How to Be a Male at Different Elevations: Ecology of Intra-Sexual Segregation in the Trawling Bat Myotis daubentonii

Abstract

Intra-sexual segregation is a form of social segregation widespread among vertebrates. In the bat Myotis daubentonii, males are disproportionately abundant at higher elevations, while females are restricted to lower altitude. Intra-male segregation is also known to occur yet its ecological and behavioural determinants are unclear. We studied male segregation along a river in Central Italy where we tested the following predictions: 1. Upstream ( > 1000 m a.s.l.) males will rely on scarcer prey; 2. To deal with this limitation and exploit a cooler roosting environment, they will employ more prolonged and deeper torpor than downstream (< 900 m a.s.l.) males; 3. Body condition will be better in downstream males as they forage in more productive areas; 4. To cope with less predictable foraging opportunities, upstream males will use more habitat types. Consistent with our predictions, we found that prey were less common at higher altitudes, where bats exhibited prolonged and deeper torpor. Body condition was better in downstream males than in upstream males but not in all summer months. This result reflected a decrease in downstream males’ body condition over the season, perhaps due to the energy costs of reduced opportunities to use torpor and/or intraspecific competition. Downstream males mainly foraged over selected riparian vegetation whereas upstream males used a greater variety of habitats. One controversial issue is whether upstream males are excluded from lower elevations by resident bats. We tested this by translocating 10 upstream males to a downstream roost: eight returned to the high elevation site in 1-2 nights, two persisted at low altitude but did not roost with resident bats. These results are consistent with the idea of segregation due to competition. Living at high altitude allows for more effective heterothermy and may thus be not detrimental for survival, but by staying at lower altitude males increase proximity to females and potentially benefit from summer mating opportunities.

Habitat usage of Daubenton's bat (Myotis daubentonii), common pipistrelle (Pipistrellus pipistrellus), and soprano pipistrelle (Pipistrellus pygmaeus) in a North Wales upland river catchment

“…Suitable habitat (smooth water with trees on one or both sides) was readily available in transect seven, yet there were far fewer detections of M. daubentonii and P. pygmaeus than in transect 6 which was nearly 30 m lower in elevation. It may be that although sufficient habitat is available at higher elevation, other factors such as lower temperature and less predictable insect availability restrict bats in these areas (Capaverde et al, ; Dunn & Waters, ; Nardone et al, ; Todd & Waters, ). Indeed, foraging activity of bats and insect availability has been shown to decrease with increasing elevation (Grindal & Brigham, ), as has bat species richness (Patterson, Stotz, Solari, Fitzpatrick, & Pacheco, ); however, detections of P. pipistrellus were higher in transects six and seven than in lower transects.…”

Dark side of climate change: species‐specific responses and first indications of disruption in spring altitudinal migration in myotis bats

“…Linear regression analysis indicated a significant negative trend for the presence of this species at lower elevations as June temperatures have warmed 1.8°C in the area. It should be noted that there is evidence of sexual‐segregation in bats living in mountainous regions in the New (see Cryan et al ., for review) and Old World (Russo, ; Nardone et al ., ) wherein males and nonreproductive females of some species reside continuously at higher elevations. At our field sites, we capture large numbers of males at lower elevations for most species with the exception of M. volans wherein nearly 97% of all captures were females, even in cooler years (Adams & Hayes, under post‐revision review).…”

Sociality influences thermoregulation and roost switching in a forest bat using ephemeral roosts

“…We also verified the reliability of calibration in the laboratory for a subset of tags (Stawski & Geiser, ). We timed the duration of 21 pulses three times every 15 min for all bats from dawn to dusk emergence and calculated hourly means of such measurements, resulting in 15–17 values per bat/tracking day (Otto, Becker, & Encarnação, ; Nardone et al., ). At the same time intervals, ambient temperature ( T a ) was measured with a digital thermometer (precision: 0.1°C) placed in the shade near the roost at ca.…”