Captivated by Chital
Anyone who has seen live chital will first make note of their strikingly handsome appearance. The second observation is they are exceptionally ‘nervous’. My first realisation of this was following a long period of sitting motionless in full camouflage, watching a nearby open paddock in hopes of glimpsing a chital. The wind was consistently in my favour and the morning was still. After several hours, I watched a single animal expose only the front of its face, its body remaining within dense cover. It proceeded to scan the open paddock for a full thirty minutes, remaining virtually motionless, assessing every detail of its environment. The animal stepped back into cover, vanishing, as though it was never there. Naturally, I was disappointed, but similarly captivated by the experience. It was one of my first encounters with wild chital and left me with many questions relating to this sort of behaviour, known within scientific literature as “vigilance”.
What is vigilance?
The image of a meerkat bolt upright, scanning the horizon for danger is seamless visual definition. The term refers to the behaviours used by animals to detect and avoid predators – it has evolved in response to the constant threat of death by predation over tens of thousands of years of interactions between predator and prey, sculpting the species through natural selection. Dimond & Lazarus (1974) defines vigilance as being “a measure of the probability that an animal will detect a given stimulus at a given instant in time”. Greater vigilance leads to a higher probability of detecting danger. Chital are native to the Indian Subcontinent, where they share their environment with 200kg cats and highly coordinated packs of native dogs; their survival depends on vigilance.
Vigilance in chital is characterised by any ‘alert’ body language – head up, ears forward. Momentary pauses in activity are made periodically to scan their surroundings, consider the smells carried by the air and focus on any sounds that may suggest danger. Schaller (1984) describes a characteristic ‘head-up, tail up’ stance, demonstrating a heightened state of vigilance in response to a stimulus suggesting danger. Their senses are extremely well developed, particularly their sense of smell which is reported by Graf & Nicholas (1966) to be capable of scenting danger up to a mile upwind. A detailed study of chital behaviour by Sharatchandra & Gadgil (1980) developed three behavioural sub-categories relating to antipredatory behaviour:
a) standing, scanning for anything suspicious;
b) an alert posture with the neck outstretched pointing in the direction of the disturbance;
c) giving alarm signals which include tail raising, alarm calls, stamping the ground with forefoot, and when actually confronted with a predator stotting and bunching into a tight herd.
The following video from BBC’s ‘Life’ effectively demonstrates each of these vigilance behavioural categories.
Evolutionary Context
Chital are a favoured food source for three main predators, which occupy the same native range; the tiger (Panthera tigris), leopard (Panthera pardus) and dhole (Cuon alpinus), a native species of wild dog. Ramesh (2011) found that that chital (and sambar) comprised >77% of the diets of these predators within the area studied. Given this, it is reasonable to assume a significant proportion of mortality in wild chital could be attributed to predation. It is useful to develop an understanding of the typical hunting strategies particular to each predator, to better understand the selective pressures which have shaped the behaviour of chital throughout their evolution.
Coursing vs Stalking Predation
The dhole or Asiatic wild dog, primarily hunts in packs of typically around 10 individuals, with as many as 30 in a single unit reported by Fox (1984). They are ‘coursing predators’, preferring to chase their prey in open areas in a coordinated approach involving multiple animals (Johnsingh, 1992). Previous work by Johnsingh (1983) determined that dhole preferred to target lone animals, presumably to better coordinate the effort of the pack. The efficiency of a coordinated pack hunt is demonstrated by Johnsingh’s findings that the majority of hunts (96% of 48 hunts) resulted in a kill within 500m from the starting point. Multiple animals hunting in coordination are able to chase an animal to exhaustion, and in some cases even drive the deer into a line of dhole lying in ambush (Sillero-Zubiri et al., 2004). Live consumption of prey was noted during a study conducted by Ramesh (2011), with a graphic example of this contained in the video below, followed by a coordinated dhole hunt on a chital stag.
Both the leopard and tiger utilise ‘stalking’ as opposed to ‘coursing’, as in the case of the dhole. Given both tigers and leopards are primarily solitary animals; they must utilise a slow and methodical approach, utilising available cover to successfully kill prey. Success is dependent on the prey being unaware of the predator’s presence, until the predator is within a proximity that does not give the prey sufficient time to escape. Johnsingh (1992) found that proportionally higher number of sambar were preyed upon then chital, given sambar preferred denser habitat and lived in smaller groups, thus putting them at greater vulnerability to predation by cats. Leopards were found venture into human inhabited areas far more readily then tigers, resulting in a proportionally greater predation on chital then tigers, given chital’s preference for human inhabited areas (see ‘yarding’ behaviour below).
Feeding makes Deer Vulnerable
Foraging is one of the most dangerous activities for deer. It shifts their focus toward selecting and consuming food, and therefore, decreases their spatial awareness and overall vigilance. This weakness is readily exploited by predators. Given the unavoidable need for consumption of food, chital must place themselves at risk at least part of the time, making a ‘trade-off’ between vigilance and foraging. The two activities are mutually exclusive; therefore, other strategies must exist to minimise the risk, some of which are detailed below. Vigilance behaviours are well studied in the animal kingdom, however, the relatively recent findings of Ghosal & Venkataraman (2013) form the basis for our scientific understanding specifically in relation to chital. Much of the subsequent content has been derived from these research findings, unless otherwise stated.
Herding
Chital form herds commonly averaging around 10 individuals, but can form herds of 150 (Schaller, 1967). Herding behaviour is an anti-predator strategy which decreases individual risk i.e. ‘safety in numbers’. Every individual is afforded the “collective vigilance” of the entire herd, therefore enabling each individual to dedicate less personal investment in vigilance, without a significant compromise in safety. This enables a more concentrated foraging effort to be undertaken, providing the added benefit of reducing the total time an individual spends in a vulnerable position. As group size increases, any given individual was found to be less vigilant within a given time period, with individuals in isolation dedicating significantly more time to vigilance. Similarly, it was found that as group size increases, the number of vigilant individuals at any given time was proportionally higher. Given this, would it not be logical for chital to form massive aggregations of several hundred animals? The ‘optimal’ herd size is dependent on several other ecological factors – there becomes a point where too many animals increases competition for resources such as feed, or results in greater concentration of predators, thereby negating the benefits provided by a larger group size (Ghosal & Venkataraman 2013). Herd size therefore changes depending on the environment at any given time.
The video below demonstrates a truly spectacular congregation of chital on the Banks of the Kabini River, India.
Yarding
Johnsingh (1992) observed mass congregations of chital estimated at 500+ individuals, in close vicinity of the tourism complex in Bandipur Village (the video above, filmed on the banks of the Kabini River is in close proximity to Bandipur and likely constitutes similar ‘yarding’ behaviour). The author considered this location a “favourite resting site” of chital within the night, acting to reduce the opportunity for predation by tigers which prefer to avoid human contact. Personal conversation with Australian hunters with experience in North Queensland chital have revealed similar observations, where free ranging chital were found to preference land in the vicinity of farm houses, sheds etc. despite having access to limitless bushland seemingly identical in all other factors. These deer are certainly predated upon by wild dogs/dingos in this area, so it is plausible North QLD chital have developed similar ‘yarding’ behaviours as an anti-predator response.
Stag vs. Hind Vigilance
An observational study of chital alertness by Graf & Nicholas (1966) found that mature stags “appear[ed] a bit less alert”, apparently depending on the alertness of the female deer to minimise their vulnerability. The authors also found that lone stags were “usually somewhat easier to approach” in comparison to female deer, a factor which seems to be in contrast to what many would assume to be the case. A study by Sharatchandra & Gadgil (1980) found that adult hinds dedicated nearly double the resources to anti-predator strategies than adult males, confirming the observations of Graf and Nicholas. Additionally, they found that the larger bodied males easily forced their way to the centre of the herd when a predator was detected, thus minimising their personal risk. Given that stags are also well equipped at defending themselves when in hard antler, and have no role in the nurturing and protection of young, it makes sense for stags to have a reduced need for vigilance in comparison to females. Stags developing velvet were still less vigilant then females, but slightly more so then hard antlered males, indicating the presence of antlers (or possibly another associated factor such as hormonal differences) plays a role.
Conclusion
When chital are considered in their native context, it becomes far easier to develop an understanding of the reasoning behind their behaviour. The fact that these behaviours are very apparent within herds which do not experience any predation at all (such as in captivity, or in exotic herds elsewhere in the world) indicates how deeply anti-predator behaviours are embedded within their DNA. If ever you have the opportunity to watch undisturbed chital first-hand, take note of these behaviours and enjoy the fortunate position you’re in – evolution has done its best to make such encounters unlikely.
References
Fox, M.W. 1984. The whistling hunters: field studies of the Asiatic wild dog (Cuon alpinus). State University of New York Press, Albany, NY, USA.
Dimond, S., & Lazarus, J. (1974). The Problem of Vigilance in Animal Life. Brain Behavioural Ecology, 9, 60–79.
Ghosal, R., & Venkataraman, A. (2013). An adaptive system of vigilance in spotted deer ( Axis axis ) herds in response to predation, 104(6)
Graf, W., & Nicholas, L. J. (1966). The Axis Deer in Hawaii, 63(3), 629–750.
Johnsingh, A. J. T. (1983). Large Mammalian Prey - Predators in Bandipur. The Journal of the Bombay Natural History Society, 80(1)
Johnsingh, A. J. T. (1992). Prey selection in three large sympatric carnivores in Bandipur. Mammalia, 56(4), 517–527.
Ramesh, T. (2011). Prey selection and food habits of large carnivores: tiger panthera tigris, leopard panthera pardus and dhole cuon alpinus in Mudumalai Tiger Reserve, Tamil Nadu. Population Estimation of Large Carnivores, (May 2010), 206.
Sharatchandra, H. C., & Gadgil, M. (1980). On the time-budget of different life-history stages of chital (Axis axis). Journal of the Bombay Natural History Society.
Sillero-Zubiri, C., Hoffmann, M., & Macdonald, D. W. (2004). Canids: Foxes, Wolves, Jackals and Dogs. Canids: Foxes, Wolves, Jackals and Dogs.
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