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Morphometric characterisation of wing feathers of the barn owl Tyto alba pratincola and the pigeon Columba livia.

Bachmann T, Klän S, Baumgartner W, Klaas M, Schröder W, Wagner H - Front. Zool. (2007)

Bottom Line: Even though there is some information available on the mechanisms that lead to a reduction of noise emission, neither the morphological basis, nor the biological mechanisms of the owl's silent flight are known.We also present a quantitative description of several characteristic features of barn owl feathers, e.g., the serrations at the leading edge of the wing, the fringes at the edges of each feather, and the velvet-like dorsal surface.The quantitative description of the feathers and the specific structures of owl feathers can be used as a model for the construction of a biomimetic airplane wing or, in general, as a source for noise-reducing applications on any surfaces subjected to flow fields.

View Article: PubMed Central - HTML - PubMed

Affiliation: RWTH Aachen University, Institute of Biology II, Aachen, Germany. bachmann@bio2.rwth-aachen.de.

ABSTRACT

Background: Owls are known for their silent flight. Even though there is some information available on the mechanisms that lead to a reduction of noise emission, neither the morphological basis, nor the biological mechanisms of the owl's silent flight are known. Therefore, we have initiated a systematic analysis of wing morphology in both a specialist, the barn owl, and a generalist, the pigeon. This report presents a comparison between the feathers of the barn owl and the pigeon and emphasise the specific characteristics of the owl's feathers on macroscopic and microscopic level. An understanding of the features and mechanisms underlying this silent flight might eventually be employed for aerodynamic purposes and lead to a new wing design in modern aircrafts.

Results: A variety of different feathers (six remiges and six coverts), taken from several specimen in either species, were investigated. Quantitative analysis of digital images and scanning electron microscopy were used for a morphometric characterisation. Although both species have comparable body weights, barn owl feathers were in general larger than pigeon feathers. For both species, the depth and the area of the outer vanes of the remiges were typically smaller than those of the inner vanes. This difference was more pronounced in the barn owl than in the pigeon. Owl feathers also had lesser radiates, longer pennula, and were more translucent than pigeon feathers. The two species achieved smooth edges and regular surfaces of the vanes by different construction principles: while the angles of attachment to the rachis and the length of the barbs was nearly constant for the barn owl, these parameters varied in the pigeon. We also present a quantitative description of several characteristic features of barn owl feathers, e.g., the serrations at the leading edge of the wing, the fringes at the edges of each feather, and the velvet-like dorsal surface.

Conclusion: The quantitative description of the feathers and the specific structures of owl feathers can be used as a model for the construction of a biomimetic airplane wing or, in general, as a source for noise-reducing applications on any surfaces subjected to flow fields.

No MeSH data available.


Length of barbs in barn owl and pigeon wing feathers. The normalised length of barbs of the inner (iv) and outer vane (ov) of remiges (A, B) and coverts (C, D) from the barn owl (A, C) and the pigeon (B, D) are shown. The length was measured from the base to the tip and then normalised with respect to the whole length of vane. The area outside the dotted lines indicates regions of unconnected barbs forming the plumulaceous barbs (in both species), the fringes (in the barn owl) or serrations (p10 and gpc10 in the barn owl).
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Figure 4: Length of barbs in barn owl and pigeon wing feathers. The normalised length of barbs of the inner (iv) and outer vane (ov) of remiges (A, B) and coverts (C, D) from the barn owl (A, C) and the pigeon (B, D) are shown. The length was measured from the base to the tip and then normalised with respect to the whole length of vane. The area outside the dotted lines indicates regions of unconnected barbs forming the plumulaceous barbs (in both species), the fringes (in the barn owl) or serrations (p10 and gpc10 in the barn owl).

Mentions: In both species, the outer vane was homogeneous, which means that the edge was smooth and the surface regular. However, by taking a closer look at the length of the barbs and the angle of attachment of the barbs to the rachis, two different principles of construction were revealed. The length (Fig. 4A) and the angle of attachment (Fig. 5A) of the barn owl's barbs were nearly constant. By contrast, the pigeon's barbs varied in both parameters (Fig. 4B, Fig. 5B). The normalised length of the barbs increased towards the middle of the rachis (feather centre) and decreased towards the tip (Fig. 4B). The highest increase was found at the pigeon's feather s8. Here, the length of the barbs increased by a factor of three compared to those at the base of the feather. For most feathers of the pigeon, the angle of attachment decreased from the base to the tip of the feather. The change in the angle of attachment together with the variation of the length resulted in an almost constant depth of the outer vane as can be seen in Fig. 2B. The pigeon's feather p10 and all feathers of the barn owl had an almost constant angle of attachment. The angle of attachment of the barbs of the inner vane showed a similar, but less pronounced distribution than that of the outer vane. The most acute as well as the most obtuse angle was measured at the inner, respectively at the outer vane of feather p10 for both species.


Morphometric characterisation of wing feathers of the barn owl Tyto alba pratincola and the pigeon Columba livia.

Bachmann T, Klän S, Baumgartner W, Klaas M, Schröder W, Wagner H - Front. Zool. (2007)

Length of barbs in barn owl and pigeon wing feathers. The normalised length of barbs of the inner (iv) and outer vane (ov) of remiges (A, B) and coverts (C, D) from the barn owl (A, C) and the pigeon (B, D) are shown. The length was measured from the base to the tip and then normalised with respect to the whole length of vane. The area outside the dotted lines indicates regions of unconnected barbs forming the plumulaceous barbs (in both species), the fringes (in the barn owl) or serrations (p10 and gpc10 in the barn owl).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2211483&req=5

Figure 4: Length of barbs in barn owl and pigeon wing feathers. The normalised length of barbs of the inner (iv) and outer vane (ov) of remiges (A, B) and coverts (C, D) from the barn owl (A, C) and the pigeon (B, D) are shown. The length was measured from the base to the tip and then normalised with respect to the whole length of vane. The area outside the dotted lines indicates regions of unconnected barbs forming the plumulaceous barbs (in both species), the fringes (in the barn owl) or serrations (p10 and gpc10 in the barn owl).
Mentions: In both species, the outer vane was homogeneous, which means that the edge was smooth and the surface regular. However, by taking a closer look at the length of the barbs and the angle of attachment of the barbs to the rachis, two different principles of construction were revealed. The length (Fig. 4A) and the angle of attachment (Fig. 5A) of the barn owl's barbs were nearly constant. By contrast, the pigeon's barbs varied in both parameters (Fig. 4B, Fig. 5B). The normalised length of the barbs increased towards the middle of the rachis (feather centre) and decreased towards the tip (Fig. 4B). The highest increase was found at the pigeon's feather s8. Here, the length of the barbs increased by a factor of three compared to those at the base of the feather. For most feathers of the pigeon, the angle of attachment decreased from the base to the tip of the feather. The change in the angle of attachment together with the variation of the length resulted in an almost constant depth of the outer vane as can be seen in Fig. 2B. The pigeon's feather p10 and all feathers of the barn owl had an almost constant angle of attachment. The angle of attachment of the barbs of the inner vane showed a similar, but less pronounced distribution than that of the outer vane. The most acute as well as the most obtuse angle was measured at the inner, respectively at the outer vane of feather p10 for both species.

Bottom Line: Even though there is some information available on the mechanisms that lead to a reduction of noise emission, neither the morphological basis, nor the biological mechanisms of the owl's silent flight are known.We also present a quantitative description of several characteristic features of barn owl feathers, e.g., the serrations at the leading edge of the wing, the fringes at the edges of each feather, and the velvet-like dorsal surface.The quantitative description of the feathers and the specific structures of owl feathers can be used as a model for the construction of a biomimetic airplane wing or, in general, as a source for noise-reducing applications on any surfaces subjected to flow fields.

View Article: PubMed Central - HTML - PubMed

Affiliation: RWTH Aachen University, Institute of Biology II, Aachen, Germany. bachmann@bio2.rwth-aachen.de.

ABSTRACT

Background: Owls are known for their silent flight. Even though there is some information available on the mechanisms that lead to a reduction of noise emission, neither the morphological basis, nor the biological mechanisms of the owl's silent flight are known. Therefore, we have initiated a systematic analysis of wing morphology in both a specialist, the barn owl, and a generalist, the pigeon. This report presents a comparison between the feathers of the barn owl and the pigeon and emphasise the specific characteristics of the owl's feathers on macroscopic and microscopic level. An understanding of the features and mechanisms underlying this silent flight might eventually be employed for aerodynamic purposes and lead to a new wing design in modern aircrafts.

Results: A variety of different feathers (six remiges and six coverts), taken from several specimen in either species, were investigated. Quantitative analysis of digital images and scanning electron microscopy were used for a morphometric characterisation. Although both species have comparable body weights, barn owl feathers were in general larger than pigeon feathers. For both species, the depth and the area of the outer vanes of the remiges were typically smaller than those of the inner vanes. This difference was more pronounced in the barn owl than in the pigeon. Owl feathers also had lesser radiates, longer pennula, and were more translucent than pigeon feathers. The two species achieved smooth edges and regular surfaces of the vanes by different construction principles: while the angles of attachment to the rachis and the length of the barbs was nearly constant for the barn owl, these parameters varied in the pigeon. We also present a quantitative description of several characteristic features of barn owl feathers, e.g., the serrations at the leading edge of the wing, the fringes at the edges of each feather, and the velvet-like dorsal surface.

Conclusion: The quantitative description of the feathers and the specific structures of owl feathers can be used as a model for the construction of a biomimetic airplane wing or, in general, as a source for noise-reducing applications on any surfaces subjected to flow fields.

No MeSH data available.