Long-term occurrence of Chuck-will's-widow (Antrostomus carolinensis) beyond contemporary IUCN range

Effective conservation of wildlife requires current and accurate range maps of a species' distribution. While maintaining these resources can be challenging, especially for poorly documented species, the map is important for scientists, land managers, and decision makers alike. The International Union for the Conservation of Nature (IUCN) Red List of Threatened Species is a leading information source on the global extinction risk status of flora and fauna and provides current range maps for use in wildlife conservation and listing decisions. Chuck-will's-widow (Antrostomus carolinensis), a declining aerial insectivore whose contemporary range includes North and South America, is a near-threatened species according to IUCN, but its range map excludes areas known to support breeding populations. Here we compiled occurrence of Chuck-will's-widow within the state of Illinois across 6 data sources over a 65+ year period to highlight the occurrence of the species throughout the region. Although excluded from the current IUCN range map, we documented 947 occurrences of the species within Illinois since 1957. Through the use of minimum convex polygons (MCP), we report consistent and stable occurrence of Chuck-will's-widow, with the composite MCP ranging across the southern half of the state. Our results suggest that Chuck-will's-widow distribution within Illinois is not a result of recent colonization nor a climatic-induced shift in the species' distribution, but rather likely an underreporting of the species. This research illustrates how nocturnal or otherwise difficult to detect species may be widely underrepresented in public biodiversity databases and, as a result, have several gaps in their IUCN range maps. In addition to eBird and GBIF, we therefore encourage the inclusion of researchers and land managers along the range boundaries in the development of IUCN range maps, as local knowledge may be needed to fully describe the distribution of declining and underrepresented species.