How high is high? Using percentile thresholds to identify peak bat activity

Passive acoustic monitoring is a common tool used for monitoring bat activity levels. Identifying periods and locations of peak levels provides insight into bat ecology and has important management implications. One limitation of passive acoustic monitoring is the relative nature of the data, often relying on subjective interpretation of descriptive terminology such as “higher” or “lower”. We propose the use of percentile thresholds (PTs) for objectively identifying peak activity. By compiling a reference data set, it is possible to define percentiles of the observed activity levels and these percentiles can provide objective thresholds for comparing activity levels. We used acoustic recordings from sites in Canada and calculated PTs based on the distribution of the number of calls per hour across all nights and sites for three species of bat. Given species ecologies (e.g., hibernating, migrating), we were able to use PTs to objectively identify peak activity levels on a species-specific basis. Percentile thresholds are also a replicable method of describing within-night activity by evaluating species-specific activity patterns and important times of night. Our analyses and examples represent a proof of concept. The next step is to move towards a standardized distribution to generate PTs. Creating a public repository of acoustic data sets to evaluate activity of a species in the context of its entire range would allow us to standardize terms such as “high” activity in an objective manner.

Download Full-text

Bioacoustic characterization of mating calls of a freshwater fish (Prochilodus magdalenae) for passive acoustic monitoring

Biota Colombiana ◽

10.21068/c2021.v22n01a07 ◽

2021 ◽

Vol 22 (1) ◽

Author(s):

Sebastián Muñoz-Duque ◽

Silvia López-Casas ◽

Héctor Rivera-Gutiérrez ◽

Luz Jiménez-Segura

Keyword(s):

Pulse Rate ◽

Peak Frequency ◽

Acoustic Monitoring ◽

Passive Acoustic Monitoring ◽

Natural Habitats ◽

Train Duration ◽

Acoustic Characterization ◽

Species Specific ◽

Passive Acoustic

Fish produce sounds that are usually species-specific and associated with particular behaviors and contexts. Acoustic characterization enables the use of sounds as natural acoustic labels for species identification. Males of Prochilodus magdalenae produce mating sounds. We characterized these sounds and tested their use in natural habitats, to use passive acoustic monitoring for spawning ground identification. We identified two types of acoustic signals: simple pulses and pulse trains. Simple pulses were 13.7 ms long, with peak frequency of 365 Hz, whereas pulse train were 2.3 s long, had peak frequency of 399 Hz, 48.6 pulses and its pulses lasted 12.2 ms, with interpulse interval of 49.0 ms long and 22.3 Hz pulse rate. We did not detect spawning in absence of male calls nor differences in male sounds at different female densities. We found differences in train duration, pulse rate, and pulse duration in trains, according to the fish's source sites, but these sites were not well discriminated based on bioacoustical variables. In rivers, we located two P. magdalenae spawning grounds and recognized calls from another fish species (Megaleporinus muyscorum). We did not find a significant relationship between fish size and call peak frequency for P. magdalenae.

Download Full-text

Winter activity of boreal bats

Mammalian Biology ◽

10.1007/s42991-021-00111-8 ◽

2021 ◽

Author(s):

Anna S. Blomberg ◽

Ville Vasko ◽

Melissa B. Meierhofer ◽

Joseph S. Johnson ◽

Tapio Eeva ◽

...

Keyword(s):

Site Selection ◽

Barometric Pressure ◽

Acoustic Monitoring ◽

Passive Acoustic Monitoring ◽

Rock Outcrops ◽

Echolocation Calls ◽

Bat Activity ◽

Winter Activity ◽

Passive Acoustic ◽

Positive Effect

AbstractNatural hibernation sites used by bats in areas that lack cave features have long remained unresolved. To investigate hibernation site selection and winter activity of boreal bats, we recorded bat calls using passive acoustic monitoring at 16 sites in South-Western Finland. These sites included four rock outcrops with crevices and cave features, three glacial erratics or boulder fields, three ancient shores, three root cellars and three control sites where we did not expect bats to be overwintering. Our results revealed echolocation calls of Eptesicus nilssonii, Plecotus auritus and Myotis sp. We recorded significantly more activity near rock outcrops compared to other habitats, excluding root cellars. We also found that ambient temperature had a positive effect on bat activity and found evidence that P. auritus may be using low barometric pressure as a proxy for suitable foraging conditions during the winter. Our results suggest that rock outcrops may be more important to bats than previously acknowledged, highlighting the need to take these sites in account in planning of conservation measures. Furthermore, our findings underline the suitability of using acoustic monitoring in homing on hibernation sites that are not otherwise accessible.

Download Full-text

Passive Acoustic Monitoring Reveals Spatio-Temporal Distributions of Antarctic and Pygmy Blue Whales Around Central New Zealand

Frontiers in Marine Science ◽

10.3389/fmars.2020.575257 ◽

2021 ◽

Vol 7 ◽

Author(s):

Victoria E. Warren ◽

Ana Širović ◽

Craig McPherson ◽

Kimberly T. Goetz ◽

Craig A. Radford ◽

...

Keyword(s):

New Zealand ◽

Acoustic Monitoring ◽

Critically Endangered ◽

Blue Whale ◽

Passive Acoustic Monitoring ◽

Animal Populations ◽

Spatio Temporal ◽

Species Specific ◽

Passive Acoustic ◽

Blue Whales

Effective management of wild animal populations relies on an understanding of their spatio-temporal distributions. Passive acoustic monitoring (PAM) is a non-invasive method to investigate the distribution of free-ranging species that reliably produce sound. Critically endangered Antarctic blue whales (Balaenoptera musculus intermedia) (ABWs) co-occur with pygmy blue whales (B. m. brevicauda) (PBWs) around New Zealand. Nationally, both are listed as “data deficient” due to difficulties in access and visual sub-species identification. PAM was used to investigate the distributions of blue whales via sub-species specific song detections in central New Zealand. Propagation models, incorporating ambient noise data, enabled the comparison of detections among recording locations in different marine environments. ABW detections peaked during austral winter and spring, indicating that New Zealand, and the South Taranaki Bight (STB) in particular, is a migratory corridor for ABWs. Some ABW calls were also detected during the breeding season (September and October). PBW calls were highly concentrated in the STB, particularly between March and May, suggesting that an aggregation of PBWs may occur here. Therefore, the STB is of great importance for both sub-species of blue whale. PBW detections were absent from the STB during parts of austral spring, but PBWs were detected at east coast locations during this time. Detection area models were valuable when interpreting and comparing detections among recording locations. The results provide sub-species specific information required for management of critically endangered ABWs and highlight the relative importance of central New Zealand for both sub-species of blue whale.

Download Full-text

Winter activity of boreal bats

10.1101/2020.10.19.345124 ◽

2020 ◽

Author(s):

Anna S. Blomberg ◽

Ville Vasko ◽

Melissa B. Meierhofer ◽

Joseph S. Johnson ◽

Tapio Eeva ◽

...

Keyword(s):

Site Selection ◽

Barometric Pressure ◽

Acoustic Monitoring ◽

Passive Acoustic Monitoring ◽

Rock Outcrops ◽

Echolocation Calls ◽

Bat Activity ◽

Winter Activity ◽

Passive Acoustic ◽

Positive Effect

ABSTRACTNatural hibernation sites used by bats in areas that lack cave features have long remained unresolved. To investigate hibernation site selection and winter activity of boreal bats, we recorded bat calls using passive acoustic monitoring on 16 sites. These sites included four rock outcrops with crevices and cave features, three glacial erratics or boulder fields, three ancient shores, three root cellars and three control sites where we did not expect bats to be overwintering. Our results revealed echolocation calls of Eptesicus nilssonii, Plecotus auritus and Myotis sp. We recorded significantly more activity near rock outcrops and root cellars compared to other habitats. We also found that ambient temperature had a positive effect on bat activity and found evidence that P. auritus may be using low barometric pressure as a proxy for suitable foraging conditions during the winter. Our results suggest that rock outcrops may be more important to bats than previously acknowledged, highlighting the need to take these sites in account in planning of conservation measures. Furthermore, our findings underline the suitability of using acoustic monitoring in homing on hibernation sites that are not otherwise accessible.

Download Full-text