Variable/scale Definition
Above nestbox scale Above nestbox scale
Tree canopy closure
Total percentage of tree canopy and understorey vegetation cover above the focal nestbox estimated as the average cover from two measurements in May and July (to account for seasonal variability in leaf growth). Cover was defined as the percentage of black pixels in processed photos taken with an Apple iPhone 11 levelled-flat on a tripod set at 1 metre from the ground and as close to the nestbox as possible without including the box in the photo. Original photos were desaturated to grayscale with the colour curve adjusted to make all pixels either black or white using GIMP 2.10.24.
5m radius
Tree canopy cover Percentage of the tree canopy (in 10% increments) occupied by trees of the same species taller than 4 m within a 5m radius circular area around the focal nestbox. 10 separate variables for each identified species: Ash Fraxinus excelsior, Beech Fagus sylvatica, Field Elm Ulmus minor, Field Maple Acer campestre, Holly Ilex aquifolium, Lime Tilia x europaea, Oak Quercus spp., Sweet Chestnut Castanea sativa, Sycamore Acer pseudoplatanus, Yew Taxus baccata.
Understorey cover Percentage of the canopy (in 10% increments) occupied by trees of the same species smaller than 4 m within a 5m radius circular area around the focal nestbox. 19 separate variables for each identified species: Alder buckthorn Frangula alnus, Ash Fraxinus excelsior, Beech Fagus sylvatica, Blackthorn Prunus spinosa, Cherry Plum Prunus cerasifera, Elder Sambucus nigra, Field Elm Ulmus minor, Field Maple Acer campestre, Hawthorn ‎Crataegus monogyna, Holly Ilex aquifolium, Lime Tilia x europaea, Oak Quercus spp., Rowan Sorbus aucuparia, Spindle Euonymus europaeus, Sycamore Acer pseudoplatanus, Wayfaring Tree Viburnum lantana, Whitebeam Sorbus aria, Wild Cherry Prunus avium, Hazel Corylus avellana.
Field layer cover Percentage of the field layer (in 10% increments) occupied by plants of the same species within a 5m radius circular area around the focal nestbox. Climbing species cover was estimated up to a height of 10 m. 16 separate variables for each identified species or group: Bluebells Hyacinthoides non-scripta, Bramble Rubus fruticosus agg., Cleavers Galium aparine, Cow Parsley Anthriscus sylvestris, Dogs Mercury Mercurialis perennis, Ground Ivy Glechoma hederaceae, Hedge Woundwort Stachys sylvatica¸ Speedwell Veronica spp., Herb Robert Geranium robertianum, Honeysuckle Lonicera pericylmenum, Lords and Ladies Arum maculatum, Meadow Buttercup Ranunculus acris, Nettles Urtica dioica, Yellow Archangel Lamiastrum galeobdolon, Fern (group, not identified to species)”, Grass (graminoid group, not identified to species).
Ground cover Percentage of the ground (in 10% increments) occupied by bryophytes within a 5m radius circular area around the focal nestbox. [Data were also collected for cover of fungi, leaf litter and bare ground too but due to low variability among sites were not considered in the analyses].
Quadrat
Quadrat cover Mean percentage cover of individual species over four 2m x 5m quadrats starting 5 m from the focal nestbox and running North, South, East and West. 2 separate variables for each key species identified: Bramble Rubus fruticosus agg. and Honeysuckle Lolium periclymenum.
5 m + quadrat
Tree abundance Relative abundance of individual tree species within a 10m radius from the focal nestbox. Obtained by adding the total number of individual trees with a trunk circumference >40cm within a 5m radius circular area and in four 2m x 5m quadrats starting 5 m from the focal nestbox and running North, South, East and West. Abundance within the 5m radius area included every individual tree, whilst the four quadrats provided relative abundance within the area 5m-10m from the nestbox based on quadrat totals. 20 separate variables for each identified species: Ash Fraxinus excelsior, Beech Fagus sylvatica, Blackthorn Prunus spinosa., Cherry Plum Prunus cerasifera, Elder Sambucus nigra, Field Elm Ulmus minor, Field Maple Acer campestre, Guelder Rose Viburnum opulus, Hawthorn ‎Crataegus monogyna, Hazel Corylus avellana, Holly Ilex aquifolium, Lime Tilia x europaea, Oak Quercus spp., Plum Prunus domestica, Spindle Euonymus europaeus, Sweet Chestnut Castanea sativa, Sycamore Acer pseudoplatanus, Wayfaring Tree Viburnum lantana, Wild Cherry Prunus avium, Yew Taxus baccata.
Total trees
Combined relative tree abundance. Sum of “Tree abundance” for all 20 recorded species at each nestbox.
Tree richness
Observed tree species richness calculated adding all species with “Tree abundance”>0 for each nestbox.
Local (GIS)
Distance to nearest footpath
Distance in metres from focal nestbox to the nearest footpath. Collected via GPS with minimum 3m accuracy and mapped using ARCGIS
Distance to nearest nestbox
Distance in metres from focal nestbox to the nearest nestbox. Collected via GPS with minimum 3m accuracy and mapped using ARCGIS
Distance to nearest woodland margin
Distance in metres from focal nestbox to the nearest woodland margin. Collected via GPS with minimum 3m accuracy and mapped using ARCGIS