Frequency alternation and an offbeat rhythm indicate foraging behavior in the echolocating bat, Saccopteryx bilineata
The greater sac-winged bat, Saccopteryx bilineata (Emballonuridae), uses two distinct echolocation call sequences: a ‘monotonous’ sequence, where bats emit ~48 kHz calls at a relatively stable rate, and a frequency-alternating sequence, where bats emit calls at ~45 kHz (low-note call) and ~48 kHz (high-note call). The frequencies of these low–high-note pairs remain stable within sequences. In Panama, we recorded echolocation calls from S. bilineata with a multi-microphone array at two sites: one a known roosting site, the other a known foraging site. Our results indicate that this species (1) only produces monotonous sequences in non-foraging contexts and, at times, directly after emitting a feeding buzz and (2) produces frequency-alternating sequences when actively foraging. These latter sequences are also characterized by an unusual, offbeat emission rhythm. We found significant positive relationships between (1) call intensity and call duration and (2) call intensity and distance from clutter. However, these relationships were weaker than those reported for bats from other families. We speculate on how call frequency alternation and an offbeat emission rhythm might reflect a novel strategy for prey detection at the edge of complex habitat in this ancient family of bats.
KeywordsSensory ecology Foraging Behavioral flexibility Source level Detection distance
- dB SPL RMS
Decibel sound pressure level re. 20 μPa root mean square
We thank Signe Brinkløv for field assistance. Signe Brinkløv, Brock Fenton, Kirsten Jung, Björn Siemers, Sub Zawadzki and two anonymous reviewers provided constructive criticism that helped us improve upon previous versions of the manuscript. STRI provided full access to research facilities and excellent logistical support. This study was funded by research grants from the Danish Natural Science Research Foundation (JMR, AS), the Oticon Foundation (LJ), STRI (EKVK) and the German Science Foundation (EKVK).
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