Sex, bowers and brains

Area of Science:

• Avian biology
• Neuroscience
• Evolutionary biology

Background:

• Specific avian brain regions vary with behavioral complexity.
• A link between overall brain size and behavioral complexity is hypothesized but not demonstrated.
• This hypothesis is proposed to explain the large human brain size.

Purpose of the Study:

• To investigate the relationship between gross brain size and behavioral complexity in bowerbirds.
• To test if bower complexity correlates with relative brain size across bowerbird species.

Main Methods:

• X-ray imaging of museum specimens from various bowerbird species.
• Comparative analysis of brain size relative to body size.
• Controlling for phylogenetic relationships and ecological similarities.

Main Results:

• Bowerbird species that build bowers possess relatively larger brains than non-bower-building relatives.
• A positive correlation exists between bower complexity and relative brain size within bowerbird clades and the family.
• The relationship is more pronounced in males, the primary builders, but also present in females.

Conclusions:

• Gross brain size in bowerbirds is associated with behavioral complexity, specifically bower construction.
• Cognitive demands of bower building likely contribute to larger brain sizes.
• Sexual selection, driven by female choice for complex bowers, may be a key factor in driving brain enlargement.