I'm Sophie Estor and I'm speaking to someone with a very enviable job, a safari guide in Tanzania, Nima Amos.

I'm in the vehicle right now.

What I'm seeing in front of me is the woodland area.

A lot of birds, the greenery of the woodland area.

It's beautiful.

I don't see any animal for the moment.

I know at night there's going to be a lot of them because when everybody is sleeping, that's the time that these animals are going to roam around like, OK, this is our land, especially hyenas.

It's a pretty incredible place to call your office.

Yes, for sure.

And what animals are you following at the moment?

At the moment, great migration.

Great migration is among the biggest thing that our guests love to see because it's very amazing to see the number of the wildebeest that we have, the number of the zebras.

This week we're tracking some of the largest animal migrations on earth.

The hundreds of thousands of wildebeest, zebras and gazelles that stomp through East Africa.

And the great white sharks that hunt the oceans.

But the world is warming.

So I want to know, how is climate change impacting these epic animal journeys?

Migration is the biggest migration that we have here in Tanzania.

We have these millions of wildebeests mixed with zebras that you have here in Serengeti, moving from one place to another for availability of food and water.

And what does it look like?

I mean, I've only seen it in videos, but it must be a pretty awesome sight with so many animals.

Yes, it's plenty of animals, a lot of wildebeest.

When you see thousands of them running together, I mean, it's, I don't know, it's something that you can't even be able to explain it well, if you see it, it's a magical thing.

Yeah.

And do you get the other animals running after them?

I mean, the predators, the lions and the cheetahs?

For sure, yes.

Wildebeests, they're the main source of the Serengeti ecosystem.

They help to increase the number of the predators.

So whenever the migration pass, the lions, the vultures, hyenas, everybody's happy because food is everywhere.

And what kind of noise does this great migration make?

Is it pretty noisy?

Wow, it's a funny noise for sure.

I get this from a lot of my guests when the migration, they're around here, they're like, OK, you know what?

We couldn't sleep at night.

Somebody was all the time.

They're making the noise like, all the time.

Imagine with thousands and thousands of wildebeest around.

It must be quite hard to sleep.

For sure.

It's very hard.

As the seasons change, the wildebeest move from the Serengeti in Tanzania to the Masai Mara in Tanzania.

For the last few months, the hungry herbivores have been busy giving birth to their calves.

I've been working for more than five years as a safari guide.

So it's always the great moment when I get to see the wildebeest giving birth.

I'm telling you, it's a wonderful moment seeing how they're giving birth and straight ahead after one minute, two minutes, the calf can be able to walk.

The mother can be able to lactate the calf.

It's a moment that whenever you see it, OK, these are incredible animals.

But recently, Nima's seen the patterns of this birthing change.

Because of the climate changes last year, we had unexpected rain, a lot of rain, which made even the wildebeest being a little bit confused.

I was at the eastern part of Serengeti this January and there were plenty of the wildebeest giving birth around that area where they were supposed to not be at this time.

But because it's raining everywhere, so they are like scattered, going up and down, going east to west.

So it has been a little bit confusing.

Climate change is making rainfall in the Serengeti and the Masai Mara more unpredictable.

Last year, vast quantities of rain on the Tanzanian side meant the grass grew everywhere, so the wildebeest were giving birth in different areas than usual.

And it's not just Nima who's concerned about this.

I first got involved in this when I was an undergraduate student in Kenya in the early years.

During that time, we went to visit Masai Mara and I got really interested in the place ever since.

Joseph Ogutu moved to Germany, where he's a senior statistician at the University of in this very ecosystem.

He's been analysing data captured by the Kenyan government, which sends people in low-flying planes over this vast savannah to painstakingly count by the human eye and with photographs the number and timings of wildebeest.

And climate change is causing the great migration to change.

We are seeing that the migration used to visit Masai Mara in much larger numbers in the 70s and the 80s.

There used to be at least over one million wildebeest alone coming to Masai Mara from the Serengeti.

But over the years, that number has gone down.

And nowadays, it is hard to find more than just about 250,000 visiting the Mara.

That's a big change from over a million to 250,000.

It's a massive change.

It's a massive change indeed.

The other change is that these few that do make it to the Mara each dry season, spend less time in the Mara than they used to do in the early years.

And they're spending about one and a half months less based on our estimates than they used to do in the early years when they were coming in larger numbers.

Those are huge shifts over the decades.

The wildebeest are spending less time in Kenya.

They prefer it on the Tanzanian side, where Nima says there's been more rain and therefore more grass.

Climate change is affecting the animals in lots of different ways.

The first is through the Mara River.

So in recent years, the Mara River nearly completely dried out, which represented a serious challenge.

Secondly, when the rainfall reduces, then the amount of grass produced also reduces, forcing the migration to move over longer areas looking for water and food.

They go closer to villages or the homes of poachers.

So the number of the wildebeest that are killed as a result of this increases.

So when there's more drought that pushes wildebeest closer to humans, how much have the numbers gone up in terms of wildebeest being poached?

About 100,000 wildebeest are poached every year.

On top of that number, you would add more in years which have got less rainfall due to drought.

So it's a massive loss.

Joseph's seen drought get more intense and more frequent in recent years.

Since 2021, East Africa has been gripped by a horrific three-year drought, and scientists say it was made 100 times more likely by climate change.

We've made a whole programme about ways to tackle drought in this region.

Just search our back catalogue and type, how can we fight drought in the Horn of Africa, wherever you get your podcasts.

It's not just drought that's causing a problem.

The temperature is increasing in Masai Mara.

The average minimum temperature at night used to be about seven degrees Celsius in the 1960s, but that has now increased to 11 degrees, which is an increase of four degrees Celsius.

That's a massive change in temperature.

It means that the water that is in the ground and the river evaporates faster, so there's less for the animals to drink, and it's harder for grass to grow in Kenya.

So they stay longer in Tanzania, where they're more likely to come into contact with poachers as they roam the plains for food and water, and they're also more likely to overgraze the grass.

Climate change isn't the only factor.

Joseph says there's been dramatic changes in land use since the 1970s.

There are far more livestock, which means competition for grazing, and there's been an increase in human settlements, which come with a lot of fencing, so it's harder for the wildebeest to roam freely through the territory.

Yeah, I think the animals are trying to do the best they can to adapt.

The habitats are getting lost or degraded in various ways.

So climate change just continues to pile more pressure on these animals and accelerate the loss of the animals and the loss of their habitats.

And Joseph, you're Kenyan yourself, and you're obviously really passionate about these animals and this place.

Does it make you sad that such fewer numbers are coming to the Kenyan side?

Yeah, I am concerned about the migration, not just because the few are crossing into Kenya, because, you know, from the perspective of the wildebeest, they really do not know Kenya or Tanzania.

They see the old Serengeti Mara.

They don't have passports.

They don't have passports.

They see the Serengeti Mara as one ecosystem.

So if one part of the system is not working well, then the whole system gets affected.

So if we really want to preserve the migration into the future, then we really need to make sure that the whole system as a whole is working.

For tour guides like Nima, these changes make her job a whole lot harder.

So you get some of the guests like, OK, maybe my map shows me I have to go to the northern part of Serengeti because it's going to be a crossing at this time of the year.

And then perhaps because of the climate change, the wildebeest can delay to go there.

So it gives maybe as a safari guide a lot of pressure because there is no wildebeest here.

And I want my guests to get the same same experience.

My guests have travelled maybe from UK, from US, from all part of the world for this.

So it gives us a lot of pressure.

And also it's the best time also to explain to our guests about the climate change and to give them the education about it.

I mean, these changes that you've seen with the wildebeest, I mean, how worried are you about climate change and what's Yes, it's something that gives you a lot of worrying about the migration and everything.

Wildebeest migration in Serengeti is very, very important.

You know, when they move from one place to another, they shape the landscape, eating the grasses, opening the woodland area, helping other animals to increase, helping also our country because I mean, the wildebeest migration is among the most famous in Africa.

So it helps to increase money in our country, people to get employed in our national parks.

So the migration is very important, not only for the animals, but for the ecosystem and for the humans too.

You're listening to the Climate Question from the BBC World Service.

I'm Sophie Estor, and we're hearing the stories of incredible animal migrations and how they're being affected by the changing climate.

The UN recently released a landmark report on the state of the world's migratory animals, from turtles and fish to reptiles and birds.

It studied more than 1000 creatures and found that nearly half are in decline.

Climate change was one of the top threats.

We've heard a story about land migration on the plains of the Serengeti and the Masai Mara.

But what about animals that prowl the ocean?

I love sharks.

I think they're super interesting because they just capture people's imaginations.

This is Tricia Atwood.

She's Associate Professor of Watershed Sciences at Utah State University in the US.

There's been a couple of close encounters.

I just happened to be in a very tight area in a boat channel and a very large tiger shark just kind of came up right behind me.

He was trying to get around me and I didn't really know what he was doing.

But it did cause me a little bit of panic.

I bet.

Was it a close shave?

I mean, he was so close behind me, I could have kicked it in the face, but he just went right past me.

I do remember my husband was with me and he was still on shore and he was yelling at me, Tricia, Tricia.

Wow, how dramatic.

Well, all went well and you're here talking to us.

What we're here to talk about is migratory animals and sharks migrate.

Can you tell me why they migrate?

Yeah, so animals migrate for all types of reasons.

Some of them migrate for food resources, but animals, including sharks, will also migrate to locations that are more suitable for things like mating or for giving birth.

For example, lemon sharks in the Bahamas will travel back to the same location where they themselves were born to give birth to their own food resources or are attempting to get to places that are more suitable for the activities that they are doing during that season.

And what kind of distances are we talking with these migrations?

Are they covering huge swathes of ocean?

Oh, absolutely.

Some of these shark species can travel massive distances.

We've seen great white sharks that have traveled from the coast off of like Perth, Australia, all the way to South Africa.

Wow, that's incredible.

And so we know that climate change is increasing temperatures, including ocean temperatures.

Is that impacting sharks?

Absolutely.

So sharks and lots of other animals sometimes are cued by water temperatures or air temperatures that is telling them, hey, this is the season for you to go somewhere else.

Because climate change is altering those temperatures, they may choose to Then when they get there, there's no food and now they're in trouble.

Animals are also moving because where they currently are located may be completely uninhabitable for them now.

So all animals have a thermal temperature limit that their body operates at.

And if you exceed those limits, the temperatures are too high or those temperatures are too cold, the body can't function anymore and it will start to die.

Really?

So have there been some examples where sharks have moved because of rising sea temperatures into other places?

Yes.

So we have seen that great white sharks are moving to cooler waters.

So great white sharks are kind of like the Goldilocks and they like these temperate waters that aren't too hot and aren't too cold.

Just right.

Yeah, just right.

Well, where they're currently living isn't just right anymore.

And so they're having to move in search of colder waters.

In California, that means they're having to move north.

And we've seen that since 2014, great white sharks have moved about 600 kilometers more north than we would expect to find them.