TABLE 1.
Average innervation density and range of best hearing across avian species
| Species | Hair-cell number | Sources | No. of papillar afferent fibers | Sources | Ratio of affs./HC | Prop. of aff.-innervated HC (Köppl et al. 2000) | Ratio of affs./HC innervated | Frequency range (Hz) | Sources |
|---|---|---|---|---|---|---|---|---|---|
| Chicken | 11,000 | (Tilney and Tilney 1986) (Manley et al. 1996) | 12,406 | (Köppl et al. 2000) | 1.13 | 80 % | 1.41 | 10–5,000 | (Gleich et al. 2004) |
| Pigeon | 9,610 | (Gleich and Manley 1988) | 5,136 or ~10,000 | (Boord 1969) (Winter 1963) | 0.5–1 | Assume 80 % | 0.6–1.2 | 50–5,000 | (Smolders et al. 1995) |
| Emu | 17,564 | (Köppl et al. 1998) | 10,038 | (Köppl et al. 2000) | 0.57 | 80 % | 0.71 | 50–5,000 | (Köppl and Manley 1997) |
| Starling | 5,830 | (Gleich and Manley 1988) | 8,775 | (Köppl et al. 2000) | 1.51 | 75 % | 2.01 | 30–6,000 | (Gleich et al. 2004) |
| Canary | 3,000 | (Gleich et al. 1994) | 6,080 | (Gleich et al. 2001) | 2.03 | Assume 75 % | 2.70 | 400–7,500 | (Gleich et al. 2004) |
| Budgerigar | 5,372 | (Manley et al. 1993) | 9,766 | (Manley et al. 1993) | 1.82 | Assume 75 % | 2.42 | 200–6,000 | (Gleich et al. 2004) |
| Barn owl | 16,300 | (Fischer et al. 1988) | 31,142 | (Köppl 1997) | 1.91 | 64 % | 2.99 | 100–10,000 | (Köppl et al. 1993) |
| Kiwi | 4,000 | (Corfield et al. 2011) | 6,936 | This study | 1.7 | Assume 75–80 % | 2.1–2.3 | 400–6,000 | (Corfield et al. 2011) |
For a total of 8 avian species, the table lists published counts of basilar-papilla hair cells and auditory afferent axons from the sources given in adjacent columns. From these numbers, the average ratio of afferent fibers to hair cells was derived in column 6. For the chicken, emu, starling, and barn owl, where quantitative data on innervation are available, Köppl et al (2000) calculated the proportion of afferently innervated hair cells (column 7). For the remaining species, an estimate was added, based on the most closely related species with actual data. This enabled the calculation of a corrected ratio of afferent fibers to hair cells, taking only those hair cells into account which actually receive afferents (column 8). The last two columns list the range of characteristic frequencies represented on the basilar papilla. For the canary, budgerigar, and kiwi, these are estimates based on a multitude of data detailed in the respective sources. Note the clear trend for species with a higher average afferent innervation density to also have a more restricted and higher-frequency-biased range of best hearing