Fig 1.
Serrations of T. furcata pratincola in different magnifications.
(A) Photograph of a 10th primary showing serrations along the outer vane. (B) Close up as indicated by the white rectangle in (A). Now the bending of the serrations is clearly visible. (C) Three-dimensional reconstruction of a serration. The serration was taken from the region marked by the white rectangle in (B). The barb shaft and the bow and hook radiates can be seen. The serration is divided into an unbent base and a serrated tip. The coordinate system, with the x-axis in the direction of the unbent barb shaft, the y-axis in the plane of the radiates with the positive direction towards the tips of the hook radiates, and the z-axis directed upwards, will be used in the further descriptions (adapted from [6]).
Fig 2.
Leading-edge serrations occur on the 10th primary remex and the 3rd alula. Serrations occur also on the 9th, 8th and 7th primary remiges.
Table 1.
Distribution of leading-edge serrations on different wing feathers of all owl species investigated.
Fig 3.
Measurement of shape parameters of serrations.
(A) Measurement setup. The outer vane was mounted in the horizontal plane (x-y plane). The y-axis is in the direction of the unbent barb shaft. Serrations were photographed with a microscope camera or a digital camera from above as indicated by the positive z-axis pointing downwards. (B) Sampling points on a 10th primary. The proximal end of the feather vane corresponds to sampling position 0, the wing tip, the most distal part of the feather vane, is set as sampling position 1. Sampling positions of 0.2, 0.4, 0.6 and 0.8 were investigated.
Fig 4.
Quantification of barb and serration shape.
(A) Rachis with a barb. The barb is divided into a base and a serrated tip. The base of the barb extends from the origin at the rachis to the point of separation. The positions of the bow and hook radiates are indicated as well. Two angles characterized the geometry. The inclination angle α is the angle between rachis and the base of the barb. The tip displacement angle β is the angle between the base of the barb and the tip of the serration measured from the point of separation. (B) Orientation and placement of a serration for the measurement of serration length.
Fig 5.
Three-dimensional reconstructions and images of outer vanes from different 10th primaries.
(A) Top view of a leading edge of C. livia domestica. The leading edge forms a distinct edge with small indentations at the interface between adjacent barbs. The white dotted line depicts the rachis of the feather in this area. Note the tilting of the barbs towards the rachis. (B) Three-dimensional reconstruction of consecutive barbs at the leading edge of C. livia domestica. The bow radiates are missing at the barb tip, exposing the outermost part of the barb. (C) Leading edge of 10th primary of L. fuscus (ventral view). (D) Leading edge of 10th primary of A. arvensis (top view). (E) Leading edge of 10th primary of Lanius spec. (top view). h.r.: hook radiates, b.r.: bow radiates.
Fig 6.
Leading edges on feathers of S. habroptilus and P. strigoides.
(A) Horizontal view on flight feathers of S. habroptilus from a dorsal perspective. (B) Horizontal view on a 10th primary feather of P. strigoides at 20% of the feather vane from a dorsal perspective. The barbules may be reduced in length at the barb tip.
Fig 7.
Outer vane of the 10th primary feather tip of T. furcata pratincola.
(A) Photograph of the leading edge of a 10th primary of T. furcata pratincola taken at 0.95–0.97 of the vane length. Note the denticulate leading edge. Note also that the barb shafts are straight or bent towards the rachis. (B) Frontal view of a three dimensional reconstruction of the outer vane. The tips of three barbs are presented in this reconstruction. Note that the Yf-Zf plane is perpendicular to the view present here, and can, therefore, not be seen. Note the tilt of the barbs. h.r.: hook radiates, b.r.: bow radiates
Fig 8.
Serrations at 50% of the outer vane on a 10th primary feather of T. furcata pratincola.
Isometric-like view on a three-dimensional reconstruction of five serrations. Note the upward bending and the twisting as indicated by the coordinate systems (for more information see text).
Fig 9.
Serrated structures on owl wings.
The serrations of all 7 investigated owl species are presented for 4 different measurement positions. Note the variation in shape between the different species and between the different positions within one species. The black bars represent 1 mm.
Fig 10.
At each position, the inclination angles of five serrations were measured for each feather. Five feathers were measured per species and feather position resulting in 25 measurements per species and feather position. Black circle: nocturnal species, white circle: diurnal species. (A) Plotted are the mean values and standard deviations of these 25 measurements. The inset in (A) shows how the inclination angle was measured. The color of the bars depicts the position at the feather as indicated in the inset. (B) Statistical comparison. Results of comparisons between species and positions. Abbreviations: B. bu.: B. bubo; B. sc.: B. scandiacus; T.f.p.: T. furcata pratincola; A. ot.: A. otus; A. fl.: A. flammeus; A. fu.: A. funereus; A.no.: A. noctua. *** and black: significance in more than 99% of the runs; ** and dark grey: significance in more than 95% of the runs, but less than 99% of the runs; * and light grey: significance in more than 67% of the runs, but less than 95% of the runs; white: significance in less than 67% of the runs. Note that for different activity patterns in 20 of 24 comparisons 99% of the runs yielded significance.
Fig 11.
(A) Plotted are the mean values and standard deviations of these 25 measurements. The inset in (A) shows how the displacement angle was measured. The color of the bars depicts the position at the feather. (B) Statistical comparison. The data base is the same as in Fig 10, and the measurement results for the tip displacement angle of all investigated owl species were compared in the same way as the inclination angles (see legend to Fig 10). Note that similar to the data for the inclination angle, in 20 out of 24 comparisons, more than 99% of the runs were different.
Fig 12.
(A) Plotted are the mean values and standard deviations of these 25 measurements. The inset in (A) shows how the length of the serrations was measured. The color of the bars depicts the position at the feather. (B) Statistical comparison. The data base is the same as in Fig 10, and the measurement results for the serration length of all investigated owl species were compared using the Monte Carlo method in the same way as the inclination angles (see legend to Fig 10). Note that serration length seems to be determined by a mixture of size and activity pattern, with no clear separation according to either of the two.
Fig 13.
Dendrograms were separately created for the different measurement positions based on the unweighted average distance and using the Euclidean distance metric at the corresponding position. The values next to the branches represent the distance between data points. (A): 0.2 of vane. (B): 0.4 of vane. (C) 0.6 of vane. Note that in (B) and (C) the diurnal species are clustered separately from the diurnal species, while in (A) the biggest species, B. bubo is clustered separately, while the remaining 6 species are clustered according to their activity pattern.