Abstract
Migration and hibernation are survival strategies that require physiological preparation using fattening. Bats employ both strategies in times of resource shortages. However, because males and females vary seasonally in their reproductive physiological needs, they may employ different fattening patterns. Whilst fattening, migration and hibernation are common in temperate bats, little is known about subtropical migratory insectivores. This study investigated seasonal variation in body mass of the regionally migrating Natal long-fingered bat Miniopterus natalensis to determine if males and females show fattening in preparation for migration/hibernation. Seasonal change best explained the variation observed in overall body mass, whilst sex and forearm length explained the variation to a lesser extent. Body mass between males and females differed significantly by reproductive category among the four seasons. Forearm length was a significant predictor of the body mass of males. Scrotal males had a higher body mass in summer compared to autumn. This pattern of mass gain was not observed in non-scrotal males. The summer body mass of nonpregnant and post-lactating females was not significantly higher than the autumn body mass of nonpregnant females, which did not support the hypothesis that females would exhibit fattening during summer before migration. Results suggest that males and females employ different mass-gain strategies related to reproductive investment rather than fattening preparation for migration or hibernation.
Highlights
Seasonal changes in resource availability induce various adaptations in animals
This study investigates the seasonal variation in body mass of male and female M. natalensis
Season best explained the overall variation in M. natalensis body mass, as well as forearm length (x2 = 31%) and sex (x3 = 27%) to a lesser extent (Table 2)
Summary
Seasonal changes in resource availability induce various adaptations in animals. Some notable adaptations, for vertebrates, include hibernation (prolonged periods of inactivity to save energy) and migration (periodically relocating to geographically distinct areas; Zubaid et al 2006, Kronfeld-Schor & Dayan 2013). Bats are unique among mammals, because they employ both migration and hibernation as adaptive strategies to changes in resource availability (Fleming & Eby 2003). The majority of bat migration studies have focused on temperate species (Fleming 2019). Studies have highlighted fat as the primary fuel for bat migration (Hedenstrӧm 2009, McGuire & Guglielmo 2009, Krauel 2014) and fat deposition can increase bat body mass by 12-26% (Krulin & Sealander 1972, Kunz et al 1998, Speakman & Rowland 1999). Unlike birds that fuel only migration through fattening (Rubolini et al 2002), bats must use fat stores for both migration and the subsequent hibernation, but the two fattening strategies are not mutually exclusive or separated (McGuire & Guglielmo 2009, McGuire et al 2013, 2014)
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