Resource partitioning within wolf packs during the summer period has already been studied, for example, by Bryan, H.M. et al. (2006) where it was found that adult wolves consumed a greater proportion of adult deer meat compared to their pups who seemed to feed mainly on deer fawns.
The findings were explained by the possibly lower parasite and pathogen load in deer fawns.
Accordingly, fawn meat might be ‘cleaner’ for pups whose immunity has not yet been developed to withstand many of the pathogens and parasites that adult wolves are not affected by to the degree of compromised fitness and mortality.
Fawn meat does not have higher protein concentrations, nor fat concentrations than adult deer meat and, subsequently, the diet differences between pups and adult wolves were not attributed to the behaviour by adult wolves to deliver higher protein and fat content food to their young.
However, deer meat fat and protein as such might not differ as greatly between these age groups (adult deer vs. fawns) and perhaps adult wolves do not discriminate with regard to these resources.
Meanwhile, where accessible (the study was conducted in the coastal regions of British Columbia where some packs had access to ‘sea-food’), adult wolves appeared to provision their pups with seals to a greater extent than they were consumed by the adult wolves themselves.
Seals might be appreciated as higher fat resources (unlike deer where adult and young individuals might not be contrasted as greatly in their fat/lean quality) and thereby delivered to the pups purposefully.
I, personally, also believe there is another explanation to the observed slight niche partitioning, i.e., fawn meat might be more easily digested by pups than the meat of adult deer.
Even if fawn meat does not have higher fat and protein content, its overall nutritional accessibility might be greater while the ‘tougher’ meat of adult deer might result in a digestive challenge for the pups and pups might not be able to extract the nutrients presented in the adult deer meat as efficiently.
Additionally, there might be some nutrients that are more available in fawns than in adult deer or that are assimilated more readily when uptaken from fawn meat.
I believe it might be one of the reasons why wolves have adjusted their reproductive cycles to these fawn/calf pulses in order to provide the young pups who are transitioning from milk to solid food with young, tender meat.
It is also known that pups can supplement their summer diet with small prey that have caught by themselves (voles, grasshoppers etc.).
However, I began wondering furthermore if the summer hunting pattern by wolves (solitary hunting or hunting in smaller groups) might lead to spatial/temporal niche partitioning (which could sometimes result in prey resource type partitioning) in adults and subadults of the wolf family.
If summer tends to be a scarcer time (due to invulnerability of adult ungulates), perhaps adult wolves have developed a family system whereby they do not exploit the same food patches and resources.
I first considered it when I read the Twitter post by the Voyageurs Wolf Project regarding the breeding female of Windsong Pack O4D and the fence that had been installed around a huge ranch in the Voyageurs Ecosystem.
This female was finding any possible way to get back on the ranch despite the fence and the many efforts to stop her and to prevent further entry.
As O4D has not been involved in livestock depredation, is thought that O4D had learned to feed on calf poop which has nutritional value and can be obtained in great amounts without investing her energy in hunting (as a mother, she has to spare her energy because it is needed to provision for her pups).
Windsong Pack is not a very large pack but it has its subordinates staying beside the pups of the year, and Voyageurs Ecosystem, overall, is not that highly productive.
Many wolf packs there face the issues of starvation that cause mortality both in pups and adults.
I was wondering if the female’s persistence was the manifestation of her reluctance to relinquish a food source that did not affect the quality of her milk (during nursing) but that could let her feed on resources other than fawns (which could then be brought to pups).
Perhaps adult and subadult wolves attempt to carve their own foraging niche so that the best food was left to the pups and so that they did not interfere with one another’s survival, either.
For example, if this female was nimble and stealthy enough to ‘steal’ calf poop off the ranch, she would have allowed for her mate and older offspring to utilize other types or resources (deer meat, beavers etc.) that they are more proficient at obtaining and that they would otherwise share and exploit commonly with a lower proportion available per each wolf.
Summer kills are very difficult to study and mostly only one or two wolves are monitored per pack.
Thus, we do not really know whether the family providers might attempt to find hunting/foraging niche that befits the individual’s skills and that allows for each individual to try to be fed and to provide for the pups.
Such resource partitioning might become apparent on spatial and/or temporal and/or resource type basis.
For example, if some wolves in the group are more adept at hunting beavers, it could be their niche and resource type but it might also mean that they would hunt in spatial patches where beavers are accessible leaving other parts of their territory to other pack members who do not hunt beavers (unless the opportunity arises).
Wolves are also known to use their territories on a rotational basis or sometimes also in a manner that prevents visiting previously depleted sectors soon after kills have been made there (Jedrzejewski, W. et al., 2001; Gurarie, E. et al., 2022).
I think it is important that in the study by Gurarie, E. et al., 2022, high degree of individuals variants were found among different wolves (in different packs) with respect to their spatial and temporal planning of territory use.
There could be a temporal element to the spatial partitioning of summer territory use.
For example, if the prey species is not easily subdued by a single individual, those pack members who hunt in groups, might account for prey distribution (either returning to abundant prey patches or avoiding patches where previous kills were made) and other pack members who ‘pick up fawns’ (which is likely a strategy that depends on approaching unnoticed which would make solitary hunters more successful if the ungulates do not form herds of mothers or if they have not yet regrouped with other mother-offspring units) might try to ‘stay out of way’.
Thusly, groups might utilize different parts of territory (where adults can be found) than solitary foragers (who would seek out the refugia selected by ungulate mothers to seclude their offspring until they reach sufficient level of mobility to follow the mother).
The timing might depend also on other factors, e.g., the degree of dependence on visual vs. olfactory cues to obtain the specific type of prey.
If wolves, indeed, attempt to partition their hunting and provisioning within the group so that they utilized resources other than those most needed by fawns and so that each pack member used the resources they are best equipped to obtain, this would also suggest that summer foraging is even less opportunistic than winter foraging.
In regions where prey is very abundant, such differences might not arise at all.
But, for example, in Voyageurs where prey is often scarce during summer, I wonder if the inability by the Windsong breeding female O4D to access these specific parts of her family territory and these specific resources (calf poop) that she had learned to use will not result in a greater pressure on the commonly shared resources (including spatial resources) and lower reproductive success (pup mortality) and/or increased subordinate dispersal rates.
Having food for everyone in the group and having the best food for the pups is crucial in ensuring not merely the breeding success during that year but also the pack’s persistence in their territory because small packs without subordinates might not be able to defend their range during winter and they might not be able to hunt as efficiently in order to ensure high reproductive output in the following year.
I hope that the Windsong female finds other opportunities to forage for herself while being mindful of the needs of her other family members as she has probably been.
References
Bryan, Heather & Darimont, Chris & Reimchen, Thomas & Paquet, Paul. (2006). Early Ontogenetic Diet in Gray Wolves, Canis lupus, of Coastal British Columbia. Canadian Field-Naturalist. 120. 10.22621/cfn.v120i1.247.
Gurarie E, Bracis C, Brilliantova A, Kojola I, Suutarinen J, Ovaskainen O, Potluri S and Fagan WF (2022) Spatial Memory Drives Foraging Strategies of Wolves, but in Highly Individual Ways. Front. Ecol. Evol. 10:768478. doi: 10.3389/fevo.2022.768478
Jedrzejewski, Wlodzimierz & Schmidt, Krzysztof & Theuerkauf, Jörn & Jedrzejewska, Bogumila & Okarma, H.. (2001). Daily movements and territory use by radio-collared wolves ( Canis lupus ) in Bialowieza Primeval Forest in Poland. Canadian Journal of Zoology-revue Canadienne De Zoologie – CAN J ZOOL. 79. 1993-2004. 10.1139/cjz-79-11-1993.
Notes by Ieva 