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00:00Winter's a time when we all slow down. The day lengths shorten and the temperature plummets.
00:14It's a hard time for all and especially for our wildlife. From bustling pond floors to
00:21hibernating bats, in this episode we're going to be looking at how our wildlife adapts to
00:28this most challenging of seasons. Welcome to Winter Watch in Wales.
00:58Welcome to Llangors Lake here in Bannau Brycheniog or the Brecon Beacons. Now it's a very mild,
01:06quite a sunny day here today but 60 years ago it was very different. We went through an extreme
01:14winter now known as the big freeze. Temperatures plummeted to minus 20 degrees. 20 foot snow
01:23drifts were recorded in South Wales and along the seafront of Penarth and Swansea the sea itself
01:31froze. It was a difficult time for everyone but especially for our wildlife. It lasted from
01:39December 1962 until February 1963 and it's said that in the UK as a whole we lost 50% of all of our birds.
01:51Now it's mild, it's just started to rain here today but these extreme weather conditions are getting
01:59more and more common because of climate change. For us of course we can to an extent adapt to it
02:07but for our wildlife it's much much harder. They don't have warm homes, they can't nip down to the
02:14supermarket in their cars. But in fresh water, even under winter's grip, life goes on.
02:24Come winter and a once buzzing pond grinds to a halt. Above the surface anyway.
02:40As emergent plants wither and die, a sub-aquatic survival story is just beginning.
02:46Beneath the ice, predators patrol the open water, poised to pick off unwary prey.
03:00But lower down, an unexpected haven.
03:06Here, the water is a constant four degrees. It'll never freeze.
03:11The creatures are safe, from the elements at least.
03:29A new tadpole, an eft. It hatched late in the summer. It failed to metamorphose before winter took hold.
03:38And now it's trapped. It must wait until spring to leave the pond and complete its transformation.
03:49The eft's feathery gills extract oxygen from the water, before blood vessels ferry it to vital organs.
04:00Its metabolism is barely ticking over, but it still needs food to seed through the winter.
04:08The eft's feathery gills.
04:19Daphnia. Barely a millimetre long, living in herds and grazing on microscopic algae.
04:26These are the watery equivalent of wildebeest on the African plains.
04:30For much of the year, they reproduce asexually, producing clones which look like Russian dolls as they grow inside the mother's body.
04:43But come the cold, some alter their sexual habits and mate to produce eggs.
04:52Resistant to freezing, these eggs are like time capsules and will only hatch in milder weather.
04:58The adults are slowing down, making them easy prey.
05:10In a cold winter, few insects last long in the world above the surface, but many persist as nymphs at the bottom of the pond.
05:23Despite their aquatic armour, sticks and stones fall short when there are predators lurking.
05:28The larvae of a broad-bodied chaser, a dragonfly regularly found in British gardens.
05:38They spend their first two years under water.
05:45Extendable mandibles make them truly formidable predators.
05:49Around 20 dragonflies and damselflies use our garden ponds to breed.
06:07And their nymphs are superbly adapted to this alien environment.
06:11They even breathe through their bottoms, gently drawing in water and extracting the oxygen with gills in their guts.
06:31The arrival of snow disturbs the pond's delicate balance.
06:36Now, little light penetrates the surface.
06:38Photosynthesis grinds to a halt and oxygenating plants shut down.
06:47Larger residents may suffocate and die.
06:52For scavengers, it's a time of plenty.
06:58Water hoglice thrive on the spoils.
07:02And ramshorn snails join in the feast.
07:08The worst of the winter weather is now over.
07:15When snow and ice melt, pondweed kicks back into action, re-oxygenating the water.
07:23Soon, the young newt will escape its watery prison.
07:27The pond and its resilient inhabitants have made it through another winter.
07:33Never underestimate how important one small habitat can be for wildlife.
07:50And of course, those nymphs and larvae, well, they will hatch out into beautiful damselflies and dragonflies in the spring.
07:58And it's so important that we provide that kind of habitat for our wildlife, especially garden ponds.
08:06Right from below the water to the surface now.
08:10This time of year, wetlands across Wales are brimming with activity, as wildfowl that has migrated here feed up on winter's bounty.
08:19This includes the incredibly rare green and white-fronted goose.
08:24And despite only a very small number residing here, Wales is still a stronghold for this threatened species.
08:32Wildfowl that make their way to these wetlands every winter, well, they have to survive freezing conditions.
08:40Have you ever walked out onto a frozen lake naked?
08:46Well, I tell you, I haven't, partly because I don't want to be arrested, but also because I don't want hypothermia.
08:53But our wildfowl have adapted incredible techniques to cope with these conditions.
09:00Chris Packham investigates.
09:01Feathers.
09:08I love feathers.
09:09They're truly remarkable.
09:10One of nature's greatest fabrics.
09:14And they've been around in a form like this for no less than 135 million years.
09:20So in evolutionary terms, why have they endured?
09:25Well, firstly, they're extremely tough.
09:28They're also essentially repairable.
09:33If you pull them apart like this, I can preen that quickly back together.
09:39Now, how do they manage that?
09:40Well, let's take a look at one of these that we've got under the microscope.
09:47So what we're looking at here on the screen is a section of the feather here.
09:51And each of these parts of the feather is called the barb.
09:55And in between those, you've got what we call the barbules.
10:00And on those, which we can't see at this magnification, are the barbicells.
10:04Tiny, tiny little hooks, which the birds are able to tease together, a bit like rejoining Velcro.
10:11All of the exterior feathers have this clever adaptation, and they knit together to create an outer barrier.
10:21But duck feathers also need to be waterproof, so a special gland near the tail, the uropidial gland, produces protective oil.
10:34It's spread over them through preening, helping to keep out the cold and the wet.
10:38But their body heat is trapped by a totally different type of feather, down.
10:45And look at that for a contrast between the two.
10:49Their structure is very different than these contour feathers.
10:52So what we're looking at here are barbs, and these tiny hairs are the barbules.
11:03What's interesting is that they lack those barbicells, those tiny little hooks which would otherwise repair the feather.
11:11Because down feathers essentially don't want to be repaired.
11:15They want to be disheveled.
11:16They want to be fluffy, so that they can trap air.
11:20And it's that air which retains the heat.
11:24But there's just one part of the plan which has been overlooked by the birds.
11:28Naked feet.
11:38Imagine this duck's leg and foot here was similar to mine.
11:42The blood would be pumped into that foot through arteries from the heart.
11:48And it would come down here as nice warm blood.
11:51And it would return to the body through a vein.
11:55Coming up here like this.
11:59But there is a serious problem here.
12:01You're pumping all of this lovely warm blood into a part of your anatomy which has got no insulation whatsoever.
12:08So it's going to cool down really quickly.
12:11And then worse, it's going to be pumped back up into the body when it's cold.
12:16The last thing you want in winter if you're wildfowl.
12:24Right, well I've come outside on this chilly winter's afternoon and I've put my downfield jacket on.
12:30Ethically sourced, I have to tell you.
12:32And I'm feeling pretty cosy given that it's about 7 degrees out here.
12:37So without my clothing, in the space of just a few hours, I'd be getting hypothermic.
12:42And in the space of a few more, I'd probably be dead.
12:46But it's not that I'm not losing heat.
12:48I'm actually losing quite a lot of heat.
12:50And you can see that on this thermal camera.
12:52So look at my face.
12:54No insulation there, not even a beard.
12:56And it's glowing bright yellow with all of that heat that's emanating from it, as are both of my hands, look.
13:03And these are what we call heat windows.
13:06And my body heat is quite literally going out the window of my face and hands.
13:12But what does our thermal camera reveal about the wildfowl?
13:16If they come in nice and close, we can get a view of these greyleg.
13:20Their bodies are obviously pretty cool.
13:24They're not radiating any heat at all.
13:27But look closely at the tops of their legs.
13:31You can see them glowing there, which means that they're hot.
13:35But then look further down to the feet.
13:37They're virtually invisible.
13:39Let's contrast their feet with my hand, my heat window.
13:45And look at that.
13:46My hand is glowing with all of the heat that's being lost.
13:49But the greyleg goose's foot is much colder.
13:54So why aren't they losing heat at the same rate?
13:59This is how a real duck's leg and foot looks.
14:04It's still got the artery coming down.
14:06But when it gets to here, that artery fragments into a lot of smaller blood vessels like this.
14:14And it's something that we call a reet.
14:18The vein, which is returning the blood back to the heart, as it rises through the leg, breaks into smaller vessels too.
14:29And it closely intermingles with all of those arteries in the reet, like this.
14:38And this is how the heat exchange mechanism works.
14:43The warm blood is coming out of the body down here.
14:47And it is chilled by the cooler blood that's rising up through the veins here.
14:54So when it gets to the foot, it's already nice and cool.
14:59But then, when that cold blood is rising back through the vein, it's intermingling with all of the warm blood that's coming down from the body.
15:08So that when it does go back into the bird's body, it's been pre-warmed, not chilling that bird.
15:15You see, when it's confronted with a problem, nature invariably comes up with a neat solution.
15:22I'm so glad I've got all these warm clothes to wear.
15:42Now, back in 2022, Gillian and I were very lucky to feature a special camera inside a bat roost in Stackpole in Pembrokeshire.
15:54It was the maternity roost of the Greater Horseshoe Bat.
15:59And there were up to a thousand individuals in there.
16:02Now, this is one of our largest bats.
16:05It's about the size of a pair.
16:07And its wingspan can be up to 40 centimetres.
16:11It was an incredible thing to see.
16:14Traditionally, they've been confined to southwest England and Wales.
16:18Wales is a real stronghold for them.
16:20And I'm pleased to say that numbers are now increasing and they're starting to spread eastwards.
16:27Now, it was brilliant to have that camera in there, but I wanted to try and get a little bit closer.
16:33So I got my bat detector out and went down just as the animals were emerging from the roost.
16:41There are cameras set up both inside the roost and also outside.
16:47So all I've got to know is wait for it to get dark and for the bats to emerge.
16:51No visit to a bat roost is complete without a bat detector.
17:04So what happens when I do that?
17:09Which will transform the bats' echolocations into a sound I can hear.
17:13Here we've got the first few bats are just starting to emerge.
17:22They're kind of having a look around.
17:24They're emerging, flying around once or twice and then going back in.
17:28There's a big wood at the back of here.
17:30They'll head out probably to feed around there and some of them will go 10 kilometres or more.
17:35They go a long, long way.
17:36It's a fabulous thing to witness.
17:39Just watch them flying around up ahead.
17:42They're starting to pour out now.
17:44It's like water out of a tap.
17:46They really are coming out of it.
17:48What an experience, standing here, watching and listening to all of those bats head off.
18:09Oh, that was a real privilege.
18:29But please don't forget that all bats and bat roosts are protected by law.
18:34So give them plenty of space.
18:37Bats, of course, they disappear over the winter months.
18:42Where do they go?
18:43Well, the bats we saw there, the greater horseshoe bats, they leave the maternity roost and they seek out caves, mines and cellars.
18:52And they do this because they're looking for somewhere where the temperature is constant.
18:58They want to avoid fluctuations.
19:00They enter a period of torpor where they slow down their metabolic rate.
19:07They lower their body temperature in order to conserve energy.
19:12And that is how they survive the winter months.
19:16But there's one small creature that can't afford to snooze in winter because this is the most important time in its development.
19:26Chris Packham takes us underwater to have a look.
19:29At this time of year, whilst other places are conserving their energy, the river still flows with ferocity.
19:38And here, one water-loving bird remains busy all year.
19:47The dipper.
19:49It spends up to 66% of the day foraging for food.
19:53And this remarkable little bird lives up to its name by dipping beneath the surface in search of invertebrate prey.
20:10Underwater, most insects are vulnerable, so they hide away under rocks and stones.
20:15But these stones aren't quite what they seem.
20:24Living inside is a particularly resourceful inhabitant.
20:30A caddisfly larvae.
20:31There are around 200 species of caddisfly in UK waters.
20:37This one is Limnophilidae.
20:43In the depths of winter, they're on their own search for food.
20:50Walking across the gravel, they feed on dead vegetation and organic material that clings to underwater surfaces.
20:56Like these rocks.
21:08And in an attempt to go about this feeling unnoticed, they adorn themselves with debris from the riverbed.
21:14As they grow, they must adapt their home, searching out new materials amongst the rocks and gravel.
21:28When the right piece is found, extraordinary care is taken to find precisely the right fit.
21:35Silk is produced from specialist glands in the jaw, which stick the stones around its body.
21:45It looks like a 3D printer, as it works methodically, back and forth, back and forth, creating the ideal camouflage.
21:53And with naturally soft bodies, this also offers some protection from hard fragments that may be thrown around in this fast-flowing river.
22:14This caddisfly may have a mobile home, but others opt for a more fixed abode.
22:21This is Hydrocycidae.
22:30It doesn't have a case, but makes a retreat in stones which are fixed to rocks.
22:38Down here, it's safely hidden from predators, and that's just as well.
22:44It's hard to blend in when you have such flamboyant gills.
22:48And a brush tail.
22:53The gill throngs maximise the oxygen that can be taken from the current.
23:02The best territory not only comes with a good home, but also prime feeding grounds.
23:08This caddisfly has another use for its silk gland.
23:14It builds a net.
23:15These super-strong structures are used to capture passing algae and other organic material, which the caddisfly larvae feed on.
23:30All these caddisfly larvae take months to develop and will remain in these cold rivers throughout the winter.
23:48And if they can escape the beak of the river-dwelling dippers, the caddisfly adults will emerge into the form that we know them best.
23:59From one insect adaptation to another, many butterflies survive the winter by hibernating and emerging in the spring.
24:16Butterfly conservation is the charity that carries out the citizen science project, the big butterfly count.
24:25And they reveal that 2024 was the worst year on record.
24:32There's a combination of reasons, including extremes of weather conditions, but the main one is habitat loss.
24:39And the ones that have been particularly badly hit are the ones that are dependent on flower-rich grasslands, on heathlands and on woodland glades.
24:48One of those is the marsh fertility.
24:51This is a butterfly that overwinters as a caterpillar that spins a protective web.
24:58I went out with butterfly recorder Paul Taylor to see how one local population in Wales was faring.
25:12Marsh fratilleries were once widespread across Britain and Ireland,
25:16but declined dramatically over the last century.
25:19Now they're considered to be threatened, not just here, but in Europe as well.
25:25It's autumn and I'm meeting Ceredigion County butterfly recorder Paul Taylor to find out more.
25:33Now, mass fratilleries, they've declined over the years.
25:37Why is that?
25:39It's mainly because of lots of habitat.
25:40Lots of these areas that used to be pastures have been dried up and it's ended up that the devil's bit scabious has died back and consequently the food plant for the marsh fratilleries disappeared.
25:53Right, OK.
25:53And devil's bit scabious is this lovely purply flower here, isn't it?
25:57The butterflies deposit their eggs on the leaves of the devil's bit scabious.
26:05When the larvae emerge, they have a food source ready and waiting and they've come up with an ingenious way of protecting themselves from parasites and predators alike.
26:15Larval webs.
26:16These webs can be counted from late summer to early autumn to give an indication of how populations are doing in strongholds like this.
26:26How are they doing locally here in Ceredigion?
26:29We're quite surprised how well they're doing actually because lots of the sites that we've been surveying, we've found more larva webs and we've actually found butterflies on the sites that have previously not had them on before.
26:42So across the road there's a site called Rosgelly and we've actually found 13 larva webs in there this year and that was unoccupied for the last seven years.
26:54We're finding that people are actually sending in pictures of butterflies they've seen that they don't know what it is and it's a marsh fratillary so, you know, that is really positive.
27:12It's very positive indeed and reassuring to know that Wales is a real stronghold for these micropopulations too.
27:23And we saw there how the caterpillars spin a web to protect them from parasites and from the weather, but in winter they adapt their web especially for hibernation.
27:37It's formed deep down in grassy undergrowth, it's more compact, it's more dense and it's so hardy that even in the coldest of frosts those hibernating caterpillars won't be affected.
27:50How amazing is that?
27:54And it goes to show, doesn't it, that just leaving some taller vegetation, leaving that leaf litter for our wildlife can make such a significant difference over the winter months.
28:06And when you're wrapped up warm underneath your blanket in front of the open fire, think of all those ingenious ways in which our wildlife has adapted to survive this challenging season.
28:19Till the next time, Hwyl Fawr, take care.
28:36Hwyl Fawr, take care.
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