Transcript
Phil Battley
So this is D-zero, the first of the satellite-tagged birds tonight. So he's ready for release, he's strolling off down the beach towards the tide edge, then he'll take stock of his surroundings, and he'll be heading off.
David Steemson
And next stop Alaska?
Phil Battley
Yeah, in a manner of speaking.
David Steemson
Well, next stop the Yellow Sea.
Phil Battley
Yeah, next stop the bit of shelving just over the creek.
Reporter
Well, that was back in February. Our reporter David Steemson joined scientist Phil Battley and his team at Miranda in New Zealand where a group of Alaskan bar-tailed godwits were fitted with electronic tags so we could follow their migration north. At the end of March the godwits left New Zealand and flew a mere 6,000 miles to Asia. After stopping off to feed for several weeks, they left for their breeding grounds in Alaska, then at the beginning of July they moved to the Yukon Delta in South West Alaska to fuel up. Critical, because sometimes towards the end of August or early September these birds will set out on their journey south back to New Zealand and will attempt to do that with no stopover. However, after all that travelling, only one godwit is left with a transmitter which is still working, so all eyes are fixed on a bird named D8. So to find out how D8 and the other godwits are preparing for this epic journey I rang Phil Battley who began by explaining how feeding up results in both internal and external changes.
Phil Battley
Well, for a start, when they're feeding they're putting on a lot of fat so that's going to go in a thick layer under their skin, right around their body, and also inside their abdomen, so it'll pack around their internal organs, and it's going to cause the bird to get a lot heavier and, because they're heavier, then they're going to need to have bigger flight muscles and leg muscles to carry that. And they're also going to need bigger hearts to pump their blood around faster, their blood's probably going to get thicker as well, their lungs will probably get bigger, so sort of everything that's associated with exercise will get bigger in that bird, probably dramatically bigger. But the flip side of that, as we know from other birds, smaller ones called knots that have a very big stomach, a big gizzard, once they take off on a long flight things like the digestive system is just waste sort of ballast, so they may have the option of shrinking their guts down just before they leave, and saving themselves a few grams in weight along the way. We haven't had a conclusive demonstration of that in godwits but it's quite likely for a bird that flies this far that they may do something like that.
Reporter
Extraordinary changes, and physically would you be able to see that? Is there appearance change?
Phil Battley
Oh, it certainly does. Now when you see a bird that's not migrating, it's skinny, you can see lots of legs. By the time they're ready to leave, it's like a brick with wings, is one way I've had it described, so they're, you know, their backside is hanging out, their breast is bulging down towards the ground, so they are quite a different bird really.
Reporter
It doesn't really conjure up an image of a sleek, lean flying machine preparing for this journey of brick with legs.
Phil Battley
No, it doesn't really, but it's a very streamlined brick. It is a finely honed flying machine, it just happens to be a rather fat one at the time, but if you ever see a photograph of a bird flying in a wind tunnel it's a revelation. It looks like this animal is swimming underwater, its feathers are just so sleek on its body so you can take that image and put it on to this godwit, and imagine it, and you can see once they're up in the air they cut through it, you know like it's nothing, really.
Reporter
So what cues trigger that migration south? What makes them think right, now's the time to go, do we know?
Phil Battley
There is one quite strong correlate with wind as they leave Alaska and that's the presence of a large low pressure system in the sort of Northern Pacific and when they've done the modelling of the wind systems around it, it looks like they can probably get tail winds of the best part of 30 km an hour off those. Now these birds will be flying at something like 60-70 km an hour under their own steam, so a 30k tail wind is, you know, as much as half of your own airspeed so it's a real good boost. But the really amazing thing is that the juveniles, the young birds, which have never done this flight before, some of them will be ready to fly with the adults, but a whole lot of them will get left behind at the end, after the adults have gone. They will have to advance on a trans-Pacific flight of some kind, you know, without ever having done it before.
Reporter
Well, last year one bird, E7, stayed airborne for 7,150 miles, the longest non-stop flight of any bird. Energetically this is a massive challenge for a bird, so I asked Phil about the benefits of flying non-stop back to New Zealand.
Phil Battley
The benefit of it is that it gets them to New Zealand directly, it gets them here very quickly, and they don't have to go through Asia, so some of the benefits that may be there is that because they aren't stopping they're not exposing themselves to predation risk. Every time a bird goes somewhere new there could be new risks to it, or it could be that the islands that they have an option of landing on, and it's all really good for refuelling. The other thing for them is that they're likely to fly at quite high altitudes so if they come right down low, then they have to get up to altitude again and that's quite expensive for them. And also if they travel direct here then there's no risk of encountering any new parasites or pathogens, or something like that, so it seems extraordinary, but if they can do it, it seems very sensible.
Reporter
Well our own strategy seems to be quite high risk now, not because we've chosen it, but because we only have one godwit left to track. So I mean how high is the likelihood that we'll be able to follow them home, do you think?
Phil Battley
Well, it's 50/50 I'd say. If he's transmitting we will know when he arrives absolutely.
Reporter
So that is D8, you're our only hope!
Phil Battley
Exactly! Not quite... but, you know, one step better.
Reporter
Phil, thank you very much.
Phil Battley
My pleasure.