Seasonal and Ecological Determinants of Wild Boar Rooting on Priority Protected Grasslands

Abstract

Wild ungulates can influence various trophic levels, regulating carnivore abundance and affecting habitat structure. Conservation problems can arise when high ungulate densities threaten species or habitats with conservation concern. Assessing factors influencing the intensity of their impact is important to identify appropriate measures enhancing habitat conservation. We assessed factors influencing wild boar Sus scrofa pressure on EU protected grasslands in three protected areas of central Italy, by modelling the effects of environmental variables and wild boar density on rooting activity. We seasonally estimated rooting in 126 sampling plots from spring 2019 to spring 2021, and we used faeces counts to estimate summer wild boar densities. Estimates of density and rooting varied from 3.5 to 22.2 individuals/km² and from 1.1 to 19.2%, respectively. We detected a clear seasonal trend in rooting activity, that peaked in autumn and winter. We also found a strongly positive correlation between spring-summer rooting and summer density, across sites. Rooting intensity was negatively related to the local extent of rock cover and increased with the 1 month-cumulative rainfall, the perimeter of the grassland patch, and the forest cover around plots. These results emphasise the tendency of wild boar to exploit feeding sites in ecotonal areas, i.e., at the interface between forest and meadows, which maximises security and ease of finding food resources. Actions aiming at the protection of focal plants in grassland habitats, as well as reducing wild boar presence, are supported (e.g. fencing and/or targeting population control at vulnerable patches).

Keywords: Sus scrofa; Foraging activity; Wild pigs; habitat conservation; habitat-wildlife relationships; soil erosion.

Fig. 1

Location of our study areas: MRP (Maremma Regional Park), MPNR (Monte Penna Natural Reserve) and ALNR (Alpe della Luna Natural Reserve). The red line indicates regional borders

Fig. 2

a Seasonal estimates of rooting (mean for each season ± SE) and (b) wild boar density estimated in summer (mean for each year ± SE), from 2019 to 2021 in each study area

Fig. 3

Effect of one month-cumulative rainfall on wild boar rooting, estimated by GLMMs. Prediction accounts for plot-repeated surveys and study year as random intercepts, showing the average effect across the three study areas. Marks along x-axis show the distribution of observed values for this covariate. Black lines: predicted values. Grey bands: 95% confidence intervals

Fig. 4

Effects of slope and rock cover on wild boar rooting, estimated by GLMMs. Predictions account for plot-repeated surveys and study year as random intercepts, showing the average effect across the three study areas. Marks along x-axis show the distribution of observed values for each covariate. Black lines: predicted values. Grey bands: 95% confidence intervals

Fig. 5

Effects of woodland cover in a 1100 m buffer and 6210/6220 habitat extent (approximated by patch perimeter) on wild boar rooting, estimated by GLMMs. Predictions account for plot-repeated surveys and study year as random intercepts, showing the average effect across the three study areas. Marks along x-axis show the distribution of observed values for each covariate. Black lines: predicted values. Grey bands: 95% confidence intervals

Fig. 6

Correlation between wild boar density estimated in summer and rooting percentage in (a) June and (b) September