A base station (12) and a method therein for adapting a triggering threshold for cell re-selection measurements performed by a mobile terminal (20) served by a macro cell (14). The macro cell (14) is supported by the base station (12), and the base station (12) and the mobile terminal (20) are comprised in a wireless communications network (10). The base station determines a serving cell signal strength threshold to be used for triggering cell re-selection measurements by the mobile terminal (20) in dependence on the availability of small cells (18a,18b) within or neighboring the macro cell (14). The base station (12) further transmits the determined serving cell signal strength threshold to the mobile terminal (20).