Male long-distance migrant turned sedentary; The West European pond bat (Myotis dasycneme) alters their migration and hibernation behaviour

Abstract

During autumn in the temperate zone, insectivorous male bats face a profound energetic challenge, as in the same period they have to make energy choices related to hibernation, mating and migration. To investigate these energetic trade-offs, we compared the body mass of male and female pond bats (Myotis dasycneme) through the summer season, characterized the known hibernacula in terms of male or female bias, and subsequently compared their population trend during two study periods, between 1930-1980 and 1980-2015. Towards the end of summer, males began losing weight whilst females were simultaneously accumulating fat, suggesting that males were pre-occupied with mating. We also found evidence for a recent adaptation to this energetic trade-off, males have colonised winter roosts in formerly unoccupied areas, which has consequently led to a change in the migration patterns for the male population of this species. As male bats do not assist in raising offspring, males have ample time to restore their energy balance after hibernation. Our results suggest that choosing a hibernacula closer to the summer range not only decreases energy cost needed for migration, it also lengthens the mating season of the individual male. Our findings have important conservation implications, as male and female biased hibernation assemblages may differ critically in terms of microclimate preferences.

Fig 1. Fluctuations in the body mass of the adult population during the year (data collected in period 2002–2015).

Fig 2. The (imputed) total annual abundance of pond bats in hibernacula in the provinces of Gelderland, Zuid-Holland and Limburg.

The three lines represent three groups of hibernacula; core sites (12 roosts, unbroken line), satellite sites (30 roosts, broken line) and limestone mines (59 roost, grey line).

Fig 3. Boxplot showing the microclimate range in the hibernacula and the microclimate near hibernating pond bats in bunkers (54 sites, 1,072 observations near pond bats) and limestone mines (32 sites, 401 observations near pond bats).

The box plots show the 25–75 percentiles (box), the 10 and 90 percentile (T). The line within the box indicates the mean. The broken lines indicate the observed temperature range inside both hibernaculum types (1,578 bunker and 1,406 limestone mine temperature observation points).

Fig 4

Map of recoveries from former (a) and recent (b) migration studies. Both maps are north orientated. In both figures’ males are shown in blue and females in red. The age of an animal is indicated by the shape of the points (square = unknowns age, circles = adult, triangle = sub-adult). The lines connect the point of capture and the point of recovery (adult / unknown age = unbroken line, sub-adult = broken line).