This study is the result of a long-term teamwork that is still in progress. Nothing would have been possible without the involvement and support of Julie Bachellerie , Anne-Sophie Benoiston , Sonia Cerutti, Thibault Guiragossian, Jean-Baptiste Javel , Laurent Pallas , Jordan Romeyer and Robert Russ, as well as all the volunteer students who were engaged in the fieldwork.