Kin selection, not group augmentation, predicts helping in an obligate cooperatively breeding bird

Area of Science:

• Evolutionary Biology
• Behavioral Ecology
• Animal Behavior

Background:

• Cooperative breeding, where non-breeders assist in raising young, is traditionally explained by kin selection theory.
• The role of kin selection has been questioned in obligate cooperative breeders, with group augmentation proposed as an alternative or addition.
• Empirical tests distinguishing between kin selection and group augmentation in obligate cooperative breeding systems are scarce.

Purpose of the Study:

• To test whether kin selection or group augmentation best explains helping decisions in the obligate cooperative breeder, the chestnut-crowned babbler (Pomatostomus ruficeps).
• To investigate the factors influencing decisions of whether, where, and how often individuals help raise young within their social group.

Main Methods:

• Correlational and experimental data were collected on helping behavior in chestnut-crowned babblers.
• Helping decisions were analyzed in relation to the presence and relatedness of kin, and the size of breeding units.
• The intensity of helping behavior was quantified based on relatedness to the brood being helped.

Main Results:

• No evidence was found that helping decisions were based on the size of breeding units.
• 98% of individuals with kin present in the group provided help.
• Individuals preferentially directed care towards the most related brood, with those helping half/full-sibs providing approximately three times more care than those helping less/non-related broods.

Conclusions:

• Kin selection, rather than group augmentation, is the primary driver of helping behavior in the chestnut-crowned babbler.
• These findings underscore the central role of kin selection in maintaining cooperative breeding systems, even in species living in large social groups.