There has been much debate regarding the pack size evolution in wolves and the adjustment of the pack size to such possible factors as prey abundance, territory size, prey size etc.
It has not been conclusively proven that packs were necessarily larger upon the conditions of greater prey abundance.
In fact, if prey abundance is also translated into greater prey density, wolf packs might become smaller (under saturated wolf population conditions) because large territories are no longer needed to track sparsely-encountered prey.
While the pack size does not correlate with territory size discernibly (i.e., if the territory is larger, the pack does not necessarily grow in numbers), with higher prey densities, territories might be small and unable to accommodate very large packs.
Similarly, while there is perhaps a slight tendency for wolf packs to grow larger if their prey is larger, as well, there is no evidence that larger packs improve hunting success in all predator-prey systems.
For example, in the study by McNulty, D.R. et al. (2014) it was found that peak prey capture performance levelled off at 2 – 6 wolves when hunting elk while it levelled off at 9 – 13 wolves when hunting bison (and possibly continued to increase).
Bison is considered more formidable prey than elk and tighter cooperation by a larger pack might be needed to conquer these animals.
Meanwhile, it does not necessarily hold true that predominantly elk-based wolf packs are smaller than bison-hunting wolf packs.
Also, in larger packs, individual hunting success might even decrease at a certain group size (e.g., 4 wolves in elk-based Yellowstone wolf packs; see MacNulty, D.R. et al. (2012)) and as the group exceeds this number, many individuals (e.g., younger, inexperienced wolves) are ‘free-riding’ and not participating or barely participating in the hunt.
Pack size might not always be correlated with high hunting success even when formidable prey is involved.
For example, in Scandinavia and on Isle Royale, it has been often observed that pups are afraid of the main prey (moose) and it is possible that during their first winter, they are inefficient hunters and rely on their parents.
Thus, if the wolf pack consists of 2 adults and 5 pups, it might not have higher success rates even while preying on large ungulates such as moose or bison because the juveniles are not taking full part in the process (although this is not always so and some young wolves probably become efficient hunters early on).
In order to improve success respective to pack size, the pack probably needs to include more experienced subordinates (yearlings, two-year-olds and perhaps even older offspring or other related or non-related older pack members).
The pack size might also be of importance where the prey needs to be ‘herded’ into smaller groups, ambushed etc., i.e., where the strategy involves not only the actual attack on an individual ungulate but where it involves tactical planning which cannot be achieved by one or two wolves.
For example, it appears important for wolves to entice their prey to run.
This might be how the wolves test the prey vulnerability.
When wolves approach larger herds, they frequently fan out covering the possible escape routes and sometimes other pack members even lie in wait in the direction which the ungulates are likely to take.
This stage in the hunt might be thereby vital in some circumstances and even if the additional members are not taking part in the actual bringing down of the prey (which might only call for 2 – 4 wolves to bite into the nose and into the hindquarters so that the prey is haltered and finally dragged down to the ground), some prey species (e.g., bison in their large herds) might not be spooked by 2 – 4 wolves and if it is necessary for them to start running, a larger number of wolves might be needed to upset the bison sufficiently for them to flee (and to panic).
A greater number of wolves might also be needed where the ungulates have a strong tendency to stick together in big groups and to keep their young in the central part of these herds (compared to ungulates which might keep vigilance commonly but which might not form a socially consolidated herd and which thereby, upon danger, might more easily split into subunits).
Accordingly, under some circumstances, large packs might be needed but, under other circumstances, pairs might be even more efficient than full packs if accounting for prey acquisition rate in terms of biomass per wolf, i.e., if a pair hunts down a prey item, they might each come by a larger share in meat than a pack of 5 – 6 wolves bringing down the same type of prey item (under circumstance that the pack of 5 – 6 wolves is not overall more efficient at hunting and does not acquire meat more often or with higher success rates per the total number of trials or per distance travelled to find the prey in the first place).
However, a pair of wolves might have a hard time keeping the carcass to themselves.
Indeed, scavenging might be one of the fundamental reasons (and even a more reliable prognosticating factor) behind the evolution of large pack sizes (see, e.g., Kaczensky, P. et al., 2005, where it was found that ravens remove ca. 75% of kill biomass from small packs and almost none from very large packs).
Some naturalists and scientists have observed that wolf packs fit very neatly around the type of prey they normally hunt once it has been killed and is being fed upon.
Thus, the pack leaves little space open for scavengers and the pack also leaves little behind (or is more capable of defending the carcass and returning to it regularly in order to ward off scavengers between feeding bouts).
This having been stated, I also believe there is an additional reason why wolves have evolved pack sizes that frequently perhaps do not improve their hunting success and might even imperil their own survival (if the biomass acquisition rates per wolf are low and if some individuals must invest disproportionately in provisioning).
Of course, the pack is typically comprised of the breeding pair and their offspring.
I do not believe that parent wolves expect their pups to be full-fledged hunters during their first winter and the wolves obviously do not consider weaning as the terminal stage in the care they are providing for their young.
Pups are educated in different skills throughout their first year of life (and even longer than that) and the first winter is likely a stage when the pups are only learning to hunt and to cooperate.
Thus, the pack size, from the perspective of the wolf with regard to hunting efficiency, might not be regarded as the total number of individuals in the pack because the parents might account for the pups’ dependency.
The hunting success might rather concern the breeding pair and the older subordinates.
Consequently, the evolution of the pack size might be analyzed differently when evaluating the core unit (parents + pups) vs. the larger family (parents + pups + older subordinates) because the evolution of the core unit might depend on different type of motivation and investment than the evolution of the entire pack.
To offer a comparison, it would akin to asking why we keep our toddlers or school-age children at home with us vs. why (and under what conditions) we allow for our children 18+ to live with us.
My perspective on the pack size and hunting success, however, includes both groups.
I think that it is scary and psychologically (as well as, of course, physiologically) challenging for wolves to bring down prey (especially, large and formidable prey).
Many accounts in different wolf-related literature mention pups who are clearly frightened of large ungulates and who might be even traumatized by the hunting event during their first autumn and winter.
Ungulates can kill wolves, including experienced adult wolves, or they can severely injure them.
It is not infrequent, either, to read accounts of lone wolves or two wolves or very few wolves approaching prey and then retreating or even running away.
Some very large ungulates (such as muskoxen or bison but also elk) at times appear to be harassing the wolves and making them rise up, making them move out of their way or even chasing them.
Wolves are often much smaller than their prey and they often they also weigh less than their prey.
Wolves are not the fastest of sprinters, either, and many prey species (elk, red deer, caribou) can run faster than wolves while others (moose) have enormous endurance and yet others (mountain sheep) live on rugged terrain to which they are adapted far better than the wolves.
Still, the hunt demands for decisive action and confidence because any wavering can be used by the prey to escape or to launch a counter attack.
I should say that wolves frequently must perform under conditions that are actually beyond their physical capacity and as a species that is exceptional at noting vulnerabilities in other species, I find it unlikely that wolves are unaware that they are not necessarily in advantage.
Wolves cannot rush into hunt hot-headed, either.
Until the last moment, they have to keep their cool because strategizing is essential to their success.
Thus, I find it improbable that wolves rely on adrenaline of the hunt which might give them an edge.
It is more likely that wolves are calculating every move but the cognitive effort probably disallows them to give in to pure instinct that is more energy-preserving and that might allow to ‘forget’ the true balance of power.
Wolves also have to travel a lot and test many prey/herds before they are successful (the kill per all trials rates can be as low as 5 – 28% and the average success rate is only 15%; see Living with Wolves website).
This truly calls for determination and persistence although, partly, I believe that wolves enjoy travelling and the group interaction that is implied in testing the prey might be rewarding, as well.
I think that it is very difficult for wolves to hunt their large prey and in order to accomplish this task on regular basis (especially, where formidable prey is involved), the wolves have to motivated and encouraged by one another.
Motivation that is rooted in the need to provision for pups is great, and this motivation must be crucial during the first year of pack establishment because the new parents must bring down prey frequently without the aid of older subordinates, and they must bring down enough prey to provision for themselves as well as for the pups.
Perhaps, partly, the timing of pup birth which coincides with the rise in smaller prey items, has been advantageous as the first-time parents can, at first, hunt winter-weakened ungulates (that improve the breeding female’s ovulation and fitness) and then they can spend the first months hunting small and vulnerable prey before the late summer/autumn/early winter period when their skills are tested as they hunt both for themselves and for their pups (in some systems, such as moose-wolf systems, with little investment from the pups themselves).
However, I do believe that pups assist their parents in provisioning since an early age (perhaps since before they are born) and even if they are not actively hunting themselves.
It is not merely through the future promise of the dispersal of one’s genes into the population but also through the induction of the production of hormones in the parents that the pups (and later older offspring and other subordinates) invest in the fitness and motivation, and preparedness to endure the rather uneven odds (between wolf and its prey) of their parents.
It is known that having offspring as well as engaging in social activities (in social species) results in the production of many hormones and many of these hormones (if not all) are involved in our energy levels through, e.g., affecting the rates at which ATPs are converted into cell-usable energy.
Thusly, I believe that the adult wolves who must exert themselves almost beyond their physiological capacity (and possibly beyond that with hopes that their energy balance might be recovered at a later time) are in true need of the interactions with their pups and that additional interactions with older offspring (mediated through different hormonal pathways that are less related to reproduction and more related to social living) might ensure that the parents can perform the tasks expected from them.
For example, it is known that prior to departing to hunt and also sometimes prior to approaching prey or even during the hunt wolves can engage in social activity which is sometimes described as ‘milling’ and which is also explained as the need to keep the group cohesive and to coordinate the group’s behavior under the guidance of the leaders.
However, I believe that these activities also serve to physically and psychologically inspire the leading wolves who will soon need to undertake an enormous, possibly fatal and certainly highly demanding task of tackling their large prey.
These interactions might improve the energy metabolism rates by the adults who profit from the social encouragement even if they might not profit from generally great investment in the very hunting effort on behalf of their subordinates.
Perhaps wolves might not be able to perform this well at all if they only had to rely on their own self-motivation and parents might run out of energy providing for their pups year after year unless there were subordinates boosting their hormonal levels and increasing the overall amount of social interactions in the pack.
It is possible that the breeding pair can produce more litters if they also have older subordinates not just because these older subordinates provide actual, direct help but also because the subordinates provide a good feeling (they play with one another and with the pups which must be gratifying for the parents, as well, to behold while the parents, had they been alone year after year, might be too exhausted to uphold as much play and social activity) and the subordinates also have a true understanding of the leadership that the parents provide.
For example, during the first winter, the pups learn from their parents and the parents are probably empowered by the awareness that they are teaching their offspring and being good role models.
However, the additional presence of older subordinates might create an even greater sense of self-worth in the wolf parents because these older subordinates are already capable of many of the same deeds yet they revere their parents (very openly and physically) and heed their mastery and leadership.
Coincidentally, the presence of older offspring might initiate the youngsters into participating in the hunt sooner in their development because it might be less scary to approach the large ungulates when the group of the wolves is larger (and healthy competition in the form of wishing to keep up and to assert themselves could be a factor).
In small wolf families where only the parents and the pups are present, the pups might be more timid (and of lesser help to the parents) for a longer time.
The presence of the parents might not always be sufficient to encourage the pup to forget its fears and to give it a try because parents might be regarded differently than older siblings (parental figures might not assist in overcoming anxiety if the pups, for example, regard their parents as somewhat exulted and as individuals they have no hopes to compare themselves to while experiences with less dominant, more peer-like older wolves could lead to bolder and more self-reliant pups who already have positive experience in tackling someone way larger than themselves and coming out on top or at least unscathed).
Thus, the presence of older siblings could initiate the pups into hunt sooner.
I believe that social interactions within wolf packs and other types of hormonal production-inducing factors (such as having pups) might benefit the pack’s adults physically and psychologically as well as provide motivation and encouragement in performing the daily tasks of an adult wolf which are often exerting to the last and beyond.
Play, milling, touching noses etc. could be activities that are not only necessary for pack’s coordination but that also improve the fitness of the wolves, boost their energy levels and mitigate anxieties.
Parents without subordinates might sooner exhaust themselves reproductively due to the limited opportunity of the social interactions that older subordinates can provide in the family even while the parents are too tired to play.
Alternatively, by taking on some of the parental roles, the subordinates might free up time for the parents to interact with their pups and older offspring (and with one another).
I also believe that the responses that we sometimes observe in leaders and which, as humans, we find more difficult to understand (namely, the submissive approach by a subordinate which provokes a seemingly ‘aggressive’ response by the adult, e.g., a snap or a growl but which is never taken seriously by the subordinate who continues to harass the adult; also, the milling around the leaders and licking their muzzles etc.), are founded not upon dominance assertion but by social mechanisms that serve to empower the leaders to perform their tasks that the entire group depends on.
When an adult wolf ‘snaps’ at a subordinate, it might not be a message of ‘can you not see I am tired?’ or ‘mind your status’.
It might be a message of ‘my nature is benevolent but my nature does not suffice to ensure your wellbeing and I am prepared to go beyond my nature and to achieve acts of predation that overreach my size and even my speed in order for you to thrive’.
Similarly, when the subordinates are milling around the adult and making themselves way smaller than they are, licking at the muzzle of the adult, they might be saying – ‘I acknowledge that you are greater than a wolf can even be when you are hunting for me and while I am a big and clever wolf, too, I submit to you because you are superior to a degree that makes you a Superwolf (akin to Superman who is someone with superhuman abilities and who applies these abilities for the good of all).’
Because is it not a superpower to hunt someone 4 – 10 times one’s weight, to travel 50 km daily and to risk one’s life every time when making a kill for the benefit of one’s offspring and even for the benefit of the entire ecosystem (including the prey population)?
Is it not conceivable that social support is vital when approaching someone 2 – 2.5 times taller than oneself and considering tackling them in a mortal battle?
Perhaps the success of larger pack size in bringing down bison is only partly based on the investment by the pack members in the coordinated hunt.
Partly, it could be based on the social motivation, encouragement and the socially-mediated production of actual energy (also, in a very immediate timeframe by increasing the metabolic rate) that allows for the wolves in larger packs to hunt bison, musoxen etc.
References
DID YOU KNOW? Predators hunt in different ways… Dutcher, G., Mar 10, 2021, Living with Wolves, https://www.livingwithwolves.org/hunting-style/
Petra, K. et al. “Effect of raven Corvus corax scavenging on the kill rates of wolf Canis lupus packs,” Wildlife Biology, 11(2), 101-108, (1 June 2005)
MacNulty, D.R. et al. Nonlinear effects of group size on the success of wolves hunting elk, Behavioral Ecology, Volume 23, Issue 1, January-February 2012, Pages 75–82, https://doi.org/10.1093/beheco/arr159
MacNulty, D.R. et al. (2014). Influence of Group Size on the Success of Wolves Hunting Bison. PloS one. 9. e112884. 10.1371/journal.pone.0112884.
Notes by Ieva 