 It was originally suggested that cooperative breeding developed among bird species with low mortality rates as a consequence of “overcrowding” and thus fewer opportunities to claim territory and breed.However, many observers today believe cooperative breeding arose because of the need for helpers to rear young in the extremely infertile and unpredictable environments of Australia and sub-Saharan Africa under the rare favourable conditions.Across all mammalian species, less than 1% exhibit cooperative breeding strategies.