(a) Scatter plot of LOG olfactory bulb length (OBL) to LOG cerebral hemisphere length (CHL) (as in Ref.22), with the ten extant owls (large black dots; green–blue triangle for O. sunia) and the Rodrigues owl O. murivorus (orange circle), together with published bird data18,22. The Rodrigues owl shows the highest olfactory bulb ratio among strigids, and one of the highests among all birds. Abbreviations additional to this owl’s study (two owls from Ref. 22): B.v., Bubo virginianus; Asio f., Asio flammeus. Linear regression line is Y/X type (r2 = 0.48). Slope = 1.1. The translucid grey zone represents a 95% confidence interval around the regression. Bubo scandiacus is positioned at the opposite (with lowest olfactory bulb ratio among strigids). Dashed arrow symbolizes evolutionary trajectory from O. sunia to O. murivorus. (b–d) Cranial endocasts of O. murivorus (b), O. sunia (c) and A. cunicularia (d). The red arrows show the length of the olfactory bulb (measured as in Ref.22). Not to scale.