Figure 4
From: Aquatic birds have middle ears adapted to amphibious lifestyles
Relative sizes of auditory structures, adjusted for head mass and phylogenetic relatedness and grouped by ecological group (a) and order (b). Data are residuals of univariate PGLS regressions relating head mass with each respective ear measure, both as log-transformed variables. Negative values (left of the black vertical lines) indicate smaller values than expected for the bird’s head mass, and positive values indicating greater values than expected. Box plots show the distributions of residuals by ecological group in (a) and individual data points represent different species in (b). Colors indicate ecological groups (white for terrestrial, orange for surface-foraging, black for plunge-diving, blue for underwater-pursuit). (i) tympanic membrane area, (ii) columella footplate area, (iii) tympanic membrane-to-columella footplate area ratio, (iv) columella offset from center of tympanic membrane, (v) umbo height, (vi) tympanic membrane angle, (vii) round window area (RW), (viii) cochlear aqueduct area (CA), (ix) extrastapedius length, (x) columella length, (xi) columella volume (xii) cranial air volume. An asterisk is present if the best-supported model for that ear measure included ecological group. In panels xiii and xiv, bar plots indicate the proportions for three levels of cranial air connectivity for the interaural canal and interbullar passage, respectively (white for air-filled connection, grey for connection present but filled with soft tissue, black signifies no pneumatic opening in the bone).
