A practical comparison of manual and autonomous methods for acoustic monitoring
Article first published online: 16 MAY 2013
© 2013 The Authors. Methods in Ecology and Evolution © 2013 British Ecological Society
Methods in Ecology and Evolution
Volume 4, Issue 7, pages 675–683, July 2013
How to Cite
Digby, A., Towsey, M., Bell, B. D., Teal, P. D. (2013), A practical comparison of manual and autonomous methods for acoustic monitoring. Methods in Ecology and Evolution, 4: 675–683. doi: 10.1111/2041-210X.12060
- Issue published online: 2 JUL 2013
- Article first published online: 16 MAY 2013
- Accepted manuscript online: 13 APR 2013 08:56AM EST
- Manuscript Accepted: 2 APR 2013
- Manuscript Received: 24 JAN 2013
- Victoria University of Wellington (VUW) Doctoral Assistantship
- VUWCentre for Biodiversity and Restoration Ecology
- VUW School of Engineering and Computer Science
- Bank of New Zealand Save the Kiwi Trust
- acoustic monitoring;
- automated animal call recognition;
- research techniques
- Autonomous acoustic recorders are widely available and can provide a highly efficient method of species monitoring, especially when coupled with software to automate data processing. However, the adoption of these techniques is restricted by a lack of direct comparisons with existing manual field surveys.
- We assessed the performance of autonomous methods by comparing manual and automated examination of acoustic recordings with a field-listening survey, using commercially available autonomous recorders and custom call detection and classification software. We compared the detection capability, time requirements, areal coverage and weather condition bias of these three methods using an established call monitoring programme for a nocturnal bird, the little spotted kiwi (Apteryx owenii).
- The autonomous recorder methods had very high precision (>98%) and required <3% of the time needed for the field survey. They were less sensitive, with visual spectrogram inspection recovering 80% of the total calls detected and automated call detection 40%, although this recall increased with signal strength. The areal coverage of the spectrogram inspection and automatic detection methods were 85% and 42% of the field survey. The methods using autonomous recorders were more adversely affected by wind and did not show a positive association between ground moisture and call rates that was apparent from the field counts. However, all methods produced the same results for the most important conservation information from the survey: the annual change in calling activity.
- Autonomous monitoring techniques incur different biases to manual surveys and so can yield different ecological conclusions if sampling is not adjusted accordingly. Nevertheless, the sensitivity, robustness and high accuracy of automated acoustic methods demonstrate that they offer a suitable and extremely efficient alternative to field observer point counts for species monitoring.