your destination without getting lost? - I'm  going this way! - Oh, we're going this way!  

My recent trip to Belize took me 5,000 miles,  11 hours on a plane, six hours on a bus and  

a lot of time zoning out while watching pretty  terrible films. But long before we humans devised  

our ingenious technology and transportation for  getting around, animals of all kinds have been  

making their own spectacular journeys across  the globe. And that's what we're exploring on  

CrowdScience from the BBC World Service. I'm Anand  Jagatia, and I'm taking you on a two-part journey  

to the Americas to try and understand some of the  most impressive feats of animal migration on Earth.  

- This is a greycap bird. This individual probably  made about three or four trips already to Belize.  

Birds like this greycap arrive in Belize  from North America for the winter, year in,  

year out, but how do they, or in fact any migrating  animal, know where they're heading? It's something  

that's been bothering one of our listeners  in Kenya, called Moses. Here's his question:  

Moses: Hi CrowdScience. My question is, how are long-distance migrating birds like the Arctic tern  

able to navigate vast oceans and distances in  flight? How come they never get lost? Similarly,  

how do turtles not get lost traversing  thousands of miles under ocean water?  

Anand: Thanks Moses. It's such a great question and it's  also a huge one. So much so, that we've decided to  

make it into a two-part CrowdScience special:  the science of how animals actually find their  

way around is a fast-moving and really exciting  area of research, and we're dedicating the next  

episode to that. But before we can answer Moses's  question about how animals navigate over such huge  

distances, you need to understand where they  go and why they go there in the first place,  

and it's these amazing voyages that we're covering  in this episode. So let's get to it.   

David Barrie: The amazing thing is

that animals are migrating all over  the planet, large animals, small animals, birds,  

whales, insects, you name it, fish...  Anand: This is David Barrie. He's a sailor with plenty of  

his own experience navigating out at sea, but he's  also written a book on animal migration called  

Incredible Journeys.  

DB: At one extreme you've got a  bird like the Arctic tern which, with the help of 

tracking devices, we now know may travel a hundred  thousand kilometres in the space of a year between,  

as it were, the Arctic and the Antarctic and back  again, and then you've got a huge animal like the  

humpback whale, which will spend a long period of  time feeding down in the southern ocean around  

Antarctica, building up its reserves of fat before  cruising steadily north into warm waters around  

the equator where it will breed and have its young.  Then you've got the monarch butterfly, which is a  

famous example of a migrant, and less famous, but I  think almost as fascinating, is the bogong moth of  

Australia, which starts its life in Queensland and  then it flies about a thousand kilometres south,  

travelling by night, and spends the summer months  hidden away in little caves, little cracks in the  

rocks on the top of the snowy mountains in new  South Wales, and then amazingly at the end of  

the summer months it emerges and then flies  all the way back to Queensland, and we're now  

beginning to get to grips with how these  navigational feats are performed.  

Anand: You might have seen some of the astonishingly long journeys  that animals can make on television in wildlife  

documentaries, and the fact that many animals,  from whales to wildebeest, migrate over their lives  

probably isn't news to you. But that wasn't always  the case. People had some very different ideas for  

what happened to the animals around them when they  vanished for large parts of the year.   

DB: Migration was kind of a controversial idea until the 19th  Century. I mean, nobody was really quite sure where  

birds went, for example, during the winter. And  there were these bizarre theories that people  

cooked up like, you know, swallows maybe went to  sleep at the bottom of ponds during the winter  

months when they disappeared. But it was really  in the 19th Century that people finally confirmed  

that migration was a real thing and it was first  really established in relation to birds and  

one of the more bizarre episodes was the discovery  in north Germany of a stork which had been  

shot with an arrow that was plainly of African  origin. This poor wretched beast arrived in  

northern Germany with this arrow stuck in it and  and it was obvious that it must have been to  

to Africa because of this arrow. So that  was the first sort of hard evidence, if you like...  

Anand: The poor bird was still alive, sort of  struggling? 

DB: Yes, it was still alive, I guess 

it got shot because it ended up in a museum,  poor thing. But after that, people of course  

gathered more and more evidence of of migration  in a whole host of different animal species.  

Anand: It might sound slightly ridiculous that people  back then seriously thought that swallows went to  

sleep in the bottom of ponds, but when you think  of the alternative: that swallows fly thousands  

of miles from the uk all the way to South Africa,  you can see why people were a bit sceptical that  

migration was a real thing. Take the case of birds  like the Arctic tern, which listener Moses asked  

about, and David mentioned might travel a hundred  thousand kilometres in a year. What could possibly  

be worth the immense effort that a trip like that  would involve? Why don't birds just stick to the  

places where they're born?

Tim Guilford: Not all birds migrate by  any means. In the tropics, long-distance migration  

is relatively rare; in the seasonally constant rich  tropical regions of Earth then it makes sense to  

to breed and live all year round in approximately  the same place.  

Anand: This is Tim Guilford, professor of 

animal behaviour at the University of Oxford, where  he studies bird migration. 

TG: But a very striking 

feature of our planet is that it is seasonal, so  as soon as you start getting into higher latitudes  

then you have lots of sunlight in summer and  not very much in winter, and this drives massive  

seasonal differences in resource availability.  In the Arctic, for example, is very unproductive  

on land in the winter, a very harsh place to live, but  in the short summer season it's almost constant  

energy, and that feeds through into resources,  plant growth, insects, and therefore food.  

And so in order to exploit them, you've got to  make these very long journeys. It's got to be a  

trade-off between the risks and energetic costs  of these long journeys, and the rewards of  

essentially being able to exploit an endless  summer. There are many different kinds of migration,  

even long-distance migration, and different  species and different groups of animals and  

different groups of birds handle this problem in  in very different ways. For example, some species  

are only partial migrants, which means that only  a proportion of the individuals will migrate,  

and presumably there are differences between  these individuals in their energetic balances or  

whatever which makes the trade-off change. But in  terms of how migration is sort of executed, if we  

can use that word, this also varies between small  songbirds, which have to make very long journeys  

over harsh terrain, for them, like crossing the  Mediterranean or the Sahara, places they can't stop,  

and seabirds which can effectively stop  wherever they want on their nonetheless long  

journeys. So sometimes the dangers and the trials  that have to be overcome lead to very different  

kinds of migratory strategy.  

Anand: Different species  of birds will face different balances between 

these trade-offs, and some species take their  dedication to migration to the next level. 

TG: Some really sustained migratory birds, like the bar-tailed  godwit, they will start to digest, internally, the  

organs that they don't need whilst they're on  passage, whilst they're making these journeys,  

they actually eat their  own gizzards and stomachs, in large measure,  

in order to make themselves lighter so they can carry  more fuel, and then when they reach a stopover site,  

or reach their destination, the first thing they  do is to regrow those internal organs. I mean it's  

an extraordinary level of preparation. You're only  allowed to carry a small hand baggage, essentially,  

on these long flights, and so you've got to  adapt to that.   

Anand: The food at their destination

must be unbelievably good for a bar-tailed  godwit to eat part of itself just to get there.  

Our understanding of bird migration has come a  long way from thinking that birds hibernated at  

the bottom of ponds. But how exactly have  scientists mapped out avian flight paths  

across the globe? Sounds like an obvious question,  but birds have wings and we don't, so how have they followed them?  

Well, much of it has been based on  a deceptively simple system that was devised some  

time ago, but is still used very much today.

TG: The classic technique was to place a mark, a little  

metal ring, on a bird's leg, with an individual  identity number and probably an address that  

somebody who found the bird anywhere in the  world could send the ring to, and then to plot  

the distribution and timing of these recoveries  of birds that have been ringed. So this ringing  

started really at the very end of the 19th Century,  I suppose, in Denmark, and has been going strong  

ever since. Thousands of people still go out  putting rings on birds of all sorts of different  

species and people observe them with binoculars  in different places or recover them from birds  

that have finally died. And that information  and the timing of these recoveries has allowed  

scientists to reconstruct the migratory routes  and journeys of many, many species over the decades.  

Anand: Ringing, or banding, is a very clever solution  for keeping tabs on bird populations.  

It's a straightforward idea in theory,  but in practice it takes a lot of work.  

So to see how it happens in the feathered flesh  and to hear about how it's useful, we're heading  

to Belize, one of the top destinations for  migrating birds in the Americas, in the hope  

that we can catch some. We drive in our 4x4 along  bumpy, muddy roads into the heart of Cockscomb Basin  

Wildlife Sanctuary, which is co-run with the Belize  Audubon Society. It's full of lush, tropical forest  

and we've come to meet a team of biologists and  birders who are working here for the next week.  

- I like your t-shirt, by the way! What does your  t-shirt say? - I'm not lost, I'm just bird watching!  

This is project leader Abidas Ash. She's a  bird biologist from the University of Belize's  

Environment Research Institute.

Abidas Ash: We have a bird-banding station here for long-term monitoring.  

We're catching and releasing birds,  but while doing that we're actually  

getting a lot more data on them, so we're looking  at ageing, sexing, looking at the status of the bird,  

the conditions of the birds, and tagging them.

Anand: You can hear that the dense trees  

around us are full of birds which, just like  me and producer Mel, are beginning to wake up  

as dawn is breaking. It's a cool and clear morning  and we've actually been really lucky with the  

weather, because it's been raining pretty heavily  for the past few days.

- 06:30? Okay yeah so it's 06:30.

The first step in putting a band on a bird is to  catch yourself a bird, and that is no easy feat.  

It involves using a series of specially  designed nets that surround the research station  

and a team of people, including our  guide Emmanuel, who have to open them  

up every morning.   

Emmanuel: So we'll be opening nets  every half an hour, and then here we have

net number 13, yeah. These nets are  pretty much blind to the bird  

so whenever a bird would fly, it will just fly  through, and then we have what we call the pockets  

and then that's where the birds get trapped. 

Anand: Imagine a long volleyball net or a badminton net  

which is made of very very thin fibres that are  almost impossible to see in the dim morning light.  

Trust me, I almost walked into a few. - So what  happens, so the birds kind of come fly down to this sort of level?

Emmanuel: So most of our target species, they  will fly low, like the warblers, the thrushes.  

So now this is the the best time to have  your nets open, when it's early morning,  

because this is the time when the birds are  usually active.

Anand: So the early bird catches the worm, 

but the early bird-catcher catches the birds!

Emmanuel: Yeah! So banding has showed that yes, birds are more active early morning.  

Anand: As the birds make their first  flights through the canopy the team are hoping  

that a few unwitting individuals will fly into the net.

Emmanuel: You have to be a trained extractor  

for you to take out the bird. So usually it takes  about a minute, because we try to do it fast so  

the bird doesn't get stressed. Yeah. And then  hopefully we get some birds in the net.  

Anand: With all 16 nets assembled, we head back to the  banding station, in a clearing in the jungle, to wait.  

And while we do that, it's a good time to  mention that you're listening to CrowdScience  

from the BBC World Service. And this week is the  first of a two-part special on animal migration.  

So far, we've heard some of the reasons why animals  bother travelling thousands of miles on a yearly  

basis, when they could just stay put. And now we're  meeting the scientists who are working out where  

migratory birds in Belize fly off to. A career in  monitoring bird migration takes a lot of patience.  

So while we're wandering around waiting for the  nets to fill up, I caught up with Abidas about what  

makes Cockscomb such a sanctuary for wildlife.  - So walking around this place, you can really  

hear, especially at night, loads of different types  of bird calls. How many different species of birds  

live in the sanctuary?

Abidas Ash: I think about 300+  species have been recorded here in  

the sanctuary, and here where we're doing some  banding, in just six hours yesterday we recorded 72-75 species.

Anand: What's special about this kind  of climate and this environment that the birds like?  

Abidas: Well, it's all about resources availability. The  wildlife sanctuary is pretty big and there is  

just enough space for them to be able to occupy  the area.