1 Tahrcountry Musings: Spatially balanced acoustic surveys for bats

Tuesday, July 26, 2011

Spatially balanced acoustic surveys for bats

A practical sampling design for acoustic surveys of bats

Thomas J. Rodhouse, Kerri T. Vierling, Kathryn M. Irvine
Wildlife Management - Article first published online: 21 APR 2011

Acoustic surveys are regularly put to use to find out bat occurrence and activity patterns. It comes in very handy for addressing concerns for habitat management, wind energy, and disease on bat populations. 
When a probabilistic sample is required for drawing inference to unsampled areas,  devising these surveys becomes a wee bit difficult. Sampling frame errors and other logistical constraints often makes it essential for survey sites to be dropped from the sample and new sites added. Here crops up difficulties.
The authors of this paper say spatially balanced sampling designs recently developed to support aquatic surveys along rivers provide solutions to a number of practical challenges faced by bat researchers. These techniques allow sample site additions and deletions, support unequal-probability selection of sites, and provide an approximately unbiased local neighborhood-weighted variance estimator that is efficient for spatially structured populations such as bats.
Taking cue from the above mentioned technique the researchers implemented a spatially balanced design to survey canyon bat (Parastrellus hesperus) activity along a stream network. This provided leeway for typical logistical challenges and yielded a 25% smaller estimated standard error for the mean activity level than the usual simple random sampling estimator.
The authors signs off like this  “Spatially balanced designs have broad application to bat research and monitoring programs and will improve studies relying on model-based inference (e.g., occupancy models) by providing flexibility and protection against violations of the independence assumption, even if design-based estimators are not used. Our approach is scalable and can be used for pre- and post-construction surveys along wind turbine arrays and for regional monitoring programs.

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