The most notable species listed is the otter which passes through the Fen and can be detected by finding otter spraint and with an infra-red camera trap, which provided this picture on Boxing Day 2018:

Small mammals are probably under recorded but we have evidence for water voles:

'His and hers' water vole droppings

Otter print

Otter spraint

Otter kit in the Itchen beside Clausentum Fen 20.45 on 22 May 2017. Thanks to Brian.

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Bank vole
Eurasian water shrew
European mole
European water vole - top middle
Otter - top right
Red fox
Roe deer - top left
Yellow-necked mouse

Stoat - 13.5.18

Brown Long Eared