Vocalisations of Yellow-browed Warbler and Hume's Leaf Warbler in autumn and winter

 

Teus J. C. Luijendijk



 

This article has been published in 2001 in Dutch Birding Vol. 23 (5), p. 275.

Hume's Leaf Warbler Phylloscopus humei Katwijk aan Zee ZH, 8 November 1999 (Jaap Dijkhuizen)

Introduction

The genus Phylloscopus comprises, dependent on the views of the taxonomists, 43-52 species. Several of these occur in so-called species pairs. They have been lumped together as one species in the past, but were recently assigned specific status. In some of these cases, vocal characters have played a major role in the delimiting process. Western and Eastern Bonelli's Warblers P. bonelli/orientalis, for instance, are very much alike in plumage and morphology, but have recently been split, largely due to their differences in call (and some details in song, too).

Another example of such a species pair is Yellow-browed Warbler P. inornatus/Hume's Leaf Warbler P. humei. The differences between these two taxa are quite straightforward and birds can be recognised in the field on plumage characters alone, although (especially in late winter) they both may become rather grey, making identification to the taxon slightly more difficult.

However, and this is what I intended to be the scope of this article, the two taxa can in autumn and winter be separated by their calls. Indeed, their songs are very much different, so breeding birds should not pose any problem, but as wintering birds will refrain from singing (and since I have never heard a singing Hume's Leaf Warbler), I will focus here on the calls.

At present, the calls of humei and particularly those of inornatus are well, though briefly, described in literature (see below). However, it was with a bird discovered in Flevoland (The Netherlands) in the winter of 1990/1991 that it became clear that the differences weren't always that easy and that humei's call was rather prone to vary. Although the standard of the field guides available nowadays is without doubt high, the descriptions of the call of humei still seem to be rather simplistic and do not mirror the degree of varaition possible. To give further insight in these variations I have here summarised the calls of humei I managed to record, in comparison to those of inornatus.

Literature

Lewington et al. (1991) describe the calls of the two taxa as "a distinctive, loud, penetrating, rather high-pitched tsuee-eep, or differently transcribed tsweet" for inornatus and "visu, uttered singly or repeated" for humei.

Jonsson (1992) describes them as "a longish indrawn tsueeht often with peculiar lisping tone" for inornatus and "... a clearly double-note tze-veet or sle-wee, can be likened to a slow-downed version of Greenish Warbler's" for humei.

Finally, Mullarney et al. (1999) describe them as "a loud, penetrating, high-pitched sweest or tsoeest, the quality of the call often recalling Coal Tit, though higher-pitched and more clearly rising" for inornatus and "a forceful whistling dsweet, or disyllabic, slightly descending dseewo" for humei.

Materials

Recordings were made using a Sony TCS-450 walkman (until 1991) or a Sony Professional WM-D3 cassette recorder, combined with a Audiotronic (until 1991) or Sony ECM-Z157 video-microphone. As cassette tapes I always used ferro tapes as these appeared to give a better result in the higher frequency range. Sonograms were made by manual editing of the digitalised recordings.

Results

I have given sonograms and (very short) *.wav files for a number of birds I have managed to make recordings of. Unfortunately, the sound files had to be kept very short as they quickly take up too large disk space. Another option, conversion into Real (*.ra) files, resulted in bad quality and distortion (particularly in the high frequency range), and was therefore avoided. All sonograms are given for a full second, in a frequency range of 0-10 kHz (top figures). The respective wave-figures are given, too (bottom figures), to give an idea of the amplitude of each call.

For more information, click how to read a sonogram.

My personal experience is that sonograms may be very helpful in detecting differences between bird sounds. Some differences may be that slight, however, that, although they result in similar sonograms, still remain well audible for the human ear. Therefore, it is advised not to rely on graphic interpretations alone, but to listen carefully to the recordings as well.

 

Table 1.  Data of the birds recorded.


1

Hume's Leaf Warbler P. humei

Wassenaar, ZH, The Netherlands

13 December 1990

example

2

Hume's Leaf Warbler P. humei

Den Haag, ZH, The Netherlands

2 January 1996

example

3

Hume's Leaf Warbler P. humei

Katwijk aan Zee, ZH, The Netherlands

8 November 1999

example

4

Hume's Leaf Warbler P. humei

Zwartewaal, ZH, The Netherlands

8 January 2000

example

5

Hume's Leaf Warbler P. humei

Blocq van Kuffeler, Fl, The Netherlands

30 December 1990

example

6

Hume's Leaf Warbler P. humei

Katwijk aan Zee, ZH, The Netherlands

8 November 1999

example

7

Hume's Leaf Warbler P. humei

Zwartewaal, ZH, The Netherlands

8 January 2000

example

8

Yellow-browed Warbler P. inornatus

Vlieland, Fr, The Netherlands

28 September 1997

example

9

Yellow-browed Warbler P. inornatus

Vlieland, Fr, The Netherlands

8 October 1999

example



    humei

The calls of humei can roughly be divided in single-tone and multisyllabic calls. The latter are mostly disyllabic calls, but trisyllabic calls also occur. They are highly variable.

A. multisyllabic calls

Nr. 1 is the 'classical' humei call, a somewhat sparrow-like tswee-up, with an obvious downward inflection. Duration is approx. 0.2 sec.

 

example of this call

Nr. 2 is less obviously multisyllabic, but there still is a clear 'partition' in the call. The second part has, in contrast to Nr. 1, an upward inflection. Duration is approx. 0.27 sec.

 

example of this call

Nr. 3 also has un upward inflection, but is rather short, with an approximate 0.23 sec.

 

example of this call

Nr. 4 is again somewhat shorter and is becoming more single-toned. Duration is very short, approx. 0.15 sec.

 

example of this call


B. single-tone calls

Nr. 5 is a call that confused a lot of observers. Its quality is almost like the common contact call of (nominate subspecies) Chiffchaff P. collybita. At the time of the observation (1990), nothing was documented about such aberrant calls for humei. This bird was - as far as I know - not heard calling otherwise. The bird showed itself very well, however, so there was in the end little doubt about its identity as a humei. Pictures of this bird were published in Dutch Birding (Anonymous 1991) and in 'Rare birds in the Netherlands' (van den Berg & Bosman 1999). The duration of the call is only 0.17 sec.
example of this call

Nr. 6 is another example of this call, but this bird uttered it in a more rapid and repetitive way. These series were heard only a few times. The bird would more often give a disyllabic call (nr. 3), but was on the whole rather silent. Duration of this call: approx. 0.17 sec.

 

example of this call

Nr. 7 is, more like nr. 5, an example of a call uttered only every now and then (not in series). This bird was more vocal than the previous one, but shared its preference for calling disyllabically. Duration is somewhat longer (approx. 0.20 sec.). Frequency was the highest of all Hume's I have ever heard.

 

example of this call

 

    inornatus

The calls of inornatus are less variable than those of humei and have (as far as I know) always the character reminiscent of that of Coal Tit Parus ater. Nominate inornatus normally has a multisyllabic call, but this can (in some cases) be squeezed into a(n almost) single-tone type call. I have heard a bird giving this call in the autumn of 1999 on the isle of Vlieland, The Netherlands, but unfortunately I was unable to make a recording of it. If I am lucky enough to record it next autumn, I will include it here.

Nr. 8 is an example of the typical multisyllabic call. This bird was very quiet during most of the time, but once called 72 in little more than a minute, a series I managed to record as a whole. Duration of each call is approx. 0.38 sec.

 

example of this call

Nr. 9 is an example of the inornatus call which is slightly more single-tone-like. This can thus be more humei-like. The duration, however, is too long (approx. 0.36 sec.).

 

example of this call

 

Conclusions

In general it can be said, that humei's call hardly ever reaches a frequency higher than 6 kHz (see graphs 1-7) but there are exceptions, especially for the single-tone call. On the other hand, the call of inornatus almost always reaches a frequency of 7 kHz or even higher (see graphs 8-9).

The duration of the call may even be of more significance. However, at this time, I still do not have sufficient information regarding the near-monosyllabic inornatus-call to be 100% sure. On average, the duration of the contact call of inornatus is over 0.30 sec., a length humei never seems to reach.

In conclusion, the contact calls of humei and inornatus seem to be distinguishable on two points:

One must keep in mind, however, that the degree of variation is high in humei's calls. It is therefore always wise to make sound recordings, especially if more types of calls are heard. Only then one can really compare the calls with reference material.

 

References

Anonymous 1991. Humes Bladkoningen. DB Actueel. Dutch Birding 13: 38-40.

van den Berg AB, Bosman CAW 1999. Zeldzame vogels van Nederland - Rare birds in The Netherlands. GMB Uitgeverij, Haarlem, p. 301.

Jonsson L 1992. Birds of Europe, with North Africa and the Middle East. First edition. Christopher Helm, London.

Lewington I, Alström P, Colston P 1991. A field guide to the rare birds of Britain and Europe. HarperCollins, London.

Mullarney K, Svensson L, Zetterström D, Grant PJ 1999. Collins bird guide. HarperCollins, London.

 

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Copyright © Teus Luijendijk 2000