So guess what species these images show...

Look out for the answers at the end of the series.

But what do you think? Should we save red squirrels at all costs? Are greys pests or now as much a part of our natural surroundings as their red cousins? What methods should we use to save the reds? Please post a comment below.

Below we've laid out what we think are the key arguments and facts in the debate.

The grey squirrel threat
It is widely accepted that a significant factor in the decline of red squirrels was the introduction of grey squirrels to the UK in the late nineteenth century. Grey squirrels threaten red squirrels in two main ways.

Firstly, they compete with red squirrels for food. Grey squirrels eat seven times more food per hectare than red squirrels. They aggressively compete with the red squirrels for food, and they also eat food before it is ripe enough for red squirrels to eat.

Secondly, grey squirrels carry a virus called squirrelpox (SQPV), which they are immune to, but which is deadly to red squirrels. It's estimated that 60% of grey squirrels carry the virus and they suffer no ill effects from it, but if a red squirrel catches it, it will be dead within weeks. Grey squirrels have probably evolved immunity to the virus, but because it is new to red squirrels, they are not immune, and it is lethal to them on an epidemic scale.

There's more detail on how the greys threaten the reds on the Save Our Squirrels website [PDF].

Conservationists now estimate that there are only about 160,000 red squirrels nationwide compared with 2.5 million greys.

Plans to save them
So what do we do about this? Like all conservation issues there has been a lot of debate about the best course of action. It has been argued that red squirrels are a lost cause, and it is too late to save them.

But it shouldn't be argued that it's natural selection, because the problem is undoubtedly man-made. Red squirrels were never equipped to compete with grey squirrels, having evolved in Europe alone. Grey squirrels in contrast came from a highly competitive environment in North America.

One way to conserve the reds is to control the greys. There are two main approaches here. Some believe in attempting to eliminate grey squirrels altogether. But this would require huge resources, would be controversial, and may not even be possible. The favoured approach is to protect red squirrels in designated areas and cull grey squirrels in the buffer-zone areas surrounding them.

Grey squirrel control is carried as humanely as possible, by trained, licensed individuals. A clever trapping system based on weight balance is used. It means that red squirrels can escape from the traps, but the greys can't. The traps are covered, so the squirrels in them aren't exposed but are kept warm and dry, and checked twice a day.

These red squirrel refuges are also managed and enhanced in other ways. For example, ensuring they have the correct composition of tree species to suit red squirrels as much as possible.

Recently money has also been put into study to map grey squirrel control efforts that are currently in place. This will take into account work by landowners, institutions, volunteers and local groups, with the aim of gaining a greater understanding of existing work and helping with future red squirrel conservation strategies.

There are also other long term strategies that are being researched. For example scientists are working on a vaccine for red squirrels against the squirrelpox virus, but this is thought to still be about ten years off.

There has also been work into mass sterilisation programmes to stop the spread of grey squirrels. But there are many complications with this. For one, how do you feed the medication to grey squirrels without affecting other rodents? Difficult, considering that squirrels cache a lot of food.

So what do you think? Please tell us below.

Unfortunately things don't always go as planned...

Within the Borrowdale Valley lies the small hamlet of Seathwaite. With 3,500mm of rain every year, it's one of the wettest places in England. The average in Manchester is just over 800mm in London it's 600mm in London, which gives you some idea of how wet it is. Maurice, the National Trust warden, says they get 100 dry days every year, which sounds great. But it isn't. It means they have 265 wet days a year.

Although this is far from the dream climate for many Autumnwatchers, it's perfect for the hundreds of species of mosses, lichens and bryophytes, many of which need this climate for their survival.

Borrowdale and Cumbria also represent the front line against the introduced grey squirrel population which has dramatically affected the numbers of the native red squirrels (Scuirus vulgaris). The first grey squirrels were seen in the valley in 2001 and spread fast, causing a huge decline in the red squirrels population. Organisations here realise they cannot get rid of the greys completely, but they can work to manage the grey squirrel numbers effectively.

(Red squirrel conservation is a tricky subject. Find out more about it and have your say about what should be done.)

If you want to see red squirrels in the UK, try one of these places:

• Brownsea Island, near Poole
• Formby, near Liverpool
• Mount Stewart House, Northern Ireland
• Dodd Wood, Cumbria
• South Scotland

While in the Borrowdale valley, the home of Beatrix Potters Squirrel Nutkin, we also concentrated on another main character from this classic book, Old Brown, the Tawny Owl (Strix aluco). At this time of year tawny owls are becoming incredibly territorial, and subsequently are very vocal. The team spent a few nights in the dark woods of Borrowdale attempting to find and film these elusive nocturnal predators, using all the equipment and techniques we could.

On the weekend of November 7th the BTO want Autumnwatch viewers to help them with their nationwide tawny owl survey. Most birdwatching is done during the day so the BTO are hoping our viewers can take on the night shift. This doesn't necessarily mean that you have to get out there in the woods like we did.

This is one of the easiest surveys you can take part in, because if you don't want to go out into the woods in the dark, you can contribute from the comfort of your own bed. All you need to do is open a window, listen out for the synonymous 't-wit'('kewvick') or 't-woo' of the tawny owl, and then let the BTO know. Easy!

Check out the BBC Wildlife Finder and RSPB websites to help you identify tawny owls by their calls.

Martin Hughes Games also came along to the Lake District to investigate Britain's ancient trees. He has a big passion for these pieces of natural history, and Borrowdale has three (previously four) very famous trees, which are incredibly old.

The Borrowdale yews are all recorded as being over 1,500 years old. They have lived through world wars, influential lifetimes and momentous historical events. They have been canonized by poets such as William Wordsworth, and still grow, photosynthesise and live healthily in complete peace. Well, apart from the 265 days of rain, wind and snow every year, so almost peaceful...

• The Borrowdale Yew on The National Trust
• The Ancient Tree Hunt
• Some of Britain's oldest trees on the Guardian

Being ducks, bad weather won't really reduce your chance of seeing a goldeneye (unless of course it keeps you indoors). In fact the cold weather forecast for Monday and Tuesday may push more birds in from Scandinavia. Stunning males like the one below stand out in even the gloomiest conditions. Females are greyer above with a brown head, though they still have that gleaming yellow eye.

Next up is a weird and wonderful wader that will be winging its way westwards this week: the woodcock, a magical bird. Any favourable weather conditions over the coming week will allow more of these superbly camouflaged birds to reach Britain and Ireland; there has already been a sharp rise in reports over the last fortnight.

Not only does the woodcock give the 'w' key a much-needed work out but it also gives me a chance to use an excellent word: crepuscular (which means that they are active at dawn and dusk). Despite this, dog-walkers have a good chance of seeing them as dogs may disturb woodcocks from their daytime roosts, often in damp fields or tangled woodland undergrowth. Please do remember to keep dogs on leads if you are in a protected area or there is livestock present.

Sadly, cold snaps at this time of year are likely to spell trouble for any remaining insectivorous summer visitors like the swallow. Fortunately most have already left, as you can see in the BirdTrack weekly reporting rate.

Now this is really amazing - some swallows have started to stay in the UK over winter and have found a remarkable way to survive our cold: they hang round places like power stations and oil-refineries. Last winter was the third in a row when a handful of hardy swallows used the Chevron oil refinery in Pembrokeshire, monitored by refinery inspector and bird ringer John Hayes. There have, though, been no swallows there this year.

Finally, don't forget the tawny owl survey. The same frosty weather that may push in more goldeneye but spell doom for any remaining swallows is also great for listening out for the hooting or 'kewvick' calls of your local owls (though sadly not in Ireland, from which they are absent).

Here's another selection of our favourites from the last few weeks.

Thanks for your contributions!

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Using common plants for medical purposes is an historical practise and a complicated science. The oldest recorded history of herbalism in the UK takes us way back to the Roman invasion. The Romans brought with them a wealth of knowledge that had been gleaned together from other civilisations.

It's easy to forget that long ago, before the days of modern medicine, herbalism was the best, if not the only, way that people could fight disease, heal injury and treat all manner of ailments related to everything from allergy and digestion to fertility and fatigue. It also set the foundation for much of our medical knowledge today.

My stroll in the Wiltshire hills gave me a chance to see some of our common plants in a new light and learn about how they can be used in clever ways.
In many cases botanical substances that we consider useful, serve to protect the plant against bacteria, insects and herbivores. We're not the only species to have learnt the benefits of plant extracts: just recently it was discovered that blue tits line their nests with aromatic substances to deter bacteria.

The best way to learn more about herbalism is to go on a guided walk. Many organisations including the Wildlife Trusts run events throughout the year where you can learn about wildflowers and other plants and their useful properties.

However, be careful, because where some plants heal, others are very toxic (for example, foxglove, hemlock and deadly nightshade) and some wildflowers are illegal to pick.

A few well-known plants with medical uses:

Stinging nettles extracts are used to treat rheumatism, arthritis and aching joints.

Elderberry has been shown to be effective in treating Influenza B.

Self-heals are used to stop bleeding when chewed and applied to cuts.

Ginger compounds are active against some types of diarrhoea.

Red clover extracts have been used to treat symptoms of menopause as well as easing eczema, coughs and even asthma.

Learn more about Herbalism from these websites:

Herbs in History

Wildflower Information: Herbs and medicinal flowers

The Herb Society: Herbs in Medicine

The National Institute of Medical Herbalists: Herbal medicine

Grow your own medical cabinet by planting a wildflower meadow. See these links for information:

BBC Breathing Places: Find nature events near you

BBC Gardening: Create a wildflower meadow

Plant Press: Wildlife Habitats

Foxes and tawny owls patrol its leafy lanes, woodpeckers flit through the trees, and rare birds like firecrests are known to breed here. It's an island of green in a sea of concrete and it's right in the middle of London.

Thought you might also like a few photos of the crew and equipment behind the scenes...

They're here! Fieldfares have started to arrive. A BirdTrack report of 8,000 individuals over the Humber Estuary on Tuesday (accompanied by 6,000 redwing) gives an idea of the scale of the arrival that happened this week. In Staffordshire and Cambridgshire, 3,000 and 1,466 flyovers the following day shows that migration doesn't just happen around our coasts.

A smartly-dressed member of the thrush family, fieldfares can be distinguished from their relatives by their grey hood, ruddy-brown back, grey rump and entirely black tail. Migrating flocks often communicate using a distinctive 'chack-chack-chack' call.

There has also been a dramatic rise in reports of lesser redpolls over the last couple of weeks. This is probably the result of birds arriving at wintering sites in central and southern Britain from further north. These small finches breed in Britain, Belgium, Germany, Holland and a few isolated mountain areas in southern Europe, including the Alps. They have a penchant for alder and birch trees and can sometimes be seen with their better-known relatives, siskins.

Look out for jays this week. They are quite secretive in the breeding season but become noisy and obvious in autumn. You can see them in woodland, parks and gardens at this time of year. I've seen them and heard their harsh calls right in the centre of Bristol and even around the main BBC Bristol site.

One things that makes them easier to see is their hording behaviour. They will return time and time again to a food source, such as a fruiting oak tree or birdtable, carrying off acorns or peanuts to bury for leaner times later in the winter. Jays can carry several acorns at a time, which explains why you may find a few oak seeds growing together in your lawn next year!

The rafters of Woodchester mansion are home to a colony of greater horseshoe bats. The big, open space in the abandoned mansion is a perfect hideaway for these bats: cool, quiet and out of the way.

During the night, these nocturnal mammals are out in the surrounding woodland, voraciously feeding up on beetles, moths and flies in preparation for their forthcoming hibernation. The greater horseshoe is categorised as rare by Natural England, and the Autumnwatch team had to apply for a licence to approach and film the roost.

October is the month which sees greater horseshoes mating. Following insemination, a vaginal plug forms inside the female storing the sperm until fertilisation occurs in the spring. In a matter of weeks, the whole colony will leave the mansion for their winter roosts, where they'll hibernate through the cold months.

Unlike the fluctuating conditions inside Woodchester mansion, the location the greater horseshoes select for the winter (tree hollows or caves) will be regular in temperature and humidity, allowing these small mammals to hibernate undisturbed. The bats are loyal to their roosts and will return to the same location year after year.

Woodchester is also home to the greater horseshoe's cousin, the lesser horseshoe. As the name suggests, the main difference between the two species is their size. Greater horseshoe bats are the size of a pear, whereas the lesser horseshoes are more like the size of a plum.

These are Britain's only bats to have a horseshoe-shaped fleshy structure called a nose-leaf surrounding the nose, which amplifies the ultrasonic calls that the bat emits when searching for food. The horseshoe bats are unique in that all of Britain's other bats echolocate using their mouths alone.

If you would like to know more about the species of bats in your area and would like to get involved in their conservation then contact the Bat Conservation Trust who will be able to put you in touch with your local bat group. There are over one hundred throughout the UK. Martin has blogged about getting more involved with bats.

The Autumnwatch team also struck upon a row of badger latrines in the fields surrounding the mansion. The badgers use their faeces to mark their territorial boundaries, giving notice of occupation to other potential badger intruders. Researchers at Woodchester bait badger food with harmless, coloured plastic discs and record where they are distributed to in an attempt to determine the different badger clan territories around the park.

(BBC Gloucestershire have made a photo slidehow of the Autumnwatch team's visit to Woodchester. The visit even made BBC Points West.)

So armed with all this infomation about wildlife that goes bump in the night, get into the Halloween mood by taking a night time woodland walk. Listen out for the sounds of surrounding wildlife: the eerie hooting of tawny owls from the tree tops, female foxes screaming in the distance, deer rustling close by in the undergrowth and, of course, the unmistakeable whoosh of bats as they fly past your ear...

(Chris Packham has created a downloadable guide to sounds of the night for BBC Breathing Places.)