This post is scheduled to go online while I am flying over the Pacific Ocean from New Zealand to Los Angeles. It is a journey of 10,500 kilometers (6,500 miles) and about 12 hours. That’s a long flight, although short of the record held by Qantas for the route from Sydney to Dallas, a distance of 13,880 km (8,500 miles) which takes 15 h 25 min by a Boeing 747-400.
Until fairly recently it was hard to imagine an airplane conveying more than 500 people so far in a single hop. Although marvels of engineering, modern aircraft are still nothing like as breathtaking as the tiny fliers created by nature.
A few weeks after I leave Auckland, thousands of bar-tailed godwits will be taking off from New Zealand for their breeding grounds near the Arctic Circle. They will stop once around the Yellow Sea to refuel on seafood for putting on fat for the second leg of the journey. Soon after their family duties in Alaska are over they will complete the circle by returning to New Zealand. No other creature migrates as far or faster or without stopping than godwits on their flight south.
These are wading birds weighing a little over 500 g (1 lb). You may see them probing mudflats on stilt-like legs with long bills that look as if they were dipped in black ink. Like long distance aircraft, including 747’s, godwits have large wings for their bulk.
During a long flight their brain shuts down one side at a time to ‘sleep,’ rather like a co-pilot taking turns at the controls of a jet to give the captain a break. And like a long-haul jet they pile fuel onboard with voracious appetites before setting off. Half their body weight is burned off on the trans-Pacific route, so they arrive at their destination with ‘tanks’ almost empty. Flying economy is critical for a bird that can’t stop to feed while crossing the Pacific, but at altitudes of 3-4 km they find favorable winds to save energy.
It is just as important for birds to avoid getting lost as for aircraft. Godwits fix their course from the sun, analyzing polarized light on cloudy days, and navigating by the stars at night. Crossing from northern to southern skies doesn’t confuse them. We might fly round in circles without our instruments.
The migration routes and stopping places of godwits have been mapped by fitting them with feather-weight satellite telemeters on their backs. One of them, a female code-named E7, was tracked for nearly 30,000 km over six months. After waiting for a tailwind E7 departed Alaska on August 30 and arrived in New Zealand only 8 days later having traveled 11,700 km (7,270 miles) at average speeds of 50-60 km/ hour. She stayed there with 100,000 others throughout the warm southern spring and summer.
The same bird began her return journey to Alaska on March 17 of the following year. She arrived in China 7 days later after flying 10,300 km (6,400 miles). Six weeks later she was on her way again and arrived in Alaska on May 8 after a 6 day flight of 6,500 km (4,040 miles). Instead of collapsing with exhaustion and jet-lag as we might after a long journey, godwits are soon busy dating because raising a family in the short breeding season mustn’t be delayed.
While I waited in Auckland for my flight I was musing which of us was the more economical traveler, energy-wise. Would it be the small bundle of fat and feathers or a passenger squeezed between others in a fuselage? I made some rough calculations on the back of an envelope (quite literally), to confirm my suspicions.
Birds and airplanes burn different types of fuel but their calorific values can be compared. Assuming the same as human adipose tissue, godwit fat has an energy value of 30 MJ/ kg. This is not so very different to jet fuel at 46 MJ/ kg.
If E7 lost half her weight on her longest journey by burning most of her fat, say 300 g, she would have consumed 9,000 KJ.
A Boeing 747 burning 70,000 kg of jet fuel on my route to L.A. consumes 3,220,000,000 KJ. This is a rate of 20 liters or 5 gallons per mile, but much more at take-off.
This titanic energy looks more moderate when you divide it by the number of passengers onboard which is, conservatively, 500. Then it drops to 6,440,000 KJ per person. Although this still seems enormous, jets are in fact more economical with fuel for transporting a passenger than an automobile over the same distance (unless the car is fully-occupied when they are about the same).
But it still isn’t a fair comparison because an average passenger like myself weighs 70 kg (~160 lb), equivalent to about 150 birds. So, last of all, I divided energy by body weight to find—
godwits consume 460 J (1,900 cal) per kilogram per kilometer traveled,
whereas I burn 9,000 J (157,000 cal) for the same weight and distance.
We travel by airplane only 5% as efficiently as godwits. I never expected to outdo a bird that has perfected its flying machine over eons of natural selection. Feathers motored by muscles will always beat alloy propelled by aviation fuel, but what we lose in economy we gain in speed. Icarus take note.
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