Satellite remote sensing of environmental variables can predict acoustic activity of an orthopteran assemblage

Abstract

Passive acoustic monitoring (PAM) is a promising method for biodiversity assessment, which allows for longer and less intrusive sampling when compared to traditional methods (e.g., collecting specimens), by using sound recordings as the primary data source. Insects have great potential as models for the study and monitoring of acoustic assemblages due to their sensitivity to environmental changes. Nevertheless, ecoacoustic studies focused on insects are still scarce when compared to more charismatic groups. Insects’ acoustic activity patterns respond to environmental factors, like temperature, moonlight, and precipitation, but community acoustic perspectives have been barely explored. Here, we provide an example of the usefulness of PAM to track temporal patterns of acoustic activity for a nocturnal assemblage of insects (Orthoptera). We integrate satellite remote sensing and astronomically measured environmental factors at a local scale in an Andean Forest of Colombia and evaluate the acoustic response of orthopterans through automated model detections of their songs for nine weeks (March and April of 2020). We describe the acoustic frequency range and diel period for the calling song of each representative species. Three species overlapped in frequency and diel acoustics but inhabit different strata: canopy, understory, and ground surface level. Based on the acoustic frequency and activity, we identified three trends: (i) both sampled cricket species call at lower frequency for shorter periods of time (dusk); (ii) all sampled katydid species call at higher frequency for longer time periods, including later hours at night; and (iii) the diel acoustic activity span window seems to increase proportionally with dominant acoustic frequency, but further research is required. We also identified a dusk chorus in which all the species sing at the same time. To quantify the acoustic response to environmental factors, we calculated a beta regression with the singing activity as a response variable and moon phase, surface temperature and daily precipitation as explanatory variables. The response to the moon phase was significant for the katydids but not for the crickets, possibly due to differences in diel activity periods. Crickets are active during dusk, thus the effects of moonlight on acoustic activity are negligible. The response to precipitation was significant for the two crickets and not for the katydids, possibly because of higher likelihood of rain interrupting crickets’ shorter diel activity period. Our study shows how the local survey of orthopteran acoustic assemblages, with a species taxonomic resolution coupled with remote-sensing environmental measurements can reveal responses to environmental factors. In addition, we demonstrate how satellite data might prove to be a useful alternative source of environmental data for community studies with geographical, financial, or other constraints.

Time and habitat structure shape insect acoustic activity in the Amazon

“…Nevertheless, the differences found were still significant. Our results agree with prior research in tropical forests from Panama [14] and Colombia [31], where acoustic activity of crickets and katydids also significantly varied throughout the night. However, the results were species-dependent.…”

“…The amount of minutes manually reviewed was similar or higher than that considered in most prior research using acoustic indices and sonotypes (e.g. 228 min or 0.4% of the total in [35], 672 min or 0.7% of the total in [36], 63 min or 0.03% of the total in [18] and 1342 min or 47% of the total in [31]).…”

“…However, the results were species-dependent. For example, in Colombia two cricket sonotypes were more often detected around sunset while five katydids sonotypes were detected more homogeneously throughout the night [31]. The authors attributed some of this variation among groups to cricket acoustic activity being influenced by rainfall, while katydids were more influenced by moonlight.…”

“…We also predict that (b) insect acoustic activity will vary among recording hours because several environmental factors (e.g. moonlight, temperature) may influence their activity and sound production throughout the night in tropical forests [12,19,30,31]. Our findings will contribute to a better understanding of the role of time, habitat and vegetation structure in shaping insect acoustic activity within diverse Amazonian ecosystems and might be useful to guide future research on other tropical regions.…”

Multi-year soundscape recordings and automated call detection reveals varied impact of moonlight on calling activity of neotropical forest katydids

“…In laboratory experiments, Botha et al [29] found no impact of manipulated light levels on song rate or structure in the cricket Teleogryllus oceanicus, whereas Levy et al [30] found that lifetime exposure to light affected circadian activity in the cricket Gryllus bimaculatus. In field studies, Gomez-Morales & Acevedo-Charry [31] examined moonlight impacts on the calling of orthopterans in Colombia, determining that cricket calling was unaffected by moon phase, but that there was a negative relationship between moon illumination and calling activity in all five sampled katydid species (or sonotypes, when animals could not be captured or identified). Lang et al [32] studied katydid activity in older growth neotropical forest quantifying katydid captures at lights, katydid bycatch in mist nets (set for bats), and total sound levels in ambient forest recordings throughout the moon cycle.…”