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:Little is known about the ranges at which toothed whales detect prey in the wild (Au et al. 2004, Madsen et al. 2004), but the extensive studies on trained delphinids in target detection experiments may offer a useful framework to estimate the range at which a squid of known TS can be detected.
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