Physiological Traits Affecting the Distribution and Wintering Strategy of the Bat Tadarida teniotis

Abstract

The ability to enter torpor at low ambient temperature, which enables insectivorous bats to survive seasonal food shortage, is often seen as a prerequisite for colonizing cold environments. Free-tailed bats (Molossidae) show a distribution with a maximum latitudinal extension that appears to be intermediate between truly tropical and temperate-zone bat families. We therefore tested the hypothesis that Tadarida teniotis, the molossid species reaching the highest latitude worldwide (46Њ N), lacks the extreme physiological adaptations to cold that enable other sympatric bats to enter further into the temperate zone. We studied the metabolism of individuals subjected to various ambient temperatures in the laboratory by respirometry, and we monitored the body temperature of free-ranging individuals in winter and early spring in the Swiss Alps using temperaturesensitive radio-tags. For comparison, metabolic data were obtained from Nyctalus noctula, a typically hibernating vespertilionid bat of similar body size and convergent foraging tactics. The metabolic data support the hypothesis that T. teniotis cannot experience such low ambient temperatures as sympatric temperate-zone vespertilionid bats without incurring much higher energetic costs for thermogenesis. The minimum rate of metabolism in torpor was obtained at 7.5Њ-10ЊC in T. teniotis, as compared to 2.5Њ-5ЊC in N. noctula. Field data showed that T. teniotis behaves as a classic thermo-conforming hibernator in the Alps, with torpor bouts lasting up to 8 d. This contradicts the widely accepted opinion that Molossidae are nonhibernating bats. However, average body temperature (10Њ-13ЊC) and mean arousal frequency (3.4 d in one bat in January) appear to be markedly higher than in other temperatezone bat species. At the northern border of its range, T. teniotis selects relatively warm roosts (crevices in tall, south-exposed limestone cliffs) in winter, where temperatures oscillate around 10ЊC. By this means, T. teniotis apparently avoids the risk of prolonged exposure to energetically critical ambient temperatures in torpor (Ͻ6.5Њ-7.5ЊC) during cold spells. Possibly shared by other Molossidae, the physiological pattern observed in T. teniotis may clearly be linked to the intermediate latitudinal extension of this bat family.

Foraging Behaviour and Habitat use by the European Free-Tailed BatTadarida teniotis

“…They had probably entered torpor, since Arlettaz et al (2000) demonstrated that the ideal range of ambient temperatures for torpor in this species is 7.5-10ºC, unusually high for crevice roosting temperate bats. Although most of the night active period was used for foraging, a considerable amount of time was spent flying in the immediate vicinity of the roost.…”

“…family living in a temperate zone (Arlettaz et al, 2000). Although this peculiarity may strongly influence various aspects of the ecology and behaviour of the species, it remains one of the least known bats of the European fauna.…”

New distributional records for bats of the Argentine Patagonia and the southernmost known record for a molossid bat in the world

“…Among molossids, the species of the genus Tadarida seems to be the most latitudinally extended, both northward and southward. For instance, Tadarida teniotis (Rafinesque, 1814) has been recorded as far up as 46 ° N latitude (Arlettaz et al 2000 ), representing the northernmost known record for a bat. On the other hand, vespertilionids can reach even higher latitudes, considering that Myotis chiloensis (Waterhouse, 1840) was recorded at 55 ° S in Chile, which is the southernmost known record for any bat in the world (Koopman 1967 ).…”

Heterothermy in free-ranging male Egyptian Free-tailed bats (Tadarida aegyptiaca) in a subtropical climate

“…Hibernation is widespread in temperate-zone bat species that experience low environmental temperatures and reduced food availability during winter (Lyman et al 1982;Arlettaz et al 2000;Humphries et al 2002). Bats often hibernate in thermally stable microsites such as caves and buildings during winter, which allows them to maintain more-or-less constant T b between interbout normothermic periods (Lyman et al 1982;Arlettaz et al 2000;Humphries et al 2002;Boyles and Willis 2009).…”

“…Bats often hibernate in thermally stable microsites such as caves and buildings during winter, which allows them to maintain more-or-less constant T b between interbout normothermic periods (Lyman et al 1982;Arlettaz et al 2000;Humphries et al 2002;Boyles and Willis 2009). In contrast, daily torpor appears to be a more common response in species inhabiting lower latitudes (Geiser and Brigham 2000;Turbill et al 2003;Willis et al 2005;Jacobs et al 2007;Vivier and van der Merwe 2007).…”