Before the invention of fossil-fuel-driven engines human beings were mostly sedentary creatures. My grandfather barely left the Cotswold valley where his ancestors had lived for generations. In stark contrast there are animals a fraction of our size that undertake the most incredible journeys each year. These are the world’s authentic wanderers. The Bar-tailed Godwit’s epic migration is on a bewildering scale. Despite weighing only 300g its home range is a quarter of the planet. Each year it travels over 10,000 km and does this in a single flight.
One-stop flights across the Pacific Ocean
Ten years ago shorebird researchers in New Zealand put satellite trackers on Bar-tailed Godwits [1] and worked out that they fly in a circuit around the Pacific between breeding and wintering grounds. Ongoing work by one of the paper’s authors, Adrian Riegen and the Miranda Shorebird Centre allows us to watch these flights in almost real time.
One individual labelled ‘4BBRW’ holds the record for a single one-hop flight from Alaska to Tweed Heads, Australia, in September 2021. A distance of 13,050km, which was done in a little over ten days. By the 16th September 2022 they were half way back to their non-breeding grounds in New Zealand.
Source of images: Miranda Shorebird Centre Facebook page.
To prepare for such a flight Bar-tailed Godwits alter themselves physically. Not only do they put on a huge amount of body fat (which accounts for 55% of their weight) but to accomodate this, they shrink their ‘gizzards, livers, kidneys, and guts’ [2]. Only those organs essential for long-distance flight are maintained. Then they ‘rebuild these organs upon arrival at the migratory destination.’
They use a mental-map for navigation which almost certainly includes star-charts and beak-compasses. The birds don’t so much ‘read’ these as ‘know’ where to go, as these are migrations that have co-evolved with the continents over many thousands of years. This, as I will explain later, is an insight into to their planetary importance.
How is something so implausible even possible?
The movement of abundant animals across planet Earth are based on behaviours developed over time-scales longer than any of us can imagine. Like rivers, animals carve out ecosystems and create their own habitat. In the case of the Bar-tailed Godwits, they have been nurturing wetland ecosystemsHow ecosystems function An ecosystem is a community of lifeforms that interact in such an optimal way that how ecosystems function best, is when all components (including humans and other animals) can persist and live alongside each other for the longest time possible. Ecosystems are fuelled by the energy created by plants (primary producers) that convert the Sun's heat energy More since the last ice-ageA period of reduction in Earth’s temperature of between about 4–7 degrees that resulted in the rapid expansion of ice sheets and glaciation of much of the Earth’s surface. More. Ten thousand years ago Bar-tailed Godwits were already achieving mind-boggling journeys further than any human can imagine even today. Since the beginning of evolution their ancestors have been learning to do similar things.
Something so unlikely-seeming to us cannot have evolved unless it was vitally important to the world’s ecosystems
They don’t ‘choose’ to migrate, ‘follow’ a celestial map or ‘decide’ where to feed. The birds follow patterns of movement engrained into a culture that evolved with the ecosystems they inhabit today. They are as much part of our landscape as a rock that sits in a riverbed. Unlike rocks and plants though, they can move and this makes them key to a stable and habitable planet.
Why can we assume this importance? For starters, because something so implausible, couldn’t exist if it wasn’t incredibly important. Nature is unforgiving and unyielding. Only the likeliest to survive got to make it into the world we see today. Something so unlikely-seeming to us cannot have evolved unless it was vitally important to the world’s ecosystems.
An incalculable impact on global water
From fledging to death every individual bird is connecting countless times every day with ecosystem processes. Bar-tailed Godwits literally build and maintain the processes that keep coastal estuaries functioning. Without them we would lose our coastline and with it, our own livelihoods.
‘Very little, if any, work has been done on the value of shorebirds to nutrientA substance that contains the raw materials for life. At a chemical level, these are contained inside compounds that are absorbed into the body and essential energy-containing molecules are extracted, so that energy can be transformed into other chemical processes that use the energy for living. More flow in estuaries, or on their importance in amplifying and transporting nutrientsEnergy and nutrients are the same thing. Plants capture energy from the Sun and store it in chemicals, via the process of photosynthesis. The excess greenery and waste that plants create, contain chemicals that animals can eat, in order to build their own bodies and reproduce. When a chemical is used this way, we call it a nutrient. As we More between tides. Each bird, all day, is consuming, moving and re-depositing waste into the system, and they migrate on an enormous global scale as well.
Simon Mustoe, ‘Wildlife in the Balance’.
The function(Of an ecosystem). A subset of ecosystem processes and structures, where the ecosystem does something that provides an ecosystem service of value to people. More they perform has been repeated millions of times over millions of hectares, over tens of thousands of years and longer. The birds cover vast distances and each season, concentrate their activities on wetlands of international importance: ecosystems recognised because they create life-supporting global water resources essential to human life.
If we lose birds like Bar-tailed Godwits, we not only lose a key factor in building a habitable planet, we also lose the ability to understand this. Animals are our only hope of knowing how ecosystems work. Without them ecological science is blind.
Small birds with huge animal impact
It only takes small numbers of animals to have enormous and positive impacts on the environment. For instance, twelve thousand years ago, the human population was only about four million yet we’d already modified 95% of the world’s land surface.
The global population of Bar-tailed Godwits today, is estimated as just over one million birds, a figure that may have declined by at least half since the 1980s.
Humans are not more (or indeed less) significant than any other animal.
The extraordinary feats that Bar-tailed Godwits undertake each year are a reminder that all animals are part of ecosystem-stabilisation machinery that keeps Earth habitable for all animals, including us. When we collectively get this right, it makes a stable climate. This is when the energy that ‘fuels’ these processes is used most efficiently. It is consumed into rich food chains rather than spilling out and polluting the places we live.
Bar-tailed Godwits have done their part by becoming one of many notable species on Earth that amplifyAmplification (of nutrients and energy). Animals consume plants and other animals and in doing so, reintroduce important energy-containing nutrients back into the environment, at even higher concentrations and in patches. Amplification of energy is driven by migration and happens at every scale, from insects moving daily in and out of your vegetable patch, to African wildebeest herds and the seasonal More, concentrate and transfer(of nutrients) the thing that sets animals apart from plants, is that they can move. Some of the biggest migrations on Earth every day, are the movement of insects like caterpillars, from the stem of a plant to a leaf and back, before turning into butterflies and transferring the energy elsewhere. Large-scale migration of grazing animals and migratory songbirds moves More nutrients on an epic scale. The abundance of they and their kind has made it possible for humans to feed themselves and created a habitable climate for the development of our civilisation.
Compared to most animals modern human civilisation’s connection to country is for the briefest of time. Lest we forget, we have animals to remind us. Because it’s their relentless and indefatigable routines for millions of years that led to our success today.
To see this we need look no further than amazing birds like Bar-tailed Godwits that visit our own neighbourhoods each year.
References
- Battley, Phil & Warnock, Nils & Tibbitts, T. & Gill, Jr, Robert & Piersma, Theunis & Hassell, Chris & Douglas, David & Mulcahy, Daniel & Gartrell, Brett & Schuckard, Rob & Melville, David & Riegen, Adrian. (2012). Contrasting extreme long-distance migration patterns in Bar-tailed Godwits Limosa lapponica. Journal of Avian Biology. 43. 10.1111/j.1600-048X.2011.05473.x.
- Piersma, Theunis & And, Tm & Gill, Jr, Robert. (1998). Guts Don’t Fly: Small Digestive Organs in Obese Bar-Tailed Godwits. The Auk. 115. 196-203. 10.2307/4089124.
