Timed surveys and transect walks as comparable methods for monitoring butterflies in small plots
Butterflies are widely used in biodiversity surveys, and several methods of relative abundance counts have been developed. The most frequently used linear transects are praised for a good replicability, but recently have been criticised for poor species detecting ability, especially for poorly visible or extremely sedentary species. As an alternative, timed surveys, based on zigzagging study sites and flexibly checking transient butterfly resources, have been proposed by some authors. We tested the utility of the two methods while studying the effect of restoration practices on butterfly assemblages in limestone quarries in the Czech Republic. Numbers of species and individuals detected per 10 min transect walk were compared with numbers of species and individuals detected during 10 min timed survey. Mobile and imperceptible species were compared in separate analyses as a measure of detection efficiency. More species and individuals per visit were recorded by timed surveys. No difference in detectability of mobile and imperceptible species between both methods used was observed. Whereas linear transects will probably remain the method of choice for long-term monitoring programs employing armies of recorders, timed surveys appear more appropriate for studies in which it is important to obtain the most comprehensive check-list of species occurring at study sites, which is often the case in conservation inventories in species rich regions with limited number of experienced researchers.
KeywordsButterfly counting Lepidoptera Insect sampling Monitoring methods Pollard walks
J. Benes contributed by many constructive suggestions and fruitful discussions, Fric and M. Trnik helped us in the field, and S. Polakova and P. Smilauer consulted the statistics. We acknowledge funding from the University of South Bohemia (SGA2008/005), the Czech Science Foundation (206/08/H044, 206/08/H049, P505/10/2167), and the Czech Department of Education (MSM 6007665801, LC06073).
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