Weasel (Mustela nivalis) decline in NE Spain: prey or land use change?

In this note, we reported the decline of weasel populations in NE Spain between the end of the last century and present. Our results suggested a delayed numerical response of weasels to wood mice abundance during the first study period (1995–1998), but no response at all in the second and longer period (2008–2015). Small mammals’ outbreaks triggered weasel’ populations in the first period, but they did not in the second period. Other factors may be invoked to explain the recent lack of numerical responses of weasels to mice. Population declines of small mammals have been noted in the study area in recent years, whereas an increase of casual predation records of weasels by generalist raptors has been documented. Both trends seemed to be related to the effects of the process of natural afforestation experienced by Mediterranean areas due to land abandonment. Top-down increased predation may add to bottom-up decreasing prey availability to explain current weasel declines.We are indebted to Diputació de Barcelona and Parc de Collserola (and their technical staff), which gave financial and logistic support during the study period. The project SEMICE benefitted from a grant to the Spanish Society of Conservation and Study of Mammals (SECEM) by Fundación Biodiversidad from the Ministerio de Agricultura, Alimentación y Medio Ambiente de España (2015)