European Badger Territoriality & Home Range
Territories of 20 to 50 hectares (49–124 acres) are common in rich habitats, covering areas as large as 150 ha (370 acres or half sq-mile) or more in poorer regions. According to Michael Clark's book Badgers, the smaller territories observed in badger clans from Gloucestershire were about 40 ha (100 acres), with the smallest being 15 ha (38 acres). Roughly 70 ha (175 acres) was more typical for southwest England, while in the low-density areas of Scotland, territories were around 180 ha (400 acres). The largest territory Clark mentioned was 309 ha (773 acres) in a clan from Scotland, although studies in Poland have documented home ranges exceeding 1,000 ha (1,280 in Białowieża Forest) and there may only be two or three inhabiting this area.
The urban colonisation, or at least use of our towns and cities, by badgers is a relatively new phenomenon and one that’s only recently received much study. The picture emerging is that urban badgers may range over significantly smaller areas than their suburban or rural counterparts. In a 2015 paper to Mammal Review, Martin Šálek and colleagues reviewed the literature on carnivore home ranges and, based on 31 studies (25 rural and six urban, illustrating the disparity in research) established that urban badgers may hold home ranges just less than half the size of those in the countryside.
Earlier work by the University of Sussex’s Maren Huck and her co-workers subjected badger hair collected from setts in Brighton to genetic analysis. The genomic data, published in the Journal of Animal Ecology in 2008, showed that allelic richness of the population was low compared with other British populations, but that the rate of extra-group paternity (i.e. number of cubs sired by individuals outside the group) was higher. This suggests that as the badger population increased in density in the city the result was a proliferation of social groups. In other words, the badgers split into numerous small groups, rather than living in fewer large ones. The observation that extra-group paternity is high, however, implies that badgers move between groups more frequently in urban areas than rural ones, in Brighton at least.
Finally, a recent series of tracking studies, also in Brighton, by Bryony Tollhurst and Dawn Scott revealed some very short-range movements. One badger, named “Cherry” by the researchers, produced a GPS track covering an area of only 200 by 100 metres (about two hectares or five acres) around her group’s sett, located in a graveyard in the city. Likewise, another female (“Lottie”) was found to move over a small range that covered an allotment and only about 25 peripheral gardens during her nightly foraging. This is not an unexpected finding and something we see in many carnivores because resources tend to be more concentrated in urban areas, so animals need to move less to fill their nightly quota and the result is that higher densities can be attained.
Studies from Ireland indicate that males play a greater role in maintaining the clan's territory than the females and that these territories are fixed. In other words, when a neighbouring badger group was removed, the clan in question did not extend their territory to 'take up the slack' (as has been observed in foxes). This observation is interesting considering that debate has raged for years over what regulates the size and configuration of badger territories.
One leading theory proposes that the availability of suitable sett sites directly determines sett density, thereby dictating social group density; social group density in turn determines the size of the territory. Indeed, studies from Gloucestershire suggest that when badgers are recolonising an area, their first action is to occupy the setts before re-establishing the territory. This implies that, at least in some (probably lower-density) areas, setts are a crucial resource within the clan's territory. Data from Wytham Woods suggest, however, that these badgers were constrained by food availability rather than suitable sett sites and a change in the distribution of food, with a subsequent increase in the carrying capacity, resulted in new setts being dug – this is known as the “Resource Dispersion Hypothesis” (or RDH) and seems to best describe badger distribution.
Badgers within a given clan are usually closely related, although more than one family may sometimes make up a single sett. A well-defined territory is established and marked by scent, primarily via the use of latrines. Core areas of the territory are generally vehemently defended against intruders, while feeding grounds may overlap with neighbours. To-date there are no confirmed records of a hierarchy among badgers feeding at the same location, although there is evidence that during times of limited food resources, adults may restrict subordinate access to key foraging areas. Computer modelling of badger territory use suggests they use a passive range exclusion mechanism.
Feeding excursions deep into neighbouring territories aren't worth a badger's time and energy, because areas of lower food availability are encountered and the travel time (returning to their own sett) is lengthened. The idea is that badger territories are roughly hexagonally-shaped areas, each border touching that of a neighbour's range, such that they form a honeycomb mosaic. Each sett is roughly in the middle of the territory and badgers forage closest to the sett first, moving further away as they exhaust the food reserves.
The upshot of this is that “ridges” of higher food availability build up at the periphery of each range because these sites are visited less often than those closer to the sett. If we remember that every badger clan in this mosaic is doing the same thing (i.e. eating outwards from the main sett), the further into your neighbour's territory you go, the less food you're likely to find. This means that, when you weigh-up the pros (i.e. food) with the cons (i.e. further to walk, more danger of attack from resident etc.), it is simply not energetically viable for a badger to wander outside its own clan's area when looking for food. Thus, these territories can be maintained passively, through exploitation competition and feeding optimization. The benefit of this is that the badgers don't need to put themselves at risk by seeing off intruders who are trying to raid their resources. Aggression is not uncommon, but this theory suggests that it may be unnecessary for territory maintenance.
Although a territory will often be defended against intruders, there is often an overlap between neighbouring clans; the degree of which seems related to the availability of food. In 1987, Hans Kruuk made the curious observation that the overlap between clan territories was greatest when food availability was lowest. Logically, it might be expected that territoriality would be highest when pickings are slim, but it actually appears that territory systems may break down when conditions are poor because the costs of defending a territory outweigh the benefits that a territory usually provides. In other words, when times are tough it’s every man, or badger, for itself. Under most circumstances, however, interlopers will be chased off by the resident animals and fights can be prolonged and violent. Indeed, deep wounds to the rumps of badgers, particularly males, are not uncommon.
Territory boundaries are marked with scent, either urine or a hormonal secretion from glands located either side of the anus and at the base of the tail, and shallow un-covered dung pits. While moving around their home range the animal will periodically stop and squat, depositing scent on the ground or objects (rocks, logs, etc.). Faeces are also deposited near the sett and at significant territory boundaries (e.g. a border shared between two neighbouring clans) - a collection of dung pits is called a latrine. Latrines are used year-round, but particularly during the spring and autumn and about half of all badger visits to them result in droppings being added. Presumably, the faeces contain hormonal cues about the territory owners and badgers certainly seem able to tell droppings from clan members apart from those left by strangers.
The observation, by Kate Palphramand and Pirian White, that wild badgers in the North York Moors National Park could tell clan droppings those of their neighbours and from “alien” droppings lends support to an earlier theory that clans have their own unique scent. If you spend time watching badgers, it soon becomes obvious that as well as marking their territory, they also mark other members of their group - a behaviour known as musking. A musking badger will back onto another with its tail raised, secreting an odorous substance onto the conspecific’s fur. There's more on this in the Behaviour & Social Structure section, but the upshot is that this mixing of scents may help produce a clan smell.
Latrines may cover several square metres, while individual dung pits are commonly associated with linear features, such as footpaths, woodland edges and hedgerows. A study by Michael Hutchings and colleagues back in 2001 found that badgers in south-west England preferentially selected woodland as latrine sites, avoiding arable land. They also found that faecal scent marks were strongly associated with the edge of pastoral fields rather than being in the middle, which is typical of territorial marking.
We don't know much about how badgers use urine to mark their territories, although several different urination behaviours have been described, including digging specific pits in which to urinate, squatting on the ground and cocking a leg to urinate up a vertical object. The most detailed account of badger urination came from a study investigating the potential for bovine TB transmission between badgers and cattle conducted by Julian Brown, Stephen Harris and Chris Cheeseman in the Cotswolds. The researchers injected three badgers with a 0.38g per mL solution of fluorescein LT, a biomarker that would be excreted in the urine and faces, making it glow under UV light and tracked their movements over a night. Using this technique, it was established that about half of the urinations took place at latrine sites, with the other half typically being made at “crossing points”, where the badgers' nightly wandering crossed linear features such as paths, hedgerows or woodland edges. In common with other territorial mammals, badgers seem to urinate several times in the single night, rather than just emptying their bladder at a latrine, suggesting urination has an important territorial and/or social application.