Family living: an overlooked but pivotal social system to understand the evolution of cooperative breeding

Bird breeding systems are more diverse than previously appreciated. Here we show that defining an intermediate breeding system, family breeding, where individuals postpone their dispersal but do not cooperate in reproduction, is a natural extension of the widely accepted 2-category system (pair vs. cooperative breeding). Evolution of prolonged association of offspring with parents appears to be possible in cases where it extends into unfavorable periods of environmental conditions such as autumn/winte