Thanks to Birding-Aus there is an interesting pattern emerging here. Both
Reg Clark and Graham Turner (in northern Sydney and Lower Blue Mountains
respectively) reported particularly low numbers of migrating honeyeaters
this year, while as I mentioned before, here in the upper Blue Mountains it
seems very much the opposite. At fist glance this seems to suggest that
some of the birds I am seeing this year travelled the coastal route in
previous years. However, as others have pointed out, the coastal Swamp
Mahogany is booming this year, so why would they change their route away
from the coast?
I'll throw in another theory. Perhaps the birds which travel the coastal
route, upon finding plenty of flowering, have slowed or even stopped their
migration as they linger around the concentrations of nectar. Hence the
lower numbers of migrating birds closer to the coast - they haven't needed
to move far this year. On the other hand, the birds which travel over the
mountains have not yet come across any significant flowering, so just keep
going north, hence the high numbers of migrating birds. As David suggested,
these birds may then drift eastwards to the coast after a while. If this is
the way it works then I would also expect very large numbers of migrating
birds just west of the ranges this season, as there is no flowering at the
moment in the box-ironbark belt, at least in this part of NSW.
Of course this is probably a gross over-simplification, but is borne out to
some extent by the following. Two years ago in 2000 we had a boom year for
the flowering of banksias here in the Blue Mountains. That autumn I saw
almost no migrating honeyeaters. However during that winter, the
banksia-rich heathlands here were absolutely full of honeyeaters
(Yellow-faced, White-naped and a few other species) - the largest
concentrations of wintering honeyeaters I can ever remember seeing.
I have been fascinated by the paths these birds take ever since I first
started seeing them almost 20 years ago. The birds which fly over my house
almost certainly have come up from the Jamison Valley, being funnelled up
gullies onto the escarpment and then following a creekline which forms a
north-south corridor through west Katoomba. They go almost directly due
north over my place, but the exact line of flight varies a little from day
to day, I assume due to weather conditions. It would be quite difficult to
determine the pathways of the honeyeaters before and after they fly over
the upper mountains, as there are large areas of wilderness, relatively
hard to access, to the south and the north of here.
>From reading postings on the Canberra birding list, I gather there is some
east-west movement in that area. Any comments from Canberra birders?
By the way, today is heavily overcast here at Katoomba and the migration
has slowed to a mere trickle.
Blue Mountains NSW
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