How do they do it?

Dr Phil Battley, from Massey University, describes what godwits have and do to be able to make the long flight.

Transcript

Dr Phil Battley

It’s interesting godwits manage to make the biggest flight of any bird in the world, but when we look at them, it doesn’t seem like they do anything particular that’s different, but they just do everything very well.

Structurally, they’ve got the same sort of wing shape that a lot of long-distance migrants do – they’ve got quite a pointed wing with a reasonably long outer wing, and that’s really good for fast efficient flight. We know it’s quite fast because the satellite-tracking data tells us how far they’ve gone and how long it took them, so we know that they fly at around about 60 kilometres an hour.

But it’s no good flying quickly if you run out of fuel. The main fuel that these birds use is fat, so they put a big layer of fat on underneath the skin around the whole body and inside the abdomen, so all around their intestines, and their stomach, their gizzard, their heart is just packed with fat, so a godwit about to leave on migration is one of the fattest animals in the world. They can be 40 or 50% fat – in fact, they’re the fattest birds on record.

But it’s not the only energy that’s used. They also break down some of the muscle proteins in their flight muscles and their leg muscles so they leave with enough fat but they also have to have enough muscle tissue in their bodies to be able to keep their chemical cycles going as well. The other thing is, when a bird takes off, it’s twice as heavy as it was earlier in the season, so it’s a lot harder for that bird to fly so their exercise organs – the flight muscles and the lungs and the heart – all have to be up-tuned as well.

So they’ve increased the size of their muscles before leaving. As they fly and get lighter, they don’t need those muscles to be as big, so they can afford to let those get smaller as well. So it’s quite a complex set of changes going on inside the body at that time.

Acknowledgements:
Adrian Retigan
Pete & Judy Morrin Productions
Pennycuick, C. J. and Battley, P. F. (2003), Burning the engine: a time-marching computation of fat and protein consumption in a 5420-km non-stop flight by great knots, Calidris tenuirostris. Oikos, 103: 323–332. doi: 10.1034/j.1600-0706.2003.12124.x
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