Acoustic profiling of Orthoptera for species monitoring and discovery: present state and future needs

Background: Bioacoustic monitoring and classification of animal communication signals has developed into a powerful tool for measuring and monitoring species diversity within complex communities and habitats. The high number of stridulating species among Orthoptera allows their detection and classification in a non-invasive and economic way, particularly in habitats where visual observations are difficult or even impossible, such as tropical rainforests.

Methods: Major sound archives where queried for Orthoptera songs, with special emphasis on usability as reference training libraries for computer algorithms.

Results: Orthoptera songs are highly stereotyped, reliable taxonomic features. However, exploitation of songs for acoustic profiling is limited by the small number of reference recordings: existing song libraries represent only about 1,000 species, mainly from Europe and North America, covering less that 10% of extant stridulating Orthoptera species. Available databases are fragmented and lack tools for song annotation and efficient feature-based search. Results from recent bioacoustic surveys illustrate the potential of the method, but also challenges and bottlenecks impeding further progress. A major problem is time-consuming data analysis of recordings. Computer-aided identification software has been developed for classification and identification of cricket and grasshopper songs, but these tools are still far from practical field application.

Discussion: A framework for acoustic profiling of Orthoptera should consist of the following components:

(1) Protocols for standardised acoustic sampling, at species and community level, using acoustic data loggers for autonomous long-term recordings;

(2) Open access to and efficient management of song data and voucher specimens, involving the Orthoptera Species File (OSF) and Global Biodiversity Information Facility (GBIF);

(3) An infrastructure for automatised analysis and song classification;

(4) Complementation and improvement of Orthoptera sound libraries, using Orthoptera Species File as taxonomic backbone and repository for representative song recordings. Taxonomists should be encouraged to deposit original recordings, particularly if they form part of species descriptions or revisions.