Ditching work at Holkham's marshes
Anyone
glancing over the marshes at Holkham in September and October is bound to have
seen a large yellow tracked digger. Many people stop and ask what sort of work
is it doing? The simple answer is that it is dredging the ditch systems, yet
really the answer is a lot more involved than just simply doing a bit of dredging
work. Together with a series of sluices
the ditches help us manage the water levels. For the ditches to do their job a
certain amount of maintenance has to be done regularly and this means dredging
out silty mud that accumulates and impedes the water flow. As you can imagine the wildlife of the dykes
is varied and often prolific. For that reason we try to work on a seven year
rotation so that there is plenty of time for the flora and fauna to
re-establish.
The Grey Herons of the marsh become most confiding during ditching work ever on the lookout for fish and eels.
Whilst
we do not actually drive the machines ourselves we are often at hand assisting
the driver in clearing up rubbish that has been ‘slubbed’ out or helping
replace culverts and gateways. It can be
messy work but the amount of wildlife seen can be quite astounding. The dykes
of Holkham are an incredibly important part of our ecosystem and a great
indicator of their health is the presence of Eels. They are always encouraging
to see and form an essential part of the menu of birds such as Bitterns and
Grey Herons. It is quite normal to see two or three Grey Herons or even the odd
Little Egret wandering about on the ‘slubbings’ metres away from the digger looking for rich
pickings. A good number of fish are also present, Roach in particular. We are
quite unaware at just how many we have, but suffice to say there must be plenty
judging from the concentrations we occasionally see and the constant fishing
activities witnessed by our newest residents, the Great White Egrets. They are constantly
pacing back and forth through the shallows of the dykes these days in search of
fish to eat.
The Willow Emerald Damselfly, a new species for the reserve
As
I was helping out one day this year a flash of green caught my eye on some
waterside reed. It was a small elongated yet dainty damselfly. A closer
inspection revealed it to be a Willow Emerald and a new species for the
reserve. This southern European species first colonised the Suffolk coast in
2009 and has been slowly pushing north ever since. This year has seen more than
normal numbers appear along the coast of north Norfolk
A fearsome looking Water Scorpion
Another
interesting insect seen was a Water Scorpion. This rather fierce looking insect
(unrelated to a true scorpion) has a long ‘sting’ like protuberance at its rear
end yet this is actually a respiratory tube that it holds above the water thus
allowing it to breath underwater. Instead of having claws on its front legs
like a Scorpion it actually has scythe-like front legs that are still used in a
similar fashion to catch its prey.
Water Shrew, a rarely seen inhabitant of the reserve's dykes
For
me however the most exciting find of the year was a Water Shrew. Having been a
keen naturalist for 36 years it was a species that I should have seen before
but it had always eluded me. It is also said to be a relatively common well
distributed species across the British Isles yet one that is pretty much solely
aquatic and that was my excuse for not having seen one. There have been one or
two sightings through the years on the reserve, yet never by me so when I saw a
very dark almost black shrew, I knew my luck was about to change. It proved to
be a very worthwhile learning experience. Water Shrews have Mole-like black fur
above and most have contrasting white underparts; this one however was more
dusky coloured below making it not so easy to identify. Certain features could
be seen that eliminated the more widespread Common Shrew such as its larger
size, its pale tipped ears and its hairy feet, toes and tail which have evolved
to enable it to swim through the water with ease. It could well be a common
species on the reserve or it could be a rarity, something we currently cannot
answer.
The fresh foot prints of an Otter
Another
mammal that continues to elude me on the reserve is the Otter. A regular recently
told me when he was young in the early 1950s he used to ‘bunk off’ school especially to watch a
family of Otters sliding into one of the ditches on the marsh. Following the
species nationwide demise due to the use of organo-chloride pesticides running
off into river systems it took until after the new millennium for Otters to
return to Holkham. Since 2012 we know through finding foot prints that the
species is now present again, but being mostly nocturnal it remains very
difficult to see. I think I must now be the only member of staff who works on
the reserve who has yet to see an Otter here, but I’m sure that time will come
soon. Another reason they are so difficult to see is the sheer distance they
travel. Between Wells and Burnham Norton the reserve’s three main areas of
grazing marshes are an intricate wetland of cattle grazed fields that are all bordered
and inter connected by a series of fresh water dykes and ‘drains’. This again brings us back to the management of the reserve and the reasons for dyke dredging. The basic
system works like this; water accumulates, be it rain water or from in-field
springs and drains into the dykes which then ultimately flow out through the
fields to the sea. Some are old ‘foot’ drains used from the 1700s onwards when
the fields (formerly brackish and salt marshes) were drained so that the arable
crops could be grown. We are able to control this flow due to a series of dams
and sluices that allows us to either hold back and retain water (giving us
wetter fields) or release it (thus drying areas out).
Andy
Bloomfield
Warden