"Mike Tullett" wrote in message
...
On Sun, 8 Feb 2004 20:32:01 -0000, J.Poyner wrote in

snip
It is quite common in Spring for a wave of migrants to arrive with a
push of
warm air from Europe and Africa, but this early in the year is highly
unusual.
Any thoughts?

As Martin has written, the winds for some days early in the month may well
have encouraged them, but I still find this most fascinating. I know next
to nothing about such migration, but would reckon it must be very early
indeed. I imagine the mild conditions further south in recent weeks may
be
a another factor in encouraging this early move north.

It does look as if, at least for western areas, there will be a renewed
flow of warm air from the SSW. It will be most interesting to hear if
more
arrive and just how far north they get. I don't normally see any of the
swallow family here until well into April. I'll be on the lookout.

--
Mike 55.13°N 6.69°W Coleraine posted to uk.sci.weather 08/02/2004
21:35:38 UTC

Most of these birds wintering in northern Africa would have begun to
gradually push north by now slowly, so does seem that some have been caught
up in these winds and made a very fast track.
It isn't unheard of for the odd one to turn up by February as some may spend
the winter around the Med region. However the influx over this week-end is
pretty unusual with flocks of up to 9 House Martins seen. Reports have come
from Scilly across to Sussex.
It suggests that warm air from the African continent may well be pushing
further north earlier than in the past....taking insects with it and thus
the birds? Insectivorous aerial species such as Swallows being a pretty good
indicator as they rely on quite subtle temperature changes in order for
enough food to be present in the air. In spring their migration is often
"blocked" by cold fronts as happened last March around Spain.
Likewise during April/May arrival waves often occur with warm fronts moving
north from the continent.
One other related point of interest is that this winter has seen record
numbers of "overwintering" insectivorous passerines such as Chiffchaff in
the south. There have obviously been enough frost free days on average for
them to survive so they have not been forced to move further south to France
and Spain as they would have done in the past. As with most animals they
take the easiest option...why waste energy and risk a potentially dangerous
sea crossing when you can stay put.

Thanks for all the very useful contributions.

JP