My spring ritual of lying in wait at the Waterworks Reserve for the first welcome swallows to arrive has been thrown into disarray this year.
During the winter I had already seen swallows at the Queens Domain and at Howrah on the Eastern Shore.
I am not alone in my winter swallow spotting. BirdlLife Tasmania reports there have been many swallow sightings in the months when the swallows should have been in their wintering grounds on the mainland. The swallows leave in late March and return in early September.
The swallows usually travel as far north as Queensland but many have decided to brave the Tasmanian winter, finding their flying-insect food still available in sheltered, relatively warm places.
The sightings have prompted BirdLife Tasmania to dig out its records on over-wintering swallows, which date back more than a century.
The affiliate of the national ornithological organisation, BirdLife Australia, is known to have the oldest data sets on shorebird numbers in the country – going back 50 years – but the information on the swallows comes as a surprise. BirdLife Tasmania’s convener, Eric Woehler, tells me they have 900 records of sightings from 1901 to 2017, with the last three years still to be added to the database.
A table of sightings measured in 10-year increments shows a sharp rise in over-wintering swallows in the second half of the 20th century, which coincides with rising winter temperatures in the past half century. These higher temperatures would be favourable for insects, enabling them to survive the winter.
BirdLife Tasmania notes that it is ”quite likely that climate change is also contributing to the observed increase in swallow numbers, with an increase in the frequency of milder winters”.
As far as I can ascertain a member of the swallow family which also migrates to Tasmania, the tree martin, has not been seen during the winter months. The reason for this could be, despite warmer winters, the tree martin hunts insects that fly above the tree line rather than low-flying ones like the swallow, and in this air space insects might be less hardy.
My own observations indicate another harbinger of spring, striated pardalotes, have arrived earlier than usual in the past two years. By the middle of August they were already scouting nesting sites.
And anecdotal evidence suggests that greater numbers of grey fantails and silvereyes are overstaying during the winter here instead of crossing Bass Strait. It is estimated that half the population of both species choose to leave Tasmania each winter.
Confounding the trend, another migrant that is usually an extra-early arrival, the fan-tailed cuckoo, was not heard until late August. Instead swallows being my harbinger of spring, I listened for the cuckoo’s plaintive, descending song coming from the forest above my home in the Waterworks Valley.
Tasmania’s four species of cuckoo time their arrival to await the first eggs being laid in nests.
Birdlife Tasmania urges Tasmanians who watch birds to keep records and enter them in a national database at http://birdata.birdlife.org.au/