Should I Stay or Should I Go? Seasonal Fluctuations of Wood Mouse Populations in Fields Surrounded by Woodlands

Simple Summary The abundance and distribution of rodents are driving factors in shaping ecosystem structure and functioning. In the Mediterranean region, the wood mouse is among the main representatives of small mammal communities, inhabiting both fields and different woodland types. The former are strongly seasonal environments which can represent a temporarily suitable habitat for mice. We investigated the seasonal pattern of wood mouse occurrence in three different habitats (fields, oak forest, and coniferous plantation) in central Italy, monitoring the number of captures and the population structure of the wood mouse for three years. We found that, unlike woodlands, fields are less suitable in autumn-winter than in warmer months, being characterized in colder months by a lower number of mice, a lower number of adult and reproductive individuals, lighter individuals, and a higher number of resident mice. Conversely, in spring-summer, we observed an increase in individuals caught in fields, especially breeding adults. These seasonal variations provide evidence that fields can represent a suboptimal habitat in this area, whilst playing, at the same time, a potential role as a source of food and cover resources and mates for mice in spring-summer. Our study contributes in filling the knowledge gap on wood mice ecology in the Mediterranean region. The wood mouse Apodemus sylvaticus is common in woodlands and open areas of the Western Palearctic. Despite extensive research, little is known about its population ecology in fields in the Mediterranean area, where the climate involves great seasonal changes in environmental features. Here, we investigated wood mice seasonal fluctuations in the number of captures and population structure by sampling long-fallow fields and woodlands, i.e., oak forest and conifer plantation, in a heterogeneous landscape of central Italy. Mice were live-trapped every two months for three years (23.814 trap-days). The number of captures, mice body weight, and proportion of adult, residents and breeding individuals were analyzed. Mice dynamics changed across seasons and habitats. In fields, we recorded more captures, more reproductive individuals, and fewer non-adults and resident individuals in the warmer months compared to the colder months; mice were heavier in warmer months. During the cold season, the captures and adult proportion in fields were lower than in resource-rich woodlands. Breeding and non-resident mice were more abundant in fields than in woodlands in warmer months. Overall, the seasonal demographic variations we recorded provide evidence that fields can represent a suboptimal habitat in Mediterranean heterogeneous landscapes, acting nonetheless as a source of food resources, cover, and mates for mice in spring-summer.