Re: migration

Dear Ray /Simon

I read with interest your items on the Painted Lady migration. I live in
North Norfolk but originally come from Sussex and retain an interest in the
county's natural history (hence follow Adastra). East Anglia saw a massive
movement of Painted Lady butterflies and one idea for their movement within
the UK was that they were following rivers to make their way inland.
Impressive numbers were recorded in the city of Norwich flying along King
Street close to and parallel with the River Wensum and I had massive numbers
through my garden (up to 20 per minute) close to the river valley some 25
miles upstream and flying precisely parallel with the river. They were not
noted further away from the river in this part of North Norfolk and
generally had an uneven distribution - hence the thoughts about rivers as a
navigation aid. It would be interesting to know if their distribution in
Sussex had any sort of pattern.

Best
Mike


 
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Today's Topics:

   1. Re: PL Migration (Ray Hamblett)


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Message: 1
Date: Fri, 29 May 2009 18:25:11 +0100
From: Ray Hamblett <ray.hamblett@...>
Subject: Re: [Adastra] PL Migration
To: Adastra discussion group <adastra@...>
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thank you simon.Your thoughts are welcome and have helped.
I wonder  is their any evidence of them using earth's magnetic fields ?
Any thoughts anyone...

Ray

:)


2009/5/29 Simon Davey <srdavey@...>

>  Dear Ray
>
> The main reasons, as I understand it for dramatic migrations of the sort
we
> are now experiencing with Painted Ladies are.
>
> 1. That the population density where the insects hatched goes over a
> certain level. This causes the insects to disperse as in migratory
locusts.
>
> 2. That the prevailing weather conditions are such as to carry insects
that
> have been effected by an over crowding signal to move in a direction, in
> this case northwards. I did in fact one year, see a Painted Lady that had
> gone all the way to Iceland where there are no native butterflies of any
> kind.
>
> 3. There are a few insects, such as the Monarch Butterfly that have a
built
> in need to migrate at certain times of the year. This does not appear to
be
> such a regular phenomenon in the Old World.
>
> The butterflies arriving in the UK will breed until weather conditions in
> the late autumn, or early winter become sufficiently adverse to make
further
> breeding impossible, and the population will diminish to the normal levels
> that exist here. In the case of Clouded Yellows, which may well exhibit
> similar behaviour this year, conditions become so unfavourable that the
> population disappears altogether, though I have heard rumours of a very
few
> surviving our winter. I guess global warming may help.
>
> In the autumn, several American birds make it across the Atlantic carried
> by strong weather systems that push them off their usual migration routes.
> Although they cause great excitement amongst the birding world, they are
> mostly lost, and will never find their way back to their breeding grounds.
> Some bird groups, notably waders do appear to have a worldwide
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