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:…the avian auditory forebrain (e.g. see Wild et al., 1993) consist of a large number of small, densely packed somata with average diameters in the range of 5±7 mm (Saini & Leppelsack, 1981; Hose et al., 1987) preventing the isolation of single units in the current study with freely moving animals.
Category: