Field identification of Apodemus flavicollis and Apodemus sylvaticus: a quantitative comparison of different biometric measurements

The identification of the wood mouse Apodemus sylvaticus and the yellow-necked mouse Apodemus flavicollis in the field has challenged many generations of field mammalogists, particularly in northern Spain and continental Italy. These two species present highly similar morphologic and morphometric characteristics especially when they are sympatric. Existing identification methods rely on morphometric and biometric measurements collected on killed or etherized animals, whereas in many field studies measurement may be taken only on live and awake animals. Genetic methods, instead, are time consuming, expensive and do not allow immediate identification in the field, which is a requirement in many types of ecological works. To contribute in filling this knowledge gap, the aims of this research were: 1) to assess biometric measurements (weight and length of hind foot) that allow species identification on live and awake animals and 2) to develop a predictive model and related software that, subject to refinement based on study area, will allow researchers to prioritise the selection of individuals to be identified by molecular approach. This model, based on a large (>1500) sample of individuals captured in two different sites in central Italy, should help to classify live and awake individuals of Apodemus species. Attached to this paper is a Microsoft Excel spreadsheet that may be used to apply the model to new data.