Recently I read the publication, ‘Individual foraging specialization in a social mammal: The European badger (Meles meles)’ by Robertson, A. et al., 2014.
In this study, the highly social British badgers were analyzed respective to the foraging specialization level by individuals (i.e., whether individuals tend to use resources differently than the rest of their group despite having access to the same resources that the entire group has).
It was discovered that individual specialization could explain 44% of population niche variation (individual specializing was more pronounced than even group specialization (2%) relative to other groups which should be substantial due to the use of different resources that lie on the social group’s range because badgers are territorial and groups have exclusive ranges).
This variation could not be explained by sex or age (not significantly) which also excludes social dominance factors (some individuals in the group excluding other individuals from resource use).
I found this interesting.
Why would an individual deny himself/herself the use of common resources if they are freely available and why would the individual choose to utilize only a limited portion of what is available?
Two days after reading the publication by Robertson, A. et al., 2014, I came across another publication on gray wolves in British Columbia where niche differentiation between subpopulations, groups and individuals was assessed in a spatially heterogeneous landscape (Darimont, C. et al., 2009).
Due to the temporal proximity of these readings (as well as the method applied which was that of stable isotope analysis), I could not help but keep the badger research in mind as I was reading about the wolves.
The wolf publication looked at an aspect which, if I understand correctly, was not estimated within the researched badger population.
Specifically, it was the individual niche breadth relative to the group niche breadth but not from the perspective of assessing whether individuals specialized relative to the group resources (whether individual niche breadth was narrower when compared to group niche breadth).
Instead the association was evaluated from the perspective of whether the individual niche breath increased or decreased if the group’s niche breadth increased or decreased relative to the niche breadth of the population.
Namely, whether there would be a greater number of specialized individuals (with narrow niche breadth) in groups that also attest to lower niche breadth (compared to other groups in the population).
And whether individuals would show wider niche breadth (a lower degree of specialization and a more diversified diet) in groups that also have wider niche breadth relative to other groups in the population.
That is to say, do individuals keep to their preferred (or otherwise selected) resources at a certain degree regardless of the resource availability to their specific group? Or do individuals use a greater variety of resources if the group has access to a greater variety of resources?
Of course, this would be difficult to assess because a wider group niche breadth implies more diversified resource use by its individuals and, possibly, group size should be accounted for or resource availability should be quantified rather than the niche breadth itself.
Probably it would make more sense to determine whether the individual used resources as available according to mean niche breadth within their group or less than that.
Low specialization levels even at wider niche breadth might be detectable with the data already accessible.
I thought it might be an important (and interesting) aspect to consider because if individuals demonstrated about the same specialization level irrespective of the group niche breadth (relative to other groups), this would indicate an even more pronounced specialization.
It might also point at possible reasons behind the individual specialization because if the specialization is very high irrespective of the group’s social structure and resource availability, the factors influencing the individual specialization could be… well, individual or unrelated to the group and/or the resources themselves.
For example, the wolf research alluded to the niche variation hypothesis – i.e., niche variation is influenced by (intraspecific and/or interspecific) competition.
Badgers can dominate most other species they share resources with and other species even seem to demonstrate a tendency to ‘hang out’ around badgers and their setts.
However, I began wondering if perhaps the badger individual specialization was related not to within group factors per se but to the pressure that is exerted on the species due to recent evolution of sociality (while most mustelids are not social at all) as well as external factors such as competition with other species and the necessity to interact with other species.
It could be possible that badgers do not enjoy agonistic encounters with other predators / omnivores that they share resources with.
For example, if the entire group consumes specific invertebrate taxons, these taxons would be shared with other species that consume them, as well, and that live on the badger group’s territory.
Badgers would be forced to share space and to interact with these species.
Due to the solitary foraging pattern by the badgers, the other species that belong to the guild would distribute themselves evenly over the badgers group range because there would be a lower chance to avoid all individual badgers (as opposed to attempting to spatially or temporally avoid the entire group of badgers if the badgers foraged together in one spot at the same time leaving the rest of similar habitats accessible for the moment).
Meanwhile, if only a few badgers specialize on specific invertebrates that dwell in specific habitats etc., competitors of other species might avoid the currently badger-utilized and badger-depleted patches because it would be easier achieved – they could simply locate themselves elsewhere, i.e., on other patches that have the same resources but that do not have badgers foraging actively there at the time.
Specialized foraging would be more concentrated and more easily avoided (compared to the situation when all badgers forage on the same taxon in a similar habitat and the foraging activity is distributed more homogeneously over the range because badgers forage solitarily).
However, I do not think that it is competition predominantly that aggravates the badgers.
I believe that badgers have a need to limit their interactions that involve high cognitive functioning due to their comparatively recent evolution as a social species.
Perhaps the badger has to invest a lot of energy in their own social group interactions because the social behaviour is in its early state of evolution.
As social behaviour evolves and becomes established, it likely becomes more instinctual and ‘automatic’ rather than actively cognitive.
In long-time social species many reactions are probably derived without active processing because it has been well established what the interaction involves, what its costs are and what its benefits are.
For example, reciprocity (the ‘sense of justice’ regarding the exchange of favours over time and regarding delayed gratification) is likely not processed awarely but rather manifested as a psychological and physiological reaction (contentment or discontent).
In a species evolving sociality, the inherent structure and order as well as the physiological and emotional reactions to certain social conditions and situations could be less pronounced and less directed (even scientists cannot be certain why badgers have evolved social living and where their sociality is going, i.e., what new types of cooperation might arise out of it eventually).
Badgers might have to invest a significant amount of energy-demanding brain activity in resolving group situations (although I am not saying that badgers do not enjoy living in groups which they apparently do).
It becomes even more complicated due to the fact that badger groups are not consistently comprised of close kin (which might facilitate interactions).
It would be interesting to study if solitary foraging, using outliers or other types of group interactions avoidance (however, here I mean active interactions and not, e.g., hibernating together) are more frequently observed during periods of lower food abundance or higher energy demands, or by individuals at higher risk of energy depletion.
For example, it is also possible that breeding females sometimes exclude other individuals from dens or foraging sites simply because lactation and rearing of the young is already too energy-demanding to invest in additional socialization that not directly benefits the caring for offspring.
It might be difficult to tease apart solitary resource use and low resource availability because these factors might be correlated.
To conclude, it might be costly for the badger to additionally engage in frequent interspecific interactions and the badger, outside of the social group, might seek to rest from social ‘pressure’.
(Cognitive activity can demand a great deal of metabolic resources.)
However, I have seen many videos (e.g., this video by Malcolm J Ingham) where badgers interact with, e.g., sheep.
I believe it does not contradict my theory.
Badgers appear to be very playful and they do not seem to try to avoid certain interactions such as allogrooming, playing etc.
Similarly, they might not avoid interactions with other species that do not involve high pressure situations and active decision making and that are more relaxed in their nature (for example, badgers do not appear to mind if other species use the vacant chambers in their setts; therefore, they do not seem to avoid the presence of others altogether but agonistic presence might be different because it involves reactions that are cognitively derived rather than experienced instinctively and because they are not pleasant and relaxing).
Perhaps badgers, while foraging, are seeking a ‘refuge’ from cognitive processing invested in social interactions within their group (hene, the solitary foraging patterns) as well as agonistic or otherwise congitively active interactions with other species.
Interactions with other species can be somewhat social, as well, because they involve reading the other individual’s signals, understanding the situation, assessing the current risks, responding according to the assessment etc.).
Additionally, I have read references (although not quantified) that other species might follow badgers to find good foraging spots.
If all badgers specialized on the same resources, these resources could become depleted sooner because other species might notice the badger activity and become attracted to the potential feeding grounds.
Individual and specialized foraging could provide a mechanism that is more cryptic and which other species might not utilize to access the same resources.
It is more difficult to follow an individual badger to a foraging ground which offers the desired resource than it would be to follow the entire group (especially, if other species cannot differentiate between badger individuals and thereby they cannot always follow the same individual).
If there is slight soil or vegetation disturbance resulting from a badger’s foraging (although badgers do not appear to be invested in digging up their forage), the disturbance is also reduced in intensity if fewer badgers create the same disturbance.
And a lower number of other species would be able to use it as an indicator of resource location (or if badgers disturb the soil – as a facilitated foraging ground).
There could be other factors at play.
For example, it appears to me that badgers prefer to differentiate among activities and to categorize them not mixing them up greatly – sett activities are sett activities (digging, bedding collection, playing, grooming) and foraging activities are foraging activities, and the twain should not be intermixed 🙂
There could be certain aspects of badger psychology that involve compartmentalization and a preference for specific things (foraging locations, foraging resource types etc.).
Badgers might be able to apply a wide range of foraging strategies or social interactions but perhaps they enjoy practicing their favourite rather than constantly engaging their whole arsenal.
Maybe they are a species that has developed a strong ‘favouritism’ – favourite patch, favourite food etc.
If different types of forage demand for different foraging activities and are located in different sites, the badger might select the type of forage that befits the badger’s subjective and individual understanding of what feels good and what relaxes them (which could depend on the individual badger’s physiological and psychological make-up).
Generally, it seems to me that badgers can be rather individualized and not possessive of many stereotyped, common behaviours.
When they play, it appears that the individuals have their own playing ‘styles’ which could be derived from non-uniform faculties.
It might be interesting to learn if there are any patterns that can be associated to, for example, sensory traits or personality traits and which are consistent as the individual badgers change the use of resources seasonally (e.g., some badgers constantly prefer foraging in patches that are dimmer, lighter, nosier, quieter; or on resources that require greater physical involvement vs. lesser physical strain or that require using visual vs. olfactory cues etc.).
It could be rather energy-demanding to lead an individualistic lifestyle in a social environment that is only just settling into the inherent response matrix.
All in all, it would be interesting and informative to learn if individuals specialize narrowly also when the group as a whole has a very wide niche breadth compared to other groups (and whether niche breadth in individuals changes according to modifications in group niche breadth).
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As I have been reading ‘The Social Badger’ by Hans Kruuk (1989) that presents some badger foraging observations, I also wonder if the individual foraging might be the result of the necessity to reduce the density of foraging animals per area in order not to spook their prey (e.g., worms).
Excessive trampling (many tiny paws stomping about) might cause vibrations alarming earthworms (and similar prey) thereby limiting the feeding efficiency.
Notes by Ieva 