European conservation policy needs a clear definition of ‘wolf-dog hybrid’

Anthropogenic hybridisation, especially when introgressive through backcrossing into parental species, is a global threat to many wild taxa, including wolves ( Canis lupus ) interbreeding with dogs ( C. familiaris or C. l . familiaris ) (i.e., wolf-dog hybridisation, WDH). Despite the Standing Committee of the Bern Convention's recently approved proposal to reduce the protection status of wolves from Appendix II to Appendix III, the assessment of Favourable Conservation Status (FCS) for wolves within the EU Habitats Directive does not consider anthropogenic hybridisation as a separate threat category. Hybrids being increasingly recognised as a relevant threat to European wolves, we advocate that WDH should be considered in assessing their conservation status. However, the lack of a clear and commonly accepted definition of wolf-dog hybrids has been limiting progress on legislation, policy, and conservation management. Therefore, to help mitigate the threat of WDH to wolves, we hereby propose a science-based definition of wolf-dog hybrids as a reference for conservation management. The definition is not intended to prescribe management, which will require case-by-case consideration of various factors including local regulations, conservation priorities, ethics, animal welfare, and human dimensions. It (1) provides an entity for legal and policy efforts, (2) promotes shared and transparent technical standards for hybrid identification, and (3) acknowledges the need for nuanced, population-based management policies. The definition provides an essential first step and an international reference that we envision will help mitigate the threat of WDH to wolves and preserve wolf ecological function. • Anthropogenic hybridisation is a threat to many wild species, including wolves. • The lack of a commonly accepted definition of wolf-dog hybrids impedes progress. • We present a science-based wolf-dog hybrid definition for conservation management. • A clear, common definition will advance legislation, policy, and management. • We propose including hybridisation in Favourable Conservation Status guidelines.