Is more always better? Investigating helper effects on nestling condition in an obligatory cooperative breeding bird, the Arrow-marked Babbler

Cooperative breeding, where individuals assist in raising offspring that are not their own,  contradicts the evolutionary expectation of selfish behavior. While the advantages of this system are diverse, understanding its evolution is challenging due to different effects on reproductive success among species and the limited study of many cooperatively breeding species. This study focuses on the Arrow-marked Babbler (Turdoides jardineii), an obligate cooperative breeder, where previous findings suggest that group size does not enhance the number of fledged nestlings. The benefits of cooperative breeding in this species can be more subtle, potentially enhancing offspring quality rather than quantity.

 

Data is collected over three breeding seasons, covering 38 breeding attempts, analyzing group sizes, nestling growth, and provisioning rates. These results indicate that while nestling growth rates, condition, and provisioning rates slightly increased with group size, these increases were not statistically significant. This suggests that the primary benefits of cooperative breeding in Arrow-marked Babblers may not lie in increased reproductive output but rather in reduced individual workloads or enhanced adult survival.

 

This study emphasizes the need to consider a broader ecological context to fully understand the advantages of group living in cooperatively breeding species. 

This knowledge may have  important future implications, as cooperative breeding behaviour is expected to become more common with an increase in extreme and harsh environments associated with future climate change.