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:A similar protocol has been adopted by several previous studies (e.g. Almasi et al. (2010) who restrained barn owl nestlings for 26 ± 6 (SD) min; Liebl and Martin (2012) who restrained the birds for 30 min).
Category: