Editor's Choice - Technological developments and their associated opportunities in animal ecology: microphone arrays as an example
May 2011 (Issue 48:3)
Blumstein, D.T., Mennill, D.J., Clemins, P., Girod, L., Yao, K., Patricelli, G., Deppe, J.L., Krakauer, A.H., Clark, C., Cortopassi, K.A., Hanser, S.F., McCowan, B., Ali, A.M. & Kirschel, A.N.G. (2011) Acoustic monitoring in terrestrial environments using microphone arrays: applications, technological considerations and prospectus. Journal of Applied Ecology, 48, 758-767.
|Drs. Daniel Mennill and Stephanie Doucet set up one of eight microphones for acoustic array recordings used to monitor the position of duetting wrens in Santa Rosa National Park, Costa Rica. Photo by Dale Morris.|
As the biodiversity crisis has intensified and the challenges posed by global environmental change strengthened, the need to detect and predict changes in biodiversity and ecosystem functioning has become more and more urgent (Naeem et al. 1999). Such urgency has helped uncover the mismatch between the need to collect relevant information on species location and density worldwide, and the logistical constraints associated with visually locating and/or handling wildlife. To bridge this gap, ecologists and wildlife managers have increasingly been drawn towards new technological developments for non-invasive, remote-based biodiversity monitoring. This is well exemplified by the success stories of animal tracking devices such as camera traps (O’Connell, Nichols & Karanth 2011) or habitat monitoring sensors on board satellites (Turner et al. 2003; Pettorelli et al. 2011). For this issue’s Editor Choice selection, Blumstein et al. (2011) review the current successes of another promising remote monitoring technology, namely the use of microphone arrays for bioacoustic monitoring. Sounds produced by animals, such as for communication or navigation, most often encapsulate species-specific and individual-specific information exploitable by ecologists, rendering geo-referenced bioacoustic monitoring potentially suitable and attractive for non invasive biodiversity monitoring in inaccessible habitats.
|Map showing array-estimated positions of duetting wrens in Costa Rica. The shaded polygon shows estimated territory size. Males (blue squares) and females (red circles) are connected with white lines each time the pair performed a vocal duet. Orange circles show positions of eight microphones. Image by D. Mennill|
Bioacoustic monitoring techniques are not new, as they have been used extensively to monitor marine wildlife worldwide for several decades (see for example Richardson et al. 1995). Their potential for animal monitoring in terrestrial environments, however, has only been recently identified. As highlighted by Blumstein and co-workers, bioacoustic monitoring is not just about gathering information on species presence. Recent advances in bioacoustic technology means that such an approach can also help estimate species richness and species density, inform animals’ activity patterns and reproductive phenology, or understand the factors shaping signalling interactions among individuals. Such information can then be used to track the effects of climate change, habitat fragmentation or anthropogenic disturbances on behaviour, distribution or density of wildlife.
Yet this wealth of opportunities comes with its own set of challenges. First, this technology does not always come cheap: purchase of adapted recording devices, access to computer and memory resources, relevant algorithms and software packages for data analysis and display, as well as access to the relevant expertise, are all associated with costs that will need to be factored in before considering making use of bioacoustic monitoring methods. Unfortunately, such costs will be considerable for some of the countries where monitoring would be the most beneficial. Second, reliable signal recognition is still sometimes a challenge. Automatic species identification is sensitive to noise and may require extensive preliminary study to establish templates for recognition processes, detailed acoustic analyses and complex computational methods (Sueur et al. 2008). Third, environmental noise, equipment failure or biological variation can create heterogeneous datasets and reduce the potential for inter-site or inter-species comparisons. As underlined by Blumstein and co-workers, some of these issues might be resolved by (1) focusing on developing a common framework where new bioacoustic recognition systems could be developed, run and fully evaluated; (2) setting up a website or wiki to serve as a repository for collective experiences and knowledge; (3) developing and capitalizing on industry partnerships; and (4) fostering discussions and collaborations within the bioacoustic community and among disciplines.
|Yellow-bellied marmots (Marmota flaviventris) and a recording node. Copyright: Travis Collier.|
With the increased appearance of international treaties and conventions aiming at coordinating efforts among countries to face global environmental change and its expected consequences on biodiversity, there is an urgent need to develop a global monitoring framework for biodiversity (Pereira & Cooper 2006). Such a framework will need to make use of standardized methodologies that collect information at relevant spatial and temporal resolutions and extents. According to Blumstein et al. (2011)’s review and as demonstrated by initiatives such as ibats (see http://www.ibats.org.uk), it might well be that one such methodology could be derived from the growing field of bioacoustic monitoring.
Naeem, S., Chapin III, C.F.S., Costanza, R., Ehrlich, P.R., Golley, F.B., Hooper, D.U., Lawton, J.H., O’Neill, R.V., Mooney, H.A., Sala, O.E., Symstad, A.J. & Tilman, D. (1999) Biodiversity and ecosystem functioning: maintaining natural life support processes. Ecological Issues 4.
O'Connell, A.F., Nichols, J.D. & Karanth, K.U. (2011) Camera traps in animal ecology. Springer, 280 pp.
Pereira, H.M. & Cooper, H.D. (2006) Towards the global monitoring of biodiversity change. Trends in Ecology and Evolution, 21, 123-129.
Pettorelli N., Ryan S., Mueller T., Bunnefeld N., Jędrzejewska B., Lima M. & Kausrud K (2011) The Normalized Difference Vegetation Index (NDVI): unforeseen successes in animal ecology. Climate Research, 46, 15-27.
Richardson, W.J., Greene, C.R. Jr, Malme, C.I. & Thomson, D.H. (1995) Marine Mammals and Noise. London, Academic Press.
Sueur, J., Pavoine, S., Hamerlynck, O. & Duvail, S. (2008) Rapid Acoustic Survey for Biodiversity Appraisal. PLoS ONE 3 (12): e4065. doi:10.1371/journal.pone.0004065
Turner, W., Spector, S., Gardiner, N., Fladeland, M., Sterling, E. & Steininger, M. (2003) Remote sensing for biodiversity science and conservation. Trends in Ecology and Evolution, 18, 306-314.
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