Check out this annual commute, suffered by that long-distance migrating champion, the Bar Tailed Godwit (Limosa lapponica). As reported on the Asia-Pacific Shorebird Network, one of these Godwits has just been observed making a non-stop flight of 11,570 Km from Alaska to New Zealand. The female known only as E7 (the name is Godwit; Bar-tailed Godwit… etc.) flew for 8 days and 12 hours clear across the Pacific (not even stopping at Hawaii or Fiji en route!) before arriving, on September 7, close to where she was tagged last February at Piako in New Zealand. This is one of the coolest results of new satellite tracking technology that is allowing such extreme flights to be monitored. You can even watch the whole flight path on your computer if you have Google Earth – just download the kmz file for an interactive version of the image below.
The kmz file has data from all birds followed in this project, allowing you to trace movements of individual birds, and isolate ones of interest, as I did above. You will also be able to follow future movements (e.g., see how and when the other birds make it down to NZ) as long as the transmitters are active, and someone is updating the database online.
Until now, the evidence that these birds actually flew back across the Pacific non-stop was indirect and circumstantial (Gill et al 2005). As described in that paper, it took much greater detective work to follow the trails of these birds, piecing together information on when and where different kinds of godwits had been seen, comparing occurrences in spring vs. autumn, and using flight simulation models to estimate if they could do such long-distance flights. And their conclusion was that the birds hewed closer to shore during spring (northern hemisphere spring), stopping to refuel at various depots along the way, but took a direct route across the Pacific in autumn (northern). Well, we can put all the detective tools and models aside and celebrate their accuracy in predicting what we now know: at least this one female (E7) actually did it last week, flying solo across the length of the Pacific – even weighed down with a satellite transmitter! I wonder how much faster it would have been if it didn’t have that added load – but we can’t know that! I wish I could track the movements of my beloved little Phylloscopus Leaf Warblers – but that may never happen without much greater miniaturization, perhaps even some nano-technology (like something out of Star Trek), I’m afraid, given that those birds themselves weigh between 7-13 grams.
The Bar-Tailed Godwits, meanwhile, have also been the subject of some really cool research (see Landis-Ciannelli et al 2003) on how their bodies can take the punishment of such extreme flights. It turns out that the internal organs of these birds (and probably most long-distance migrants) are much more flexible that one might imagine: they are literally able to re-arrange their tissues to prepare for and sustain the long flights. And the tissue-reorganization is quite dynamic. First, the digestive organs (stomach, liver, kidneys, intestines) show considerable growth (hypertrophy) either before autumn migration, or more quickly, at stopovers en-route during spring migration (why do they stop during spring, but not autumn?), which makes sense as they need to load up on fuel for the flight. But its not just fuel they are adding for the next phase, for in addition to extreme fat loads, they also bulk up their flight muscles, which reach peak mass just before departure. Meanwhile, as fuel reserves and muscles build up, the intestines shrink, atrophying to minimal levels, presumably reducing extra baggage for these long flights: these birds are literally jettisoning (or rather repackaging) as much cargo as they can, from everything except the engines (flight muscles) and fuel tank (fat reserves)! How cool is that! Talk about breaking your tooth-brush in half to cut down your backpack weight for a long climb…
A consequence of losing all that gut mass is that, upon arrival (either at refueling stops or eventual destinations) these birds are not only exhausted, but they even lack the capacity to eat and digest a proper meal. They first have to re-grow those intestines to be able to process any food they might find. So, if you live along coasts where migrants routinely make landfall after long oceanic flights, and come across exhausted birds landing in unlikely places (e.g., hummingbirds at off-shore oil-rigs in the Gulf of Mexico; Indian Pittas turning up in the middle of Bombay), and want to rescue them, perhaps you should pause before trying to (force-)feed the birds, for they may not have the ability to digest any food at all. And it can take 24 hours or more for the guts to regrow, as tissue is being reallocated from elsewhere (muscles?) to intestines. Which may be why these birds appear particularly vulnerable at that stage.
And what about that question I raised earlier: why do these Godwits make stops during spring, but not autumn migration? I think it has to do with their need to be the first ones on the breeding grounds to maximize breeding success, and uncertainty about conditions on the northern breeding grounds: it pays to get to the breeding grounds early enough, but not too soon, if you know what I mean. In addition, spring migration is all about breeding, another energetically demanding act, for which you have to have some reserves available; in autumn on the other hand, all you have to do is to get to the wintering ground with the arctic cold chasing yout tail, and focus on staying alive through the next few months for another shot at the reproductive lottery. This sets up different selection pressures on the two migratory phases, resulting in different strategies. It also sets up differences between males and females: in spring, it is usually the males who are in a greater hurry to get up and establish breeding territories before females show up; females (like E7), on the other hand, need to conserve more resources to cover their higher energetic/nutritional demands. And ongoing work should help us test and understand some of these ideas better.
Meanwhile, I’ll think twice before complaining about the stiffness of my body when I fly across the Pacific en-route to India next time.