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).