Influence of night length on home range size in the northern bat Eptesicus nilssonii

Abstract

The northern bat Eptesicus nilssonii is widespread in Fennoscandia, with breeding populations well above the Arctic Circle. I studied this species at its extreme northern limit, at 69 °N in Norway. I radio-tracked 17 bats from 2 maternity roosts during 2003-2006 to study the influence of the midnight sun and increasing lengths of darkness on activity (time spent out of roost) and home range size. Activity and home range was highly correlated with night length (light intensity); both increasing progressively with season. Bats were classified into 3 groups based on the time of the season they were tracked (basically July, August and September-October); short activity (average 1.57 hours) and small home range (average 0.91 km 2), medium activity (3.69 hours) and medium-sized home range (4.58 km 2), and long activity (4.80 hours) and large home range (17.2 km 2). Bats visited roosts several times during the night, and the duration of roost visits increased significantly by group. The number of periods out of roost increased from the first to the second group (1.45 vs. 2.36 flight periods per night), but insignificantly to the third group (2.37 flights). The most significant increase in activity and home range was associated with the first flight of juveniles in early August. These bats appeared to have a threshold level of around 1700 lux for activity out of roost, with little difference between light levels at emergence and return (the second group returned in significantly poorer light than they emerged in). Although the northern bat at this extreme latitude had adapted to the ambient light conditions, the bright nights under the midnight sun and the short season strongly reduced their window of opportunity for activity and may possibly reduce survival and reproductive success.

Large Home Range Size in the Ground Foraging Bat,Mystacina tuberculata, in Cold Temperate Rainforest, New Zealand

“…Low invertebrate abundance is a common feature of cold temperate climates (O'Donnell, 2001) and of beech forest ecosystems Meads, 1985, 1987) such as the Eglinton Valley. Flight is energetically expensive (e.g., Racey and Speakman, 1987;Speakman and Thomas, 2003;Frafjord, 2012), implying that M. tuberculata must benefit from being active over such a large area. Mystacina tuberculata may have to search widely in order to obtain sufficient food.…”

Estimating population density of insectivorous bats based on stationary acoustic detectors: A case study

“…We estimated density D by dividing the mean λ by the median of various minimum convex polygon figures as a measure of home range size obtained from the literature (for P. pipistrellus: Davidson‐Watts & Jones, and Davidson‐Watts, Walls, & Jones, , for E. nilssonii: Frafjord, and Haupt, Menzler, & Schmidt, , for M. nattereri: Siemers, Kaipf, & Schnitzler, and Smith & Racey, ) . Density was only calculated when models were successfully fitted to the data (nonsignificant chi square value of the goodness of fit statistics, p > .05; Appendix S3).…”

Summer temperature and precipitation govern bat diversity at northern latitudes in Norway

“…In northern Europe, both summer and winter temperatures drop with latitude, the duration of summer shortens, and the length of summer nights decreases and is finally void. These factors should strongly affect energy budgets and thus survival and ability to successfully reproduce in sedentary bats (e.g., Speakman 1991, Hamilton and Barclay 1994, Jones and Rydell 1994, Rydell et al 1996, Humphries et al 2002, Lourenço and Palmeirim 2004, Frafjord 2007, 2012a,b, Michaelsen et al 2011. For a given latitude, temperature varies with several factors, the most obvious being altitude (Schönwiese andRapp 1997, Moen 1999).…”

“…To the north and beyond the Arctic Circle, only the northern bat Eptesicus nilssonii (Keyserling and Blasius, 1839) forms lasting reproducing populations (Rydell 1993, Frafjord 2001, 2012a, Gerell and Rydell 2001. Most other European bat species are rare or void long before reaching this climatic landmark (MitchellJones et al 1999, Dietz et al 2007, and only a few extreme records of other species are reported far north (Siivonen and Wermundsen 2008).…”