Ecogeography of group size suggests differences in drivers of sociality among cooperatively breeding fairywrens

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Allison E. Johnson, Joseph F. Welklin, Ian R. Hoppe, Daizaburo Shizuka


Cooperatively breeding species exhibit a range of social behaviors associated with different costs and benefits to group-living, often in association with different environmental conditions. For example, species in which collective-care of offspring reduces the cost of reproduction are more common in harsh environments (true cooperative breeding), while species that collectively defend resources are present in benign environments (family-living). Here, we examine whether environment also shapes sociality within cooperatively-breeding species. We illustrate that Purple-backed Fairywrens, which primarily gain intrinsic, or collective-care benefits, have larger groups in hot, dry environments and smaller groups in cool, wet environments, whereas Superb Fairywrens which primarily gain extrinsic, or resource defense benefits, exhibit the opposite trend. We suggest differences in the costs and benefits of sociality contribute to these opposing ecogeographic patterns, demonstrating that comparisons of intraspecific patterns of social variation across species can provide insight into how ecology shapes transitions between social systems.



Behavior and Ethology, Biology, Ecology and Evolutionary Biology, Evolution, Integrative Biology, Life Sciences


Cooperative breeding, dual-benefits, ecological constraints, ecological gradient, fairywrens, social benefits


Published: 2022-01-06 07:24

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CC-BY Attribution-No Derivatives 4.0 International

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Data and Code Availability Statement:
Raw social group size data will be deposited to OSF data repository pending manuscript acceptance to peer reviewed journal. Climate rasters can be acquired from the Australian Bureau of Meteorology ( Any additional information required to reanalyze the data reported in the paper is available from the lead contact upon request.