Bergmann’s (Not Really a) Rule


Several readers asked about Bergmann’s Rule, mentioned by WC in a recent Great-horned Owl post. Bergmann’s Rule isn’t really a rule; it’s not even a principle. It’s more like a guideline. Bergmann’s Rule is an ecogeographical “rule” that states that within a broadly distributed taxonomic clade, populations and species of larger size are found in colder environments, while populations…