I've been a member of Birding Aus for a couple of years, but rarely posted
anything, so this is in some respects introductory. I'm a research scientist
by training, commercial scientist by vocation, meaning that my career was
primarily in the commercial domain of companies like Bunge, Cadbury and the
sugar industry. I semi-retired 10 years ago and moved about 6 years ago to
Swanwick, near Coles Bay on Tassie's beautiful East Coast. I'd previously
lived in East Gippsland, Melbourne, Canberra, Daylesford/Ballarat, Brisbane
and Mackay (but there is no migratory pattern in that). I've birded over a
wide range in Australia, including many of the must-visit spots like Bowra,
Winton, Mt Isa, Karumba, Eungella, Barrier Reef islands, Cairns/Atherton
Tableland, Gluepot, Cocoparra, most of Tas including Eaglehawk Neck pelagics
etc. I'm not a lister, but have some enthusiasm for non-invasive wildlife
photography, including habitats. The Swan River at Swanwick forms the lower
extreme of a Ramsar wetland known generally as Moulting lagoon.
Since moving here I've become very aware of the apparent randomness of bird
migrations, with many of my observations not reproduced from year to year,
or involving few or solitary birds. A few examples:
Grey-tailed tattler: solitary bird turned up in late spring, at a place
called River and Rocks, on the Swan River estuary 1km upstream from Swanwick
township, for 3 successive years from 2009-2011; arriving variously from
late October through early December, and leaving from late February through
mid-April. Has not been seen since.
Latham's Snipe: Starting with a solitary bird in spring 2010 and reaching a
maximum of 3 birds in spring 2013, these birds occupied a small damp grassy
area adjacent the Swanwick golf course only until mid summer at the latest.
After some interference with this tiny habitat, they did not return in 2014.
Banded stilt: On one occasion only, in autumn (20/4/14), a migratory flock
of about 50 birds turned up on a shallow tidal flat upstream from Swanwick
in the Swan River. They stayed tightly packed, just resting, then flew on
overnight or early the next morning. I have not seen them since in this
location, but I have a vague recollection of someone (a non-birder) seeing
something similar in autumn this year, without precisely identifying the
Hoary-headed grebe: a large flock (about 250 birds) arrived in late July
2014. Initially very flighty, they settled into several (3-5) flocks
dispersed over a stretch of Swan River 1-2 Km upstream from Swanwick, where
they stayed until mid-September. I had not seen in earlier years, and it has
not happened this year.
Bar-tailed godwit: A small flock turn up on the Pelican roost (a tidal
sandbank opposite River and Rocks) every year, usually in October and
staying until March/April. Numbering 12-15 birds in 2009-11, only 7 arrived
last year, tending to support a pattern of decline seen more generally.
I have images of most of these if anyone wants them.
There are other examples I could give, but suffice to say I'm reaching an
obvious conclusion; that Tassie is at the migratory extreme range for a
number of species, hence the apparently random events.
On the other hand, a number of land species have patterns much more
consistent, for example, some altitudinal migrants arrive in the coastal
fringe in June/July each year and depart to higher altitude to breed in late
winter/early spring (eg Crescent honeyeaters, Golden whistlers, Bassian
thrushes). Others arrive in this area in late winter/early spring to breed
through the summer months (Spotted Pardelotes turned up on 19/8 (normal), a
Pallid cuckoo was heard on 22/8 (early by 2 weeks), but not heard since, and
a Fantail Cuckoo was heard on 25/8 (at least a week later than last year).
It has been the coldest winter for some years down here , and one could
speculate on the relative influence of climate change, local or regional
short-term climate variations, and increasing or decreasing day length as a
migratory trigger, but they are discussions for another day, and need a lot
more data than I can offer.
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