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Key facts

  • 40% - percentage increase in bodymass that the Godwit goes through before migration
  • 26 hours - time the Pronghorn Antelope can run non-stop for

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The 2008 Beijing Olympics was a display of humankind in peak condition, excelling in many athletic events with a performance that most of us dare not even dream of. This in itself is an interesting statement. Why is it we’re not always capable of peak performance?

In the world of animal migration every individual who embarks on a great journey is a peak performer: a long distance flyer, swimmer, runner, walker. Within the population of a species that migrates there are not many couch-lizards. If there were stay-at-home sorts presumably they wouldn’t reap the benefits of a successful migration.

What are the tweaks in body build and function that allow the athletic stamina that is migration?

Fuel Use

Let’s take the greatest non stop migrant of all – the Alaskan Bar-tailed Godwit. This medium sized bird migrates from New Zealand to Alaska flying over the Pacific on a remarkable 11,000km journey. Outbound it stops once, inbound to NZ it flies non stop. Take a breath.

This bird is a wader and feeds on invertebrates which provide it with fat and protein.

The available fuel in its various fuel tanks are: Fat deposited in its body cavity and around its organs; Protein in the form of flight and other muscle – And the protein that make up its body organs (heart, intestine, liver etc) - And sugars in the form of glycogen stored in the muscle tissues and in the blood.

The clever trick employed by the Godwit is how it uses its on board fuel and how much of its engine and body it’s prepared to burn to complete this marathon flight.

Here goes:After a successful breeding season in Alaska it feeds veraciously on the abundant insects on the tundra and increases it’s body mass by about 40%.

This automatically makes it different to us. Imagine yourself as a 100kg individual, and you deliberately put on 40kg with every expectation you will lose it!

With its wings having to support this extra weight, the flight muscle is also increased to power the wings to get the Godwit airborne. So it’s altogether a beefier, bigger bird.

It’s guts are also swollen and large because it has been feeding so much to get this fuel on board and to build the muscle.

On migration the Godwit burns the storied glycogen in the blood and muscle quickly, probably small number of hours into the flight. The bird then switches to fat, it’s main fuel for the journey.

As the fat is consumed (and fat yields the most energy per g in weight) so the Godwit gets lighter. As it gets lighter it needs less power from it’s flight muscles, so it has the nifty trick of switching to both fat and protein as fuel. By doing this it conserves fat and reduces the muscle/engine mass to maintain exactly the right power to continue the journey (the adaptive significance here being, why have a huge engine if you don’t need the power).

During this time of burning its power house, so the bird migration physiology taps into other protein reserves. It begins to digest the guts, reducing this non-vital organ at the same time as reducing the engine.

The Godwit continues the journey on fat and protein taking each down in a steady ratio.

And so successful is this bird at doing this, not only is it capable of reaching its destination 11,000km away non stop, it has about 1000km of reserve in case it's blown off course.

The bird arrives in NZ which no recognisable gut, highly reduced flight muscles, minimal blood volume and just traces of fat remaining – flying like a fluttering butterfly.

Tweaks in the Anatomy

If you are in Europe you can hold two Robins in your hand. We’ll call one Robin the UK Robin, the other the Euro Robin.

The UK Robin is a stay-at-home sort, residing in gardens, parks and woodland glades and barely dispersing beyond them. The Euro Robin is much the same, excepts migrates to sub-Saharan Africa each winter.

In your hand these two Robins would look the same, weigh much the same and when flying look the same in the air. Yet one flits from garden to garden, the other able to sustain a 6000km migration.

What is the difference between them?

Part of the answer lies in the composition of their muscle, especially the little minute objects called mitochondria. Mitochondria are “organelles” of a cell that convert sugars to energy. The metabolic spark. With the Robin, it’s quite simple: the Euro Robin has many ore of these mitochondria.

And there’s more:

In North America there is an antelope that migrates across the northern forested states and grasslands. The Pronghorn. The impressive observation of this animal is it can run for 26 hours, with out stopping, and not get tired!


The answer here is small tweaks in all of its “systems”. This is not body building – this is not getting unnecessary musculature. Its heart is slightly bigger than an antelope of a similar size, it’s muscles have slightly more fibres and mitochondria than other antelope, it’s lungs are slightly larger and so on. Small changes in capacity and efficiency give the Proghorn an athleticism beyond comparison.

Over the year we’ll discover more and more about the special ability of migrating animals to put on weight and lose weight and turn on their peak performance.

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