Introduction
The distribution and status of Yellow-necked Mouse Apodemus flavicollis in Norfolk is uncertain. It has traditionally been reported from the southeast of the county, particularly in a triangle between Norwich, Diss and Haddiscoe where it would appear to be relatively widespread. In recent times, records from the northeast Brecks have extended its known range in the county westwards. More intriguingly, there are isolated records from the north coast and the Broads, well outside of the core range in the southern half of the county with a further isolated record at Haveringland, north of Norwich.

In Great Britain, Yellow-necked Mouse is mainly associated with mature deciduous woodland, particularly those wooded areas that are long established/ancient and areas with higher summer temperatures, possibly linked to better tree seed production (Marsh 2001). Less favoured habitats include coniferous woodland, mature gardens, hedges, heathland and occasionally reeds and wet woodland.
Throughout much of its GB range, it is typically infrequent in woodland small-mammal communities throughout much of its range but, at times, it can be more abundant than Wood Mice Apodemus sylvaticus.

Methods
My study is an ongoing small mammal-trapping project to further assess the status of Yellow-necked Mouse (as well as other small mammal species) in Norfolk. The intention is to carry out relatively large scale trapping surveys in at least one woodland site in all 10km tetrads that are wholly or partly located in the county. Due to the apparent habitat preferences of Yellow-necked Mouse in Britain, I have tried to focus on ancient broad-leaved or replanted ancient broad-leaved woodland where possible (identified on magic.gov.uk). A number of tetrads do not hold such habitats and also, access was not possible to certain woods. In such circumstances, I have identified non-ancient broad-leaved (or mixed) woodland in which to survey. Between December 2012 and June 2016 I completed mammal trapping at a total of 23 sites.

To complement this status update, the Norfolk Biodiversity Information Service (NBIS) have supplied me with all records of Yellow-necked Mice that they hold on their database.

Results

To date, I have found Yellow-necked Mouse at three new sites (Table 1):

• Lower Wood NWT, Ashwellthorpe – two adults on 30th January 2014 (but none caught during second trapping session here on 30th September 2014).
• Keswick Church – two adults on two dates (30th September 2014 and 1st June 2016).
• Dreadnought, Croxton – single adult on 9th June 2015.

Both Keswick Church and Lower Wood, Ashwellthorpe are within the previously known range, while the Croxton record extends the known range c10km to the southwest.

Table 1. Small mammal trapping survey results December 2012 – June 2016

Site (AW, AWRe, NAB, NAM) Date/s Trap nights YnM Other species
Bacton Wood (NAM) 09/12/2012 28/01/2014 130 WM. BV
Potter’s Grove, East Ruston (NAB) 05/03/2014 60 WM
Attleborough Wood, Fiddler’s Green (AW + AWRe) 28/11/2012 70 WM, BV
Foxley Wood (AW + AWRe) 31/01/2013 60
Haveringland Hall Park – Great Wood (AW + AWRe) 14/12/2012 70 WM
Hevingham Wood, Stratton Strawless (AWRe) 04/12/2012 70 WM, BV
Honeypot Wood, Wendling (AW + AWRe) 16/02/2013 60 WM, BV
Lower Wood, Ashwellthorpe (AW + AWRe) 30/01/2014 30/09/2014 150 2 WM, BV
Swanton Novers Little Wood (AW + AWRe) 05/09/2014 60 WM
Thursford Woods (AW) 02/02/2014 60 WM, BV
Keswick Church (NAM) 30/09/2014 01/06/2016 20 4 WM, CS
Zigzag Covert, Mundford (NAM) 15/02/2014 60 WM, BV
Groundsel Wood, Wymondham (AW + AWRe) 13/03/2014 62 WM
Birch Wood, Eastmoor (AW) 24/03/2014 61 WM
Lion Wood, Thorpe Hamlet (AW) 25/03/2014 30 WM
Sporle Wood (AWRe) 10/09/2014 60 WM, BV
Syderstone Common (AWRe) 15/03/2015 30   WM
Waveney Forest (NAM) 15/02/2015 10 WM
Chedgrave (NAB) 03/05/2015 10 HM, HoM
Dreadnought, Croxton (NAM) 09/06/2015 22 1 WM
Muckleburgh Hill (NAB) 22/06/2015 22 WM
Bottom Field Belt, Kilverstone (NAM) 10/06/2015 22 WM
Coll’s Plantation, Hickling Broad (NAB) 14/07/2015 22 WM

Key:
Sites: AW – Ancient woodland; AWRe – Ancient woodland replanted; NAB – non-ancient woodland broadleaf; NAM – non-ancient mixed woodland

Species: YnM – Yellow-necked Mouse; WM – Wood Mouse; BV – Bank Vole; HM – Harvest Mouse; HoM – House Mouse

Discussion
My results so far have extended the known range of this species in the southwest of Norfolk with the record from Croxton, and consolidated its core range with records from Lower Wood and Keswick Church.
Yellow-necked Mouse is considered likely to occur across the southern half of the county, although perhaps not extending west into the Fens beyond the Brecks. Given the paucity of records between Norwich and the north coast, records of this species from Cley-next-the-Sea, Kelling and Weybourne are considered likely to have emanated from an apparent illegal release of the species at West Runton around 40 years ago (Keith Zealand, National Trust pers comm.). Records of this species at Catfield (2002), Burnham Deepdale (1988) and a single unverified, non-submitted record from Roydon Common c2005 (Ashley Murray, Natural England pers comm.) (not included on map) are intriguing and extend the potential range of this species considerably in several directions. Further small mammal survey work would help confirm the species range in these areas.

Richard Moores, BiOME Consulting

Email: richard@biomeconsulting.com

References
• Marsh, A.C.W (et al). (2001). The Yellow-necked Mouse Apodemus flavicollis in Britain: status and analysis of factors affecting distribution. Mammal Review, 31: 203-237.
• Harris, S. & Yalden, D.W (eds) (2008). Mammals of the British Isles: Handbook 4th Edition. The Mammal Society
• Norfolk and Norwich Naturalists Society. Norfolk Bird and Mammal Reports 1993-present).

The above article has been reproduced from the ‘Norfolk Bird and Mammal Report 2015’. Many thanks to the Norfolk and Norwich Naturalist’ Society for allowing this.