Redpoll calls on North Ronaldsay autumn 22

 We were lucky to be involved in the Hornemann's Arctic Redpoll influx on North Ronaldsay this autumn, with several individuals recorded. There were also a range of other Redpoll 'taxa' recorded, with Mealy Redpolls, a couple of Lessers and some North Western/Icelandic birds. I tried to sound record examples of each out of curiousity to compare their calls and found the results quite interesting. I also downloaded calls of Xeno-Canto and had a look at their sonograms on Raven for comparison.

Click on the video thumbnails to play the calls. I recommend enlarging the videos to fullscreen.

Hornemann's Arctic Redpoll calls. This recording shows two call types: the "chooee" call, which I find difficult to distinguish from other Redpoll taxa, and the chatter call. The "chooee" calls here last about 0.25s each, with the sonograms formed of three bold upslurred lines and 4+ fainter ones. The chatter call is distinctive in my opinion, being more drawn out and sounding lower pitched than the notes in other Redpoll chatter calls. It also has more of a buzzy quality to it. The calls are strongly concentrated around a region between 2.7kHz and 5kHz and each call lasts between 0.15s and 0.17s (compare with other redpoll calls below).

From my personal experience on North Ronaldsay this year, the Hornemann's "jeep" calls seemed to be mainly given in 1s or 2s, as opposed to other taxa which can give chatter calls comprised of multiple notes in quick succession, creating a "ji-ji-jit" type call (as well as single notes). However, looking at Xeno-Canto, some Hornemann's seem to also produce a succession of notes so I no longer think this is as useful as I originally thought. 

Interestingly, there are only 9 recordings on Xeno-Canto of confirmed (or where subspecies if specified) Hornemann's Arctic Redpoll. Recordings of Coues's to me sound slightly less drawn out in general and a bit higher pitched, although I find some very difficult to distinguish any differences. Greenland rostrata birds also seem to produce similar low pitched calls.

Photo of the bird below:

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Probable Icelandic Redpoll flight calls. This bird gave what I thought sounded like more 'typical' redpoll chatter calls. The energy in each call seems to be concentrated between 2.5 and 5.5kHz. Each note lasts between 0.05s and 0.09s (compare with longer Hornemann's calls) and they are mostly delivered in twos or threes. If you zoom in on this sonogram, they look neatly hockey-stick shaped, making them sound very subtly downslurred and 'cleaner' than the more buzzy Hornemann's calls.

Note: There are also some Meadow Pipit calls in this recording, which are the higher pitched calls between about 5kHz and 7kHz, along with some Redshank calls forming 'squiggly lines' at around 2.5kHz during the first 4 seconds. These make the sonogram a bit confusing in places - e.g. the Redpoll call at 3.7s is perfectly timed with a Meadow Pipit and Redshank call. It seems like the first note ranges up to 7kHz, where in reality the Redpoll call stops at about 5kHz and the Meadow Pipit call is responsible for this.

Pictures of this bird below; larger and bulkier than any Mealy I've seen (I thought it was going to be an Arctic originally), with very bold black markings on the face, bold extensive 'triple' flank streaking and a long and deep-based bill. Based on my current knowledge, I don't think this is a 

rostrata Greenland bird, although I personally think it looks good for a Dark Icelandic individual (as opposed to Pale Icelandic). It was paler in the face and general ground colour compard to the photos of darker Greenland birds I've seen online, which seems to match the general characteristics of Icelandic. It was certainly strikingly different from Mealy Redpolls I've seen before. There were a few of these individuals seen on North Ronaldsay during a period of NW winds which also coincided with one of the best periods for Hornemann's sightings. I'd be interested to hear other opinions on this bird.

The recordings I've found of Icelandic Redpolls on Xeno-Canto seem pretty similar to this recording: https://xeno-canto.org/species/Acanthis-flammea?query=ssp:%22islandica%22. It seems like 0.07s is a typical call length for Icelandic, which seems consistent between recordings (and matches my own recording here). However, the pitch of calls seems to vary a bit online, with some of the recordings sounding identical to my recording here, and some of them being a bit lower pitched. Could call be another way of distinguishing between Greenland and Dark Icelandic individuals? 

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Mealy Redpoll "chooee" calls. Some "chooee" type calls here and a few faint chatter calls from about 13s. The "chooee" calls last about 0.3s. The sonogram is formed of 4 distinct upslurred lines here and seems more strongly upslurred at the end compared to the Hornemann's I recorded. Of course, this is just a comparison between two individuals and looking at Xeno-Canto, it seems like this is just individual variation in this case. 

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Redpoll flight calls (either Mealy or Lesser). This bird was a flyover, although I'd seen a Mealy Redpoll well on the ground about 20 minutes previously. This was during late October when there had been a Hornemann's and a few Mealys and Lessers around (no NW type things seen for at least 3 weeks). The sonogram spans from 3kHz to 6kHz, although this bird was more distant so the recording quality will not be as good.

I'm not sure I can personally tell much difference between these calls and the calls of the possible Icelandic bird from earlier. I've zoomed in on the sonograms and compared them below, which does reveal some differences between the two, although I think these are largely due to individual variation. At least the Hornemann's is obvious!

Comparison of chatter notes between taxa. Mealy recordings aren't as good quality as the top two (so may have lost parts of the sonogram at higher frequencies). I think this demonstrates quite nicely why the Hornemann's call sounds more buzzy and drawn out compared to other taxa.

Overall, I think calls are a very interesting aspect of the variation between Redpoll forms and perhaps an underrated aspect of their identification in some cases. It seems as though each form occupies a space on a continuum, much in the same way their plumage does. However, I wonder if the duration of calls and shape of sonograms might reveal some more diagnostic aspects of the calls of each form. Given the number of recordings available on Xeno-Canto is fairly limited for some Redpoll forms, I think there is potential for new things to be discovered.