Thursday, 9 February 2017

Walthamstow Mammals

Working minutes away from the marshes means that you can sometimes spend mornings, lunches or afternoons observing and recording the mammals present there.

The tools of the trade: A Longworth Small Mammal Trap (with shrew hole) and other small mammal recording bits and bobs.

Most of the time, upon returning to the trap (having been left overnight), it looks like the above – trap door shut! Meaning something’s tripped it. Occasionally, it’s empty (bar a few tiny poops) – because a shrew has gone in through the tunnel, tripped the trap, munched some bait and departed through the shrew hole.

[if you leave a trap for longer than four hours, your trap must have a shrew hole as their metabolism is so high that if they don’t eat every four hours, they die]

But mainly, the trap has been getting these guys.

The (very common) Wood Mouse

When your trap’s been tripped:

Empty the trap into a deep bag (those fellas can jump).

 Measure some mice bits with a ruler.

Take out the bedding.

Weigh the bag + Wood Mouse, then weigh bag - the mouse and do a bit of math.

Snip a bit of hair off its haunches, so you don’t record it twice should you catch the same one later.

 Record its sex. In this case a male.


Then release the mammal (and note the record on GiGL).

And then reset the trap.

Lots of Wood Mice (an abundant UK mammal) have spent the night in the trap, but not a sniff of Field Vole or Bank Vole yet. Shrews are for another day. And Weasels are too quick for the camera so far.

So, on the marshes there is an unsurprisingly large amount of one of the UK’s most abundant mammals, the Wood Mouse. What is slightly ironic (as nothing in between seems to have materialised yet) is the much more significant presence of THE most endangered mammal species in the UK - the Water Vole.

Nearly 90% have disappeared in the last seven years, mainly due to habitat loss and predation from the American Mink.


But a very small population has been hanging in there on the marshes over the years.


This one’s a big adult. Only one has been sighted this year so far. Most of the time this is all the vole will let you see of it before it plops back under the water. 

This could be a Water Vole’s burrow entrance, but having observed the behaviour of the present vole, it’s more probable that the vole’s burrow entrances are under the bank.

The site is now being recorded in the People’s Trust for Endangered Species (PTES) National Water Vole Monitoring Programme.

If you read this and see Water Voles at any place or time on Walthamstow Marshes, please drop a quick email to

Finally, if you care, please heed the (small) signs. Keep your dogs out of the ditches …

 … and try not to throw your rubbish in the ditch.

 Not good for Water Voles.

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