutes, which suggests time spent at one type of odour did not reduce a stoat’s ability to investigate the alternative odour. In line with our prediction, risk assessment behaviour increased (Prediction 4) when stoats detected predator kairomones, with a cautious approach strongly associated with sympatric predators (Appendix II: S3 & S4). We expected that the stimuli of greatest risk would be avoided, but ferret odour, which was approached cautiously by 75% of stoats, was investigated for the longest duration. Stoats scanned more frequently when encountering cat odour than ferret odour (Appendix II: S4). Fear behaviours (Prediction 5) such as freezing or hiding were never observed during the trial. Reaction to predator odours may be affected by gender (Dickman & Doncaster, 1984), but there was no evidence that stoat sex (Prediction 6) influenced any behavioural responses.
The attraction displayed by stoats to the body odour of a dominant sympatric predator may at first appear counterintuitive. Stoats detected predator scent emanating from inside a foraging unit, but then undertook close inspection to verify that the depositing predator was absent. Mammals, particularly carnivores, are sometimes known to respond to odours with increased interest (Albone & Shirley, 1984), which is thought to relate to information acquisition (Hurst, 2005). Stoats are likely to have investigated the odour to evaluate the risk. Heightened vigilance presumably ensured a quick response should a threat have materialised. A ‘full predator stimulus’, where the dominant predator is encountered, may elicit a strong fear response whereas a ‘partial stimulus’ from odour may elicit uncertainty and a need to gather further information (Dielenberg & McGregor, 2001). Overestimation of the threat when dominant predator odour is encountered would have associated fitness costs. An animal behaving optimally should only respond to real threats rather than wasting energy and foraging opportunities in unnecessary flight (Kats & Dill, 1998). High metabolic rates force stoats to forage frequently (King & Powell, 2007), and animals with high metabolism must constantly trade off the risks of starvation and predation (Higginson et al., 2012). Also, despite their diminutive size, stoats are capable of defending themselves against larger predators. If they can identify a dominant predator prior to an encounter their chances of survival increase dramatically (King & Powell, 2007).

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CHAPTER 1 INTRODUCTION
1.1 COMPETITIVE INTERACTIONS AMONG CARNIVORES
1.2 COEXISTENCE VIA NICHE PARTITIONING
1.3 ODOUR-MEDIATED FORAGING
1.4 INVASIVE SPECIES
1.5 NEW ZEALAND INVASION ECOLOGY
1.6 NEW ZEALAND’S TERRESTRIAL CARNIVORES
1.7 NATURALISATION OF INVASIVE PREDATORS
1.8 COMPETITION AND COEXISTENCE AMONG INTRODUCED CARNIVORES .
1.9 INVASIVE SPECIES MANAGEMENT
1.10 RESEARCH AIMS AND OVERVIEW
CHAPTER 2 FORAGING ERMINE AVOID RISK: BEHAVIOURAL RESPONSES OF A MESOPREDATOR TO ITS INTERSPECIFIC COMPETITORS IN A MAMMALIAN GUILD .
2.1 ABSTRACT .
2.2 INTRODUCTION
2.3 MATERIALS AND METHODS .
2.4 RESULTS .
2.5 DISCUSSION .
2.6 ACKNOWLEDGEMENTS
CHAPTER 3 DOMINANT PREDATOR ODOUR TRIGGERS CAUTION AND EAVESDROPPING BEHAVIOUR IN A MAMMALIAN MESOPREDATOR
3.1 ABSTRACT
3.2 INTRODUCTION
3.3 METHODS .
3.4 RESULTS
3.5 DISCUSSION
3.6 ACKNOWLEDGEMENTS
CHAPTER 4 EXPLOITING INTERSPECIFIC OLFACTORY COMMUNICATION TO MONITOR PREDATORS
4.1 ABSTRACT
4.2 INTRODUCTION
4.3 METHODS .
4.4 RESULTS
4.5 DISCUSSION
CHAPTER 5 NICHE PARTITIONING IN A GUILD OF INVASIVE CARNIVORES
5.1 ABSTRACT
5.2 INTRODUCTION
5.3 METHODS
5.4 RESULTS
5.5 DISCUSSION
CHAPTER 6 CONCLUSION
6.1 CARNIVORE INTERACTIONS – INTERSPECIFIC COMPETITION AND FORAGING.
6.2 INTERSPECIFIC OLFACTORY COMMUNICATION – MESOPREDATORS INVESTIGATE SCENT TO REDUCE UNCERTAINTY
6.3 NICHE PARTITIONING – COEXISTENCE OF INVASIVE PREDATORS
6.4 HOW DO STOATS CO-EXIST WITH DOMINANT CARNIVORES IN NEW ZEALAND?
6.5 MANAGEMENT APPLICATIONS – BEHAVIOURAL CONSERVATION
6.6 RESEARCH LIMITATIONS .
6.7 FUTURE RESEARCH
6.8 CLOSING THOUGHT
REFERENCES
APPENDICES