Orientation and flight behaviour identify the Soprano pipistrelle as a migratory bat species at the Baltic Sea coast

Abstract

Migration routes of bats remain largely unknown, as previous orientation studies have been challenging even with newly developed techniques in tracking, genetic and stable isotope studies. However, a lack of knowledge about migrations poses problems for species conservation, especially in newly described species for which ecological information is not yet available. Here, we aimed to test flight orientation behaviour in the Soprano pipistrelle, Pipistrellus pygmaeus. This species has been described only 22 years ago but is now known to have a wide geographic distribution in Europe, yet virtually no information exists about seasonal movements of P. pygmaeus. In large parts of the continent, seasonal occurrence of P. pygmaeus matches with that of long‐distance migratory Nathusius' bats (Pipistrellus nathusii). To shed light on the migratory behaviour of both species, we investigated their orientation decisions at the Latvian Baltic Sea coast which is well‐known for summer bat migration along a north‐south axis. We developed an arena‐based assay designed to measure orientation of takeoffs. The arena was installed in the natural flight path of P. nathusii and P. pygmaeus, and after takeoff, bats chose the direction freely. We detected bearing fidelity between takeoff and departure flights, suggesting that bats used cues within the arena, putatively geomagnetic information, which allowed them to set a course prior to takeoff. Furthermore, our results show that P. pygmaeus orientates in a southerly, seasonally appropriate direction, similar to P. nathusii during ongoing migration. Therefore, our findings are consistent with true migratory behaviour of P. pygmaeus in the northern part of its range. Predicting flight directions of bats based on takeoff direction offers a simple test for orientation studies, and could further be used to test senses of bats under varying treatments, thereby facilitating a comparison of navigational skills across taxa, e.g., bats and birds.

In situ novel environment assay reveals acoustic exploration as a repeatable behavioral response in migratory bats

“…Though, we did not find evidence for a correlation between acoustic exploration and emergence latency, an often-used proxy for boldness (e.g., 47 ), in this study. A recent examination of in situ takeoff orientation in this species using a circular release box set-up 48 revealed emergence latency values that were highly similar (range: 6–176 s, median: 55 s) to those we report here (Supplementary Table 1 ). Both set-ups challenged individuals with a multi-directional choice for movement in a novel environment, raising the possibility that not only risk-aversion but also decision or orientation-speed may have influenced emergence latency, a hypothesis that requires further testing.…”

“…We placed the bat in the starting tube, with the exit obstructed by vertical and horizontal barriers in the form of wooden dowels. After 20 s we removed the vertical barrier and waited for a maximum of three minutes for the bat to emerge 48 . The time taken for the bats to completely emerge from the start tube was recorded.…”

In situnovel environment assay reveals acoustic exploration as a repeatable behavioral response in migratory bats

“…47 ), in this study. Recent examination of in situ takeoff orientation in this species using a circular release box set-up 48 revealed emergence latency values that were highly similar (range: 6 -176 s, median: 55 s) to those we report here (Supplementary Table 1). Both set-ups confronted individuals with a multiple directional choice for movement in a novel environment, raising the possibility that not only risk-aversion but also decision or orientation-speed may have influenced emergence latency, a hypothesis that requires further testing.…”

“…We placed the bat in the starting tube, with the exit obstructed by vertical and horizontal barriers in the form of wooden dowels. After 20 seconds we removed the vertical barrier and waited a maximum of three minutes for the bat to emerge 48 . The time taken for the bats to completely emerge from the start tube was recorded.…”

Bats and Wind Farms: The Role and Importance of the Baltic Sea Countries in the European Context of Power Transition and Biodiversity Conservation

“…This species has been identified as a long-distance migratory species too, but more data are needed to understand the behavior better. 113 Identification of its flyways and summer roosts is essential to set up a conservation strategy for this species in relevant areas. P. pygmaeus is facing a high risk of collision because of its open-space foraging behavior, therefore fatality rates must also be monitored.…”