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:To date, all studies of the circatidal swimming rhythm in ovigerous blue crabs have been conducted in an estuary with strong
semi-diurnal tides (Forward et al. 2003, 2005; Forward and Cohen 2004), and the behavior of ovigerous crabs from other tidal regimes, including estuaries with negligible…
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