|A sow with 7 piglets seen on 1st March 2012. Appearances can be deceptive.|
This is actually part of a 4 adult sounder with 22 piglets. This sow had either 5 or 6 piglets.
It is often speculated that if wild boar are not controlled by hunting, their population will grow and grow.
This has two conclusions: either the boars compete with themselves for food, leading to starvation and suffering of the less able to forage or protect territory; Or the excess boars move out of the Forest onto adjacent farmland. One gets reported as cruel (rather than natural selection!), the other unfair on farmers.
Limits to population growth are food and shelter, just as it is with humans. For both species, hunting (or war) can reduce or limit populations in the short term, but there comes a point when population rebounds to recover back to the starting position, and commonly back to the future! This is called population rebound or the compensatory rebound effect. Humans call it baby booms, conservationists call it sustainability, hunters call it business or fun.
The well-publicised scaremongering that the human population is increasing is because the food supply of humans is still plentiful (if somewhat immorally distributed!!). More food and easy supply means more humans can breed until the "natural" carrying capacity of their environment is met. Furthermore, we now know that war does not solve over-population (if that is how you see human population and how to solve it!) but as just mentioned, may in fact make it increase!
So without war on the boars, the limits to growth are food and shelter.
Boars are not fussy eaters which has certainly helped them to survive. Availability of food is cyclical and weather dependent, and as the seasons progress we see that the boar often change their diet. This is a great survival strategy and one that has helped us humans too!
In this situation, population biologists often say that populations are "density-dependent" rathar than at the mercy of predator success. It is therefore not valid to suggest that lack of predators is a reason why we need to shoot the boar! Repeat - boar numbers are not controlled by predators in any "natural" system.
The density referred to is boars per unit area. Studies of calorific content, foragability, etc for the woodlands here and abroad are not easy to evaluate for boars, so we can only be unhelpfully general on this, but density-dependence DOES seems well-established across Europe.
The statutory Forest of Dean is 15,000 acres, or 60 square kilometres (60km2), in area (figure quoted by the Deputy Surveyor in January 2012).
Quoting from several scientific studies across Europe, the highest densities of boar is 10 / km2 when artificial feeding supplements the natural diet. North European latitudes such as Sweden have 0.1-2 / km2, south European latitudes such as Spain have 5-8 / km2, whereas mid-European latitudes such as Germany and France have densities of 3-4 boar / km2 (Melis et al, 2006; Spitz, 1986; Andrzejewski & Jezierski, 1978).
Using this data, the Forest of Dean may support 180-240 wild boar. If there is artificial feeding, this number may rise dramatically to 600 boars.
Density-dependence also involves shelter from the cold. Wild boar prefer to shelter in dense conifer forests. Deciduous forest is the usual source of their food. Obviously food and shelter co-operate in density-dependent populations, so if food was a constant, the population would be at the vagaries of shelter / climate. This is seen in the latitude - boar density relationship given in the above research. This relationship would suggest that food is indeed more or less constant across Europe, or at least less relevent to survival than is shelter.
Across Europe, coniferous woodland is the dominant cover, and even in the deciduous areas, ground cover is often thick. This contrasts with the Forest of Dean and many UK woodlands where the deciduous understory is often thin and a poor insulator. Furthermore, conifer stands are routinely felled in the UK creating disturbance for the boar and a constant pressure upon them to find shelter.
The Forest of Dean, along with the New Forest is one of the greatest areas in the UK for deciduous cover. Approximately half of the tree cover here is deciduous. This leaves proportionately far less shelter in the UK compared to European forests. We cannot find data to give any relationship between shelter and boar density (please let us know if you do), but it seems very likely that the UK will have less shelter than a European forest at similar latitude (climate / temperature) and size to the Forest of Dean or indeed many UK woodlands.
|Life skills and immunity must be accomplished very quickly for these new born piglets:|
photographed on 2nd March 2012.
So, without a war on the boar, the Forest of Dean would be safe haven for 180-240 wild boar at the most.
So how quickly would the population exceed this number thus forcing wild boar out of the Forest onto farmland in search of food?
This depends on the birth /death rate of wild boar. Again, too few studies leave us in the dark, but a recent event does give some idea. The family of 4 sows and 22 piglets in the photos shown here were very quickly reduced. Within one week, piglets numbers went from 22 to 11, a 50% reduction within a few days of birth!
|A sounder of Wild Boar with 4 sows (1 out of shot) and 11 piglets. |
One week earlier, the piglets numbered 22.
We have been promised by the Forestry Commission that they are not shooting the boars, and it seems unlikely that poachers will be operative in the area of this family. So it seems reasonable to imply that the natural boar death rate is higher than is usually believed by many.
It is still too early to know how many boars will leave the forest this year in the absence of hunting, but we don't doubt that some will. These boar will ultimately be shot and probably sold for meat. Could this be fair compensation for crop damage? Many countries believe so and operate this system.
But so far, the only evidence we have to date about boar moving out of the forest is some banded around poaching figures. These are interesting, and will be the topic of our next posting, so stay tuned...