Listening to a boobook owl calling from the forest above my home in the Waterworks Valley during the spring I didn’t realise at the time this very bird could have just arrived from the mainland.
What’s more, it could have flown a remarkable 250 kilometres non-stop across Bass Strait.
Although members of the owl family have never been known for regular migratory journeys, the boobook of Tasmania is shedding new light on owl flight paths.
A recent research involving satellite tracking has confirmed our boobook are Australia’s only migratory owls, taking their place alongside the world’s only migratory parrots – the swift, orange-bellied and blue-winged which breed in Tasmania before heading to the mainland in winter.
Two researchers tracked the migration paths of Tasmanian boobooks as they crossed from Victoria to Tasmania. They found the Tasmanian boobook was indeed a regular migrant across Bass Strait. Rather than island-hopping, these small owls completed the flight in a single night non-stop.
Tasmanian boobooks are common across the state and some birders once considered them an endemic species, separate from the mainland ones.
Over time, the Tasmanian ones with specific markings were spotted periodically in Victoria and elsewhere. In recent years, a more consistent pattern was revealed when keen birdwatchers discovered small numbers of boobooks perched on Cape Liptrap, south-east of Melbourne, in spring. Could these birds actually be migrants about to make the Bass Strait crossing after spending winter on the mainland?
With thermal cameras, special nets, and lightweight miniature GPS-tracking devices in hand, researchers Jessica Wei Zhou and Rohan Clarke travelled to the south-eastern coast to catch five boobooks at headlands.
Once they had attached the tracking devices, the scientists could follow the owls’ movements for up to three weeks before the tags failed and were dislodged.
Every year, tens of thousands of land birds of at least 25 species make the long flight across Bass Strait. The boobook is what’s known as a “partial migrant” like a few other migratory species which means while some birds migrate, many other individuals remain in Tasmania year-round.
With its high winds and rough seas, crossing Bass Strait is no small feat for these migrants. Migration is stressful for birds, as they encounter inhospitable environments, predators, and weather changes while expending peak energy.
But how exactly do these birds traverse this daunting stretch of ocean? Understanding this is more crucial than ever. New developments proposed in Bass Strait, particularly offshore wind farms, may introduce challenges for migrating birds, many flying by night. And until now, no one has looked closely at the pathways of these migrants, many of them tiny like silvereyes and fantails.
The insights gained by PhD student Wei Zhou and Associate Professor Clarke may help us protect migratory birds in a rapidly changing world which threatens their very existence.