Data
First, I collected a complete checklist of butterflies of Bangladesh from the most recent national Red List databook (305 species; IUCN Bangladesh, 2015), which contains both threatened and non-threatened butterflies. While collating species distribution data, I followed a range of approaches following Chowdhury et al. (2021a, b). Initially, I downloaded spatial occurrence records from the Global Biodiversity Information Facility (GBIF; https://www.gbif.org/) using the ‘rgbif’ package (Chamberlain et al., 2017) in R (R version 4.0.4). GBIF is a global data infrastructure network that compiles species occurrence records from several sources, including museum specimens and citizen science projects (Heberling et al., 2021). To avoid repetition, I did not collect data from other biodiversity repositories. Second, I searched for species distribution records in a Facebook group: Butterfly Bangladesh (https://www.facebook.com/groups/488719627817749). Here, I searched by species common name obtained from IUCN Bangladesh (2015), double-checked the identification in each photograph, and georeferenced the observations using the Google Map (https://maps.google.com/). I excluded photographs if the identification was incomplete (not up to species level) or wrong, if the photograph was not clear (from the taxonomic viewpoint), and if the location was unspecified (Chowdhury et al., 2021a, b). Third, I included my personal field observation records. Finally, I scanned for species distribution records from the published resources. Overall, the dataset contained 27,580 spatial records.
I collected both the current and the future (2081-2100) climatic data at 21.625 km2 resolution (2.5 min) from the WorldClim database (https://worldclim.org/). For the future climatic data, I used projections developed by Coupled Model Intercomparison Project (CNRM-CM6-1) in four Shared Socio-Economic Pathways (ssp; ssp126, ssp245, ssp370, and ssp585).
To compare the results between the migratory and the non-migratory butterflies, I downloaded the list of migratory butterflies from Chowdhury et al. (2021d).