Analysis of Tail/Wing Ratios in Photographs of Honey Buzzards

An important distinction between Common Buzzard and Honey Buzzard is the length of the tail relative to the wing width. Information on total lengths L and tail lengths T can be obtained from the literature. The wing width W is taken as L–H-T where H is the length of the neck and head. The tail/wing ratio is then T/W or T/(L-H-T). There are a number of sources and the figures not surprisingly vary. Here values for L are from Forsman (1999), T from Cramp (1980) and H from this study by comparing the head+neck and tail lengths in photographs in Forsman (1999).

Why choose different sources? Cramp gives at the start of each text the protruding tail length (p.1, Introduction, Cramp. 1980) which is the ideal measure for the tail length. However, use of Cramp's overall lengths gives tail/wing ratios which appear to be out of line with those observed. Forsman's measurements are shorter (perhaps not stretched) and match the appearance in the wild more.

Ranges are given for L and T for adults in all sources. These have been considered in Table 1 by first looking at a typical small bird with lowest given values for L and T and a typical large bird with highest given values for L and T. These presumably represent the typical range and their values are shown in bold below. Also presented is the lowest possible (large bird with a short tail) and the highest possible (small bird with a long tail). It is not known how likely these are to occur in the wild. The overall typical ratios are converted into a general description of the tail/wing ratio for the species in the penultimate column. The table shows that Honey Buzzard, Black Kite and Marsh Harrier are not safely distinguishable on tail/wing ratios having values in the vicinity of 1.0. However, most Red Kite will show a higher ratio, significantly above 1 and Common Buzzard will show distinctly lower values around 2/3rds.

Table 1: Tail/wing Ratios for Five Species of Raptor from the Literature

The last column of Table 1 indicates whether the ratio differs for juveniles. Measurements for juveniles from the base of the tail to the tip are available in the section Measurements at the end of some species accounts in Cramp (1980). These measurements are longer than those given earlier for that part of the tail that protrudes. It is well-established that juveniles have shorter tails in Honey Buzzard (male juvenile 235 mm versus adult 251 mm; female juvenile 248 mm versus adult 259 mm). Juvenile Common Buzzards are often quoted as having longer tails than adults (see for instance, Forsman (1993), p.270) but the actual length difference from adults is really quite small (nominate buteo (Cramp, 1980): male juvenile 212 mm versus adult 208 mm; female juvenile 221 mm versus adult 215 mm). The apparently longer tail to wing ratio shown in photographs in various reference guides may therefore be more due to shorter secondaries (still growing?) than to a longer tail.

Actual figures from the plates of Forsman (1999) are 0.90-1.00 for juvenile Honey Buzzard and juvenile Common Buzzard. However from plates in the same source, first-summer Common Buzzard show relatively shorter tails with tail/wing ratios of around 0.75. So it appears to be strictly juvenile Common Buzzards that appear to have longer tails, possibly because of differential feather growth. For juvenile 'buzzards' long tails with short secondaries might indicate a Common Buzzard and long tails with bulging secondaries a Honey Buzzard.

Table 2 shows tail/wing ratios determined from the photographs on the web pages for Honey Buzzards. All bar two are in the range 1.00-1.06 which is consistent with their identification as Honey Buzzards and above the normal range of Common Buzzard. The two lower ratios are 0.88 for a juvenile Honey Buzzard in the South Tyne in early September and 0.92 for an adult (most likely a female showing some juvenile plumage features (Forsman (1999), plate 34)) at Baden Baden Station in late July. Text accompanying the photographs gives the reasons why they are considered to be Honey Buzzards. Both birds show bulging secondaries indicating that it is not short secondaries that are making the tail appear long.

Table 2: Tail/wing Ratios found in this Study

Some Honey Buzzard experts consider that Honey Buzzards normally have longer tails than those found in this study. The above analysis shows that the tail/wing ratios are as expected for Honey Buzzards and above those for Common Buzzards.

Also some Honey Buzzard experts feel that the photographs on this site are distorted with the telephoto lens used exaggerating the length of the tail. Examination of the originals on the main Identification page shows that the images are generally quite small and are centred completely in the middle of the lens, to benefit from autofocus. It is most unlikely that distortion will occur in this central part of the lens.

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© Copyright Nick Rossiter 2003