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Group formation and the evolutionary pathway to complex sociality in birds

Cite this dataset

Downing, Philip; Griffin, Ashleigh; Cornwallis, Charlie (2020). Group formation and the evolutionary pathway to complex sociality in birds [Dataset]. Dryad.


Group-living species show a diversity of social organisation, from simple mated pairs to complex communities of inter-dependent individuals performing specialized tasks. The advantages of living in cooperative groups are well understood, but why some species breed in small aggregations while others evolve large, complex groups with clearly divided roles is unclear. We address this problem by reconstructing the evolutionary pathways to cooperative breeding across 4730 bird species. We show that differences in the way groups form at the origin of cooperative breeding predicts the level of group complexity that emerges. Groups that originate through the retention of offspring have a clear reproductive divide with distinct breeder and helper roles. This was associated with reproductive specialization, where breeders invest more in fecundity and less in care. In contrast, groups formed through the aggregation of unrelated adults are smaller and lack specialization. These results help explain why some species have not transitioned beyond simple groups, while others have taken the path to increased group complexity.


This data was collected via literature searches using key words in Web of Science, Google and Scopus.

Usage notes

There are three files included in this upload:

- DowningetalSuppTables.xlsx

- DowningetalRcode.R

- effectSizes.txt

Please README for full details of each file.


Swedish Research Council, Award: 2017-03880

Knut and Alice Wallenberg foundation, Award: 2018.0138

Natural Environment Research Council, Award: PhD studentship

Royal Society, Award: University Research Fellowship