"J.Poyner" wrote in message
...
Thought this group might be interested to know that over the past few
days
there has been an unprecedented arrival in the south of the UK of some
summer migrants...House Martins, Swallows Sand Martins and also
continental
butterfly species.
All these bird species usually winter around the Saharan region though
a few
may stay further north, but usually don't start to appear for at least
another month to six weeks time.
Being quite interested in the effects of weather on bird migration I
wondered if any of the experts may be able to point out any possible
meteorological causes of this highly unusual activity?
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?

J Poyner.

.... we had a spell, roughly from the 2nd to 5th (February), when the
airflow in the lowest couple of thousand of feet was from the area of
the Azores (2nd), thereafter from Madiera and the Canaries or further
south - presumably there has been some mechanism to encourage migrants
out of the Saharan interior (see other thread on dust injection), and
they have been encouraged to come north-northeast on the warm, often
brisk flow. Hence the high temperatures noted earlier in the week and
the consistent warmth so far: anomaly +7degC at a conservative estimate
until the last couple of days. Yesterday and today must have been a
shock though - always a problem at this time of year: notably mild
weather cannot be relied upon, and we are about to experience a return
of somewhat more traditional February weather (frost).

Norman Elkins (who I worked with for a brief time at Lossiemouth), wrote
a book on the subject of Weather and Bird Migration - I believe it is
still regarded as a solid reference for the subject: don't know if it is
still available though.

Martin.


--
FAQ & Glossary for uk.sci.weather at:-
http://homepage.ntlworld.com/booty.weather/uswfaqfr.htm