The challenge of estimating wildlife populations at scale: the case of the European badger (Meles meles) in Ireland

Estimating population size in space and time is essential for applied ecology and wildlife management purposes; however, making accurate and precise estimates at large scales is highly challenging. An example is the European badger (Meles meles), a widespread and abundant mammal in Ireland. Due to their role in the epidemiology of bovine tuberculosis, the species has been culled in agriculturally dominant landscapes with the intention of reducing spillback infection to local cattle populations. Despite several studies using different approaches having estimated badger populations at different time points and scales, there remains considerable uncertainty regarding the current population and its future trajectory. To explore this uncertainty, we use published data and expert opinion to estimate a snapshot of probable badger population size using a Monte Carlo approach, incorporating variation in three key components: social group numbers, group size, and culling efficacy. Using this approach, we estimate what the badger population in Ireland would be with/without culling, assuming a steady-state population at carrying capacity, and discuss the limitations of our current understanding. The mean estimate for the badger population size was 63,188 (5–95th percentile, 48,037–79,315). Population estimates were sensitive to the assumption of mean group size across landscape type. Assuming a cessation of culling (in favour of vaccination, for example) in agricultural areas, the mean estimated population size was 92,096 (5–95th percentile, 67,188–118,881). Despite significant research being conducted on badgers, estimates on population size at a national level in Ireland are only approximate, which is reflected in the large uncertainty in the estimates from this study and inconsistencies between recording of data parameters in previous studies. Focusing on carefully estimating group size, factors impacting its variation, in addition to understanding the dynamics of repopulation post-culling, could be a fruitful component to concentrate on to improve the precision of future estimates.

How far from the road should land cover be assessed? A case study on mesopredator mortality on roads

The methods used to assess the significance of land cover in the vicinity of a road for the mortality of mesopredators are diverse. In assessing the effect of land cover along the road on road causalities, scientists use various buffer sizes, or even no buffer along the road. The aim of this study was to verify how results of land cover effects on the mortality of mesopredators on roads may differ when analyzing various buffer sizes from the road. We assessed road causalities in the Warmian-Masurian voivodeship (Poland) from 3 consecutive years: 2015, 2016, and 2017. The roads were divided into equal sections of 2000 m each with buffer size of radius: 10, 250, 500, and 1000 m. We analyzed the number of road kills of red fox and European badger separately in a generalized linear model, whereas explanatory variables we used land cover types (based on the Corine Land Cover inventory) and traffic volume. Mean annual mortality from road collisions amounts to 2.36% of the red fox population and 3.82% of the European badger population. We found that the buffer size determines the results of the impact of land cover on mesocarnivore mortality on roads. The red fox differed from the European badger in response to land cover depending on the buffer size. The differences we have shown relate in particular to built-up areas. Our results indicate a 500-m buffer as best reflecting the land cover effects in road kills of both species. This was confirmed by model evaluation and a tendency to use or avoid the vicinity of human settlements of the analyzed species. We concluded that buffer size will probably affect mostly the significance of cover types that are spatially correlated with roads, positively or negatively. We suggest that the home range size of given species in local conditions should be assessed before determining the size of the buffer for analysis.

EUROPEAN BADGER (MELES MELES LINNAEUS, 1758) PREFERENCES TO THE TERRAIN EXPOSURE FOR DIGGING DENS IN SOUTHEASTERN BULGARIA

A total of 47 active badger burrows in the Southeastern Bulgaria were described in order to find whether there are preferences to terrain exposure for its digging activity. The most of the dens were found on terrain with south exposure - 23.4%, followed by these on the east and west side -19.15% each. The dens faced to these three directions, together with these to intercardinal directions connected with south, represented 80.85% of the active badger dens found. A tendency in the preference of the European badger to the southern exposure of the terrain for its digging activity in the region of South-eastern Bulgaria was established.

CORTICAL BRANCHES OF THE MIDDLE CEREBRAL ARTERY IN EUROPEAN BADGER (Meles meles)

The pattern and variation of the cortical branches of the middle cerebral artery in European badger were studied for 64 cerebral hemispheres. It was found that the artery bifurcates into splits into ten permanent branches. Two olfactory arteries supply the area of the brain situated on the border between the old and the new cortex. The other eight branches get divided into three branches heading for the frontal region, two branches – to the parietal region and three temporal branches which supply only the new cortex. The frontal, parietal and temporal branches descended independently from the main trunk of the middle cerebral artery or formed a common trunk first. Common trunks for respective groups of branches have been described as the rostral, dorsal and caudal middle cerebral artery. The rostral olfactory artery in 6.3% of the cases investigated was an independent branch from the rostral cerebral artery.Key words: arteries; brain; European badgerKORTIKALNE VEJE SREDNJE MOŽGANSKE ARTERIJE PRI EVROPSKEM JAZBECU (Meles meles)Povzetek: Vzorec in razlike v razvejanosti kortikalnih vej srednje možganske arterije smo preučevali v 64 možganskih poloblah evropskega jazbeca. Ugotovili smo, da se glavna arterija razdeli na deset vedno prisotnih vej. Dve vohalni arteriji oskrbujeta območje možganov, ki se nahaja na meji med področjem neokorteksa in starejšega dela skorje možgan. Preostalih osem vej se deli na tri veje, ki se usmerijo v čelno področje, dve veji usmerjeni v parietalno področje in tri senčnične veje, ki oskrbujejo področje neokorteksa. Čelne, parietalne in temporalne veje se spustijo neodvisno od glavnega debla srednje možganske arterije, ali pa najprej oblikujejo skupno deblo. Običajna debla za posamezne skupine vej so opisana kot rostralna, dorzalna in kavdalna srednja možganska arterija. Rostralna vohalna arterija je bila v 6,3 odstotkih preiskovanih primerov neodvisna od rostralne možganske arterije.Ključne besede: arterije; možgani; evropski jazbec