Thanks, John, for the likely explanation.
I'd still argue that even leisurely random wanderings should see them arrive
down south earlier than December. Perhaps a gradient in insect availability
i.e. later emergence down south, dictates their progress.
Michael Atzeni
> -----Original Message-----
> From: [SMTP:
> Sent: Thursday, 29 October 1998 13:08
> To:
> Subject: swift migration
>
> As to Michael Atzeni's question as to why swift migration down south is so
> unswift: I guess the reason is that this migration is a migration to
> wintering quarters, not to breeding grounds. I don;t doubt that once the
> correct date comes round the swifts start off very rapidly north for their
> breeding grounds, because they have to get there, breed, get their young
> flegded, and get away again before the next autumn. But when they're
> flying
> south it's more of leisurely wander along the Great Dividing Range, and
> the
> only incentive for them to move at all is the possibility of better
> numbers
> of insects beyond the next range, or whatever.
> Some birds are in just as much of a hurry to get south as they are to get
> north because they must moult when they get there, but I'd think that
> swifts
> must moult a few feathers at a time, and so once again there's no hurry
> for
> them.
>
> John Leonard
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