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11 February 2019 Impact of capture and chemical immobilization on the spatial behaviour of red deer Cervus elaphus hinds
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Abstract

Research and management programs of wild animal populations often require intensive field actions, which make direct interventions on animals such as capture, immobilization and manipulation, frequently necessary. Such events, however, could induce a stress response causing physiological and behavioural alterations in the individuals. Knowing the impact of these practices in the post-release phase is of crucial importance when studying the spatial behaviour of wild species. Our study aimed to investigate the potential effect of narcosis and application of GPS collars on 17 red deer Cervus elaphus hinds living in a mountainous area in northern Apennine, Italy. We conducted the analysis at a temporal scale of 45 days after release, in order to assess the response of animals in terms of changes in movement rates, distance from the barycentre of their positions and distance from the capture sites. We then compared habitat selection between the period of disturbance and the following days. This work represents the first study of the behavioural responses of wild red deer to capture and handling procedures. We showed that these operations significantly affect the spatial behaviour of hinds by inducing a short-term increase in movement rates and by keeping the animals away from the centre of their activity, for a period no longer than 10 days. The habitat selection analysis remarked a tendency to escape from human disturbance, by avoiding hunting sites and anthropized locations in favour of forest cover. Red deer hinds thus, seem to cope with stressful events and disturbance by adopting a flight behaviour, which includes moving away from the capture area and seeking refuges. The differences highlighted between the ‘stressful’ period and the following one, showed that such modifications persist for a limited time frame and suggested that this capture method is unlikely to lead to permanent alterations of behaviour.

Research and management programs involving wild animal populations require intensive field actions, and direct interventions on animals are frequently necessary to ensure their monitoring and conservation. Interventions such as translocations, tagging, sampling, insertion of implants and fitting of radio-collars have different levels of invasiveness, nevertheless they require the animals to be captured, immobilised and manipulated. Such unpredictable events induce immediate physiological and behavioural adjustments in order to cope with the perturbation (Wingfield 2005) and may result in an intense stress response. In this context, response can be attributed to either the restraint during capture operations or to the pharmacological treatment. Capture stress may induce physical (Del Giudice et al. 2001, Haulton et al. 2001, Arnemo et al. 2006), physiological (Kock et al. 1987, Marco and Lavin 1999, Del Giudice et al. 2001, Montané et al. 2002, West et al. 2014) as well as behavioural consequences, such as injuries, alteration of normal patterns of behaviour or even mortality (Rachlow et al. 2014). Physiological and behavioural reactions to stress are under hormonal control: animals exposed to noxious stimuli respond by releasing glucocorticoids, i.e. cortisol in most mammals (Romero 2004), which are responsible for recovery mechanisms. Such responses can include the stimulation of the immune system, escape or avoidance behaviours, suppression of feeding as well as of reproduction and serve to focus the animal's attention to behaviours necessary to deal with the stressor (Reeder and Kramer 2005). In free-ranging animals post-capture stress can result in a modification of spatial behaviour, such as moving away from the capture site (Arnemo et al. 2006) or increasing displacement, as well as reducing or increasing movement rates (Cattet et al. 2008, Neumann et al. 2011, Quinn et al. 2012, Northrup et al. 2014). Common modifications of behaviour involve variations in activity levels or rhythms, e.g. reduced activity rates (Morellet et al. 2009, Brivio et al. 2015, Graf et al. 2016), or alteration of habitat selection e.g. refuge seeking (Argenti et al. 2015) and positive selection of wooded areas (Morellet et al. 2009) were frequently observed in wild ungulates. Moreover, changes in behavioural patterns and habits are supposed to affect the animal's life-history traits, for instance by negatively influencing fighting ability and consequently mating success (Pelletier et al. 2004) or inducing the female to separate from offspring (Arnemo et al. 2006, Del Giudice et al. 2018).

Rigorous monitoring and handling protocols have been developed to minimize capture related injuries and mortality. However, short, medium and long term effects on behaviour in sensitive species can hardly be prevented. In addition, a certain amount of time could be required for animals to be accustomed to wear monitoring devices such as GPS or VHP collars. Thus, a better understanding of the influence of capture, manipulation and monitoring devices on post-capture behaviour is mandatory to be able to work with reliable data representing the usual animals habits.

Although the effects of capture and immobilization on movement and activity were studied for diverse wild ungulate species (e.g. Capreolus capreolus, Alces alces, Capra ibex, Rupicapra rupicapra), to our knowledge no investigations were conducted on the modifications of behaviour in red deer Cervus elaphus. The aim of our study was to investigate the short-term effects of narcosis, handling and application of GPS collars on red deer spatial behaviour: we hypothesized that post-capture stress would result in displacement from the capture site as well as an alteration of movement patterns and habitat selection. We also expected that such modifications would be prominent in the first hours immediately following the operations and that, subsequently, the animal would return to a baseline situation. In order to test these hypotheses, we conducted the analysis in two stages: 1) assessing the response of animals to capture-related operations and the duration of the eventual period of disturbance; 2) comparing habitat selection between the period of disturbance and the following period, when the animal returns to its usual activities.