Imagine completing a long-haul flight to the other side of the world and returning to find you have lost your home. Jet-lagged and exhausted, you have nowhere to sleep or rustle up a meal.
This is the reality for increasing numbers of migratory birds who arrive at their breeding grounds to find them destroyed by agricultural, industrial and housing development or pollution. Hazards from human development also mean many birds are killed in collisions with buildings and powerlines or dazzled and drawn off-track by light pollution. Others are killed by hunters.
Climate change is also expected to impact migratory birds’ survival over coming decades. The timing of migratory journeys is critical. Changing seasons means that some species are migrating earlier and arriving before food is available.
Australian birdwatchers turn their attention to these migrants at this time of year when our inter-continental shorebirds return from the northern hemisphere.
A vast range of shorebirds undertake migratory journeys, including such well-travelled species as the bar-tailed godwit which, incredibly, can fly non-stop from Alaska to New Zealand in as little as 11 days. As I write, it is arriving on the mudflats of Sorell.
Bird migration is a huge feat of endurance requiring immense strength and stamina and comes with a real risk of death along the way. So, it begs the question of why birds brave these epic journeys, and how do they know when or where to travel?
This question has been a source of fascination for centuries and has inspired some wild theories, including the notion that birds migrate to the moon and back each year. While past theories are creative and entertaining, scientists now have a much better understanding of bird migration.
Birds rely on habitat that provides enough food to nest and raise chicks, but as habitat, food availability, and weather change with the seasons, birds must move from place to place to survive and thrive. A bird’s urge to migrate is hormonal, with the change in natural sunlight triggering hormones that make them become restless, gather in flocks, and eat more food to stock up for the long journey ahead.
Once ready to set off, the journey typically takes birds south for the winter where food is more abundant, then north to breed in the spring.
Migratory birds don’t embark on these journeys at random, they follow set routes that provide places to rest and refuel along the way. Many species share similar routes, or flyways, which essentially resemble super-highways across the sky.
Tasmania sits at the end of East Asian-Australasian Flyway and when we see the first of the arrivals at the end of August it is hard to imagine that many waders have stated their incredible journey from within the Arctic Circle.
The epic migratory feats of the waders were celebrated across the world on Friday, September 6 – World Shorebird Day.