The roaring red stag is undeniably one of the most magnificent performances in the animal kingdom. The sights and sounds of the ‘roar’ have captivated the minds of humans for centuries, making the monumental red stag one of the most widely recognised deer species. With wild and privately-owned herds firmly established across the globe, many of us have the opportunity to observe first-hand the spectacle that is the red deer roar. The sounds and sights themselves are extraordinary, inspiring numerous scientific studies to better understand reproductive behaviour in red deer. This article provides an overview of some of these key scientific findings in relation to roaring vocalisations, helping you ‘decode’ the roar of the mighty red stag.
Roaring vocalisations are essentially a strategy evolved by red deer stags, to maximise their reproductive success. Competition between males during the reproductive season is fierce, with stags being fixated on locating and gaining access to hinds in an effort to reproduce. Mature males actively herd hinds into a group known as a ‘harem’, which becomes a source of great conflict for rutting males. Vocalisations play a key role in the reproductive success of any given male, and therefore, represents an extremely important aspect of red deer reproduction. The basic purpose of roaring vocalisations seems quite obvious, but in reality, they are remarkably complicated behaviours, which impart a significant amount of information to other deer of both genders.
Types of Roars
Reby & McComb (2003) describe two main ‘types’ of roars produced by red stags. The first is termed a ‘common roar’, which is characterised by an initial increase in pitch whilst the angle of the head is raised. As this occurs, the larynx or ‘Adam’s apple’ is lowered down the neck toward the sternum, in effect increasing the length of the vocal tract, which in turn alters the type of sound produced. In total there are typically seven inflexions or significant ‘ups’ and ‘downs’ in pitch through the 3-4 second roar duration, but many variations of this roar exist. The video below provides many excellent examples of this type of roar – take note of the larynx moving down the neck as the roar progresses, this is very important.
The second roar type is termed a ‘harsh roar’, which is far less common and used by stags in more intense competitive situations. The stag’s neck is fully outstretched so the bottom jaw is typically at the same height as the bottom of the neck. The larynx is lowered as far down the neck as possible, all the way to the sternum. The roar is loud and chaotic, and sounds far less ‘musical’ than the common roar. It is generally used following a contest with a competitor or when herding hinds and is often associated with the repeated guttural grunting.
Both types of roars described above feature in the following video.
Can another deer (or human) age/size a deer from its roar alone?
A stag’s roar is in essence an advertisement of himself as a potential sire or breeding stag. He is simultaneously communicating to other deer information about himself, in a bid to improve his reproductive success. Given this, are the stags honest in what they communicate about themselves through their roars, or do they ‘embellish’ the message in an attempt to sound more attractive, more dominant, or bigger in body size then perhaps they really are? Reby & McComb (2003) set out to answer this question, and found through detailed analysis of the complex sound waves produced by stags of various weights & ages, they do not lie about themselves to others – quite unlike ourselves it would seem! Other deer most certainly can determine size/age of a stag from its roar alone, but not in the way we might expect – it isn’t simply the pitch of the roar or its volume, but rather, a specific characteristic of the sound at a particular point in the roar that indicates the size/age of the stag to others.
Earlier in the article the common roar was described, and it was mentioned that the lowering of the larynx was important. The sound produced by a stag is influenced by the length of the vocal tract, which influences how the sound resonates before leaving the mouth (Reby & McComb, 2003). As the larynx is lowered, the vocal tract is lengthened and hence the sound produced is altered. When the larynx reaches the sternum and cannot be lowered any further, a certain low frequency ‘layer’ within the sound is amplified (known as the ‘F1 formant’). Fitch & Reby (2001) found that the longer the animal’s vocal tract, the lower the frequency of this amplified sound layer tucked away within the roar. Since vocal tract length is proportional to a stag’s body size, then so too is the frequency of this amplified sound layer, which forms a ‘marker’ of a stag's age and size. Whether humans can hear the difference is up for debate, at least in my mind - perhaps a question for someone highly experienced with red deer, be sure to write in if this is you!
Stag responses to roars
Given that larger mature animals produce roars with a lower formant frequency, it should follow that both male and female deer should respond differently to roars which differ by this ‘layer’ alone. Reby and colleagues (2005) did exactly this, artificially modifying recordings of roars so they differed by this key feature alone, isolating all other variables. When rutting stags were played recordings with a lower formant frequency (representing a larger/older animal), the stags paid greater attention, produced more replies and offered more harsh roars in response. The responses more often involved a full lengthening of the vocal tract, indicating the stag’s increased effort to advertise their full size. The stags paid less attention to roars characteristic of a smaller bodied stags and which therefore were presumably perceived as less threatening animals. Unfortunately, the study did not review the opposite scenario, however, it would be reasonable to assume younger males ‘pick their battles’ so to speak, when present with roars of larger bodied stags.
A similar experiment conducted by Garcia & colleagues (2014) found that harem-holding stags responded differently to harsh and common roars, with stags reply more reliably to common roars. The reason for this remains unclear, but it was suggested by the author that harsh roars may have been greater cause for concern to the harem holder, as these vocalisations are generally only produced by a stag in a highly aroused state. It was suggested that by not replying, the harem holder may have been attempting to avoid escalation, which could result in losing the harem to this unseen competitor. It makes little sense for a harem holding stag to leave his hinds in response to a competitive situation, and this idea is at least partly supported by this study.
Hind responses to roars
Charlton and colleagues (2007) set out to determine if hinds showed preference for roars produced by a larger bodied stag. The hinds were played recordings of stags of different body size, from either end of an enclosure. The pattern of roars simulated a natural exchange of vocalisations between two competing males. Prior to any roaring, the hinds occupied an area equally distant from each speaker, but were able to move within the enclosure upon commencing of the simulated roar battle. It was determined that the hinds preferentially moved toward the speaker playing roars of a larger stag. Repetitions of the experiment where speakers were swapped achieve the same result – oestrous hinds can detect and respond preferentially to larger bodied stags. Experimentation on hind’s response to harsh vs. common roars found that no significant preference existed, suggesting harsh roars are more relevant to stag-stag interactions (B. D. Charlton, Wyman, Locatelli, Fitch, & Reby, 2014).
Hinds have also been found to use formant frequencies to identify roars of younger, inexperienced males, which is suggested to be less to do with attraction and more in response a potential threat which younger stags pose (Benjamin D Charlton, Mccomb, & Reby, 2008). The attention they pay to roars of younger stags has been suggested to exist out of concern for the inevitable harassment such an individual would bring, which can result in injury to hinds in severe cases.
Roaring rate has been found to be an important factor in mate choice, with hinds showing preference for recordings of stags which roar more frequently vs. those that do not (McComb, 1991). Additionally, hinds have been found to preference stags which roar first during competitive interactions. Both these findings suggest that more motivated and active stags are preferred by hinds, in addition to body size/age. Hinds have been found to be able to distinguish between the roars of familiar and unfamiliar stags, preferring a more familiar stag that had invested greater effort into maintaining the harem (Reby, Hewison, Izquierdo, & Pepin, 2001), providing further evidence that hinds actively scrutinise roars and the messages they contain.
Roaring advances oestrous in Hinds
Holding a harem comes at an extreme energetic cost to a stag. It is physically impossible for a stag to maintain a harem indefinitely – there inevitably comes a time where the stag will become exhausted and cannot continue; when ‘harem tenure’ can no longer be maintained. A stag’s reproductive success is improved if he is able to impregnate all reproductively capable females within the harem, before the point of exhaustion is reached. In order for this to be achieved, each individual hind must come into oestrus first. A study by McComb (1987) in New Zealand investigated the effect that frequent roaring has on the onset of first oestrus in hinds. Three groups of hinds were established prior to the roar; the first were played audio recordings of mature stags in patterns which replicated a harem holding stag; the second were accompanied by a vasectomized stag (stag is infertile but ruts normally); the third were kept in isolation of any stag or other associated stimulus. On April 1st, the three groups were randomly mixed and evenly distributed across three fertile sire stags. Hinds exposed to either the audio recordings or the vasectomized stag during the ‘preparatory’ period calved earlier then the third group kept in isolation. It was therefore determined that roaring advances the onset of oestrous, improving the odds that a harem holding stag will be able to successfully impregnate a majority of hinds within the harem before the point of exhaustion is reached. This to me is perhaps one of the most astonishing findings in relation to the role of roaring vocalisations in reproduction.
Conclusion
It is abundantly evident through the scientific research conducted on red deer roaring vocalisations that they are highly complex behaviours. Whilst several studies on this subject have been conducted, I think it is reasonable to assume there is still much we do not yet know, particularly in relation to wild deer. It is important to note that most studies mentioned in this article relate to captive deer, as is generally the case for studies relating to deer in general for reasons of practicality. Despite this, it is reasonable to assume a high degree of similarly exists between wild and captive deer. How other factors may influence deer’s responses to roaring vocalisations (such as population density, degree of competition for mates, topography, time within the breeding period etc.) is unclear, at least based on the literature I have been able to obtain and read as part of this article. What is absolutely certain is deer are innumerably times more perceptive at deciphering roaring vocalisations than humans, and this factor should be considered when attempting to artificially replicate a roar to initiate a competitive interaction with a wild stag during the breeding period. Making due consideration of the type of roar being made artificially, and the way in which the target animal is likely to respond, will inevitably influence the outcome of this situation.
References
Charlton, B. D., Mccomb, K., & Reby, D. (2008). Free-Ranging Red Deer Hinds Show Greater Attentiveness to Roars with Formant Frequencies Typical of Young Males, 1023–1032.
Charlton, B. D., Reby, D., & McComb, K. (2007). Female red deer prefer the roars of larger males. Biology Letters, 3(4), 382–385.
Charlton, B. D., Wyman, M. T., Locatelli, Y., Fitch, W. T., & Reby, D. (2014). Do red deer hinds prefer stags that produce harsh roars in mate choice contexts? Journal of Zoology, 293(1), 57–62.
Fitch, T., & Reby, D. (2001). The descended larynx is not uniquely human. Proceedings of the Royal Society B: Biological Sciences, 268(1477), 1669–1675.
Garcia, M., Wyman, M. T., Charlton, B. D., Fitch, W. T., & Reby, D. (2014). Response of red deer stags ( Cervus elaphus ) to playback of harsh versus common roars, 1–4.
McComb, K. (1987). Roaring by red deer stags advances the date of oestrus in hinds. Nature, 330(17), 648–649.
McComb, K. (1991). Female choice for high roaring rates in red deer, Cervus elaphus. Animal Behaviour, 41 (September 1989), 79–88.
Reby, D., Hewison, M., Izquierdo, M., & Pepin, D. (2001). Red Deer ( Cervus elaphus ) Hinds Discriminate Between the Roars of Their Current Harem-Holder Stag and Those of Neighbouring Stags, 959, 951–959.
Reby, D., & McComb, K. (2003). Anatomical constraints generate honesty: Acoustic cues to age and weight in the roars of red deer stags. Animal Behaviour, 65(3), 519–530.
Reby, D., Mccomb, K., Cargnelutti, B., Darwin, C., Fitch, W. T., & Clutton-brock, T. (2005). Red deer stags use formants as assessment cues during intrasexual agonistic interactions, (May), 941–947.
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