Alaskan Bar-Tailed Godwits just look like an ordinary shorebird. Recent research however has discovered that these waders are the new world record holders for non-stop flight. Every autumn, these extreme migrators fly an astonishing 11.000km from Alaska to New Zealand without any stopovers to rest or refuel. This roughly doubles the previous maximum known non-stop distance for migratory birds.
The non-stop flight of the godwit’s is even more impressive if one takes into account that the current world-record for a manmade flying device is 82 hours, less than half that of the godwits.
Gill and colleagues (2009) used satellite telemetry to track 23 birds on their trip across the pacific. By this relatively new technique in which the position of each individual bird is sent to a satellite every six hours, the authors found out the birds need on average 8 days to make the crossing.
These extraordinary non-stop flights establish new extremes for the flight performance of birds. There are birds however with even longer migrations than that of the Alaska Bar-Tailed Godwit. For example the pectoral sandpiper which flies 16000km with at least one break in between, and the impressive 24000km northbound spring migration of the arctic tern. The difference is that these birds have the opportunity to feed and rest at sea as they go and thus do not need to fly non-stop.
So how are these birds able to fly non-stop for 8 days across the pacific? Professor Hedenström assessed the unbelievable aerial feat in a interesting paper published in PLoS Biology this spring. He calculated that the birds only use some 0.41% of their body mass per hour which is the lowest value thus far for any powered animal flight. This is important because the godwits have to take just as much on board before departure to sustain them for the 8 day flight. Furthermore, it is important the birds have exactly the right body weight to size and have an aerodynamic body shape. Very crucial for the godwit’s journey is their high flight speed which makes them relatively immune for crosswinds.
Gill and colleagues propose that the reason why these birds travel along this transoceanic route because it may function as a safe corridor, providing a wind-assisted passage relatively free of hungry predators and harmful pathogens.
The amazing feat of the bar-tailed godwit leaves us with many new questions. How can the birds orientate while flying over the vast stretches of ocean? How do they manage to exert such high levels of exercise for such an amount of time? And how do they deal with dehydration and sleep deprivation? This is a good example again of how new scientific discoveries will often lead to even more unsolved questions. That’s the beauty of science.Gill, R., Tibbitts, T., Douglas, D., Handel, C., Mulcahy, D., Gottschalck, J., Warnock, N., McCaffery, B., Battley, P., & Piersma, T. (2009). Extreme endurance flights by landbirds crossing the Pacific Ocean: ecological corridor rather than barrier? Proceedings of the Royal Society B: Biological Sciences, 276 (1656), 447-457 DOI: 10.1098/rspb.2008.1142
Hedenström, A. (2010). Extreme Endurance Migration: What Is the Limit to Non-Stop Flight? PLoS Biology, 8 (5) DOI: 10.1371/journal.pbio.1000362