Sunday, 4 March 2012

WILD BOAR BREEDING

The main wild boar breeding season is underway and will probably last until April.  Contrary to popular myth, sows in the Forest of Dean rarely have more than 7 piglets, commonly six, and occasionally five each year. 

Despite this, we will often read in the anti-boar or hunting propaganda, that wild boar will breed twice a year or even three times a year, giving birth to as many as twelve piglets each time!

The truth is much less amazing.  They usually conceive in the winter months at the end of the year, followed by a gestation period of almost 4 months long.  This leads to a Springtime birth when food is becoming easier to find and the temperatures are not so cold to kill the piglets.

The only exception to this is first-time mothers.  They give birth in Autumn or late Summer.  This is presumably to reduce competition for food in the Spring when many more piglets are born to other sows, warmer weather, and maybe helps to avoid aggressive males in heat - who may kill her piglets (accidentally or by design).

Prestigious breeding figures often arise by mistakenly comparing wild boar to domestic pigs, who do have huge breeding success thanks to thousands of years of genetic tampering, hormone treatments, artificial insemination and taking piglets from mothers at an early age.

With very few exceptions in the UK, the wild boar gene pool appears little affected by contamination (cross-breeding) with domestic pigs.  However, low levels of genetic contamination has historically (thousands of years even!) been present in the wild boar stock due to breeding between captive wild boar and domestic pigs to select for better and leaner meat in the domestic herd, and also from accidental breeding between wild boar and domestic pigs.  The offspring of either matings have also escaped into the countryside.  Yet despite this, most domestic genes quickly disappear in domestic boar, presumably due to wild boar genes being dominant over most, if not all of the selectively introduced domestic traits.  To date, no domestic characteristic has been seen in the wild boar in the Forest of Dean, except by those with vivid imaginations!  DNA tests also conclude that the UK boars are no different than European boars, each having a small amount of domestic genes that may have derived from domestic stock many hundreds if not thousands of years ago.

It is this cloudy issue that leads Defra to steer clear of a decision as to the wild boars genetic purity and re-acceptance back into the indigenous fauna of Britain.  Furthermore, many farmers and pro-hunting lobbyists continue to feel it necessary to exaggerate sightings of wild boar x domestic pig hybrids to justify hunting the wild boar and keeping them on the list of things in the UK that is OK to hunt. 

The fact is that with very few exceptions, notably in Kent, any boars that looks like a pig IS a pig that most likely has escaped from a farm - and not a wild boar suddenly showing off any domestic inheritance!  See the British Wild Boar website for more details on this along with photos.

After a true (or near-true) wild boar gives birth, the piglets will stay with their mother for another 4 months, at least, and often for a whole year.  So unless something drastic occurs such as piglets being shot or suddenly dying off by disease or predation a typical sow will not give birth to more than 7 piglets in one year.

[Despite the usual suggestion of no predators, boars are killed by other boars, domestic and feral dogs, adders, big cats, many disease pathogens and parasites and hypothermia in freezing weather (it also promotes dehydration and starvation). This is before man has an influence.] 

It may sometimes appear that a sow has given birth to a multitude of piglets.  The truth behind such sightings is that after weaning, sows with piglets group together to form a sociable unit called a sounder.  Sows will often cross-suckle, as will sows that did not have piglets that year.  So, for example, 4 sows may group into a sounder of 24 piglets plus four adults.  If one or more adults die, it may appear that the remaining sows are prestigious breeders, but this is not so.


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.

FOOD

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.

SHELTER

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...

DJS

2 comments:

  1. Well, I will be interested in your next news item. Oh, brilliant photos.

    ReplyDelete