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:…group size on reproduction, particularly during drought conditions, probably results from reduced foraging efficiency from scramble competition (Bronikowski and Altmann 1996; Altmann and Alberts 2003a), as found in several other cercopithecine populations (van Schaik and van Noordwijk 1988;…
Category: