Having lived in the north country most of my life, certain winter storms can devastate native population of whitetail deer. I would suspect that hogs that have moved north from warmer climates of the south could be very susceptible to winter kill. European native hogs have adapted to winters there. I do suspect that the further north you go in Europe the lower the population.
This is an excerpt for a study by the European Land Owners Assc.
Several factors have been discussed as influencing factors in population trends, i.e. increased cultivation of crops and artificial feeding (Schley et al., 2008), however climate change has been posited as among the single largest contributing factors to expanding populations (Vetter et al., 2015). In this section we will provide an overview of the latest research conducted on the effects of climate change on the species.
A 2015 paper published by a team of researchers from the University of Veterinary Medicine, Vienna, reveals that mild winters are becoming more frequent, and that there is a strong correlation to increasing boar numbers (Vetter et al., 2015). The scientists believe that the increasingly frequent mild winters in Europe and the subsequent increase in acorns and beechnut production by trees are aiding boar survival rates.
As we have seen elsewhere in this paper, wild boar are extremely adaptable mammals with an enormous reproductive capacity, thus providing the potential for population growth when environmental conditions become more favourable. Wild boar can have five or more young in a litter, and females can reach sexual maturity within their first year if there is enough food available.
Vetter et al.’s analysis shows that wild boar is highly susceptible to cold winter conditions, as each incidence of this was consistently followed by population declines. Cool autumns were also shown to have a negative impact on population growth (although as the models used averages this may simply reflect an early onset of winter). Climate conditions are known to be important factors influencing many ungulate populations affecting strongly juvenile sur
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vival and reproduction (Putman et al., 1996; Saether, 1997). Cold winters lead to increased juvenile mortality, which is a major driver of wild boar population dynamics. Especially frost in spring can cause juvenile mortality (up to 90% during the first two years of life). Geisser & Reyer (2005) showed a clear correlation between higher winter and spring temperatures and a stronger population growth of wild boar by reducing the mortality of wild boar piglets. Figure 26 (Geisser & Reyer, 2005) shows 8 variables related to wild boar population dynamics between 1974 and 1998 in the canton Thurgau, Switzerland. Making use of a stepwise multiple regression analysis they showed that food and temperature conditions are key factors for the fluctuation in the wild boar density. The increased winter and spring temperatures strongly influences reproduction (winter temperatures) and juvenile survival (spring temperatures).
Milder winters lead to reduced winter mortality leads to increased survival of wild boar in all age classes (Rossi et al., 1997; Melis et al., 2006).
Temperature is essential in the survival of newborn piglets (usually born in April and June).
Several studies, conducted in several parts of Europe,
link changing climate conditions with the population growth of wild boar: Germany (Hahn & Eisfeld, 1998), France (Vassant, 1997), Italy (Boitani et al., 1995) and Poland (Jedrzejewska et al., 1997). Rapid population increases are typical for r-selected species that make maximal use of space and food to survive to produce a large offspring with limited survival. If the variables responsible for limiting the population growth (e.g. low temperatures in winter and in spring) the population starts to grow exponentially.
Climate change in Europe (Watson, 2001; EEA, 2004; Raisanen et al., 2004) is not only influencing population size of wild boar but also the mast availability and the production of agricultural crops. Those factors too have an impact on the exploding population size of wild boar in Europe.
According to Vetter et al. (2015) wild boar populations across Europe have been growing irrespective of whether the number of hunters has increased, decreased or remained stable. Their research therefore claims that increasingly milder winters as a result of climate change must be considered as a major reason for the European-wide increase of wild boar during the last decades
Here is a link to the whole study if anyone is interested.
https://www.europeanlandowners.org/images/Wild_Boar_Report_2018/122193_WILD_BOAR_GB.pdf
