What makes a good bat box? How box occupancy depends on box characteristics and landscape?level variables

1. Aktuell werden 16% aller Fledermausarten als „gefährdet“ eingestuft und Fledermauspopulationen sind weltweit von einem starken Rückgang betroffen. Ein Hauptgrund dafür ist der Mangel an natürlichen Quartieren in den heutigen intensiv genutzten Wirtschaftswäldern, welchen Baumhöhlen -spalten selten sind. Häufig daher Fledermauskästen angebracht, um zu kompensieren. Empfehlungen für die Anbringung Wahl bestimmter Kastentypen basieren meist auf Anschaffungs- bzw. Wartungskosten eher empirischen Untersuchungen Präferenzen Fledermausarten. 2. Wir untersuchten Fledermausbelegung insgesamt 13 634 Kästen Nordbayern, daraus sowie deren optimalen Anbringungsort ableiten können. Die unterschieden sich Typ, Alter Anbringungshöhe. Auch Kastentradition (Zeitraum, seit welchem eine Kastengruppe vor Ort ist), Größe Abstand weiteren Kastengruppen variierten. 3. Am häufigsten nutzten Zwerg- Fransenfledermäuse Kästen. Beide Arten bevorzugten Bayerischen Giebelkasten mit einer schmaler Einflugöffnung 14 mm. Für Zwergfledermaus war allein Kastentyp entscheidend, während bei Fransenfledermaus Abhängigkeit vom Kastenalter wichtig war. Insgesamt wurden ältere Gebieten längerer enger Nachbarschaft Fledermäusen genutzt. Anbringungshöhe hatte zwar einen leicht positiven Einfluss Kastenbelegung, Effekt jedoch nur schwach signifikant. 4. Aufgrund Untersuchung belegten artspezifischen Kombination verschiedener Kastentypen, welche mindestens (14 mm) beinhaltet, empfehlen. besten eignen Kleingruppen 3–4 kurzen Distanzen benachbarten Nähe bestehender Kastentradition. According to the IUCN Red List (IUCN, 2020), nearly of all bat species are classified as ‘threatened’. Bats Europe contribute strongly worldwide decline (Mickleburgh et al., 2002). One main drivers this is loss natural habitats and decrease roosting opportunities (Davidson-Watts 2006; Mickleburgh Woodlands provide habitat, foraging roost sites for more than 50% (Boughey 2011; Kunz & Lumsden, 2003). Tree cavities utmost importance bats they offer protection from weather daytime predation, space mating social interaction sanctuary maternity groups hibernation (Altringham, Kalcounis-Ruppell 2005; The presence cavity trees may be even important food availability (Crampton Barclay, 1998) thus assumed a limiting factor (Pereira 2016). Trees offering declining (Lindenmayer Laurance, 2017). Especially Europe, extensive deforestation fragmentation has been ongoing several centuries (Voigt Kingston, In state Bavaria Germany alone, 48% 25 native listed ‘endangered’ (three ‘critically endangered’, five four ‘vulnerable’), but two show long-term trends (Landesamt Umwelt, All insectivorous about thirds use tree hollows or roosting. Ten Bavarian form forest colony groups, some species, example Nyctalus noctula, also hibernate (Dietz Kiefer, 2016; Landesamt Thus, finding solutions increase aim conservation. many regions world, including Bavaria, boxes installed mimic cavities, often compensation measures roosts (Ciechanowski, Meddings 2011). However, effectiveness conservation tools controversial. On one hand, because it rarely used by nursery can ecological traps, increasing risk overheating (Crawford O'Keefe, 2021), there general agreement that cannot fully compensate (Chambers 2002; Griffiths 2017; Zahn Hammer, other reported useful tool (Flaquer 2006). Bat help efforts through easier collection data on local assemblages, better accessible Flaquer There need research how employ programs, maximize positive effects employing boxes. Few studies test suitability different box designs species-specific preferences (Mering Chambers, 2014; Rueegger 2019). huge variety designs, consisting types: flat designed replicate naturally occurring crevices, narrow gaps behind patches bark Rueegger, 2017), voluminous mimicking woodpecker-like nesting holes (Boye, 2005). Entrances vary shape, oval, flat, round diameter. Self-cleaning with open bottom avoid dropping accumulation hence, have minimal maintenance costs low potential disturbance occupants compared closed (Dodds Bilston, 2013; Mering 2014). It recommended self-cleaning types reduce parasite disease multiplication less minimize competition nontarget (Rueegger, therefore identify design features improve occupancy distinguish between superfluous obligatory details. factors besides influence success. indication higher positioned roosts, hence mounting height, occupied frequently (Ruczy?ski Bogdanowicz, 2005), although few exist statistically evaluated artificial As require time become occupied, positively correlated age Likewise, influenced density, nearby Conservation practices recommend installing new near pre-existing allow switching interactions individuals (Fukui 2010; Some high managed areas 2006), indicating environment which plays role. To occupancy, suggested both characteristics placement should adjusted landscape composition Most studies, however, only address (Kerth 2001) neglect account Box differs increases height age. when occur close another, placed where already cover around box. Our study aimed appropriate placements. Based our results, we developed specific recommendations promote populations. were collected project ‘Bats forests northern Bavaria’ 2020) Upper Palatinate district. They financed commissioned BaySF (‘Bavarian forestry’), LWF State Institute Forestry’) ‘Coordination Office Protection Northern Bavaria’. For details permits, see original publication website Government 2020). Palatine rural area comprises proportion (pine dominated) cover. characterized continental climate (mean annual temperatures 4.1–8.5°C rainfall 653–1121 L/m2 per year) ranges 340 800 m altitude. put up communal, private state-owned (74% coniferous 21% types; Figure 1a) (GeoBasis-DE/BKG, installations result single projects, earliest started late 1990s. These included projects initiatives stabilize populations volunteers governmental (e.g. Forestry Administration) nature organizations. distribution maps bats, 16 found within 2021). During 2017, 13,634 surveyed acted independently another. was no systematic sampling design; asked check at least once June October, cold day fly out locally asynchronous double counting. This survey 26 varying ages heights (Table SA1); these, 40.35% 12 SA2). Boxes older years dominated type, Gable Box, mostly 1–1.5 100 its nearest neighbour. later predominantly m, eight addition, same type Due unbalanced structure, decided focus three woodcrete box, Colony Flat each had 1000 replicates occurred together (1933, 1675 1614, respectively, total 5222; 1b). self-cleaning, rough inside surfaces, droppings detected side walls (estimated R. Leitl). non-self-cleaning, accumulate floor. Around 89.58% 10 boxes, 5.36% 11–44 5.32% pairs rest singles. A considered present indirect evidence obtained, pupae since last cleaning year before. Therefore, inspection flaps opened. without flap, flashlight shine gap If possible, identified evidence, noctula distinctive smell produces large droppings. When present, identified, juvenile noted roost. non-bat recorded. every northing, easting, elevation calendar week Mounting summarized categories, 2, 2.5, 3, 3.5, 4 >4 above ground. into (0 years: early 1 year: 2 2015, 3 5 mounted 2011–2013; 9 2006–2010) combination visual documentation, exact lacking prior 2014. Landscape-level variables land spatial We inspected radius km extracted following available CORINE Land Cover 10-ha resolution 2016): forest, deciduous mixed wetlands, arable land, grassland/pastures, city/traffic, industry types. water bodies known affect occurrence Kirkpatrick intended include analysis, wetlands made 1% smaller not set. Distance body recorded field did analysis. defined group 50-m size number group. measure vicinity calculated isolation distance neighbouring another (in metre) whether neighbour (0/1). Lastly, described community calculating mean maximum 1-km target calculation landscape-level variables, considered, represent surroundings subset 5222 Analyses carried using RStudio, version 4.0.3 (R Core Team, collinearity, first analysed covariation nine performed principal component analysis (PCA) revealed axes represented respectively (Figure SA1; Table SA3), non-forest excluded. correlation matrix SA2) factorial dimension set removing between-variable correlations non-informative variables. Variables coefficient r > 0.7 removed. final follows: radius, size, isolation, height. elevation, group, covariates possible temporal effects. Calendar if resulted likelihood recording occupancy. model (n = 5222), response variable ‘box occupancy’ (sighting occupancy). explanatory follows—the continuous variables: week, percentage cover; binary variable: groups. addition effects, model. size’ ‘maximum boxes’ added model, success seems likely Second, isolation’ ‘occupancy box’ thought decreases, surroundings. Lastly three-way describing characteristics: level box), full description statistical Appendix SA. consistency ran identical setup excluded (‘Box adult bats’ n 3884). Considering properties reproduction (Kunz 2003), third groups’ 3361). modelling case P. pipistrellus M. nattereri, (29 areas). unidentified Multiple nattereri removed prevent unintentional biasing species’) contained 2049 records 1910 nattereri. separate run species. total, models based subsets built generalized linear binomial error distributions 2017 Model diagnostics done plotting residuals against predicted plotSimulateResiduals testOutliers function (DHARMa package [Hartig, 2019]). R2 rsq (rsq [Zhang, 2018]). simplification remove non-significant significant term, starting highest order interaction. Graphs generated fitted values models. Effects their upper lower 95% confidence intervals (effects [Fox, 2003]), while holding constant. Post hoc tests glht (multcomp [Torsten 2008]). post terms, emmeans (emmeans [Lenth, log-transformations leverage issues. Out set, 38.40% 1). age, cover, status 2). significant, highly significant. types, increased 2.6 times 9-year-old newly 2; 2a). showed second lowest weakest ages. insignificant tendency 2b). significantly overall occupancy: depending 2c). one, almost tripled seven still effect weakening 18 change slope anymore further relation isolation. vacant, trend 2d). Higher doubled SB5a). longitude, latitude Figures SB1a SB3a). twice occupancies minimum altitude (343 masl) (715 masl; SB2a). though 10.32% nests 1), reduced SB4a), 23.42% exclusively (Aculeata, birds small mammals; 12.77% results (excluding groups) largely consistent exception weakly Here, 1.5 SB1; SB8b). these Similar steepest weak respect Increasing decreased occupied. opposite true SB7b). SB6b). SB5b) similar SB1b–SB4b). Nursery 2.76% except myotis pipistrellus, documented spite removal those returned SB1). steeper 3a). Occupancy 3b) 3c) SB6c), SB6c). contrast groups; SB7c). Forest SB5c) easting SB1c–SB4c). Overall, detected. Pipistrellus most abundant followed daubentonii 4a) SB8d). fewer older; half SB6d). well like SB5d SB7d). tested seen SB1d–SB4d). (a 10-fold increase; 4b). No any SB5e) Myotis north having ones SB1e–SB4e). characteristic here bats. degrees, type. ‘all species’, ‘only bats’, partly affected (especially boxes) bats’. larger weaker models, limitations data, lack acoustic monitoring, unable examine assemblage properly common remains unclear detection certain due absence area, unsuitable designs. likely, rates Barbastella barbastellus, bechsteinii, brandtii, leisleri pygmaeus rather rarity/endangerment category instead poor design. average (38.40%) roosts: Czech Republic (Lu?an 2009), English al. (2011) (individuals evidence) exceed 30%. Chytil (2014) 40%. studies. Within evaluated, documented. forested represents occur. season possible. checks conducted days flying and, day, occupying vicinity, would Juvenile migrating complement summer (Baranauskas, Dodds 2013), explain detectability study. study, cleaned before inspection, allowing bat's during droppings), check. Droppings sides (self-cleaning night, night. probability might bottom), direct (overall model) evidence. trends, rate play minor role reasonable minimizes Future means detection, infrared endoscope cameras, able disturbing face challenge