Badger territoriality maintained despite disturbance of major road construction

Publication history: Accepted - 19 August 2021; Published - 3 September 2021.Road ecology has traditionally focused on the impact of in-situ and functional roads on wildlife. However, road construction also poses a major, yet understudied, threat and the implications for key aspects of animal behaviour are unknown. Badgers (Meles meles) have been implicated in the transmission of tuberculosis to cattle. There are concerns that environmental disturbances, including major road construction, can disrupt badger territoriality, promoting the spread of the disease to cattle. To address these knowledge gaps the ranging behaviour of a medium-density Irish badger population was monitored using GPS-tracking collars before, during, and after a major road realignment project that bisected the study area. We estimated badgers’ home range sizes, nightly distances travelled, and the distance and frequency of extra-territorial excursions during each phase of the study and quantified any changes to these parameters. We show that road construction had a very limited effect on ranging behaviour. A small increase in nightly distance during road construction did not translate into an increase in home range size, nor an increase in the distance or frequency of extra-territorial excursions during road construction. In addition, suitable mitigation measures to prevent badger deaths appeared to ensure that normal patterns of ranging behaviour continued once the new road was in place. We recommend that continuous badger- proof fencing be placed along the entire length of new major roads, in combination with appropriately sited underpasses. Our analysis supports the view that road construction did not cause badgers to change their ranging behaviour in ways likely to increase the spread of tuberculosis.AG was supported by a PhD scholarship provided by the Department of Agriculture, Food and the Marine, Ireland. This project was conceived, carried out and funded by the Department of Agriculture, Food and the Marine, Ireland, and the National Parks and Wildlife Service, Ireland

The impact of roadworks on the ranging behaviour of European badgers (Meles meles)

The European badger (Meles meles), one of Ireland?s most iconic native species, acts as a wildlife reservoir of Mycobacterium bovis, the causative agent of tuberculosis in cattle. Badgers have been implicated in the spread of the disease to cattle in Ireland and the UK. To understand the dynamics of a disease and to control it successfully, a complete picture of ranging behaviour of the carrier species is required. Much of our knowledge of ranging behaviour in badgers derives from studies of high-density populations. There is concern that environmental disturbances, such as major roadworks, can increase movements between badger social groups, resulting in increased TB breakdowns in cattle herds. The ranging of a medium-density Irish badger population was monitored before, during and after a major road upgrade and realignment project, using GPS tracking collars. Using the GPS data, I estimated badger home range size, nightly distances travelled and the distance and frequency of extra-territorial excursions. My results show that the road upgrade and realignment project had a very limited effect on the ranging behaviour of badgers, and that territoriality in the area was not disrupted. Roadworks of this nature are therefore unlikely to result in increased TB breakdowns in cattle herds. However, my analyses highlight that there was greater connectivity between social groups than suggested in the literature. I show that badgers made frequent extra-territorial excursions throughout the year. I illustrate that some dispersing badgers travelled long distances through unexpectedly large areas. I describe a previously unrecognised type of ranging behaviour, super-ranging, found in 22% of male badgers. Super-rangers held enlarged territories that encompassed two or more traditional social group territories. All of these behaviours have the potential to increase contact between badgers from different social groups and have implications for disease transmission. My findings can be used to better understand and model the epidemiology of disease, and to formulate more effective and efficient TB control initiatives, such as vaccination of badgers. Finally, this research greatly enhances our understanding of badger ecology, by contributing to knowledge of medium-density populations, and gives a more detailed picture of dispersal in badgers than has been obtained before

Super-ranging. A new ranging strategy in European badgers

<div><p>We monitored the ranging of a wild European badger (<i>Meles meles)</i> population over 7 years using GPS tracking collars. Badger range sizes varied seasonally and reached their maximum in June, July and August. We analysed the summer ranging behaviour, using 83 home range estimates from 48 individuals over 6974 collar-nights. We found that while most adult badgers (males and females) remained within their own traditional social group boundaries, several male badgers (on average 22%) regularly ranged beyond these traditional boundaries. These adult males frequently ranged throughout two (or more) social group’s traditional territories and had extremely large home ranges. We therefore refer to them as super-rangers. While ranging across traditional boundaries has been recorded over short periods of time for extraterritorial mating and foraging forays, or for pre-dispersal exploration, the animals in this study maintained their super-ranges from 2 to 36 months. This study represents the first time such long-term extra-territorial ranging has been described for European badgers. Holding a super-range may confer an advantage in access to breeding females, but could also affect local interaction networks. In Ireland & the UK, badgers act as a wildlife reservoir for bovine tuberculosis (TB). Super-ranging may facilitate the spread of disease by increasing both direct interactions between conspecifics, particularly across social groups, and indirect interactions with cattle in their shared environment. Understanding super-ranging behaviour may both improve our understanding of tuberculosis epidemiology and inform future control strategies.</p></div

Traditional versus Super Home Ranges.

<p>Filled polygons represent traditional social group ranges, Hawthorn social group to the north and Bracken social group to the south. The dashed polygon represents the summer 2016 home range (95% MCP) of Boru, a male badger belonging to the Hawthorn social group, but who habitually ranged across the traditional boundary separating the two social groups. The dots represent Boru’s GPS locations and the arrow represents the direction of extended ranging. Thick grey lines represent the N11 and M11 roads.</p

Traditional versus Super Home Ranges.

<p>The filled polygon represents the Quarry social group’s traditional range. The dashed polygon represents the summer 2013 home range (95% MCP) of Billy, a male from the Quarry social group who habitually ranged beyond the boundary of that social group. The dots represent Billy’s GPS locations and the arrow represents the direction of extended ranging. Thick grey lines represent the N11 and M11 roads.</p

Details of super-rangers’ (SRs) home ranges and comparison with the size of their social group-mates’ (SGMs) home ranges.

<p>Details of super-rangers’ (SRs) home ranges and comparison with the size of their social group-mates’ (SGMs) home ranges.</p

Population Density Estimates (badgers/km²) for all badgers (adults in brackets) using the MNA [56] method and the M(h) method [58] in CAPTURE to account for individual heterogeneity.

<p>Population Density Estimates (badgers/km²) for all badgers (adults in brackets) using the MNA [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0191818#pone.0191818.ref056" target="_blank">56</a>] method and the M(h) method [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0191818#pone.0191818.ref058" target="_blank">58</a>] in CAPTURE to account for individual heterogeneity.</p

Boxplot of Home Range Size (km²).

<p>Here, female badgers are represented by white, TRs by light grey and SRs by dark grey boxes. Numbers in brackets indicate sample size.</p