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Do Different Methods Yield Equivalent Estimations of Brain Size in Birds?
Diego Ocampo1,2, César Sánchez3, Gilbert Barrantes4
1Department of Biology, University of Miami, Coral Gables, Florida, USA, ocampov.diego@gmail.com.
Brain, Behavior and Evolution
|September 1, 2020
Summary
Different methods for measuring bird brain size are generally equivalent, except for hummingbirds. For hummingbirds, fixed brain mass underestimates and endocranial volume overestimates brain size.
Area of Science:
- Comparative anatomy
- Evolutionary biology
- Neuroscience
Background:
- Relative brain size is a key metric in ecological and evolutionary studies.
- Various methods exist to measure avian brain size, including endocranial volume, fixed brain mass, and fresh brain mass.
- The comparability of these brain size measurement methods across diverse bird taxa remains uncertain.
Purpose of the Study:
- To evaluate the consistency of different brain size measurement techniques in birds.
- To determine if endocranial volume, fixed brain mass, and fresh brain mass yield equivalent estimations of brain size across avian families.
Main Methods:
- Data collected from fresh avian specimens and published literature.
- Comparative analysis of brain size estimations using three distinct methods: endocranial volume, fixed brain mass, and fresh brain mass.
- Statistical evaluation of measurement consistency across 48 bird families from 19 orders.
Main Results:
- Endocranial volume, fixed brain mass, and fresh brain mass provided equivalent brain size estimations for the majority of bird families studied.
- Significant discrepancies were observed in brain size estimations for hummingbirds (Trochilidae) across the methods.
- Fixed brain mass tended to underestimate hummingbird brain size due to lower tissue density; endocranial volume overestimated it by including non-brain space.
Conclusions:
- Standard brain size measurement methods are largely interchangeable for most bird families.
- Hummingbirds present a unique case where specific measurement techniques introduce significant biases.
- Researchers should exercise caution when using endocranial volume or fixed brain mass for hummingbirds, considering potential inaccuracies in relative brain size calculations.
