1. Opportunistically-collected species observations contributed by volunteer reporters are increasingly available for species and regions for which systematically collected data are not available. However, it is unclear if they are suitable to produce reliable habitat suitability models (HSMs), and hence if the species-habitat relationships found and habitat suitability maps produced can be used with confidence to advice conservation management and address basic and applied research questions. 2. We evaluated HSMs with opportunistically-collected observations against HSMs with systematically collected observations. We enhanced the opportunistically-collected presence-only data by adding inferred species absences. To obtain inferred absences, we asked individual reporters about their identification skills and if they reported certain species consistently and combined this information with their observations. We evaluated several HSM methods using a forest bird species, Siberian jay (Perisoreus infaustus), in Sweden: logistic regression with inferred absences, two versions of MaxEnt, a model combining presence-absence with presence-only observations and a Bayesian site-occupancy-detection model. 3. All HSM methods produced nationwide habitat suitability maps of Siberian jay that agreed well with systematically collected observations (AUC: 086-0.88) and were very similar to a habitat suitability map produced from the HSM with
systematically-collected observations (Spearman rho: 0.94-0.98). At finer geographical scales there were differences among methods.
4. At finer scale, the resulting habitat suitability maps from logistic regression with inferred absences agreed better with results from systematically collected observations than other methods. The species-habitat relationships found with logistic regression also agreed well with those found from systematically collected data and with prior expectations based on the species ecology. 5. Synthesis and application: For many regions and species, systematically-collected data are not available. By using inferred absences from high-quality opportunistically-collected contributions of few very active reporters in logistic regression we obtained HSMs that produced results similar to those from a systematic survey. Adding high-quality inferred absences to opportunistically-collected data is likely possible for many less common species across various organism groups. Well performing HSMs are important to facilitate applications such as spatial conservation planning and prioritization, monitoring of invasive species, understanding species habitat requirements or climate change studies.
All Siberian jay CSD presences
Presence observations of Siberian jay 2000-2013 (downloaded from https://analysisportal and processed according to Appendix S2.) Spatial reference for x and y coordinates: EPSG 3021.
Siberian jay CSD presences of 38 reporters
Presence observations of Siberian jay 2000-2013 from 38 reporters that consistently reported Siberian jay and were able to identify the species by sight and sound (downloaded from https://analysisportal and processed according to Appendix S2 & S3.) MatchYr 2000: Observations in years 2000-2002; MatchYr 2005: Observations in years 2003-2007; MatchYr 2010: Observations in years 2008-2013.
Spatial reference for x and y coordinates: EPSG 3021
Inferred Siberian jay absences
MatchYear 2000: Observations in years 2000-2002; MatchYear 2005: Observations in years 2003-2007; MatchYear 2010: Observations in years 2008-2013. Spatial reference for x and y coordinates: EPSG 3021.
SBS Siberian Jay PresAbs
Presence-absence SBS data processed according to information in the main text and in Appendix S1. MatchYear 2000: Observations in years 2000-2002; MatchYear 2005: Observations in years 2003-2007; MatchYear 2010: Observations in years 2008-2013. PA: 1 denotes presence, 0 denotes absence. Quarter gives the location of the observation unit within each SBS survey route: SW: south-west, NW: north-west, NE: north-east, SE: south-east. Karta is the survey route identifier. For further information about the SBS: http://www.fageltaxering.lu.se
Hazel grouse CSD presences
Presence observations of Hazel grouse 2000-2013 (downloaded from https://analysisportal and processed according to Appendix S2). Spatial reference for x and y coordinates: EPSG 3021.
Grey-headed woodpecker CSD presences
Presence observations of Grey-headed woodpecker 2000-2013 (downloaded from https://analysisportal and processed according to Appendix S2). Spatial reference for x and y coordinates: EPSG 3021.
Lesser spotted woodpecker CSD presences
Presence observations of Lesser spotted woodpecker 2000-2013 (downloaded from https://analysisportal and processed according to Appendix S2). Spatial reference for x and y coordinates: EPSG 3021.
Three-toed woodpecker CSD presences
Presence observations of Three-toed woodpecker 2000-2013 (downloaded from https://analysisportal and processed according to Appendix S2). Spatial reference for x and y coordinates: EPSG 3021.
Siberian tit CSD presences
Presence observations of Siberian tit 2000-2013 (downloaded from https://analysisportal and processed according to Appendix S2). Spatial reference for x and y coordinates: EPSG 3021.
Red-breasted flycatcher CSD presences
Presence observations of Red-breasted flycatcher 2000-2013 (downloaded from https://analysisportal and processed according to Appendix S2). Spatial reference for x and y coordinates: EPSG 3021.
Long-tailed tit CSD presences
Presence observations of Long-tailed tit 2000-2013 (downloaded from https://analysisportal and processed according to Appendix S2). Spatial reference for x and y coordinates: EPSG 3021.
Inferred Grey headed woodpecker absences
Inferred absences for Grey headed woodpecker. MatchYear 2000: Observations in years 2000-2002; MatchYear 2005: Observations in years 2003-2007; MatchYear 2010: Observations in years 2008-2013. Spatial reference for x and y coordinates: EPSG 3021.
Inferred Hazel grouse absences
Inferred absences for Hazel grouse. MatchYear 2000: Observations in years 2000-2002; MatchYear 2005: Observations in years 2003-2007; MatchYear 2010: Observations in years 2008-2013. Spatial reference for x and y coordinates: EPSG 3021.
Inferred Lesser spotted woodpecker absences
Inferred absences for lesser spotted woodpecker. MatchYear 2000: Observations in years 2000-2002; MatchYear 2005: Observations in years 2003-2007; MatchYear 2010: Observations in years 2008-2013. Spatial reference for x and y coordinates: EPSG 3021.
Inferred Long tailed tit absences
Inferred absences for long tailed tit. MatchYear 2000: Observations in years 2000-2002; MatchYear 2005: Observations in years 2003-2007; MatchYear 2010: Observations in years 2008-2013. Spatial reference for x and y coordinates: EPSG 3021.
Inferred Red breasted flycatcher absences
Inferred absences for red-breasted flycatcher. MatchYear 2000: Observations in years 2000-2002; MatchYear 2005: Observations in years 2003-2007; MatchYear 2010: Observations in years 2008-2013. Spatial reference for x and y coordinates: EPSG 3021.
Inferred Siberian tit absences
Inferred absences for Siberian tit. MatchYear 2000: Observations in years 2000-2002; MatchYear 2005: Observations in years 2003-2007; MatchYear 2010: Observations in years 2008-2013. Spatial reference for x and y coordinates: EPSG 3021.
Inferred Three-toed woodpecker absences
Inferred absences for three-toed woodpecker. MatchYear 2000: Observations in years 2000-2002; MatchYear 2005: Observations in years 2003-2007; MatchYear 2010: Observations in years 2008-2013. Spatial reference for x and y coordinates: EPSG 3021.