Who, what, why: Why do deer cause more car crashes in autumn?

This is the peak period for car accidents caused by deer and drivers in the UK are being warned to be more aware. So why are there so many such incidents at this time of year?

Deer could be responsible for as many as 74,000 car accidents in the UK each year, according to new statistics. Figures have been on the rise for the last 10 years and look likely to continue rising, say deer experts.

The number of deer in the UK has more than doubled in the past 10 years, according to the Deer Initiative, a group of charities and government agencies aimed at controlling deer numbers. It says the population is now in the region of two million, a number not seen since the Norman Conquest.

October until the end of November is the peak period for such accidents. So why is it such a danger period?

Shorter days is one reason. This results in more cars being on the roads at dawn and dusk, when deer activity is at its peak.

For the three larger species of deer in the UK - red, fallow and sika - it is also mating season, when stags start chasing females. This peaks in the next four weeks, a period which is known as "the rut" when males fight each other, making things even more dangerous.

"You basically have deer rushing around with sex on their minds and not thinking about much else," says Peter Watson, director of the Deer Initiative.

"In wooded areas in particular there may be very little warning before one or several deer will bolt across a road. They could be males fighting over a female. A red deer can weigh upwards of 200lbs (90kg), which can do a lot of damage.

"The mating season also results in males venturing into areas they wouldn't normally, female territory. This can take them closer to roads."

With rush hour occurring at dawn and dusk, drivers encounter deer when they are both at their most active and harder to spot.

Drivers should take notice of deer warning signs

"Deer are more active at these times because there are usually not so many humans about," says Dr Jochen Langbein, from the UK Deer Vehicle Collisions Project. "During the day they retreat and rest and get away from people. At dawn and dusk they come out to feed as they feel safer."

Such collisions are not just a rural problem. A quarter of all collisions happen within a 50-mile radius of central London, according to the Deer Initiative. A large number of black spots are within the M25 corridor. This is because of a growing deer population in such areas and there is much more traffic on the roads.

The Highways Agency has introduced preventative measures in certain hot spots, including warning signs and fencing. It has also been looking at ways to encourage deer to use existing footbridges or underpasses, rather than wander into the road.

The obvious advice for drivers is to take note of wildlife warning signs, but deer experts say people should also be aware that if they see one deer it is very likely more are about.

"So many drivers managed to miss one deer only to collide with a second," says Langbein. "Deer are rarely on their own and people should be prepare for several more being around if they spot one."

There are six main species of deer in the UK. The roe and red deer are native, while the fallow deer was introduced into the country from mainland Europe by the Normans about 1,000 years ago. The sika, muntjac and Chinese water deer were brought over here from Asia about 100 years ago.

Management of the animals comes down to individual landowners, says Langbein. If they own a gun licence they can cull as many or as few as they like, in accordance with the law. There is no prescribed amount.

"A lot of landowners don't start managing numbers soon enough, some don't manage them at all. To effectively control a deer population of two million you would have to cull 300,000 to 400,000 a year. It's quite a lot."

May is another period when accidents increase, this is put down to nursing mothers protecting their young.