IMIS

Data from 1991-2014 were collected in the INBO Vlinderdatabank (Maes et al. 2016), but have since been migrated to the meetnetten.be database, where new observations are recorded. Here, the dataset is published as a standardized Darwin Core Archive and includes for each sampling event an eventID, date, location and sampling protocol (in the event core), the cloudiness, temperature, and wind force at the time of the event (in the measurement or fact extension) and for each occurrence an occurrenceID, the number of recorded individuals in a transect, lifestage, status (present/absent), vernacular and scientific name (in the occurrence extension). Issues with the dataset can be reported at https://github.com/inbo/meetnetten-occurrences/issues
Generalized and/or withheld information: location information is generalized to 5 Universal Transverse Mercator (UTM) grid cells. Original locations are available upon request.
Taxonomic coverage: The dataset covers 51 species. Nomenclature is according to Wiemers et al. (2018).
Sampling was done using the protocol described in Maes et al. (2019). Butterfly transects are in principle up to 1 km long and are divided into sections of 50 m (cf. Pollard & Yates 1993; van Swaay et al. 2008; van Swaay et al. 2011; Sevilleja et al. 2019). The length of 1000 m with up to 20 sections is a target that depends on the size of the area. The route is drawn in on a map or read using a GPS device, for example by using the "route" option of the mobile applications of www.waarnemingen.be (iObs and ObsMapp) or via the Track-Kit application. By using markers or landmarks on the transect, the different sections can be delineated so that the transect can be easily replicated by others. If, for some reason, a section is removed from the transect (e.g. no longer accessible, became completely unsuitable), then this section can either be replaced by a new section or no longer be counted (Onkelinx et al. 2017). In both cases, this must be documented and reported to the monitoring network coordinator so that it can be taken into account in the analyses of the data. Such sections are set to inactive on the input portal, but the data and location remain available for interpretation of historical data. The original numbering of these inactive sections, however, is not reused for the new sections so that there is no confusion in interpreting the data. The location of the different areas is visible at 5 x 5 km² square level to everyone on www.meetnetten.be. The details of the locations are only visible to people who are registered and approved for the monitoring network. Transect counts are conducted between 10-17h in suitable weather conditions for butterflies: temperature ≥ 17°C without clouds or temperature ≥ 20°C if cloudy, wind force ≤ 4 Beaufort and no precipitation. The counting itself is done by walking the transect at a pace that allows the identification of species by sight and noting the number of individuals per section of 50 meters. Sometimes it can be useful to catch a few less easily distinguishable species (e.g. the cabbage whites or skippers) at the same time and to name them at the end of each section. Only butterflies flying in an imaginary cage of 2.5 m left, 2.5 m right, 5 m above and 5 m in front of you are counted. In the Flemish butterfly monitoring scheme, weekly counts are conducted, when weather permits between April 1 and September 30. This makes a total of 26 weeks.