FOXES rarely attack farm livestock, but when one does go on the rampage it can be a real menace.

Mostly Reynard and his vixen get by on a diet of voles, worms, carrion, ground-nesting birds and rabbits.

Voles are an important food source, but their populations fluctuate from year to year. Foxes dine well in those years when they are plentiful, and as a result are less likely to take other prey that are more difficult to catch.

Occasionally, they turn to poultry and young lambs, and sometimes appear to wantonly kill for pleasure.

When the opportunity arises, foxes kill surplus prey even if they are not hungry and cache it for later use. This is a good strategy, since there are likely to be some days when hunting is unsuccessful, and they can fall back on that reserve food supply.

However, in unnatural situations, such as in a henhouse, where the prey cannot escape, this behaviour, called "surplus killing" leads to foxes killing far more than it could ever consume.

I have seen over 100 hens killed in one night of carnage, and learned the hard way that free-range poultry has to be securely shut in their henhouses at dusk. Those with larger free-range poultry enterprises sometimes use electric fencing to protect their birds when they are out foraging during the day.

Few healthy lambs are killed by foxes and those that are taken alive were probably weak or abandoned. Indeed, foxes are often used as a lame excuse for bad shepherding.

Having said that, I have known foxes mutilate adult sheep. Sometimes sheep roll over to rub their itchy back on the ground, but their fleece prevents them from rolling back over onto their feet. "Couped" on their back, they have to lie and wait for the shepherd to find them before a rogue fox takes advantage of their inability to escape.

Recently a fox has been taking healthy young lambs from local farms, and it's reckoned he has accounted for about 50 and is unlikely to stop.

Dog foxes are monogamous and very faithful indeed, seldom mating another vixen should the first be killed. Vixens come down off the high ground in February to have their cubs in "earths" in sheltered woods and glens. Their mates hunt for them while they are heavily pregnant.

Reynard also helps his vixen to rear their cubs, but in this case I suspect one of a breeding pair must have died, leaving the other, probably the vixen, struggling to feed both herself and her litter of hungry mouths.

Anyway, local gamekeepers have beaten through woods in the hope of driving that fox onto waiting guns, and while a number have been shot, the rogue killer remains at large and appears to have become more cunning and evasive - but it will eventually meet an untimely end. Farmers and gamekeepers are a persistent lot.

It's reckoned that the adult population of red foxes in the UK at the end of winter dips to about 260,000, with around 14 per cent, or 36,000 of those living in our towns and cities. Something like 425,000 cubs are born every spring, but despite having a natural life span of 10-12 years, most die before their second birthday.

In the countryside this high mortality is due to human persecution with snares and guns, while the urban foxes' biggest killer is the motor car.

The average rural fox weighs about 7kg, while their better fed urban counterparts have been recorded as weighing up to 12kg.

While rural foxes mostly hunt for the prey I outlined earlier, their hefty urban cousins have more than 60 per cent of their diet given to them by suburban residents. Many townsfolk derive a great deal of pleasure watching the nocturnal activities of this urban character and regularly leave out cheese, chicken carcases, fat scraps and other kitchen waste. City-dwelling foxes also rifle dustbins or gorge themselves on the plentiful supply of discarded carry-out food.

One massive fox, weighing almost 12kg, was caught in a garden in the South East of England on Boxing Day in 2010, after apparently devouring a pet cat. That discovery has fuelled fears that urban foxes are hunting new prey after becoming bigger and bolder.

Attacks on cats are not unknown, but were rare in the past. Cats going missing is a regular occurrence, but folk should now be aware that a fox could have killed them.