Data from: Distorted views of biodiversity: spatial and temporal bias in species occurrence data

Historical as well as current data on species distributions are needed to
track changes in biodiversity. Species distribution data are found in a
variety of sources but is likely that they include different biases
towards certain time periods or places. By collating a large historical
database of ~170,000 records of species in the avian order Galliformes
dating back over two centuries and covering Europe and Asia, we
investigate patterns of spatial and temporal bias in five sources of
species distribution data; museum collections, the scientific literature,
ringing records, ornithological atlases and website reports from ‘citizen
scientists’. Museum data were found to provide the most comprehensive
historical coverage of species’ ranges but often proved extremely
time-expensive to collect. Literature records have increased in their
number and coverage through time whereas ringing, atlas and website data
are almost exclusively restricted to the last few decades. Geographically,
our data were biased towards Western Europe and Southeast Asia. Museums
were the only data source to provide reasonably even spatial coverage
across the entire study region. In the last three decades, literature data
have become increasingly focussed towards threatened species and protected
areas and currently no source is providing reliable baseline information,
a role once filled by museum collections. As well as securing historical
data for the future, and making it available for users, the sampling
biases will need to be understood and addressed if we are to obtain a true
picture of biodiversity change.