Introduction to Vocalizations of Crossbills in North-Western Europe
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Introduction to vocalizations of crossbills in north-western Europe Magnus S Robb uring the last four years, I have been record- intrigued whether they represented a distinct D ing and studying the vocalizations of cross- vocal type in the North American sense. I decid- bills Loxia, mainly in the Netherlands and other ed to study their vocalizations in greater depth north-western European countries. My interest and to document the repertoires of as many other began with Scottish Crossbill L scotica. I was crossbills as I could find. Between March 1996 curious whether it was possible to distinguish and February 2000, I sound-recorded a total of at with certainty the vocalizations of Common least 30 hours of all four currently recognized L curvirostra, Scottish and Parrot Crossbills Lpy- European crossbill species. In addition, I analysed tyopsittacus. When I immersed myself in the sub- a wide range of both private and commercially ject, I soon realized that there were many available recordings, including some obtained unanswered questions, not least regarding the from the British Library National Sound Archive, taxonomic status of various crossbill populations. London, England. In north-western Europe, I dis- It also became clear that the differences between tinguished six vocal types of Common Crossbill, the vocalizations of Common, Scottish and differing from each other across a wide range of Parrot Crossbills were often being misinterpreted vocalizations. Like their North American coun- or, at best, greatly oversimplified. terparts, Common Crossbills in north-western On 30 October 1997, I came across a flock of Europe showed discrete and highly regular pat- Common Crossbills in De Kennemerduinen, terns of vocal variation, raising the possibility that Noord-Holland, the Netherlands, which had distinct populations or even cryptic species are flight calls completely unfamiliar to me. These involved. could be described as a sharp-sounding high- In this article, vocalizations of six vocal types pitched weet. ‘Weet’ crossbill became my provi- of Common Crossbill plus Two-barred L leuco- sional name for them and I will discuss them at ptera bifasciata, Scottish and Parrot Crossbills are length below. By the time this encounter took compared. First, general categories of crossbill place, I was aware of the remarkable work of vocalizations are discussed. Then, species and Groth (eg, 1993a) in North America, summarized vocal types of crossbill are introduced and more by Sangster (1996). Groth discovered that there than 100 examples on the accompanying CD are at least eight vocal types of ‘Red Crossbill’ (the serve to illustrate their vocal repertoires. Also, American name for Common Crossbill) in the sonagrams and slowed-down recordings are used New World. These correspond to populations of to elucidate structural differences between these crossbills occurring across a wide geographical vocalizations. Parallels and differences between range, each with a narrow range of morphologi- the situations in North America and north-west- cal variation and a unique vocal repertoire. Groth ern Europe are discussed as is the assortative believes that these vocal types are cryptic species breeding of at least two vocal types of Common and has argued that they fulfil the requirements of Crossbill in De Kennemerduinen in 1998. both the phylogenetic and biological species con- This article and the accompanying CD do not cepts. In Europe, the existence of a number of aim to be a definitive guide to crossbill vocaliza- flight-call types in Common Crossbill had been tions in north-western Europe. Rather, I hope that noted by Curtis Adkisson and Alan Knox, and they will serve as an introduction to crossbill Knox (1992) had discussed their possible signifi- repertoires in the region. In particular, I hope that cance. In De Kennemerduinen, I soon noticed they will form a foundation for further studies on that ‘weet’ crossbills differed from other crossbills Common Crossbill vocal types. present not only in their flight calls but also in their excitement calls. They also seemed to have Looking for patterns in crossbill vocalizations their own repertoire of song motifs. Not knowing The most striking feature of the different crossbill where these ‘weet’ crossbills came from, I was vocal types is that their vocalizations differ con- [Dutch Birding 22: 61-107, 2000] 61 Introduction to vocalizations of crossbills in north-western Europe sistently across a range of the items in their Nomenclature and difficulty of transcribing vocabulary. Groth (eg, 1993a) discovered this in bird vocalizations North America and it seems to apply equally in Originally, I named the Common Crossbill vocal Europe. Flight calls are the most striking of a types phonetically, using descriptions of their range of vocalizations which can be used for flight calls. This simplified talking about them identification. Excitement calls, alarm calls, soft with other birders. These descriptive names have chitter calls and even motifs in the songs all some disadvantages, however. For example, in differ between the various vocal types. the past, ‘chip’ has often been used as a generic The way I distinguished the six vocal types and not inappropriate way of describing the was essentially through listening very carefully flight calls of crossbills. If all of the known both in the field and later to my recordings, and Palearctic and Oriental crossbill subspecies turn through visual inspection of sonagrams of thou- out to be vocal types in addition to the six sands of vocalizations using my computer. It described here, then we will soon run out of soon became apparent that the variation in flight- words remotely suitable to describe their flight call structures was not random. Flight calls fell calls. The differences are, after all, often very into a number of clear and discrete patterns. I subtle to the human ear. Describing bird vocali- tried to establish whether there were flight calls zations phonetically is also, of course, highly which bridged the gaps between these different subjective. A description which works for one types. Some ‘types’ were soon abandoned if it person may confuse another. became apparent that they were merely part of a The vocal types Groth (eg, 1993a) described range of continuous variation. As the extent of from North America were given the numbers 1-8. variation for each type became more apparent, A ninth, Lc mesamericana from Central Ameri- so did the discontinuities. It also became clear ca, probably also represents an additional vocal that birds of a given flight call could often be type (Jeff Groth pers comm) and more may yet be heard in homogenous-sounding flocks consisting described (eg, Benkman 1999). Partly for this of males, females and often immature birds, reason, I felt it would be a bit presumptuous and indicating that the differences between the confusing to try to fit the Palearctic vocal types various flight calls were not merely a question of into this number scheme, so I have used the let- gender or age. ters A-F instead, in addition to the phonetic The next stage was to determine whether flight-call names. I feel these names are prefer- crossbills of a given flight-call structure also had able to phonetic names, such as ‘keep’, ‘jip’ and other calls in their repertoire which they did not trip’, because the latter, based on a subjective share with crossbills producing different flight description of the sound, are more likely to lead calls. In addition to flight calls, I looked for to confusion and mistakes, especially in an inter- differences in excitement and alarm calls in par- national context. The type A-F names are only ticular. These are the three categories of vocali- provisional and, when the vocal types are better zations Groth (eg, 1993a) used to establish differ- known and their taxonomic status better under- ences between vocal types in North America. To stood, more appropriate names can be applied. my surprise, I also found that I could often pre- The differences between the flight calls of cer- dict the vocal type of a singing bird by listening tain vocal types are very difficult to describe for familiar motifs in the song. phonetically. The name ‘jip’ (Type D), for exam- If a whole array of vocalizations produced by ple, might have been applied to Type E or F by a birds of a particular flight call were also found to different observer. The phonetic transcriptions be characteristic of those birds, and produced are based as far as possible on English spelling consistently, I considered that I was probably conventions. By necessity, these descriptions dealing with a vocal type. More and more, I have exaggerate the differences I hear. I have used the found that the same correlations of calls and transcriptions ‘keep’, ‘glip’ ‘jip’ and ‘chip’ for song motifs heard in my main study areas in De three of the types because they seemed appro- Kennemerduinen and at Baarn, Utrecht, could priate to the sound in question, and are already also be heard elsewhere. This applied not only to widely used. The two different vowels used – ee other locations in the Netherlands but also to as in ‘eel’ and i as in ‘fish’ – are not intended to other parts of Europe from which I have been indicate different call durations. Rather, they are able to obtain recordings or where I have made intended to indicate the prominence of the them myself. ‘vowel’ sound in the call as a whole. The ‘keep’ and ‘weet’ flight calls sound ‘clearer’ in tone than 62 Introduction to vocalizations of crossbills in north-western Europe the rougher, more fricative ‘jip’, ‘chip’, ‘trip’ and (sonagrams 6 and 28) are shown with a vertical ‘glip’ equivalents. The order of the letters used as scale which is different from that used in the names (Type A, etc) reflects the chronological other sonagrams.