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
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
Bats:
Pipistrelle
Daubenton's
Noctule
Brown Long Eared