Biologia 65/6: 1072—1080, 2010 Section Zoology DOI: 10.2478/s11756-010-0124-5

Variability of foraging and roosting activities in adult females of Daubenton’s (Myotis daubentonii) in different seasons

Radek K. Lučan1,2 &JanRadil3

1Department of Zoology, Faculty of Science, Charles University, Viničná 7,CZ-12844 Prague, Czech Republic; e-mail: [email protected] 2Department of Zoology, Faculty of Biological Sciences, University of South Bohemia, České Budějovice, Czech Republic 3Department of Ecology, Faculty of Environmental Sciences, Czech University of Life Sciences, Prague, Czech Republic

Abstract: We radio-tracked fifteen reproductive females (5 pregnant, 5 lactating, 5 in post-lactation) of the Daubenton’s bat in summer 2005 in order to reveal the effect of reproductive state on their foraging and roosting activity. Spatial activity of females decreased from pregnancy to lactation and increased again in the post-lactation period. Overall time spent foraging did not differ among the three study periods. However, while pregnant and lactating females spent similar proportion of the night length foraging, females in the post-lactation period were foraging for shorter part of night. The frequency of nightly visits to roosts was highest during lactation but there was a trend towards shortening of particular visits during that period. All but one roost were in tree hollows excavated by woodpeckers in spatially restricted area of ca 0.7 km2. Tree cavities used during pregnancy were located higher on a tree trunk and had larger entrance area than the cavities used in the two later periods. switched roosts every 2–3 days (range 1–8) and moved to a new roost up to 800 m apart. Pregnant females tended to switch roosts more frequently than females in the two later periods. We did not observe a significant effect of minimum nightly temperature on the activity of radio-tracked Daubenton’s bats. Therefore, we suggest that observed seasonal changes in the pattern of behaviour of Daubenton’s bat females were driven by their changing energetic demands rather than by some extrinsic factors (e.g. weather conditions). Key words: radio-tracking; spatial activity; Chiroptera; tree roosts; artificial roost

Introduction matically increased energetic demands in consequence of milk production (Racey & Speakman 1987; Wilde In different phases of the reproductive cycle, adult fe- et al. 1995; McLean & Speakman 1997). Moreover, males of bats are forced to modify their activity pat- their attempts to balance the negative impact of in- tern and daily time budget with respect to changing creased energy expenditures by increasing foraging ac- energetic demands (Speakman & Thomas 2003). Each tivity are further constrained by the need of suckling period of reproductive cycle thus represents a unique their pups (Henry et al. 2002). This means they are constitution of both intrinsic and extrinsic factors that bonded to maternity roosts more than in any other gradually change as the periods pass from one to an- part of the year (Catto et al. 1996). Last but not other. For example, pregnant females are forced to sub- least, after weaning of juveniles, reproductive females stantially reduce the use of daily torpor, an energy sav- have to recover and to attain a good physical condi- ing physiological mechanism, in order to diminish neg- tion to survive the winter time (Speakman & Thomas ative impact of low body temperature on the rate of 2003). developing embryos (Racey 1973; Racey & Swift 1981; In this paper, we tested the influence of different re- Dietz & Kalko 2007). As a consequence, they have to productive state on spatial activity, roosting behaviour compensate for increased energetic demands connected and roosting preference of females of Daubenton’s bat with fetal development by prolonging the time they in a pond basin in Southern Bohemia, Czech Republic. spend on foraging bouts (Barclay 1989; Rydell 1993; The Daubenton’s bat Myotis daubentonii Kuhl, 1817 is Catto et al. 1995; Grinewitch et al. 1995; Shiel et al. a small (forearm length 33–42 mm, body mass 5–10 g; 1999; Dietz & Kalko 2007). However, as the size of em- Bogdanowicz 1994), insectivorous bat inhabiting most bryos increases, the females’ flying ability decreases and of the Palearctic region (Horáček et al. 2000). It is one they have to use different compensatory mechanisms, of the commonest species throughout most of its Eu- such as roosting in thermally optimal roosts (McNab ropean range (Mitchell-Jones et al. 1999) with marked 1982) and/or aggregation onto large colonies in order increase in numbers during past decades, perhaps due to reduce thermal losses (Kurta et al. 1987). Lactating to favourable climatic changes and increased food op- females, on the other hand, are confronted with dra- portunities (Kokurewicz 1995). Hence, it is listed as the

c 2010 Institute of Zoology, Slovak Academy of Sciences Spatial activity of a colony of Daubenton’s bats 1073

Table 1. Parameters of tree roosts used by radio-tracked bats in the three study periods.

Period

Pre-lactation Lactation Post-lactation

No. roosts 8 3 4 Height above ground (m) 8.1 ± 3.6 (3–13) 5.2 ± 1.6 (4–7) 4.5 ± 0.6 (4–5) DBH (cm) 38.3 ± 13.7 (20–58) 41.0 ± 12.3 (27–50) 30.8 ± 9.5 (25–45) Entrance area (cm2) 28.3 ± 10.6 (16–49) 14.7 ± 2.3 (12–16) 16.3 ± 7.7 (8–25) Distance to a nearest tree in the cavity direction (m) 8.3 ± 7.3 (2–20) 8.3 ± 10.1 (2–20) 12.3 ± 9.2 (2–20) Canopy cover (%) 33.8 ± 22.6 (10–80) 33.3 ± 15.3 (20–50) 27.5 ± 31.0 (0–70) Distance to nearest line element (m) 14.2 ± 18.0 (0–50) 13.3 ± 5.8 (10–20) 14.5 ± 23.7 (1–50) Distance to nearest water body (m) 96.8 ± 141.8 (0–400) 11.7 ± 7.6 (5–20) 103.0 ± 73.2 (2–170) Distance to forest edge (m) 38.6 ± 45.8 (2–120) 11.0 ± 7.9 (5–20) 103.3 ± 72.7 (3–170)

Explanations: Variables significantly different at P < 0.05 among the three periods are marked in bold. In “height above ground” and “entrance area” we pooled data for the lactation and post-lactation period prior analysis. Mean ± SD and range (in parentheses) are shown. species of the lower risk of threat by IUCN/SSC Chi- nearest meteorological station located 7 km from our study roptera specialist group (Hutson et al. 2001). area.

Radio-tracking Material and methods The bats were radio-tracked during the three periods: May 20–30 (pregnancy); June 12–20 (lactation); August 1–10 The area and studied bat population (post-lactation). We attached small transmitters (0.5 g, LB– The research was conducted in the late spring and sum- 2, Holohil System, Carp, Ontario, Canada) on inter-scapular mer 2005 in the northern part of Třeboňsko Landscape regions of bats with cyanoacrylate glue (Encarna¸c˜ao et al. ◦ ◦ Protected Area and Biosphere Reserve (49 10 N, 14 43 2004). The mass of transmitters imposed 5.5 ± 0.7% (mean E, S Bohemia, Czech Republic). The area represents a flat, ± SD; n = 15) of body mass of tagged bats. Eight of these densely patched landscape with a high number of water bod- bats were ringed in previous years and five of these (bats A, ies of different size and origin (fishponds, old sand quarries), E, H, J, M) were recaptured after the research was finished. extensive mixed and conifer forests, wet meadows, wetlands No detrimental effect, except for missing fur where trans- and arable land. The Daubenton’s bats in the study area mitters had been attached, was observed and the females roost almost exclusively in tree hollows (Lučan et al. 2009). were in good condition. After attachment of transmitters, The only exception holds for one man-made structure, called bats were released back to their roost in Vápenka. Alto- as “Vápenka”. It is an old, cellar-like building, ca 3 × 5 × gether, we radio-tracked 15 females (5 pregnant, 5 lactating 2.5 m in size that served as a lime-kiln and is abandoned at and 5 post-lactating) of Daubenton’s bat for a total of 92 present. A maternity colony of Daubenton’s bats of up to bat-days. 200 individuals has been known to occupy Vápenka at least Three researchers equipped with 3-element antennae since 1962 (V. Hanák, pers. commun.), representing, to our and receivers (LA 12-Q, AVM Instruments, Colfax, Cali- knowledge, one of the oldest known, continually inhabited fornia, USA) conducted nightly observation of the radio- maternity roost of the species in Europe. We proved by ex- tracked bats. Instead of following bats to their whole for- tensive ringing (2,000 ringed and 1,500 recaptured Dauben- aging area, we used different method to evaluate degree of ton’s bats) that Vápenka serves as a “central” roost in which spatial activity. We chose an area of ca 6.5 km2,fromnow majority of females from the study area aggregates during onward being referred as “the study area” (Fig. 1) within the pregnancy period. Later on, about half of the numbers which we were able to detect radio-tracked bats, at any time of females move to nearby tree cavities and individual an- whether present or not, We expected the shorter time bats imals or subgroups move between nearby cavities (Lučan spent in the study area, the greater spatial activity they & Hanák, in litt.). However, frequent movements between performed and vice versa. We located our bats using a com- tree cavities and Vápenka were recorded throughout the sea- bination of homing-in on the and cross-triangulation son (Lučan & Hanák, in litt.). Observed pattern of inter- method (White & Garrott 1990). The reach and spreading change of individual bats and small groups between contin- of signal of transmitters in the study area were tested prior uously occupied roosts fully conform to a “fission-fusion” to start of the research and thus we were familiar with con- model of social organisation observed in some other tree straints imposed by uneven spreading of the signal due to, roosting bats, e.g., Myotis bechsteinii (Kuhl, 1817) (Kerth e.g., terrain obstacles. While one of the three researchers &K¨onig 1999) and Eptesicus fuscus (Palisot de Beauvois, located bats in vicinity of their day roosts, two others cov- 1796) (Willis & Brigham 2004). ered the rest of the study area. The communication among Bats were captured by hands or by hand net in their researchers was mediated via radios or mobile phones. Fixes day roost in Vápenka during late afternoon. We determined were taken in 15 min intervals, however, presence/absence the reproductive state according to palpable embryo in preg- of bats in the study area was observed continuously between nant females. Lactating and post-lactating females were dis- consecutive fixes. tinguished by enlarged nipples and the absence of fur in their While we continually observed nightly returns of all surroundings. All females were weighted to the nearest 0.5 g bats to their roosts, we usually made break in observation with Pesola spring balance; forearm lengths were measured between the first and second half of night. This break was to the nearest 0.1 mm with calliper (except for 3 ind., see made in 49 of 91 bat-nights of observation. Typically, the Table 1). To assess the effect of night temperature on activ- break started at 1:00 AM and lasted for one and half hour ity of bats, we used minimum night temperatures from the (mean ± SD: 81 ± 34 min, median 75 min). The lengths of 1074 R. K. Lučan &J.Radil

Fig. 1. Schematic map of the study region with delimitation of the study area, i.e., the area of ca 7 km2 in which presence/absence of foraging bats was recorded using radio-tracking in summer 2005, Southern Bohemia. Symbols show localization of roosts used in different periods: () – pregnancy; ( ) – lactation; (•) – post-lactation. Asterisk shows localization of Vápenka – the roost of initial capture of all radio-tracked bats. these breaks did not differ between pregnancy, lactation and was strongly violated, we used non-parametric tests. We post-lactation period (ANOVA: F2,46 = 1.0644, P =0.4). tested, whether the activity of bats during the night upon Due to a methodological constraint imposed by the research initial capture and tagging had differed from the following design (see above), we were not able to detect, whether the night. Only during the lactation period, the activity of bats studied bats had not used some special night roosts beyond differed significantly (Wilcoxon matched paired test; Z = the limits of the study area. However, in some nights (n 2.0226, P < 0.04) between the first and second night after = 15, ∼ 35 bat-nights) we tried to locate the radio-tagged the transmitters were attached. Therefore, the data from bats in a broader region beyond the limits of the study area the first nights were not included in further analyses of spa- to ascertain whether they were using night roosts different tial activity (Audet & Fenton 1988). The measure of spatial from day roosts. In all cases, bats were found foraging, i.e., activity was assessed as the proportion of time spent in the we did not observe a single case of night roosting beyond study area, i.e., the number of positive locations divided the limits of the study area. Therefore, accordingly with by the total number of 15 min intervals. Bat-night and the observations by Dietz & Kalko (2007) and Encarna¸c˜ao et period of reproductive cycle were replication units in most al. (2006) we assume that vast majority of time bats spent statistical tests. We used arcin-square-root transformation outside their roosts was concerned with continual foraging on the proportional data of spatial activity to obtain normal activity. distribution. We applied analysis of covariance (ANCOVA) with minimum night temperature as a covariate to test dif- Roosts ferences in the time bats spent in the study area. We used All roost trees were assigned to a tree species and marked Tukey HSD test to compare spatial activity among particu- onto 1:10 000 map (Fig. 1). Also, we recorded following pa- lar periods. We used analysis of variance (ANOVA) to test rameters of roost trees: height of entrance above ground, for differences in the frequency and length of night visits entrance area, entrance orientation to cardinal points, roost in roosts. We used ANCOVA with minimum night temper- tree condition, diameter of a tree at breast height (DBH), ature as a covariate to test differences in the proportion distance to a nearest tree in a cavity direction, canopy cover, of night length that bats spent outside roosts in different distance to a nearest line element, distance to forest edge periods. We used Kruskal-Wallis and Mann-Whitney tests and distance to a nearest water body. The later two pa- to compare roost characteristics among the three respective rameters were measured from the map. We used clinometer periods. Finally, we applied Median test to compare number (Silva Clinomaster, Silva Ltd.) to estimate height of cavi- of days bats spent in one day-roost before they moved to a ties above ground. Tree condition was assigned to one of the new one. All calculations were performed using Statistica four following states: healthy, senescent, dying or dead tree 6.0 (StatSoft, Inc. 1984–2001). Values are given as mean ± based on overall appearance of a particular roost tree. We SD. used ladder or climbing technique to reach and measure size of entrance of roosting cavities to calculate entrance area. Results Canopy cover (%) was estimated by two researchers and the obtained values were than averaged. Spatial activity in different periods Statistical analyses Despite a considerable variation among individual bats, All data were tested for normality by Wilk-Shapiro test there was a strong impact of the period of reproductive prior to analyses. In cases, where normality in the data cycle on the time bats spent foraging in the study area Spatial activity of a colony of Daubenton’s bats 1075

Fig. 2. Spatial activity of fifteen radio-tracked females of Daubenton’s bats in three different periods of the reproduction cycle. Depicted is the proportion of time individual bats spent foraging in the study area to total time of observation. Number of nights of observation are indicated above each box. Box: mean ± 95 confidence interval; whiskers: mean ± SD.

Fig. 3. Frequency of nightly roost visitation (number of visits/night – white box plots) and the time bats spent in a roost per one nightly visit (black box blots) during three different periods of reproduction season. Numbers above white and black box plots refer to number of nights of observation and number of visits in roosts, respectively. Box: mean ± 95 confidence intervals; whiskers: mean ± SD.

(ANCOVA: F(2,73) = 14.45, P < 0.0001; Fig. 2). The Fig. 3). Frequency of roost visits increased from preg- time spent in the study area increased from pregnancy nancy to lactation (Tukey test: P < 0.01) and decreased to lactation (Tukey test: P < 0.0001) and decreased again from lactation to post-lactation (Tukey test: P again in the post-lactation period (P < 0.0001). The < 0.01). Pregnant females returned to roosts between time spent in the study area during post-lactation pe- consecutive foraging bouts on an irregular basis and riod did not differ from pregnancy period (P = 0.69) they did not visit their day roosts in 40% (n = 25) Assuming the lesser proportion of the time bats spent of bat-nights at all. Contrastingly, lactating females re- foraging in the study area the greater spatial activity turned to their roosts regularly with the only excep- they performed, we can infer on decrease in spatial ac- tion of one bat-night (i.e., 4% of bat-nights, n = 24). tivity in lactating females. In the post-lactation period, the females performed the pattern similar to pregnant females and they did not Nightly roost visitation and foraging time return to day roosts in 37% (n = 27) of bat-nights at There was a strong impact of the period of the re- all. productive cycle on the frequency of roost visitation The time spent in the roost per one nightly visit during the night (ANOVA: F2,72 = 8.53, P < 0.001; differed significantly between the periods of the repro- 1076 R. K. Lučan &J.Radil ductive cycle (ANOVA: F1,75 = 11.69, P < 0.0001; – 2 roosts, poplar (Populus × canadensis)–1roostand Fig. 3). There was a trend (not significant – Tukey test: birch (Betula pendula) – 1 roost. Three of these roost P = 0.16) towards shortening of visits from pregnancy trees were healthy, 9 were senescent, 1 was dying and 1 to lactation period. Later on, the lengths of roost vis- was dead. Roost entrances were oriented to south-west its increased from the lactation to the post-lactation (7), north-east (5) or south-east (3) and no roosting cav- period (Tukey test: P < 0.001; Fig. 3). Thus, nightly ity faced towards north-west. In most cases, we found returning to the roosts was the most frequent in lactat- no differences in external parameters and location in ing females but the time spent in the roost per one visit landscape of roosts used in different periods (Table 1). had shortened during that period (Fig. 3). Pregnant females roosted in cavities located higher than The time bats spent foraging was similar in all in the two following periods (Kruskal-Wallis test: χ2 = three periods (ANOVA: F(2,74) = 0.97, P < 0.383). 6.29, df = 2, P < 0.05). Also, entrance area of the cav- They foraged for 352 ± 57 (median = 375), 324 ± 44 ities used during pregnancy was larger than in the two (338) and 329 ± 107 (360) minutes per night during later (Mann-Whitney test; Z = 2.49, P < 0.05). pregnancy, lactation and post-lactation, respectively. On average, bats spent 1.9 ± 1.5 (range: 1–6), 2.9 However, the proportion of the time spent outside the ± 1.6 (1–5) and 3.3 ± 3.1 (1–8) days in particular roost roost to particular night length (from sunset till sun- in the three respective periods before they moved to rise) differed between periods (ANCOVA: F(2,73) = a new one. Despite obvious trend toward less frequent 3.23, P < 0.05). Pregnant and lactating females spent roost switching in the two later periods, there were no similar proportion of the night length outside their significant differences (Median test; χ2 =1.15,df=2, roosts [70 ± 12 % (median = 74) and 69 ± 9%(me- P < 0.563). In most cases, the bats switched roosts dur- dian = 72), respectively; Tukey test: P = 0.92], females ing pre–dawn swarming period. The most common ob- in the post–lactation period had left their roosts for served scenario was, that bats returned for night roost- shorter part of the night [60 ± 20% (median = 66); ing to the day roost used during previous day and then, Tukey test: P < 0.05]. after last foraging bout, they were located either swarm- ing around or roosting in a new roost. In several cases, Effect of minimum night temperature on the activity of pre-dawn swarming behaviour of radio-tracked bats was bats observed around roost used in previous day, however, Minimum nightly temperature differed among the three after some short time, the bats moved to another roost periods (Kruskal-Wallis test: χ2 = 17.46, df = 2, P located as far as few hundred meters away, and set- < 0.001). It varied between 3.5 and 15.2 ◦C(mean± tled there for next day(s). Average distance to which SD: 9.4 ± 3.7 ◦C), 6.6–15 ◦C (12.2 ± 2.8 ◦C) and 5.2– bats moved between the two roosts were 248 ± 196 m 14.5 ◦C(8.9± 3.2 ◦C) during pregnancy, lactation and (range 10–550 m), 350 ± 269 m (150–800 m) and 434 post-lactation, respectively. Despite this, the minimum ± 252 m (80–700 m) during pregnancy, lactation and nightly temperature did not have a significant influence the post–lactation period, respectively. All roosts used neither on the time bats spent foraging in the study area by radio-tracked females were situated within the area 2 (ANCOVA: F(1,73) = 0.005, P = 0.94) nor the propor- of ca 0.7 km (Fig. 1). tion of night length that bats spent outside their roosts (ANCOVA: F(1,73) = 1.34, P = 0.25). Discussion

Roosts and roost switching Spatial activity and nightly roost visitation All radio-tracked females used more than one day We documented a significant decrease in spatial activity roosts. A total number of day roosts were nine, four in females of Daubenton’s bat during the lactation pe- and five for pregnancy, lactation and post-lactation pe- riod. In line with our observation, Henry et al. (2002) riod, respectively. Number of roosts used by individual reported a pronounced decrease in home–ranges from bats (Table 1) did not differ among three study periods pregnancy to lactation, resulting in analogical decrease (Kruskal–Wallis test; χ2 = 3.00, df = 4, P < 0.558). in flight distances of observed little brown bats, Myotis With the exception of Vápenka and one tree roost, lucifugus (LeConte, 1831). Accordingly, Racey & Swift the radio-tracked females within a single study period (1985) and Shiel et al. (1999) described similar patterns used different day roosts than the females in other two in spatial activity between pregnancy and lactation in study periods, i.e., bats did not re-used roosts from pre- pipistrelles, Pipistrellus pipstrellus s.l. (Schreber, 1774) vious periods (Fig. 1). In all cases, radio-tracked fe- and the lesser noctules, Nyctalus leisleri (Kuhl, 1817), males roosted together with groups of other Dauben- respectively. Henry et al. (2002) suggested that the de- ton’s bats, based on social vocalisation audible from crease in spatial activity may probably be facilitated roost entrances and observations of evening emergence. by the concomitant increase in insect biomass during All roosts, except for Vápenka, were in tree hollows the lactation period. Alternative explanation of the de- made by greater spotted woodpecker Dendrocopos ma- crease in spatial activity in lactating females is the need jor (L., 1758). External parameters of all tree roosts are of more frequent nightly visitation of the roosts in order shown in Table 2. Roosts were located in willow (Salix to suckle their pups (Swift 1980; Maier 1992; Henry et fragilis) – 5 roosts, oak (Quercus robur) – 3 roosts, as- al. 2002). Indeed, the frequency of nightly roost visita- pen (Populus tremula) – 3 roosts, pine (Pinus sylvestris) tion increased substantially from pregnancy to lactation Spatial activity of a colony of Daubenton’s bats 1077 in radio-tracked Daubenton’s bats. There is only scarce ally, despite no effect of minimum nightly temperature information on the frequency of nightly suckling in tem- on activity of bats was proven in this study, average perate bats (cf. Racey 1982; Dietz & Kalko 2007). As- minimum temperature was highest during the lactation suming that all nightly visits of day roosts by lactating period. Consequently, availability of flying insects was females resulted in suckling their offspring, we can infer least constrained by temperature in that period and lac- a minimum number of one to four suckling events per tating females could effectively forage throughout the night. We frequently observed segregation of at least a night. part of non-volant juveniles from adult females during Post-lactating females foraged shorter part of the daytime in Vápenka. The separately roosting juveniles night than pregnant and lactating females. This fact typically formed closed clusters in a considerable dis- could result from decreased energy demands after ma- tance from adult females and could not be suckled at ternal care had ended. Dietz & Kalko (2006) observed that time. In several cases, we even observed, that lac- that thermoregulatory behaviour in reproductive fe- tating female roosted outside Vápenka during day and males of Daubenton’s bat is fully adapted to optimize came to suckle its pup in Vápenka shortly after sunset juvenile development. Therefore, reproductive females (Lučan & Hanák, pers. obs.). Therefore, the observed practically do not use daily torpor that means, they number of nightly visits of lactating females in roost have to heavily compensate their increased energetic de- most probably referred to the overall number of suck- mands by foraging. Contrastingly to the period of preg- ling events for the whole day. Similarly, Henry et al. nancy and lactation, post-lactating females use torpor (2002) argue that the majority of nursing is likely to more frequently (Dietz & Kalko 2006) and may gain occur during the night, since lactating females cannot sufficient amount of food in a corresponding or even support high energy requirements of milk production shorter time. Accordingly with this hypothesis, we ob- during the day. The nightly use of body torpor as well served that post-lactating females foraged for the same as grooming behaviour is substantially reduced in lac- time as females during pregnancy and lactation, but tating females in order to either diminish a negative as nights are considerably longer in the post-lactation effect on milk production (Wilde et al. 1999; Dietz & period, they spent longer time roosting. Besides ener- Kalko 2006) or, to reduce energy expenditures (McLean getic reasons, we suppose that time spent in roosts may & Speakman 1997), for the former and the later case, concern with social activities, such as mating, since a respectively. Thus, our reported lengths of nightly vis- majority of roosts in the study area contained mixed its in roosts by lactating females may be addressed to groups of sexually active males and females in the post- approximate lengths of particular suckling events plus lactation period (Lučan & Hanák, in litt.). Likewise, the time necessary for digesting of food acquired during Encarna¸c˜ao et al. (2004) suggest that a large propor- previous foraging bout. tion of matings in Daubenton’s bats occurs already in the day roosts within the summer habitats. Foraging time Last but not least, nightly temperature generally Despite a considerable variation among individual bats, affects foraging activity of bats through its effect on the overall time spent foraging did not differ among the activity of insects. Although this was proven in many three study periods. However, while pregnant and lac- species of aerial hawking bats (e.g., Racey & Swift tating females spent similar proportion of the night- 1985; Rydell 1989; Catto et al. 1995; O’Donnell 2000; length foraging, females in the post-lactation period Ciechanowski et al. 2007), Daubenton’s bats seem to were foraging for shorter part of the night. Our data be quite tolerant to relatively very low temperatures contrast with the observation by Dietz & Kalko (2007) (Dietz & Kalko 2007) and they were observed forag- who found significant decrease in foraging time in lac- ing at as low temperatures as –3 ◦C (Ciechanowski et tating and post-lactating females of Daubenton’s bats al. 2007). Accordingly with observations above, we did as compared to pregnant ones. They suggested that de- not observe any significant effect of minimum nightly creased foraging time in lactating females was caused temperature on the activity of radio-tracked Dauben- by (1) increased frequency of roost visitation connected ton’s bats. Therefore, we suggest that observed seasonal with suckling and warming their pups, and (2) short- changes in the pattern of behaviour of Daubenton’s ening the time available to foraging as a consequence bat females were driven by their changing energetic of short nights. Contrastingly, our data showed that fe- demands rather than by some extrinsic factors (e.g., males rather compensated increased number of visits weather conditions). by shortening the time spent in the roost. The fact that lactating females were able to attain Roosts and roost switching a sufficient amount of prey during a comparably longer Despite use of artificial (Nyholm 1965; Gerell 1985; this time than they did during pregnancy or post-lactation study) or even cave shelters (Zahn & Hager 2005) as was most likely due to an increased overall prey den- roosts of maternity colonies, the Daubenton’s bat acts sity. In the study area, the density of small Diptera, primarily as a tree dwelling bat species during the re- a main prey of Daubenton’s bats (cf. review by Bog- productive season (cf. Rieger 1996; Boonman 2000; En- danowicz 1994), reached its highest peak of abundance carna¸c˜ao et al. 2005). As observed throughout forty just in June, i.e., a time precisely corresponding to the years of extensive research (Lučan et al. 2009), Dauben- lactation period of this species (Lučan 2004). Addition- ton’s bats in the study area use almost exclusively cav- 1078 R. K. Lučan &J.Radil ities excavated by woodpeckers. The most plausible ex- 10 km apart (Lučan & Hanák in litt., for details see also planation may be a relative scarcity of natural cavities Gaisler et al. 1979). Likewise, Rieger (1996) observed, in local forest stands. For example, only seven out of 69 that roosting areas were confined to particular forest tree cavities inspected in the study area in 2005 were plots with no interchange of individuals among individ- natural cavities (Radil & Lučan 2006). ual plots. Accordingly, Kapfer et al. (2008) documented Tree cavities used during pregnancy were located a remarkable fidelity of Daubenton’s bats to particular higher on a tree trunk and tended to have larger en- roosting, but also, to foraging areas. She hypothesized a trance area than the cavities used in the two later pe- discrete distribution of different groups of Daubenton’s riods. The larger entrance area of cavities used during bats within her study area. In line with these observa- pregnancy resulted from decay processes and activity of tions we suggest that the population biology of female woodpeckers. We assume that cavities located higher on Daubenton’s bats may be determined by an existence of a tree trunk may be thermally more suitable for preg- discrete subpopulation units (colonies) that are defined nant females (e.g., from better chance of daily insula- by high fidelity to particular roosting areas with inter- tion, cf. Vonhof & Barclay 1996; Betts 1998), since the change among neighbouring groups being restricted. temperatures in that period are still quite low in com- parison with the lactation period. Also, the cavities lo- Acknowledgements cated higher above the ground may be less exposed to predation from terrestrial predators (Vonhof & Barclay We are grateful to M. Kubešová, D. Frantová, H. Jahelková, 1996; Betts 1998; Sedgeley & O’Donnell 2004; Kaňuch F. Kašparová, R. Nedoma, J. Norková, P. Pech, T. Pithar- 2005; Ruczi´nski & Bogdanowicz 2005). tová, V. Pouska, V. Půža for their help with fieldwork. M. We did not find any significant difference in the Šabacká kindly improved the English. We thank to two frequency of roost switching among the three periods anonymous reviewers for their comments that greatly im- of the reproductive cycle. However, there was an ob- proved the manuscript. The research was financially sup- vious trend toward less frequent roost switching from ported by Bat Conservation International, Czech Bat Con- servation Trust, Grant Agency of University of South Bo- the pregnancy period onward. The frequency of roost hemia and Ministry of Education, Youth and Sport MSMT switching is, beyond other reasons, often connected 6007665801. with parasite-avoiding behaviour (Lewis 1995). Preg- nant female bats often have more parasites than lac- tating ones, since ectoparasites usually switch from the References mothers to newborn pups after parturitions (Christe et Audet D. & Fenton M.B. 1988. Heterothermy and the use of al. 2000). Seasonal dynamics of infestation of Dauben- torpor by the bat Eptesicus fuscus (Chiroptera: Vespertilio- ton’s bats by spinturnicid in the study area fol- nidae): a field study. Physiol. Zool. 61: 197–204. low exactly the same pattern (Lučan 2006). Although Barclay R.M.R. 1989. The effect of reproductive condition on the foraging behavior of female hoary bats, Lasiurus cinereus. mites could not be avoided by frequent roost switch- Behav. Ecol. Sociobiol. 24: 31–37. ing, as they are bonded to their hosts’ wing membranes Betts B.J. 1998. Roosts used by maternity colonies of silver- throughout the whole life cycle (Rudnik 1960), there are haired bats in north–eastern Oregon. J. 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Foraging behaviour and habitat use of the serotine bat tial part of the reproductive season. This area covered 238: 2 (Eptesicus serotinus) in southern England. J. Zool. 623– some 0.7 km with Vápenka, the roost of initial cap- 633. DOI: 10.1111/j.1469-7998.1996.tb05418.x ture of all radio-tracked bats, located approximately in Christe P., Arlettaz R. & Vogel P. 2000. Variation in inten- the centre of this area. Maximal distance to which bats sity of a parasitic ( myoti)inrelationtothe reproductive cycle and immunocompetence of its bat host moved between two consecutive roosts was 800 m. Ac- (Myotis myotis). Ecol. Lett. 3: 207–212. DOI: 10.1046/j.1461- cordingly, Rieger (1996) found a mean distance between 0248.2000.00142.x the two consecutively used roosts about 600 m, with a Ciechanowski M., Zaj˛ac T., Bilas A. & Dunajski R. 2007. Spa- maximum of 3,922 m. 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