Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:Although all three species are relevant for primate conservation plans, Udzungwa red colobus is of particular interest; it is found only in the remaining forest fragments within and around the Udzungwa Mountains, it is listed as endangered (IUCN 2013), and is very sensitive to environmental changes and hunting (Marshall 2007; Marshall et al. 2010; Rovero and Struhsaker 2007; Rovero et al. 2012; Struhsaker 2010).
Category: