![]() ![]() Trout (1978) observed a drastic decrease in population density during three consecutive trapping years, from an average of 200 individuals/ha during autumn and winter to almost zero in late spring and summer. It is known that trappability of some small mammals may decline during summer months, as for the wood mouse ( Apodemus sylvaticus Linnaeus, 1758) ( Butet 1994, Butet and Paillat 1997), but it is even more pronounced for the harvest mouse ( Sleptsov 1947, Trout 1978). While being able to move on the ground like any rodent, the harvest mouse will also climb up tall vegetation and it is very skillful at jumping from leaf to leaf and grasping thin herbaceous stems. These nests are commonly used to detect the presence of the mice in the wild because they are easy to find, but they do not reflect the actual population size ( Riordan et al. The harvest mouse and the hazel dormouse ( Muscardinus avellanarius Linnaeus, 1758) are the only small mammals in Europe able to make aerial nests in tall vegetation. The harvest mouse is the smallest rodent in Europe, adults weighing around 7 g, and it is a solitary species with no sexual dimorphism, females sometimes being bigger than males ( Rowe and Taylor 1964, Trout 1978). Unfortunately, it is understudied in the wild compared to other European small mammals, and one of the reasons is that this elusive species appears to be difficult to capture with usual ground trapping methods. 1995, Perrow and Jowitt 1995, Blant et al. 2008), the harvest mouse has the growing attention of scientists and naturalists in some countries like Switzerland and Great Britain where its populations have declined during recent decades ( Harris et al. Although the International Union for Conservation of Nature (IUCN) has assigned the status “least concern” to this species ( Aplin et al. The harvest mouse is a tiny mammal which is widespread in the Palaearctic and Indomalayan regions ( Wilson et al. Individual detectability is thus a major issue for small mammal studies, particularly for some species with special behavior like the harvest mouse ( Micromys minutus Pallas, 1771) which is known to be difficult to trap in the wild ( Flowerdew et al. ![]() Moreover, the detection probability of occurrence can be influenced by features of the local habitat or landscape, as well as behavior of individuals ( Gu and Swihart 2004). 2004), but as animals are often not evenly distributed, traps may have different detection probability relative to food source, ways of escape or proximity of the surrounding individual’s home ranges ( Watkins et al. ![]() Live-trapping is a key technique for monitoring small mammal populations ( Flowerdew et al. Indeed, it is known that a species may not be detected in a sampling unit even if it is actually present. Occurrence detection requires the implementation of techniques that take into account each species’ detectability. For small mammal surveys, as for other taxa, applications that rely on occurrence-related metrics cover a wide range of ecological disciplines, including measures of species distribution, habitat selection and modeling, structure and dynamic population studies and wildlife monitoring programs ( MacKenzie and Royle 2005). ![]()
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