Figure 1 . Map of the surveyed nestboxes in Basildon Park House (UK) showing the main habitat types and the historical occupancy by hazel dormice M. avellanarius of 45 sampled nestboxes. Thewoodland site is on the north boundary, with the hedgelinein the South on the southern boundary, adjacent to arable land. Top left inset shows the study area location in the UK.
In 2013, 144 nestboxes were erected at two different sites within BPH: 78 were located in the woodland site and 66 in thehedgeline site (Fig. 1). Within the woodland site, mature beech (Fagus sylvatica ) is dominant in the tree canopy layer, ash (Fraxinus excelsior ) and oak (Quercus spp.) frequent, and sweet chestnut and field elm occasional. Hawthorn (C. monogyna ) and coppiced hazel (C. avellana ) are dominant in the understorey layer, with holly and young sycamore frequent, and other species such as field maple, whitebeam and rowan occasional. Bramble (Rubus fruticosus agg.) and honeysuckle (L. periclymenum ) are abundant in both the understorey and field layer. In the hedgeline site, most boxes are situated on the boundary between woodland and arable land (in 2021 the crop was rapeseed, Brassica napus ), amongst what used to be a hedge, but is now a line of mature scrub. The main tree canopy species here are oak (Quercus spp.), lime and beech which are frequent, although there are some sections where there are no canopy tree species present. In the understorey cherry plum (Prunus cerasifera ) is dominant, with spindle and young oaks occasional. The boxes within hedgeline site also extend northwards into a mature woodland, where the dominant tree canopy species are mature beech and oak, with hazel dominant in the understorey, and hawthorn and and young sycamore frequent. Bramble is dominant in the understorey and field layer species.
All nestboxes at BPH have been regularly monitored by the Berkshire Mammal Group since 2017 as part of the National Dormouse Monitoring Programme (NDMP). No monitoring occurred between 2013 and 2016. As part of the NDMP systematic survey methods, nestboxes are typically surveyed monthly (between the 15th and 25thof each month) from May-September. At BPH the Berkshire Mammal Group check the boxes up to four times a year, dependent on the availability of a licensee. Routine cleaning takes place over winter. During each survey, nestboxes are recorded as empty or occupied by hazel dormice if individual dormice are present, or there is a new nest or an old nest with signs of recent occupation e.g. faeces (Panchetti et al. 2007). Individual dormice are sexed, classified within an age class, weighed, and assessed for breeding status. Using the full survey records between 2017 and 2020 and the first season survey of 2021, we classified nestboxes as historically occupied (occupied at least once since 2017) or unoccupied (not occupied since 2017) and selected 13occupied nestboxes at the woodland site and all 8occupied nestboxes at the hedgeline site (total 21occupied nestboxes). For the woodland site we selected all boxes occupied frequently (in more than one survey) and recently (occupied at least once in the last three years). If two boxes in close proximity (<10m) met these criteria, we randomly selected one of them to avoid replicating microhabitat data. We also selected 24 historically unoccupied nestboxes (12 from each site) using the SelectRandomByPercent function in ARCGIS 10.5.1 excluding any nestboxes within 10m of selected occupied nestboxes. If two selectedunoccupied nestboxes were in close proximity (<10m) we located an alternative pair in the area at least 10m apart.