Hi all
Recent discussions on birding aus about the Forest Wagtail being possibly a
reverse migrant yet again got me thinking about this.
Do we really get reverse migration in Australia?
I’m not sure to be honest and just putting it out there but there are some
points that don’t really add up.
I guess reverse migration is often used as a term in Europe where there is a
lot of evidence to support this. So if they have it there why shouldn’t we?
Europe’s location is the most important thing. Its North of the vagrants
breeding grounds.
I guess the starting point of a reverse migrant depends on the species in
question. But to simplify things let’s say it’s a Yellow-browed Warbler. They
are vagrants in the UK but getting more numerous.
Yellow-browed Warblers breed in various places in Asia but let’s say our
warbler breeds in Mongolia.
The chick is raised and if it’s got reverse migration then instead of heading
down to the Malaysian peninsular taking a SE track it takes a NW track and ends
up in Europe. Some of these birds certainly would die during the harsh winter
but some clearly survive and in some species it is thought that they survive
and breed the following season eg back in Mongolia and their offspring may even
travel back to Europe and hence why some species that were super rare 20-30
years ago are now much more common in Europe.
Back to our Yellow-browed Warbler. He/she hangs out in Europe in some nice not
so cold climate and when the time comes heads back to the breeding grounds to
breed. Raises young and repeats.
This is reverse migration as its heading in the complete opposite direction of
where it should have been going eg NW instead of SE.
So how do we explain our Forest Wagtail. If it was raised in say northern China
and had a problem with reverse migration should it not have headed North
instead of South after it was born? Maybe our Forest Wagtail did but then
shouldn’t it now be heading further south back to the breeding grounds?
So that’s the bit I don’t understand if it’s a reverse migrant and its headed
south to Alice then where did it go after it was born? If it’s a reverse
migrant then why has it not gone back to the breeding grounds after going
North?
I hope this makes sense but to me the concept of reverse migration may work in
Europe it doesn’t seem to work for Australia.
It would make sense if it were a species that bred in Malaysia and in March
April headed north to take advantage of the Arctic summer but instead headed
south to Australia.
Why is the Wagtail not just a bird that overshot its wintering grounds in
Southern Asia in Sept Oct. (lots of birds do this) It could have been in
Adelaide the whole summer ( maybe in Tony Russel’s garden) and is or was
heading north and stopped in Alice and ended up in not its ideal habitat and
has decided to not head north this summer to breed.
Maybe it will head North but it is cutting it a bit fine. The latest personal
migration I have seen was Red Knots on the 13th of May several years ago out of
Broome.
Yellow Wagtails tend to leave Broome very late April or early May.
I’m no expert on this. It’s just my thoughts and look forward to someone coming
up with a possible explanation for me.
Maybe this is what all the OBP’s are doing and instead of heading north to the
mainland and are instead heading south and dying in Antarctica. (joking)
Cheers Adrian Boyle
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