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:…squirrels in the low elevation-meadow and alpinemeadow habitats in 2008–10, and the simultaneous extirpation of ground squirrels from the boreal forest since 1998 (Donker and Krebs 2011), provides supportive evidence that the boreal forest is functioning as sink habitat for arctic ground squirrels.
Category: