Altmetric tracks Mendeley readership by retrieving a total number of Mendeley readers for any publications that have been updated in the past day, directly from their API. The data available are a total number of readers, geographic locations (by country) of those readers, and the readers' self-identified subject areas and professional status (e.g. PhD Student, Researcher, Professor).
Mendeley data on the Altmetric Details Page
On an Altmetric Details Page, the number of Mendeley readers is displayed below the Altmetric badge, and the “Mendeley Readers” tab provides the geographic and demographic breakdown of the readership.
Mendeley readers don’t contribute to the Altmetric Attention Scores and don’t appear in the Altmetric badges.