Observations of living organisms by citizen scientists that are reported to online portals are a valuable source of information. They are also a special kind of volunteered geographic information (VGI). VGI data have issues of completeness, which arise from biases caused by the opportunistic nature of the data collection process. We examined the completeness of bird species represented in citizen science observation data from eBird and iNaturalist in US National Parks (NPs). We used approaches for completeness estimation which were developed for data from OpenStreetMap, a crowdsourced map of the world. First, we used an extrinsic approach, comparing species lists from citizen science data with National Park Service lists. Second, we examined two intrinsic approaches using total observation numbers in NPs and the development of the number of new species being added to the data-set over time. Results from the extrinsic approach provided appropriate completeness estimations to evaluate the intrinsic approaches. We found that total observation numbers are a good estimator of species completeness of citizen science data from US NPs. There is also a close relationship between species completeness and the ratio of new species added to observation data vs. observation numbers in a given year.
Future work should examine how far the results of this study can be reproduced with citizen science observation data-sets obtained from other projects with different properties, or with the same data-sets used in this study, but for other regions with different observation rates. Another important question is how our approaches would perform if applied to other species groups with different characteristics concerning mobility, detectability, and others. However, for any extrinsic completeness estimation as conducted in this study, there is always the difficulty of finding a suitable extrinsic source of reference data, especially for small focus regions.
Jacobs C. and A. Zipf (2017): Completeness of Citizen Science Biodiversity Data from a Volunteered Geographic Information Perspective. Geo-Spatial information Science, 2017. Taylor & Francis. DOI: 10.1080/10095020.2017.1288424.