Diel Niche of Sympatric Small Mammals Revealed by Year-Round Camera Trapping

At northern latitudes, small mammals are of key importance for ecosystem dynamics. Yet, few have monitored the small mammal community to accurately investigate activity of sympatric small mammals at finer temporal resolutions, and consequently their temporal niche partitioning that may provide novel insights into how they interact with their environment and each other. Here, we deployed 12 tunnel-based camera traps to continuously monitor a forest community of small mammals in South-East Norway (2018-2020). We statistically determined the diel period selection (cathemeral, nocturnal, diurnal, crepuscular) in the wood mouse (Apodemus sylvaticus), bank vole (Myodes glareolus), common shrew (Sorex araneus) and pygmy shrew (S. minutus). We analyzed how temperature and snow cover influenced small mammal occurrence in winter and whether camera trap observations correlated with numbers from ordinary trapping in spring and fall. In both winter and summer, wood mice were nocturnal, while common shrews were cathemeral. Diel period selection in bank voles and pygmy shrews varied seasonally, and both were cathemeral in summer and nocturnal in winter. The occurrence of both rodents and shrews developed from a low year in 2018, to an increase in 2019, and to a peak year in 2020, albeit at lower amplitudes for the pygmy shrew. Small mammal occurrence in winter was positively influenced by temperature, but the relationship was dependent on snow cover and was only significant at low snow levels. Camera trap occurrence correlated moderately with spatially and temporally coinciding ordinary trapping indices in spring and fall. Thus, tunnel-based camera traps captured a new level of detail in species synchrony of common small mammals in northern Europe at annual, seasonal, and diel scales, yielding a better understanding of their ecology.