Assessing the function of house sparrows' bib size using a flexible meta-analysis method
TL;DR
Any sparrow can grow a big black bib. What keeps the signal honest is that rivals attack males who wear badges beyond their fighting ability.
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Demonstrated that badge-of-status signals work through social enforcement rather than production cost. The meta-analysis showed bib size predicts fighting ability, establishing how conventional signals can remain honest when communities police deception.
Key Findings from Nakagawa et al. (2007)
- Badge size strongly correlated with fighting ability (core finding)
- Moderate correlation between badge size and age
- Weak correlation between badge size and body condition
- No correlation between badge size and reproductive success or cuckoldry
- 2018 follow-up found smaller effect sizes and publication bias