Assessment of Detection Methods and Vegetation Associations for Introduced Finlayson’s Squirrels (Callosciurus finlaysonii) in Italy

Managing biological invasions requires rapid, cost-effective assessments of introduced species’ occurrence, and a good understanding of the species’ vegetation associations. This is particularly true for species that are elusive or may spread rapidly. Finlayson’s squirrel (Callosciurus finlaysonii) is native to Thailand and southeastern Asia, and two introduced populations occur in peninsular Italy. One of the two introduced populations is rapidly expanding, but neither effective monitoring protocols nor reliable information on vegetation associations are available. To fill this gap, we conducted visual surveys and hair tube sampling in a periurban landscape of southern Italy to compare the effectiveness of these two methods in assessing presence of Finlayson’s squirrel. We also determined the species’ association with vegetation types at detection locations and nesting sites. Both visual and hair tube sampling effectively assessed the species’ presence, but hair tubes resulted in fewer false absences. Moreover, when we controlled for the costs of labor and equipment, hair tubes were 33.1% less expensive than visual sampling. Presence of squirrels and their nests was positively correlated with shrub species richness, indicating that the occurrence of forests with well-developed understory may inhibit the spread of the species.