TURNSTONES
turning stones to see what's underneath
CROSSBILL FLIGHT CALLS (2017)
how to separate Parrot Crossbill from the several Common Crossbill types - by Thijs Fijen
Was that crossbill you just recorded a type A, or a Parrot?
Figure 1. Parrot Crossbill, male, Molenhoek, Limburg, The Netherlands, 17 February 2017 (John van der Graaf). Not all crossbills can be studied like this bird!
Preface
In his ground breaking article in Dutch Birding, Magnus Robb opened our eyes and ears for the subtle differences in the vocalisation of crossbills (Loxia sp.) in north-western Europe (Robb 2000). He later elaborated on the matter in the first The Sound Approach book (Constantine & The Sound Approach 2006). During every crossbill influx, especially when Parrot Crossbills (Loxia pytyopsittacus) are also involved, birders get excited again. With the increased interest in sound recording, the number of recordings also increased steadily. And so have the number of Loxiaphiles (birders that love to study crossbills). They have documented crossbill types extensively, and we now know more and more of these types. This article summarizes the current calls of crossbill types in northwest Europe. Hopefully the explanation and sonograms will help birders to separate Parrot Crossbill from the several Common Crossbill types.
Figure 2. This is the way vis miggers get to see crossbills. Thanks to the recorded flight calls (Sjaak Schilperoort), this female could be identified as a certain Parrot Crossbill. De Vulkaan, Den Haag, Zuid-Holland, The Netherlands, 19 October 2013 (Eduard Opperman)
First a short introduction to the matter
Crossbills have different vocalisations. Next to song, two main call types are of importance to fully understand the issue: flight calls and excitement calls. Flight calls are what the name suggest: calls usually given in flight, although note that they may also be given when perched, or may even be intertwined in the song. Excitement calls are lower pitched sounds that are given when perched, usually in a context of social interacting, such as in pair bonding, or territorial conflicts. Robb (2000) showed us that in Europe (in North America this was already ‘discovered’) several types of unique combinations of flight calls and excitement calls existed; i.e. each structurally different excitement call had a corresponding unique flight call. These crossbill types (recognised by their calls) also showed some preference for a specific type of food (e.g. pine vs fir), and therefore might be at the beginning of an evolutionary process, forming separate species. Several types were found in the Netherlands, in different quantities and different numbers each season. Over the years we learned more about these types, discovered more types and learned that the flight calls of the are somewhat variable, while their excitement calls are less variable. We now know (or agreed...) that we may only call it a type if the excitement call is structurally different from the other types. The flight call alone is probably too variable to describe a (new) type. So for a certain description of a new type, recordings of both the excitement call and flight call of the same individual are required. Ongoing research suggests that there might be >30 different types of crossbills in Europe alone, but we are still awaiting the publication. To ID crossbills with certainty, it's necessary to record their calls and make a spectogram/ sonogram.
Recent influx
During the autumn of 2017 a large influx of Parrot Crossbills (Loxia pytyopsittacus) reached Denmark, Germany, The Netherlands and the UK. Along with them were many Common Crossbills (Loxia curvirostra) of several types. The most common ones this autumn were Parrot Crossbill (“Scandinavian type”), type A, two forms of type C (see below), type D and type X. I’ve come across at least four other types this autumn, though in very low numbers (less than five each out of approximately 380 recordings on the online observation database www.waarneming.nl). I will show the flight calls of the most common types and explain how to distinguish them from each other. With this knowledge it should be possible to recognise other types yourselves! Excitement calls are given less frequently, and when recorded, flight calls are usually also recorded. For typical flight calls (99% of all flight calls) excitement calls are not necessary for the identification of the type. Therefore, I will focus on the flight calls only.
Figure 3. Typical examples of the most common call types in the Netherlands in autumn 2017. Type A, type c, second form of type C, type D, type X of Common Crossbill, and Parrot Crossbill Scandinavian type, respectively. All own recordings.
To the ear, type A sounds a lot like Parrot Crossbill. This is one of the most common ID mistakes. Figure 1 shows the current form. There are several systematic differences between type A and Parrot: the crinkle in the beginning, the relatively high peak (although some Parrots may show this!) and the slowly descending arch. In Parrot the call starts with a steep ascending structure, followed by a more stepwise descend. Also see Figure 4.
Type C is the most common type in the Netherlands in the most recent years, and also the easiest one to distinguish by ear (‘glip’), clearly higher than the rest (Figure 5). But beware of the second form of type C (Figure 6), which has proven to be type C based on the excitement calls (erroneously named ‘K2’ in the past). Note that the left bow in this second form has been reduced to a more or less straight line, resembling Parrot. Quite often the right bow almost completely disappears on poor recordings, becoming a serious pitfall for Parrot. In those cases, look for a faint hint of the right bow (which is often present in one of the many calls), and check for the last ‘step’ of Parrot Crossbill, which is nearly always there.Finally, look for the steep ascending line at the beginning of Parrot; type C does not have this.
Type D is the call relatively similar to redpolls (Acanthis sp.) and should not pose any problems with other common call types (Figure 7). Similar other types have been recorded in The Netherlands, but these are quite rare.
On sonogram Type X (Figure 8) is quite different from Parrot Crossbill, but, like type A, it is quite often mistaken for Parrot by ear. The structure is quite typical, but the left part may be lost in poor recordings. Then look for the slowly descending arch, which is less regular in type A, and stepwise in Parrot.
Parrot Crossbill (Figure 9) also has separate call types, although the ‘Scandinavian’ one is by far the most common. Note that the call structurally looks like a stairs, with the highest part on the left. The beginning of the call may be a short crinkle (see type A) but is nowadays more commonly a straight line. The highest point in the call is the left ‘peak’, which might occasionally be as high pitched as in type A.
Figure 4. Variation in type A Common Crossbill. Note also how the quality of the recording (third and last call) may change the impression of the call. All own recordings.
Figure 5. Variation in type C Common Crossbill. Note, no aberrant forms are depicted here. All own recordings.
Figure 6. Variation in the aberrant form of type C Common Crossbill. Note that the quality of the recording may cause the right part to disappear (e.g. third call). Because of this, the call may seem structurally similar to Parrot, but note the faint hints of the left and right parts of the call and the lack of a stepwise descent. All own recordings.
Figure 7. Variation in type D Common Crossbill. The quality of the recording might change the impression, though always showing the characteristic double bands. All own recordings.
Figure 8. Variation in type X Common Crossbill. Not very variable, but the quality of the recording might cause the left part to be poorly visible (second call). All own recordings.
Figure 9. Variation in Parrot Crossbill (Scandinavian type). Note the stepwise descent visible in most calls. The part at the beginning might be straight, or a short crinkle, somewhat remniscent of type A Common Crossbill. First five calls of own recordings. Last call kindly borrowed from Dick Groenendijk.
Figure 10. Parrot Crossbill, male, Leusden, Utrecht, The Netherlands, October 2017 (Hemme Batjes)
Some final remarks
I think it’s fascinating that these populations/types of crossbills exist, and are apparently quite able to find mates of the same type. Following this mini-evolution of types is quite exciting stuff, but it may appear to be too complex for a beginning Loxiaphile. With this short introduction it’s possible to identify most of the flight calls in the Netherlands. But with the next invasion the common types might be different again! So keep recording crossbills!
Acknowledgements
This is not a one way street: I learned a lot from the many birders who shared their recordings and increased my knowledge about the types. However, indispensable help came from Ralph Martin, one of the best Loxiaphiles in Europe: many thanks for sharing thoughts and I look forward to your not-yet published work! Also thanks to Julian Rochefort for his devotion to crossbill calls.
Hemme Batjes, John van der Graaf and Eduard Opperman kindly provided Parrot Crossbill photographs.
References
Robb, M. 2000 Introduction to vocalisations of crossbills in north-western Europe. Dutch Birding 22: 61-107
Constantine, M. The Sound Approach. 2006 The Sound Approach to Birding: A guide to understanding bird sound.
Thijs Fijen, November 2017