known for some years that birds and fish navigate across oceans and
continents by using the earth's magnetic field as a compass - it is a truly
astounding ability. However the assumption has been that the knowledge of
where to go is either imprinted at birth or the magnetic signature of home
is remembered. There was no actual learning to navigate. However what
nobody has been able to explain is how this particular compass works. Until
I must admit I had
always thought of the geomagnetic field, to give it its correct title, as
an earth based phenomena; that shows how much attention I paid to science
at school. The electrical currents created by the movement of the molten
iron in the Earth's outer core radiate out into space. Without the magnetic
field that creates deflecting the solar wind that would otherwise strip
away the ozone layer, we'd all have been fried millions of years ago. It
seems that birds are able to 'see' this magnetic field by way of a sort of
avian heads up display.
It is, inevitably, more
complicated than that but the conclusions of two separate studies in Sweden
and Germany which found evidence of an unusual eye protein called Cry4 in
European robins and zebra finches, have come to essentially the same
It seems that the Cry4
protein is sensitive to blue light and the ability to see the magnetic
field relies on being able to see the blue wavelength of light within the
field. So the protein creates a filter, or sort of gauze, over the birds'
vision which enables it to identify magnetic north and navigate
accordingly, the process enhanced by a greater production of Cry4 during
the migration period.
The scientists at the
University of Illinois at Urbana-Champaign have created a graphic that puts
it all in a bit more context; look out for the defined arc and central
black spot in the middle column of squares. Now all we need is for someone
to check out salmon eyes .......
& Son Taster Days
will see from the video we have rather a surfeit of fish in the Nether
Wallop Mill lake. I base my stocking numbers at the start of each year with
a certain attrition rate, largely reflecting otters and people. We have had
plenty of the latter but very few of the former. Sadly I think Kuschta, the
star of The Otters' Tale has
died - we have had just the one young otter who comes and goes.
So, with fish still to
catch and half term coming up I'm running a series of special Half Day
Father & Son (or grandparent/mother/daughter) Tasters. You have the
choice of a morning or afternoon session, with full instruction and tackle
The format will be based
around an hour of casting tuition for the children (under 16's please) in a
group of three whilst the parents relax. Then we'll all come together for
some bug work before everyone fishes together for the remainder of the
session, ending up with fish gutting and some fairly rudimentary fish
biology. I am hopeful everyone will have a fish to take home.
The dates are October
20, 21, 25 and 27. The sessions start at 9.30am or 2pm. The cost is £125
for a Father & Son. To book click here, firstname.lastname@example.org or
call 01264 781988.
The rain is coming
with one of my river owners last week, who also happens to have an
extensive farming operation in Berkshire, we got to talking about the
weather and rainfall in particular.
He reminded me of an
interesting statistic: whatever period you take since 1961 the southern
England rainfall each year remains remarkably consistent at around 780mm
annually. So on that basis be prepared for a wet run up to Christmas with
six months of rain due to fall in the next three.
You have been warned!
Life of a Chalkstream talk
seems like forever since I last did one of my Life of
a Chalkstream talks; it tends to be a winter
thing so I guess the clocks must be changing soon.
My first of the 'season'
so to speak will be at the Sir Harold Hillier Gardens near Romsey in
Hampshire on Wednesday November 21st 2018. Unusually this is a lunchtime
event at 12.30pm.