Summer Temperature and Precipitation Govern Bat Diversity at Northern Latitudes in Norway

Mammalia 2016; 80(1): 1–9 Tore Christian Michaelsen* Summer temperature and precipitation govern bat diversity at northern latitudes in Norway Abstract: This study investigated bat diversity in a tem- Humphries et al. 2002, Lourenço and Palmeirim 2004, perature and precipitation gradient in fiord and valley Frafjord 2007, 2012a,b, Michaelsen et al. 2011). For a given landscapes of western Norway about 62° N. Equipment for latitude, temperature varies with several factors, the most automatic recording of bat calls was distributed in areas obvious being altitude (Schönwiese and Rapp 1997, Moen ranging from lowlands to alpine habitats with a mean 1999). Although altitude itself can be a significant explan- July temperature range of 8–14°C. A general description atory factor of both local distribution and reproduction of species distribution was given and diversity was ana- (e.g., Stutz 1989, Syvertsen et al. 1995, Cryan et al. 2000, lysed using both a generalised linear model (GLM) and a Russo 2002, Kanuch and Kristin 2006, Michaelsen 2010), mixed-effects model (GLMM). With regard to the sampling it can make no universal statement about bat distribution design, the data were analysed on a binary scale, where over wider areas (Michaelsen et al. 2011). presence or absence of any species other than the north- To the north and beyond the Arctic Circle, only the ern bat Eptesicus nilssonii is included. Models including northern bat Eptesicus nilssonii (Keyserling and Blasius, temperature and precipitation explain 79% (GLM) to 91% 1839) forms lasting reproducing populations (Rydell 1993, (GLMM) of the overall variation in bat diversity. In sub- Rydell et al. 1994, Frafjord 2001, 2012a, Gerell and Rydell alpine and alpine areas with temperature below 10°C, 2001). Most other European bat species are rare or void only the northern bat was found. This species also forms long before reaching this climatic landmark (Mitchell- maternity roosts where mean July temperatures are as low Jones et al. 1999, Dietz et al. 2007), and only a few extreme as 11°C and 10°C, below July temperatures found in the records of other species are reported far north (Siivonen warmest areas beyond the Arctic Circle. and Wermundsen 2008). In Norway, relatively high bat diversity can be found between 62° and 63° north, but the 2 Keywords: Chiroptera; climate; RGLMM ; Scandinavia; northern bat is the most recorded bat (Olsen 1996, Isaksen topography. et al. 2009). In southern Norway, the northern bat seems to be almost omnipresent below the treeline (Gjerde and Fuszara 1995, Michaelsen et al. 2003, Michaelsen and van DOI 10.1515/mammalia-2014-0077 Received May 24, 2014; accepted December 16, 2014; previously der Kooij 2006). Remarkably, few records exist from sub- published online January 20, 2015 alpine and alpine areas (e.g., Gjerde and Fuszara 1995, Lie and Skåtan 1999). In central Europe, the northern bat has a patchy dis- Introduction tribution and its main distribution is in elevated areas (Jaberg and Guisan 2001, Kanuch and Kristin 2006, Piksa Bat diversity is negatively correlated with latitude, a surro- and Nowak 2013, Piksa et al. 2013). At least in some parts of gate factor for temperature and light conditions (Kaufman central Europe, competition with species sharing similar and Willig 1998, Ulrich et al. 2007, Michaelsen et al. 2011). foraging behaviour may explain this patchy distribution In northern Europe, both summer and winter tempera- (Haupt et al. 2006). As all of the species likely to compete tures drop with latitude, the duration of summer shortens, with the northern bat (see Haupt et al. 2006) are rare at and the length of summer nights decreases and is finally northern latitudes, one should assume distribution to be void. These factors should strongly affect energy budgets either marginally or not affected by competition. and thus survival and ability to successfully reproduce This study was threefold. First, through recording in sedentary bats (e.g., Speakman 1991, Hamilton and bat calls using data-loggers over a temperature and pre- Barclay 1994, Jones and Rydell 1994, Rydell et al. 1996, cipitation gradient, binary models were made to identify important climatic factors affecting bat diversity. The *Corresponding author: Tore Christian Michaelsen, Department northern bat was excluded from statistical analysis, but of Biology, University of Bergen, P.O. Box 7800, NO-5020, Bergen, was included in descriptive statistics. The aim was to find Norway, e-mail: [email protected] boundaries for when diversity can be expected in this 2 T.C. Michaelsen: Summer climate and bat diversity in Norway landscape, i.e., where more than just the northern bats treeline (Gjerde and Fuszara 1995). This would include can be found. Second, attempts were made to estimate mean July temperatures as low as approximately 9°C how much of the deviance these models and their predic- based on the coordinates and altitude reported by Gjerde tor variables explain, applying different approaches to and Fuszara (1995). obtain the R2 parameter. Light conditions were accounted A total of 10 of Norway’s 13 species have been con- for in the study design by selecting a study area with gla- firmed at about 62° N in the study area (see Gjerde and cially carved fiords and valleys shaded by tall surround- Fuszara 1995, Michaelsen et al. 2003, 2004a,b, Michaelsen ing mountains to the north. Third, the results obtained and van der Kooij 2006, Michaelsen 2012). Northern bats, here were compared with previous knowledge of diversity soprano pipistrelles [Pipistrellus pygmaeus (Leach, 1825)], in the region, including known colonies and distribution Daubenton’s bat [Myotis daubentonii (Kuhl, 1817)] and patterns. whiskered bats [M. mystacinus (Kuhl, 1817)] are common or fairly common. Brandt’s bat [M. brandtii (Eversmann, 1845)] has been recorded only in northern parts in the study area, but not in any of the valleys investigated in Materials and methods this study. Uncommon or rarely recorded species are noct- ules [Nyctalus noctula (Schreber, 1774)], parti-coloured Study area bats (Vespertilio murinus Linnaeus, 1758) and brown long- eared bats (Plecotus auritus Linnaeus, 1758). Few records This study was conducted during a relatively warm exist of the Nathusius’ pipistrelle [P. nathusii (Keyserling period in six valleys in western Norway around 62° N and Blasius, 1839)] and only one recording of serotine in July 2013. Owing to its complex topography and posi- (Eptesicus serotinus Schreber, 1774) has been made, all tion relative to the North Atlantic Current, this area has during autumn and only on islands along the coast. The more geographic regions defined by vegetation than any three species found in Norway but not in the study area neighbouring countries in Scandinavia and Finland. are the barbastelle [Barbastella barbastellus (Schreber, Steep mountain slopes have left the bulk of the land area 1774)], Natterer’s bat [M. nattereri (Kuhl, 1817)] and the unspoilt by man, and only small patches of farmland common pipistrelle [P. pipistrellus (Schreber, 1774)], all and settlements exist. Unlike most of Europe (except found at single sites in recent years (Flåten and Røed 2007, for mountainous regions), no large fields are found. Isaksen 2007, van der Kooij et al. 2009). Relatively steep valleys were selected, where conditions such as precipitation and oceanic influence would vary relatively little within each valley. Moreover, all areas Automatic recording of bats studied have tall mountains blocking out the sun well before sunset and after sunrise. This factor can influ- Automatic recordings of bat calls were made using the ence bat distribution and behaviour at these latitudes batcorder-system (EcoObs, Nürnberg, Germany) and D500 (Michaelsen et al. 2011). Available publications from detectors (Pettersson Elektronik AB, Uppsala, Sweden). the study area (Gjerde and Fuszara 1995, Olsen 1996, Up to seven units from the same manufacturer were Michaelsen 2003, 2012, Michaelsen et al. 2003, 2004a,b, deployed each night within the same valley covering the Michaelsen and van der Kooij 2006, Isaksen et al. 2009) entire temperature gradient selected, ranging from 8 to suggest that bats can be found in all available land- 14°C mean July temperatures (Table 1). In these valleys, a scapes and habitats, ranging from alpine areas to coastal total of 45 sites had ultrasound loggers deployed, each site plains with only bracken vegetation, cliffs, cities, roads with known mean July temperature and mean July precipi- (street lamps), cultivated areas, freshwater and marine tation. Where the 45 loggers were deployed, the total vari- shores, woodlands (all sorts), coastal islands and more. ation in mean July precipitation varied from 75 to 150 mm During summer, most species and the highest densities (Table 1). The climate variables were retrieved from shape- are found close to freshwater and other water sources files based on 30 years normal (1961–1990) provided by the with low salinity in the warmest parts of the landscape Norwegian Meteorological Institute. Models behind the (Michaelsen 2012). At least some species seem to avoid shape files are described in detail in Tveito et al. (2000). open habitats (Michaelsen et al. 2011). Most efforts in At present, there are no available shape files showing the mapping bats stem from lowland areas, but altitudinal variation in precipitation during the 24-h cycle. The pre- records suggest that at least northern bats occasionally cipitation variable used in this study does not discrimi- can be found up to about 900 m.a.s.l. and just above the nate between any such temporal variations, but was still T.C. Michaelsen: Summer climate and bat diversity in Norway 3 Table 1 Names of the six Norwegian valleys sampled in this study be suitable for bats (see Fischer et al. 2009 for relevance to with coordinates, mean July temperature/precipitation ranges the statistical outcome). retrieved from GIS files provided by The Norwegian Meteorological On both hardware systems, recording time was set Institute and number of recording sites in each valley.

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