Common noctules exploit low levels of the aerosphere

Area of Science:

• Ecology
• Animal Behavior
• Bioacoustics

Background:

• Aerial insectivorous bats face challenges foraging in large vertical spaces due to echolocation limitations.
• Understanding bat vertical space utilization is crucial for conservation and ecological studies.

Purpose of the Study:

• To investigate the vertical flight strategies and height utilization of the common noctule bat (Nyctalus noctula).
• To determine factors influencing bat flight height and wingbeat frequency during foraging.

Main Methods:

• Tracking of eight common noctule bats using high-resolution atmospheric pressure radio transmitters.
• Recording full foraging sessions (average 87.27 minutes) to calculate flight height and wingbeat frequency.
• Analysis of flight strategies, including scouting flights and gliding behavior.

Main Results:

• Bats primarily foraged below 40 meters, with scouting flights reaching up to 100m and a maximum observed height of 300m.
• No significant influence of weather on foraging height was detected.
• Wingbeat frequency correlated positively with capture mass and time of night, suggesting increased load during foraging bouts.

Conclusions:

• Common noctules utilize a diverse range of airspace but generally stay at lower altitudes during foraging.
• Flight decisions, including high-altitude ascents, are not directly linked to increased foraging effort or weather conditions.
• Observed flight altitudes may increase risk from human-made structures, highlighting the need for further research on migration contexts.