Geographic and phylogenetic sampling of avian wing-bone morphology. Using measurements from 7366 skeletal specimens, we analyze variation in wing-bone length across 1520 bird species, representing approximately 25% of passerine diversity. Credit: Global Ecology and Biogeography (2025). DOI: 10.1111/geb.70033 For centuries, scientists have observed that animals in warmer climates have longer limbs—a pattern known as Allen's Rule. Long attributed to the need