Nest predation predicts infanticide in a cooperatively breeding bird

Area of Science:

• Behavioral Ecology
• Evolutionary Biology
• Ornithology

Background:

• Social conflict is often cited as the cause of destructive behaviors like infanticide in cooperatively breeding species.
• An alternative hypothesis suggests infanticide, such as egg tossing in birds, might be a parental response to nest predation, representing a life-history trade-off.

Purpose of the Study:

• To investigate the underlying mechanisms of egg tossing behavior in the grey-capped social weaver (Pseudonigrita arnaudi).
• To test the hypothesis that egg tossing is a parental response to nest predation rather than social conflict.

Main Methods:

• Utilized infrared nest cameras to monitor egg tossing events over a six-year period (2012-2017).
• Observed egg tossing in a colonial, cooperatively breeding species, Pseudonigrita arnaudi, which exhibits plural breeding with separate nests.
• Manipulated clutch sizes through natural and simulated predation to assess parental responses.

Main Results:

• Parental birds were responsible for 78% of observed egg tossing events, indicating social conflict is unlikely to be the primary driver.
• Reductions in clutch size, caused by predation (natural and simulated), directly induced parental egg tossing behavior.
• Egg tossing appears to be a strategic response to conserve resources when faced with reduced reproductive success.

Conclusions:

• Destructive behaviors in cooperatively breeding birds can arise from diverse mechanisms, not solely social conflict.
• Parental egg tossing in Pseudonigrita arnaudi is linked to life-history trade-offs in response to nest predation.
• Alternative hypotheses, including adaptive responses to predation, should be considered when evaluating infanticide in group-living species.