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:Females incubate and males fed females and chicks during the incubation and nestling phases; second broods are rare but renesting after early nest loss can occur (Rauter and Reyer 2000; Bollmann and Reyer 2001).
Category: