Migratory stopover in the long‐distance migrant silver‐haired bat,Lasionycteris noctivagans

Abstract

Summary1. Some bat species make long-distance latitudinal migrations between summer and winter grounds, but because of their elusive nature, few aspects of their biology are well understood. The need for migratory stopover sites to rest and refuel, such as used by birds, has been repeatedly suggested, but not previously tested empirically in bats. 2. We studied migrating silver-haired bats (Lasionycteris noctivagans) at Long Point, ON, Canada. We used digital radio-transmitters to track 30 bats using an array of five towers that effectively covered the entire region (c. 20 · 40 km). We measured stopover duration and departure direction, and documented movement patterns, foraging activity and roost sites. We measured body composition on arrival using quantitative magnetic resonance and simulated long-distance migration using observed body composition to predict migration range and rate. 3. Migration occurred in two waves (late August and mid-September). Most bats stayed 1-2 days, although two remained >2 weeks. One third of the bats foraged while at the site, many foraging opportunistically on nights when rain precluded continued migration. Bats roosted in a variety of tree species and manmade structures in natural and developed areas. Half of the bats departed across Lake Erie (minimum crossing distance c. 38 km) while half departed along the shoreline. 4. Simulations predicted a migration rate of c. 250-275 km per day and suggest that all but one of the bats in our study carried sufficient fuel stores to reach the putative wintering area (estimated distance 1500 km) without further refuelling. 5. Our results suggest that migrating bats stopover for sanctuary or short-term rest as opposed to extended rest and refuelling as in many songbirds. Daily torpor could reduce energy costs when not in flight, minimizing the need for extended stopovers and allowing bats to potentially complete their migration at a fraction of the time and energy cost of similar sized birds.

The insectivorous batPipistrellus nathusiiuses a mixed-fuel strategy to power autumn migration

“…A similar strategy has already been suggested for migratory nectar-feeding bats, such as Leptonycteris curasoae, that benefit from nectar provided by agave and cactus plants along a migratory corridor from the southern United States to Mexico [42]. The efficacy of such an aerial refuelling strategy is even increased in bats when migrants use torpor during daytime rest, a strategy that has been recently defined for Chiroptera as 'torpor-assisted migration' [43].…”

The Motus Wildlife Tracking System: a collaborative research network to enhance the understanding of wildlife movement

“…This can be useful for projects in which the primary goal is not necessarily spatial tracking, for example measuring temperature variation in sedentary animals (McGuire et al 2012(McGuire et al , 2014. The use of noncoded tags in the broader Motus network is somewhat limited because only a small number of such tags can be uniquely defined for any given frequency (by changing the timing between or length of pulses).…”

Obese super athletes: fat-fueled migration in birds and bats

“…Female silver-haired bats appear to use less torpor and have greater roosting energy expenditure than males during spring stopovers, when they are pregnant, which may explain their greater fat loads in spring (Baloun, 2017;Jonasson, 2017). The low and predictable energy cost of stopping may reduce the need for refueling in migrating bats, contributing to short stopovers (McGuire et al, 2012. Furthermore, bats may feed before or during nocturnal migratory flight, thus using both endogenous and ingested fuels for flight .…”

“…Fat stores of bats cannot be assessed visually owing to their thick fur; however, non-invasive QMR analysis has greatly increased our understanding of their fat storage (McGuire and Guglielmo, 2010). Silver-haired bats migrating through Ontario, Canada, in the autumn average ∼19% body fat, with little difference between ages and sexes (McGuire et al, 2012). In the spring, migrating female silverhaired bats are generally fatter than males (10-17% versus 6-11% of the total body mass depending on year), likely reflecting a more conservative energy strategy in females (Jonasson and Guglielmo, 2016).…”