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Friday, 21 March 2014

Acoustic monitoring of seabird colonies to estimate relative abundance of birds. Conservation Biology; March 2014

Vocal Activity as a Low Cost and Scalable Index of Seabird Colony Size.

Abraham L. Borker 1
Matthew W. McKown 1 
Joshua T. Ackerman 2
Collin A. Eagles-Smith 2 
Bernie R. Tershy 1 
Donald A. Croll 1

1-Department of Ecology and Evolutionary Biology, Center for Ocean Health, University of California Santa Cruz, Santa Cruz, CA 95060, U.S.A.

2-U.S. Geological Survey, Western Ecological Research Center, Davis Field Station, One Shields Avenue, University of California, Davis, CA 95616, U.S.A.

Conservation Biology 2014 Mar 14. doi: 10.1111/cobi.12264.

Although wildlife conservation actions have increased globally in number and complexity, the lack of scalable, cost-effective monitoring methods limits adaptive management and the evaluation of conservation efficacy. Automated sensors and computer-aided analyses provide a scalable and increasingly cost-effective tool for conservation monitoring. A key assumption of automated acoustic monitoring of birds is that measures of acoustic activity at colony sites are correlated with the relative abundance of nesting birds. We tested this assumption for nesting Forster's terns (Sterna forsteri) in San Francisco Bay for 2 breeding seasons. Sensors recorded ambient sound at 7 colonies that had 15-111 nests in 2009 and 2010. Colonies were spaced at least 250 m apart and ranged from 36 to 2,571 m2 . We used spectrogram cross-correlation to automate the detection of tern calls from recordings. We calculated mean seasonal call rate and compared it with mean active nest count at each colony. Acoustic activity explained 71% of the variation in nest abundance between breeding sites and 88% of the change in colony size between years. These results validate a primary assumption of acoustic indices; that is, for terns, acoustic activity is correlated to relative abundance, a fundamental step toward designing rigorous and scalable acoustic monitoring programs to measure the effectiveness of conservation actions for colonial birds and other acoustically active wildlife. La Actividad Vocal como un Índice Escalable y de Bajo Costo del Tamaño de Colonia de las Aves Marinas.

Example Figure
Figure 1. 
Seasonal mean acoustic call activity (calls per minute) relative to (a) mean nest abundance and (b) total nest abundance during the 2009 and 2010 breeding seasons of Forster's terns at colonies in San Francisco Bay, California. Black line is best fit from a linear mixed model incorporating nest abundance with site, year, and sensor type as random factors.

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