Limited but highly variable protected area use by Icelandic Whooper Swan Cygnus cygnus across the annual cycle

Protected areas form the cornerstone of biodiversity conservation, yet their utilisation by long distance migratory species, such as the Icelandic breeding population of Whooper Swans Cygnus cygnus , remains uncertain. We quantified the extent of protected area utilisation throughout the entire annual cycle using GPS tracking data from 47 individuals tagged in Iceland (>1,000,000 raw fixes, regularised to hourly positions with state-space models). Only 32.2% of all regularised hourly locations occurred within protected areas, while a 0.95 kernel density space-use isopleth had 24.5% overlap, and the 0.5 core isopleth had just 17.2% overlap. However, overlap was highly variable between individuals, ranging from 0 to 91% in some cases. Our results highlight that current protected area networks offer only partial coverage of Whooper Swan annual distributions, with a large majority of time spent in unprotected areas that may pose greater risk to populations. Our findings demonstrate how GPS tracking data can be used to assess species use of protected area networks at large spatial scales, to inform species conservation. Low protected area usage, even for a large, charismatic and conspicuous waterbird such as the Whooper Swan, illustrates the challenges of designing and implementing effective protected areas in mobile species, particularly as environmental change continues to alter space-use.