Prediction of basilar-papilla frequency map derived from hair-bundle morphology.

<p>A–C: Known frequency representations along the basilar papilla of the emu (A), chicken (B) and barn owl (C) compared to the variation in morphological factor (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0023771#s4" target="_blank">Methods</a>). Frequency maps were plotted using the equations of <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0023771#pone.0023771-Kppl3" target="_blank">[14]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0023771#pone.0023771-Chen1" target="_blank">[63]</a> and an improved polynomial fit to the data of <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0023771#pone.0023771-Kppl2" target="_blank">[13]</a>; they are shown in black, referring to the right ordinates. Stereovillar height and number for neurally-located hair cells were taken from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0023771#pone.0023771-Fischer1" target="_blank">[7]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0023771#pone.0023771-Manley2" target="_blank">[11]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0023771#pone.0023771-Kppl1" target="_blank">[12]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0023771#pone.0023771-Tilney2" target="_blank">[64]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0023771#pone.0023771-Fischer2" target="_blank">[65]</a> and the morphological factor derived from those is shown in gray, referring to the left ordinates. Note that the morphological factor correlates well with the species-specific shape of the frequency maps. D: Morphological factor and a prediction for the frequency distribution in the kiwi. The prediction is based on a linear regression of frequency as a function of morphological factor for the pooled data from emu (circles), chicken (triangles) and barn owl (diamonds), shown in the inset.</p

Overview of the kiwi basilar papilla.

<p>A: Surface view of the basilar papilla obtained from scanning electron microscopy. The tiny white dots represent individual hair-cell bundles. B: Cross section of the kiwi cochlea approximately half way along the basilar papilla. Key structures are labelled.</p

Number of stereovilli in mechanosensory hair-cell bundles increased nearly linearly along the basilar papilla.

<p>A, B: Two examples of SEM micrographs of hair bundles located at 10% from the apical end, neurally (A) and at 90%, abneurally (B). C: Boxplot of stereovillar numbers as a function of papillar position. For each longitudinal position, 3 different values are shown for hair cells located at the neural edge, near the midline and at the abneural edge, respectively.</p

Spectrograms of typical male and female kiwi vocalisations.

<p>The entire calls are shown to the left and an enlargement of one component of the calls with a power slice of the area indicated by the yellow line to the right. For details regarding recording and analysis methods see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0023771#pone.0023771-Corfield2" target="_blank">[54]</a>. Briefly, spectrograms and power spectra were produced with a Fast Fourier Transformation (FFT) size of 1,024 points using a Hamming window and 50% overlap, which produced a frequency resolution of 56 Hz.</p

Organisation of the forebrain of the Kiwi.

<p>Series of coronal sections through the forebrain of the Kiwi (top rostral, bottom caudal). Left hemisections show the regional demarcation that results from CR-LI. APH: Parahippocampal area; Bas: Nucleus basorostralis; CA: Anterior commissure; E: Entopallium; HA: Hyperpallium apicale; M: Mesopallium; MSt; Medial Striatum; N: Nidopallium; OB: olfactory ‘bulb’; St: Striatum; H: Hippocampus; Ov: Nucleus ovoidalis; SRt: Nucleus subrotundus; v: ventricle. Scale bar: 2 mm.</p

Visual fields of Kiwi.

<p>a, Perspective view of an orthographic projection of the binocular field as projected onto the surface of a sphere surrounding the bird's head. The grid shows conventional latitude and longitude at 20° intervals and the median sagittal plane of the bird's head is in the plane of the equator (which is vertical). The head is in the same posture as depicted in (c). b, Horizontal section through the visual field in the plane of maximum binocular field width which is the horizontal plane in (a) and (c). c, Drawing of a side view of a kiwi head, the bill tip projects 20° below the horizontal as shown in (a). Scale bar 40 mm.</p

Visual processing areas of the brains of four species of birds.

<p>Ventral and dorsal views of the brains of a, Emu (diurnal, flightless); b, Kiwi (nocturnal, flightless); c, Barn Owl (nocturnal, flying), and d, Pigeon (diurnal, flying). OT: optic tectum; ON: optic nerve ; OB; olfactory bulb (which actually consists of a cortical-like sheet in the adult kiwi – see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0000198#pone-0000198-g006" target="_blank">Fig. 6b</a>); V: vallecula. Note the reduced diameter of the optic nerve in Kiwi compared with that in the three other species (see text for actual measurements). In the dorsal view of Kiwi, note the caudal extension of the large telencephalic hemispheres, which completely hide the underlying midbrain. Note also in Kiwi that there is no obvious bulge on the dorsum of the hemisphere that identifies the Wulst in species such as Barn Owl and Emu. Scale bars: Emu, 1 cm; Kiwi, Barn Owl and Pigeon: 0.5 cm.</p