Although summer is in full swing, the swamp harriers are already leading the way for the myriad Tasmanian nesting species that spent their winter on the mainland.
My correspondents in country districts are reporting a steady movement of the elegant raptors towards Bass Strait.
The harriers are the first to leave, leading another early departure, the satin flycatcher, before the other migratory species follow suit as autumn bites.
I love to watch the low-flying harriers quartering open paddock and marsh but I do not often get to see them because my patch in Dynnyrne on the lower slopes of kunanyi/Mt Wellington does not provide suitable habitat for them.
To observe the harriers I usually drive to the upper Derwent beyond Bridgewater where I never have trouble finding them. Murphys Flats is a particularly productive site.
In late winter the harriers are the first migrants to arrive, and the first to leave as early as late January. They time their southward flight to coincide with the masked lapwing breeding season and that of waterfowl. The harriers are our only egg-eating raptor and they fly slowly just above the ground, hoping to surprise birds and also small mammals. It is such a slow flight that at times, as they tilt their wings, they look as though they will stall and fall to the ground.
The harriers have super-low wing loading – the ratio of weight to wingspan – and another feature that makes them deadly to their prey is the harrier’s long springy legs which lets them take off vertically. They gave their name to the Harrier jump jet.
In flight the harrier is easily identified among other raptors which look brownish in flight by a white patch on its rump.
Raptor expert Nick Mooney contacted me earlier this month to report large numbers of “swampies” moving north, a little earlier than usual.
Mooney, of the Birdlife Australia Raptor Group, said the harriers arrive and leave in waves, behaviour probably related to favourable weather fronts helping them along.
“They must be very finely tuned to weather patterns and likely changes,” he said. They appeared to bunch up along the Bass Strait coast waiting for favourable winds. “They are strong, steady flyers but not fast so a tail wind would really help them,” Mooney said.
Most appeared to cross through the Hunter group of islands at the north-west tip of mainland Tasmania. Young harriers, which follow the adults north after they have fledged, fly as far as the woodlands of the Gulf of Carpentaria in the far north of Australia, returning in a couple of years after they reach adulthood.
Looking at his records, Mooney said there was no evidence breeding had been earlier over the breeding season and no apparent reason for the early departure.
“They must know something we don’t,” he said.