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Big brains stabilize populations and facilitate colonization of variable habitats in birds


The cognitive buffer hypothesis posits that environmental variability can be a major driver of the evolution of cognition because an enhanced ability to produce flexible behavioural responses facilitates coping with the unexpected. Although comparative evidence supports different aspects of this hypothesis, a direct connection between cognition and the ability to survive a variable and unpredictable environment has yet to be demonstrated. Here, we use complementary demographic and evolutionary analyses to show that among birds, the mechanistic premise of this hypothesis is well supported but the implied direction of causality is not. Specifically, we show that although population dynamics are more stable and less affected by environmental variation in birds with larger relative brain sizes, the evolution of larger brains often pre-dated and facilitated the colonization of variable habitats rather than the other way around. Our findings highlight the importance of investigating the timeline of evolutionary events when interpreting patterns of phylogenetic correlation.

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Fig. 1: Graphical representation of our method for estimating and comparing population dynamics of North American birds.
Fig. 2: Significant two-way interactions between species traits and environmental variability on population stability.
Fig. 3: Testing the sequence of evolutionary events predicted by the cognitive buffer and colonization advantage hypotheses.
Fig. 4: Ancestral trait reconstruction of relative brain size and environmental niche.


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We thank B. Carlson for invaluable feedback on an earlier draft of this manuscript. We are also grateful to the BBS and the countless volunteers that participate annually in this yearly survey. Bayesian analyses were run in the Washington University Center for High Performance Computing (CHPC), which is partially funded by NIH grants 1S10RR022984-01A1 and 1S10OD018091-01. We thank M. Tobias for his helpful advice on HPC.

Author information




T.S.F. and C.A.B. designed analyses, compiled data and wrote the manuscript. T.S.F. additionally performed analyses and prepared figures. A.N.I. collected and compiled data, and contributed to writing.

Corresponding author

Correspondence to Trevor S. Fristoe.

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Supplementary Information

Supplementary Tables 1–3, Supplementary Figures 1–3

Supplementary Data 1

Data for 126 species used in population analyses. Variable descriptions can be found in the methods section of the manuscript.

Supplementary Data 2

Data for 2,062 species used in estimating relative brain sizes, including 1,288 species included in global evolutionary analyses. Variable descriptions can be found in the methods section of the manuscript.

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Fristoe, T.S., Iwaniuk, A.N. & Botero, C.A. Big brains stabilize populations and facilitate colonization of variable habitats in birds. Nat Ecol Evol 1, 1706–1715 (2017).

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