Common noctules exploit low levels of the aerosphere.

M Teague O'Mara,Martin Wikelski,Bart Kranstauber,Dina K N Dechmann

doi:10.1098/rsos.181942

M Teague O'Mara, Martin Wikelski + Show 2 more

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https://doi.org/10.1098/rsos.181942

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Abstract

Aerial habitats present a challenge to find food across a large potential search volume, particularly for insectivorous bats that rely on echolocation calls with limited detection range and may forage at heights over 1000 m. To understand how bats use vertical space, we tracked one to five foraging flights of eight common noctules (Nyctalus noctula). Bats were tracked for their full foraging session (87.27 ± 24 min) using high-resolution atmospheric pressure radio transmitters that allowed us to calculate height and wingbeat frequency. Bats used diverse flight strategies, but generally flew lower than 40 m, with scouting flights to 100 m and a maximum of 300 m. We found no influence of weather on height, and high-altitude ascents were not preceded by an increase in foraging effort. Wingbeat frequency was independent from climbing or descending flight, and bats skipped wingbeats or glided in 10% of all observations. Wingbeat frequency was positively related to capture mass, and wingbeat frequency was positively related to time of night, indicating an effect of load increase over a foraging bout. Overall, individuals used a wide range of airspace including altitudes that put them at increased risk from human-made structures. Further work is needed to test the context of these flight decisions, particularly as individuals migrate throughout Europe.

Highlights

The aerosphere, or the thin layer or atmosphere nearest the Earth’s surface, is a dynamic habitat posing distinct energetic and behavioural challenges and opportunities to flying animals [1,2,3,4]
Bats were tracked for their full foraging session (87.27 + 24 min) using high-resolution atmospheric pressure radio transmitters that allowed us to calculate height and wingbeat frequency
While bats predominantly flew at low altitudes, they ascended to over 100 m during 16 of 25 observation sessions and each bat used a variety of strategies throughout foraging

Summary

Introduction

The aerosphere, or the thin layer or atmosphere nearest the Earth’s surface, is a dynamic habitat posing distinct energetic and behavioural challenges and opportunities to flying animals [1,2,3,4]. Animals in this habitat respond to the availability of resources (e.g. food) and environmental conditions (e.g. wind), which may be largely decoupled from the terrestrial habitat immediately below them [1]. While there are many possibilities of why individuals move to higher foraging altitudes, how single individuals manage to successfully forage across patchily distributed food in these large volumes, as well as their decisions to do so, are poorly understood [3,4]

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