The Power of Many
As our boat rounds the bend and Tasman Island looms into view, a breathtaking swarm of birds soar around the steep, Jurassic, dolerite cliffs or swoop en frenzied masse into the ocean for food.
Thick in the sky and on the water around this oval, 1.2 square kilometer dot off the south eastern coast of Tasmania, the Short-tailed Shearwater is one of the top five most abundant seabirds in the world.
While we strive to conserve species nearing extinction at one end of a spectrum, super-abundance is a real asset to a functioning world at the other. Short-tailed Shearwater is a global super-power in its own right, a biological machine we have a lot to thank for.
Each September, like clock work, millions complete the mammoth 15,000km annual journey from Arctic Alaska to breeding colonies all over south east Australia.
Colloquiolly known as “mutton birds” (they are still caught in small numbers to eat today), most hatch their young on islands. Tasman Island caught the attention of businessman and conservationist, Rob Pennicott. Until 1977, the island was a manned lighthouse and weather station, with livestock and cats. The cats killed an estimated 50,000 birds a year for 30 years.
When Rob stepped in, the general thinking was that a bird still culled commercially for food and with numbers in the millions, wasn’t in need of saving. Rob, an avid observer of Tasmania’s wild coasts, thought otherwise.
The island is a launch pad, a place for chicks to call home, while adults ‘pop out’ south to the Antarctic seeking supplies of rich food, for a critical stage in their chicks’ development.
Fuelled by a spectacularly high-energy diet, from pole to pole, the concentrated areas where they land are thought to be among the most environmentally significant ocean ‘fertilising’ sites.
Short-tailed Shearwaters have a high energy demand which comes from frequently diving deep beneath the icy ocean surface to catch prey – constantly losing and then reconsuming heat and energy.
Their prey - krill and small squid - are the super-charged batteries of the ocean food chain, yielding hundreds times more energy, for example, than a hamburger!
Short-tailed Shearwaters eat maybe half a million tonnes of krill and fish each year - double the catch of all Australia’s fisheries combined. In calorific terms, they consume the equivalent of Australia’s total wheat consumption for only 150th of our body mass.
On the face of it, Short-tailed Shearwaters would appear to be having a huge 'impact' on our oceans but they’ve been around for millions of years longer than we have. In 1860, the human population of Australia was only a couple of million. Short-tailed Shearwaters were twenty times more abundant. Today, the numbers are about equal.
Truth is, they aren’t a competitor but are a crucial component in a natural supply chain for global fisheries. New migratory tracking data has revealed some spectularly interesting facts.
Along with a handful of other super-abundant seabirds, they flock to surprisingly small areas, the same areas essential for global ocean processes.
Short-tailed Shearwaters feed in summertime in the high Arctic off Baffin Island and in winter, off the Australian Antarctic. Both regions are mega-rich with seabirds, whales and dolphins, fish and krill.
Any nutrients at sea are absorbed almost instantaneously by a myriad of tiny animals. We can’t live on a soup of plankton and neither can many of the fish we prefer to eat. This is where seabirds come in. Their actions create conditions needed for the food chain to prosper - its like the great bakeoff on a global scale.
Seabirds constantly stir the surface, sometimes in vast densities, consuming and reactivating its ingredients. Instead of getting a mouth full of base ingredients, the end result is a fully-formed dish.
During the continually lit polar summers, nutrient-rich guano is re-absorbed by algae and recycled again at the surface, all the time refuelling the supply to other animals, generating rich fisheries and also ‘raining’ vital material into the deep ocean - this surplus is re-used later, like the ultimate in composting.
Even on the breeding islands, they are fantastically important. Though Short-tailed Shearwaters spend only a few weeks a year visiting breeding colonies, they deposit about 6,500 tonnes of guano into our coastal ecosystems. To put this in perspective, the amount of nitrogen and phosphate in their droppings is equivalent to 3.5-5% of the natural nutrient input to the entire Great Barrier Reef. Much more is spread about over their ocean foraging areas.
This nutrient recycling is a stockpile for the future, whipped up occasionally by storms and currents. It is no coincidence that the Great Ocean Conveyor, a slow-moving current that moves around the planet, surfaces in exactly the same places these birds choose to feed.
These are very important areas of 'biodiversity' where natural processes create and maintain life on Earth.
Six years ago – in concert with Tasmania’s Parks and Wildlife, the Tasmanian Coast Conservation Fund, Wildcare and Pennicott Journeys – the feral felines of Tasman Island were monitored with infrared cameras, trapped and removed. When the project started, researchers could be knee deep in dead birds. Today, the cats are gone.
Environmentalists are poor at understanding the importance of things until they are gone. This is why we tend to underestimate the significance of abundant species. It is even harder to quantify their role in the environment.
We may never know this bird’s true significance on a global scale, but each year around 50,000 visitors go to view them around Tasman Island in what Rob Pennicott hopes will be a mind changer about celebrating and preserving rather than being complacent about abundance. The island is now designated as an Important Bird Area by Birdlife International.
So, when you see these frantic little birds diving and wheeling in their millions, give them a clap for what they’ve done for us.