title: Age group estimation in free-ranging African elephants based on acoustic cues of low-frequency rumbles.
abstract: Animal vocal signals are increasingly used to monitor wildlife populations and to obtain estimates of species occurrence and abundance. In the future, acoustic monitoring should function not only to detect animals, but also to extract detailed information about populations by discriminating sexes, age groups, social or kin groups, and potentially individuals. Here we show that it is possible to estimate age groups of African elephants (Loxodonta africana) based on acoustic parameters extracted from rumbles recorded under field conditions in a National Park in South Africa. Statistical models reached up to 70 % correct classification to four age groups (infants, calves, juveniles, adults) and 95 % correct classification when categorising into two groups (infants/calves lumped into one group versus adults). The models revealed that parameters representing absolute frequency values have the most discriminative power. Comparable classification results were obtained by fully automated classification of rumbles by high-dimensional features that represent the entire spectral envelope, such as MFCC (75 % correct classification) and GFCC (74 % correct classification). The reported results and methods provide the scientific foundation for a future system that could potentially automatically estimate the demography of an acoustically monitored elephant group or population.
authors.affiliation: Department of Cognitive Biology, University of Vienna, Vienna, Austria.
authors.forename: Angela S
authors.initials: AS
authors.lastname: Stoeger
authors.affiliation: Institute for Software Technology and Interactive Systems, Vienna University of Technology, Vienna, Austria.
authors.forename: Matthias
authors.initials: M
authors.lastname: Zeppelzauer
authors.affiliation: Department of Cognitive Biology, University of Vienna, Vienna, Austria.
authors.forename: Anton
authors.initials: A
authors.lastname: Baotic
keywords: Loxodonta africana; acoustic cues; acoustic monitoring; age groups
references.citation: PLoS One. 2012;7(11):e48907
references.pmid: 23155427
references.citation: J Acoust Soc Am. 2007 Jun;121(6):3922-31
references.pmid: 17552738
references.citation: J Comp Physiol A Neuroethol Sens Neural Behav Physiol. 2004 Oct;190(10):791-805
references.pmid: 15349746
references.citation: Ann Otol Rhinol Laryngol. 1985 Nov-Dec;94(6 Pt 1):634-40
references.pmid: 4073745
references.citation: Science. 2012 Aug 3;337(6094):595-9
references.pmid: 22859490
references.citation: J Acoust Soc Am. 2011 Sep;130(3):1700-10
references.pmid: 21895107
references.citation: Conserv Biol. 2010 Dec;24(6):1578-85
references.pmid: 20666800
references.citation: J Acoust Soc Am. 2002 Mar;111(3):1465-74
references.pmid: 11931324
references.citation: J Acoust Soc Am. 1997 Aug;102(2 Pt 1):1213-22
references.pmid: 9265764
references.citation: Trends Cogn Sci. 2000 Jul;4(7):258-267
references.pmid: 10859570
references.citation: Am Nat. 1993 Sep;142(3):528-42
references.pmid: 19425989
references.citation: PLoS Biol. 2007 Apr;5(4):e111
references.pmid: 17407383
references.citation: Acta Otolaryngol. 1966 Oct-Nov;62(4):309-18
references.pmid: 5956512
references.citation: PLoS One. 2010 Apr 26;5(4):e10346
references.pmid: 20436682
references.citation: J Acoust Soc Am. 1999 Aug;106(2):1054-63
references.pmid: 10462810
references.citation: Zoo Biol. 2010 Mar-Apr;29(2):192-209
references.pmid: 19434672
references.citation: J Comp Psychol. 2009 May;123(2):222-5
references.pmid: 19450029
references.citation: J Exp Biol. 1999 Oct;202(Pt 20):2859-67
references.pmid: 10504322