Monitoring of butterflies in semi-natural grasslands: diurnal variation and weather effects

Abstract

The butterfly fauna was monitored in six semi-natural grasslands in southeastern Sweden. The aim was to evaluate monitoring criterias for wind, sunshine, temperature and time of day for butterfly species richness and abundances when using the line transect method. A total of 30111 butterflies belonging to 46 species were recorded.Data from this study suggests somewhat stricter criteria for temperature and sunshine than stated in the widely used "Pollards walk". A sharp decline in butterfly numbers were detected at temperatures below 19°C if the proportion of sunshine of the transect walk was below 80-85 %. No effect of wind speed, up to five on the Beaufort scale, on observed numbers of species or individuals were found. Several butterfly species showed welldefined diurnal rythms of flight activity, and the results indicated that transect walks can be performed between -4.5 and +4 h from the time when the sun reached its highest point. The results of this study can be used to adjust general criteria in national monitoring and also for detailed regional and local monitoring where it may be important to adjust for diurnal rhythm and weather related bias.

The utility of repeated presence data as a surrogate for counts: a case study using butterflies

“…Additionally, aside from a few spot fires (less than 1 Ha in area) at NS, WS, and RC there was no directional succession at the sites to change habitat structure. Ensuring that monitoring conditions (weather, experience of observer, habitat structure, position of resources relative to transect) remain consistent for the duration of the project is important to maintaining consistent detection probabilities (Harker and Shreeve 2007;Wikström et al 2008;Pellet et al 2012).…”

High-accuracy sampling of saproxylic diversity indicators at regional scales with pheromones: The case of Elater ferrugineus (Coleoptera, Elateridae)

“…Despite the fact that conspicuous day flying species such as these are often sampled several times per year, there is still a substantial risk of species being under-reported in broad surveys (e.g. Wikström et al 2009, Jonason et al 2010, Quinto et al 2013). Hence we risk generating expensive data of low accuracy and precision.…”

Butterfly Assemblages Associated with Invasive Tamarisk (Tamarix spp.) Sites: Comparisons with Tamarisk Control and Native Vegetation Reference Sites

“…The lowest air temperature recorded was 19 ∘ C, thus all samples were collected at temperatures greater than the 17 ∘ C suggested as a minimum temperature for butterfly counts [28] and at wind speeds that do not affect butterfly detectability [27].…”

“…We also measured wind speed (km/hr) and air temperature ( ∘ C) at the start of each sampling occasion because of their effects on butterfly detectability. Wikstroem and others [27] found butterfly detection unaffected by wind speeds up to five (29-38 km/hr) on the Beaufort scale, and Pollard [28] suggested 17 ∘ C as a minimum temperature for butterfly counts. Inclement weather was avoided.…”