Comments on Simon Elliott's Notes on Calls of Honey Buzzards and Common Buzzards
This publication (Elliott, 2005) is an important step forward, in conjunction with the work on these web pages, in converting raptor calls from phonetic strings to scientific measures of pitch, intensity and timing. It would have been nice to have had available on the British Birds web site the actual calls and perhaps spectrograms before removal of noise (assuming the latter was done to at least some extent) but presumably copyright problems were a factor here.
The model adopted that a call can be analysed completely through pitch, intensity and timing is only partial. Such a model omits tonality, that is the harmonics. While handling tonality is far from simple as the number of harmonics varies with the distance from the source of the call and the sensitivity of the recording equipment, it is essential for a full interpretation: the difference between a flute and a clarinet playing the same basic note for instance is obvious from the tonality but not from the other measures. Fortunately some data on tonality are available in the graphs presented.
Some comments on the four calls analysed:
a) Common Buzzard mewing (Figures 1 (a), 2(a) in paper) with strong upstroke, explosive start and multiple harmonics corresponds to that found in the present study. The strongest harmonic is around 2.5kHz, similar to that in the present study.
b) Honey Buzzard calls (Figures 1(b), 2(b) in paper) appear to correspond closely to anger calls in the present study. The call lasts about 0.5 seconds, has a weak upstroke and falls and rises around a central pitch, which in my study is called disyllabic but which is termed monosyllabic in the paper. There are multiple harmonics in the data in the paper and in my study with peaks at 4.5kHz and 2kHz in the paper and 4.5kHz and 2-2.5kHz (plus others at such close range) in my study.
c) Honey Buzzard calls (Figures 1(c), 2(c) in paper) appears to correspond closely to flight calls in the present study. The call lasts about 0.7 seconds, has a weak upstroke, a trisyllabic pattern with an inflexion in the long descent and a single harmonic. The frequency of the call is similar to that of Common Buzzard in the range 2.0-2.5kHz as found in the present study. Note this call is disyllabic if there is no inflexion on the downstroke.
d) Honey Buzzard calls (Figures 1(d), 2(d) in paper) with long trough in the pitch cannot be matched in the present study with this species. In the paper the length of this trisyllabic call is 0.5 seconds, there is a weak upstroke, then a decline in pitch to a long plateaux followed by a sharp rise in pitch at the end. There are two harmonics at about 2.0kHz and 4.5kHz, the lower one being the stronger.
On these web pages at calls,
calls and spectrograms are given for juvenile Common Buzzard and it is stated that
“Common Buzzard juvenile calls are perhaps more likely to be confused with Honey Buzzard calls than those of adult Common Buzzards. In particular the upstroke is weaker with the main emphasis on the long downstroke. In addition there is a clear quavering in the middle of the downstroke which might be interpreted as a trisyllabic Honey Buzzard call. However, the inflexion in the Honey Buzzard call occurs at the end of a straight-line descent in pitch whereas in the Common Buzzard juvenile the quavering runs right through the long descent. In some calls the quavering is so pronounced that there is a distinct second peak which is almost as high as the first peak. While juvenile Common Buzzard calls sound slightly thinner than those of adult Common Buzzard, the calls typically have four harmonics and hence have less of a whistled character than Honey Buzzard calls which at most have three harmonics (one strong, two weak). The exact number of harmonics recorded varies to some extent with the distance”.
It is possible that calls for Figures 1(d) and 2(d) in the paper refer to juvenile Common Buzzard and not to Honey Buzzard. The length, pitch, intensity and harmonics all point in this direction. Obviously some checks could be made from the date of the recording and listening to the recording. Also it needs to be borne in mind that Duff (2006, p.123) reports from work by Heinroth & Heinroth in 1926 that “captive fledged juvenile Honey-buzzards have been described as emitting a 'drawn-out, Common Buzzard-like mew' when agitated”.
It must be stressed that although there is this one possible disagreement, there is agreement on the other three calls.
