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:Ovigerous females (Tankersley et al. 1998; Forward et al. 2003) and females between clutches of eggs (Hench et al. 2004; Forward et al. 2005) use ETT to migrate seaward.
Category: