DOI: 10.5061/dryad.brv15dvbc
title: What makes a good bat box? How box occupancy depends on box characteristics and landscape-level variables

description: Bat populations are in steep decline and presently, 16% of all species are
 classified as “threatened”. One main driver identified for this decline is
 the loss of natural roosting opportunities, caused by the removal of
 natural habitats. Installation of bat boxes is one solution to compensate
 for the lack of natural roosting opportunities. Current recommendations
 for box design emphasize low maintenance costs and are rarely based on
 empirical evidence. We investigated occupancy of 13634 bat boxes in
 northern Bavaria, Germany. In our study boxes differed in type, age and
 mounting height, as well as in maximum community age, i.e. the length of
 time a group of boxes had been installed in a particular place, the size
 of box groups and the distance to the next box in the surrounding area,
 i.e. box isolation. Our results showed that box occupancy depended on box
 type and bat species. As a case study, we analysed the two most common
 species found within the investigated boxes, Pipistrellus pipistrellus and
 Myotis nattereri, in more detail. Both species showed preference to a
 voluminous box that had a narrow entrance (“Gable box” 14 mm). For P.
 pipistrellus, only box type affected occupancy, whereas for M. nattereri,
 the relationship between box type and box age were important. Older boxes,
 and boxes in areas with higher maximum community age of boxes showed
 higher box occupancy by bats. Box occupancy decreased with the distance
 between adjacent box groups (“box isolation”). High mounting height showed
 a tendency for increased box occupancy, but the effect was only weakly
 significant.
description: During 2017, 13634 boxes
 were surveyed by volunteers that acted independently of one another. There
 was no systematic sampling design, volunteers were asked to check boxes at
 least once between June and October, on a cold day to avoid bat fly out
 and locally asynchronous to avoid double counting. For every box, northing, easting,
 elevation, calendar week of the check, box type, mounting height and age
 was recorded. A box was considered occupied when a bat was present or when
 indirect evidence of bat box use was obtained. Also, other species groups
 were recorded. Landscape-level variables included the land cover around
 the box, and the spatial placement of boxes and were calculated with
 ArcGIS version 10.4.1. The data 13634 included 26 box
 types of varying ages and mounting heights. Boxes older than 16 years were
 dominated by one box type, mostly installed at a height of 1–1.5m and up
 to 100m to its nearest neighbour. Boxes installed later were predominantly
 placed at a height of 3–4m, in groups of 4–8 boxes. In addition, boxes
 within the same area often were of the same box type and age. Due to this
 unbalanced data structure, we decided to focus on three woodcrete box
 types: Gable box, Colony box and Flat box, where each had more than 1000
 replicates in areas where they occurred together resulting in our dataset
 "1_box occupancy.txt". To test for consistency of model
 results, we ran the identical model setup for four other
 subsets: <strong>only adult
 bats:</strong> We excluded boxes with only indirect evidence of bat
 occupancy and boxes with nursery groups. <strong>nursery
 groups:</strong> We excluded boxes with only indirect evidence of
 bat occupancy and boxes with only adult bats. <strong>Pipistrellus
 pipistrellus:</strong> We only considered areas where P.
 pipistrellus and M. nattereri occurred together. Boxes with indirect
 evidence of bat occupancy or boxes with unidentified individuals were
 excluded. Multiple species boxes that were occupied by species other than
 P. pipistrellus were removed from the dataset. <strong>Myotis
 nattereri:</strong> We only considered areas where P. pipistrellus
 and M. nattereri occurred together. Boxes with indirect evidence of bat
 occupancy or boxes with unidentified individuals were excluded. Multiple
 species boxes that were occupied by species other than M. nattereri were
 removed from the dataset.