The relative role of local temperature in the winter occurrence of woodcock Scolopax rusticola in the northern Iberian Peninsula

The dynamics of migratory populations at wintering quarters can inform on population state and size because these areas act as demographic funnels, assembling birds from different origins. Previous evidence on survival probability of woodcock Scolopax rusticola wintering in northern Spain suggested a high harvesting pressure, but whether this pressure is causing a decline of woodcock occurrence at wintering quarters is still to be assessed. We used data from 3411 surveys conducted during the winter at 434 selected grasslands in the Gipuzkoa region, Northern Spain, to investigate the dynamics of woodcock occurrence probability, conditional on detection, over a period of 10 years (2009-2019). A 47% of the variation in woodcock occurrence within and across winters was explained by the monthly average minimum temperature. The remaining variation was due to a marked increase during the winters 2016 and 2017, contrary to the progressively decreasing values detected in previous years. At present, these abrupt yearly fluctuations prevent clear predictions on woodcock presence in the Gipuzkoa region. Future studies should explore woodcock occurrence probability according to scenarios of climate and habitat changes.