Recently I read this adorable research publication (Peters, G. et al., 2007)
The publication itself was not adorable but it discussed an adorable phenomenon, i.e., humming in bears.
Humming is known in almost all bear species except giant pandas and it might have evolved in association with seasonality (hibernation).
Bear cubs tend to hum when they are nursing or suckling on an object that is not a teat (that does not reward with nutrition).
However, they also observed humming when they are on their own without the suckling behaviour (supposedly, in order to pacify themselves).
Adult bears have been observed humming, as well, but this behaviour appears to be pertinent with the cub age group.
It might be assumed that humming produces vibrations that somehow stimulate the hibernating mother to improve milk delivery.
Vibrations might be more effective than other types of vocalizations while the mother is barely perceptive of sounds (in the den during hibernation).
However, humming is observed after the nursing is over (when the cub is satiated) and therefore it is not necessarily a vocalization aimed at acquiring more milk.
Also, if cubs tend to hum while by themselves, the vocalization is not directed exclusively at the mother.
Yet it cannot assumed that it is a self-communicative sound (like, for example, sighs, moans, whimpers) because it is too loud.
The amount of energy invested in order to produce the humming is too great for it to be directed at oneself.
After I was familiar with the text, hypotheses and the behaviour, I was wondering how it had come about and what it meant.
I believe that the behaviour evolved in the den during hibernation (by the cubs) and, initially, it might have been aimed at stimulating milk production but the fundamental result of the vibrational impact could be that of relaxing, soothing the mother bear.
If the mother bear spends the first months after her cubs have been born in a hibernating state, she might experience relief (as an instinctive, bodily response) when she perceives her cubs to be alive and satisfied.
Vibrations might be perceived by the ‘sleeping’ mother and they could suggest to her that everything is alright with her cubs.
Consequently, a state of muscular relaxation could occur that would be beneficial for the cub because it could, indeed, stimulate milk production.
But if the result of the vibrational effect is relaxation in the mother and not merely an impact on the teats themselves (massage), there could be other benefits explaining why the cub would hum also after nursing.
For example, after the cub has fed, they might wish to cuddle up to their warm mother.
Nursing can cause muscle tension and the mother might not be as ‘comfy’ after a suckling bout as the cub might prefer.
Humming might relax the mother making her ‘softer’, more yielding to the cubs’ need to cuddle up to her.
Essentially, the humming vibration might work like a ‘button’ producing relaxation in the mother that can be beneficial in many ways and that can help the cub avoid harm (e.g., unaware movement on behalf of the mother that could inadvertently scratch the cub or cause a kick/punch etc.).
It is possible that relaxed body is also a warmer body (temperature-wise).
I believe that these effects are caused by hormonal pathways and that later in the cubs’ development, as they also develop the specific pathways, they can induce the state of relaxation in themselves.
Thus, the behaviour that was once directed at the mother, now can be directed at oneself.
If cubs only begin humming while on their own (humming that is not addressed to the mother) at a certain age, this could specify what type of hormones are involved (according to the cubs’ development).
Namely, if cubs begin humming only after a specific stage in development has been reached, this might indicate what hormones are involved in the humming-relaxation mechanism through determining which pathways the cubs are capable of using at this specific stage (which they were not capable of using previously).
If both male and female cubs hum while by themselves (self-directed humming), this would suggest that the hormones involved are not sex-specific and that mothers do not respond to their cubs’ humming through pathways that are strictly maternal, involved in female reproduction (because male cubs can also pacify (relax) themselves through the use of this mechanism).
I suspect that oxytocins might be involved and that cubs perhaps begin to be capable of soothing themselves as their awareness of social interactions become more explicit.
In some ways, they become their own social partner in this interaction.
It is interesting, however, why adult bears would not ordinarily hum.
If oxytocins (the social hormones) are at play, this could indicate at some change that happens in bear development as they leave the social unit of their family (mother-cub unit) and as they join the adult population which is essentially solitary.
It would be interesting to observe in what situations adult bears hum.
For example, if they only hum in captivity, this could mean that foraging/food acquisition might interfere with oxytocin production in reaction to humming.
Mothers react to humming while they are hibernating (not actively foraging, not involved in social interactions with competitors).
Cubs hum by themselves while they are young (reliant on mother and mainly interacting with their mother and siblings, i.e., somewhat buffered against the social tensions of the adult world).
Perhaps the humming effects are cancelled when social interactions (related to oxytocin production) become dominated by competitive interactions during feeding situations (also, cub, mate defense) and humming might return in artificial conditions when the bears do not have to worry and compete about the aforementioned resources.
It would be interesting to see if bears might hum, for example, nearby salmon runs in years when social dominance hierarchies become relaxed due to high abundance of salmon.
***
If humming (and its vibrational impact) could induce relaxation in bears (including adult bears in non-competitive living arrangements), the frequency could be used to calm bears, e.g., after rescue and to re-establish normal hormonal production as well as restore neural pathways involved in inducing ‘happy states’ (and possibly also social inclinations) in traumatized bears (‘anti-depressant’ effect).
For example, toys could be developed that vibrate through producing the humming sound in the appropriate frequency where the bear can learn to manipulate a purposefully-designed toy in order to switch on the vibration effect (so that the bear was not exposed to the sound and its vibrational impact in a non-voluntary capacity).
This toy could be produced in a shape and size that is ‘huggable’ mimicking the original mother-cub bond during the denning period.
Alternatively, there could be massage beds that are automatically activated by bear’s body weight.
***
Two other aspects that came to my mind:
1
If the bear hums to itself in order to produce the soothing effect, this could be a psychologically significant factor because it means that the individual is capable of recognizing their state and taking an action to alter it.
This indicates at the individual’s ability to distance themselves from the anxious circumstance (/trauma) – not in an unhealthy, ‘escapist’ manner but rather in a proactive, self-dependent manner where the individual becomes their own helper (exhibits understanding toward oneself, compassion toward oneself and competence to act in order to mitigate the circumstance).
It does not appear to me that humming is an activity that could be compared to avoidance behaviour because it establishes contact and serves as an encouraging conversation with oneself.
If bear cubs hum in the wild, this would probably be a vocalization they assume during stressful time with no actual danger involved because cubs are highly efficient at reacting toward real threat and the behaviour under conditions of real threat would be that of fleeing, hiding, investigating, looking for mother etc.
It rather seems that humming is applied when the aggravation is psychological (e.g., missing mommy, boredom) in order to remind oneself that they are not alone (they have themselves).
I think that developing a social connection with oneself is healthy and it can build confidence while realizing that the individual is never truly abandoned and helpless (which is also an essential advancement to recover from trauma).
It could be compared to a child who is old enough to sometimes be left alone for shorter periods of time and who suffers not out of real threat but rather out of the novel experience of being alone and dependent on oneself.
Being able to pass time by oneself and to cope on one’s own is an important skill.
Being alone (or feeling alone) is, coincidentally, also a state which can awaken memories of trauma and therefore not becoming ‘lost’ during such periods (not becoming overwhelmed) is essential to beginning to heal through gradual exposure to scary memories and developing acceptance of them which leads to understanding and outgrowing these states.
This is one of the reasons why I believe social hormones would be involved.
2
It is possible that humming is used as a stimulus to which the individual then reacts thus expressing their attitude at the time.
It could be a self-diagnosing mechanism under conditions when the individual cannot see their psychological state reflected in others (without social feedback).
For example, as the individual hums, they might respond to their own humming in different manners (becoming soothed, becoming irritated, deciding to continue, deciding to stop).
They become aware of their own existence (which might sound strange but it is easy to feel as if we do not exist if the world does not reflect us socially and if we have become slightly frightened) and of their own inner states and they can take decisions to alter those inner states.
It is not dissimilar to the cub’s letting know to their mother that they are alive and they are okay.
Only when cubs hum to themselves, the message is also sent to themselves (I am alive and I am fine.)
If the individual cannot, for some reason, appreciate their state internally (e.g., due to anxiety), it might be important that they can tell themselves that externally nothing bad is happening to them.
In individuals who have suffered noise-related trauma (yelling, loud bangs, other type of scary stimuli), humming (which is a sound produced in altogether benign or low-stress situations) might serve as a low-exposure method of overcoming anxieties.
The individual hears the humming (produced by themselves or an object) and they react to it according to their inner state.
Moreover, they can choose to stop it or to continue it which is an empowering change from the past condition where no such choice had been given.
Thus, the individual can slowly begin to overcome sound-related trauma by exposing themselves to a source of noise and choosing whether they are comfortable with it.
It is an intermediate and partly natural (because it belongs to the bear’s natural range of vocalizations) strategy which lies somewhere between sheltering the individual from all scary triggers of past experiences vs. exposure to the same stimuli that traumatized the individual in the past.
Notes by Ieva 