RESUMEN
BACKGROUND: Knowledge about home range size is vital to understand social systems and population dynamics of small mammals, as well as dispersal and a species' landscape use. Home ranges have been mapped for some species of voles (subfamily Microtinae) but remain virtually unknown for many species, including the grey-sided vole Craseomys rufocanus. RESULTS: A small pilot study was carried out in an inland valley of northern Norway, where six adult C. rufocanus were radio-tracked with one male and one female in each of the summers 2021-2023. Despite the small sample size, a large variation in home range size was found; males 2 294 - 36 887 m2 and females 1 728-7 392 m2 (100% MCP). Three of the voles tracked over a prolonged period of time showed a dynamic use and shifting of the range. Home range size and use was mostly related to reproduction. The male with the smallest range had probably not yet become reproductively active, whereas the male with the largest range was searching for females at a time when vole density was very low. The third male reduced his range when the reproductive season ended. For females the most important limitations were food, shelter and dependent young, those with young needed to return frequently and spend more time at the nest site. When the reproductive season ended, one female increased her range, perhaps exploring sites to overwinter. CONCLUSIONS: Home range use in this population appears to be more dynamic than has previously been reported for C. rufocanus. The large ranges of males most likely resulted from the search of reproductively active females, outside of the reproductive season male ranges approximated female ranges. Female ranges most likely were limited by the need to feed close to their nest with dependent young, being able to roam more freely when reproduction ended.
RESUMEN
BACKGROUND: Most temperate bats are regular hibernators in the winter. Knowledge about the length of their active season and how they adjust their nightly activity throughout the season, is critical to conservation. The characteristics of these are likely to vary with climate as well as latitude. This study investigated the flight activity of the soprano pipistrelle Pipistrellus pygmaeus in Frafjord, a small valley in the south-western corner of Norway (58° 50'N 6° 18'E) with an oceanic climate. RESULTS: Activity was recorded with an ultrasound recorder throughout April 2018 to June 2019 at one site, with supplemental recordings in March to June 2020, i.e., covering all months of the year. Recordings at other nearby sites were made in the summers (June-August) of 2016, 2017, 2019 and 2020, as well as some of the last days in December 2019 to the first days of January 2020. Overall, soprano pipistrelles were recorded flying in all months of the year, but very few in December-March. Regular activity was recorded from late April or early May until late October, and some recordings were also made in November. The highest numbers of recordings were made in August and September. Social calls, i.e. male song flights, were recorded from April to November, with the vast majority in August and September. Nearly all recordings were made between sunset and sunrise. CONCLUSIONS: The soprano pipistrelle in this region showed regular activity through 6-7 months of the year. It adjusted its activity to the changing night length throughout the year, closely following sunset and sunrise. It was rarely recorded flying before sunset and almost never after sunrise. Most activity was recorded in the middle of the night, and social calls also followed this trend closely. Harems in late summer and autumn were confirmed in a bat box, which was also used for winter hibernation.
RESUMEN
BACKGROUND: Nearly all insectivorous bats (Chiroptera) are strictly nocturnal, flying and feeding only between sunset and sunrise despite lower insect availability than by day, most likely to avoid predation by diurnal birds. This may represent a great challenge to bats living north of the Arctic Circle, which are exposed to bright nights in the period of the midnight sun. The northern bat Eptesicus nilssonii was studied at different latitudes in Norway (69, 66 and 58°N) by three techniques; visual counts of exits from and returns to roosts, infrared detection with a datalogger and an ultrasound data recorder, to reveal how their activity varied across latitude, season, and night, as well as across light levels. How does a nocturnal bat adjust to perpetual light and what light levels are tolerated? RESULTS: In the north the bats' active season lasted 2.5 months, 1.5 months shorter than in the south. The bats only flew in 3-4 weeks of midnight sun, and hardly ever left the roost until the sun went behind a hill in the evening. In addition, the timing of their nightly hunting was highly influenced by the darkness of the sky, and they very rarely flew in light levels above 200 foot-candles (FC). As the night became darker than twilight from early August, the bats restricted their activity to between sunset and sunrise. This was the normal situation in southern Norway, where the bats tracked sunset and sunrise throughout the entire season. Those bats appeared to prefer light levels below 100-50 FC and hence, also did fly in twilight conditions. CONCLUSIONS: The willingness to fly in twilight by the southern population may be a prerequisite to the northern bat's survival in the land of the midnight sun. These bats must accept short nights in the first part of their summer season and must be willing to fly in light levels 2-4 times higher than in the south. Most likely, this depends on a reduced predation risk and good abundance of insects at night.
RESUMEN
The relationship between home range and reproductive status of water voles (Arvicola amphibius) was studied by radio-tracking on an island off the coast of northern Norway in 2006-2009. The aim was to test assumptions about the species' social structure relative to other microtines. Juveniles used fairly small ranges (about 400 m²), with no difference between males and females. Subadults, overwintered voles in April, had ranges similar to juveniles. Reproductively active males (mean 2774.0 m²) increased their range seven-fold relative to juvenile males, with ranges on average 3.3 times larger than adult females (mean 848.3 m²), which also expanded their range. Most litters were born in May and June, and as reproduction ceased in July adult males reduced their range whilst females did not. Body mass or year did not influence home range size. Overlap of home ranges varied, but could be extensive in both adult males and females. The water vole had a social structure similar to some Microtus species, but females appeared to be non-territorial and males perhaps conditioned territorial and non-territorial.