Common Scoters by Jon Heath

Common Scoter Nocturnal Flight Calls: long calls?

Since Magnus Robb posted a Sound Approach article describing the short ‘peep‘ calls of migrating Common Scoters, this species has been a target for many UK nocturnal migration recorders. Late March and early April 2018 were memorable for the number of scoters crossing southern and central England, with many people recording the species for the first time. Here’s one such recording, from a typically noisy night in Cambridge (03:13, 14th April 2018).

 

At the time I didn’t pay much attention to the long, flat beeps, passing these off as an anthropogenic sound — maybe a reversing siren of a truck! But on 30th August 2018 I recorded a similar flat whistle, accompanied by wing beats that sound distinctly duck like. In the original Sound Approach article, Magnus Robb mentioned that Black Scoter give longer calls, but that would be an outrageous claim for Cambridgeshire…

 

Some Common Scoter recordings on Xeno-canto include longer calls, but these are at the same frequency as the peep calls, around 1.8 kHz, and sound like drawn out peep notes, as in this example I recorded in Skagen, Denmark in May 2018. Notice also the typical “steam train” wingbeat sounds.

 

In contrast, the calls from August were around 2.2 kHz, with slight modulations and slightly dropping in frequency.

Common Scoter long flat whistles 0121 30/08/2018 Cambridge (Simon Gillings)
Common Scoter long flat whistles 0121 30/08/2018 Cambridge (Simon Gillings)

Looking back through my scoter recordings I realised that “reversing vehicle noise” from 14th April was actually the same long flat calls. And then on 25th September 2018 I recorded another group of Common Scoter over Cambridge, again giving typical peep calls and 2.2 kHz long calls. I’ve since recorded these calls in combination again, in October 2018.

 

 

 

Conclusion

Unless each of these flocks had a second species lurking amongst the scoters, these recordings suggest that nocturnally migrating Common Scoters sometimes give long calls instead of, or as well as the more familiar peep notes. I don’t know how common these calls are or which ages or sexes produce them, but I would interested to hear from anyone else who has recordings of similar calls.

 

Credits: recordings © Simon Gillings; Common Scoter photo © Jon Heath.

Juvenile Goldfinch, by Simon Gillings

Nocturnal Goldfinches: never say never

The ‘ink’ had barely dried on my last post about the rarity of nocturnally migrating Goldfinches when I heard that Tim Jones had recorded nocturnal Goldfinches at Spurn twice in October 2017. Then Magnus Robb mentioned he’d recorded them in southern Portugal 13 times over nine nights in October and November 2017, plus once in April 2018. Aat Schaftenaar also provided details of his two nocturnal birds mentioned in the previous post. Tim, Magnus and Aat kindly shared their recordings, providing an opportunity to confirm what nocturnal Goldfinches sound like and how similar their spectrograms are to Ortolan calls.

First, here’s a recording of 5 seconds of Goldfinch nocturnal flight calls, probably a single bird, recorded in Portugal in November 2017 by Magnus Robb. The overall sequence is reassuringly similar to diurnal calls in consisting of single or paired upward-inflected notes, with consecutive notes often varying in frequency, giving a ‘bouncy’ impression.

 

Here’s one of Tim’s from Spurn, recorded at 00:51 on 17th October 2017:

 

And one of Aat’s from the Netherlands, recorded in March 2016:

 

Of the 18 files I examined, all consisted of sequences of these upward-inflected call notes. In 12 cases the passing bird(s) gave both paired and single notes (as in the example above); two passes consisted of only paired notes, and the remaining four consisted of only single notes. All recordings were of single birds except a small flock recorded by Tim Jones at Spurn (00:20, 17/10/2017).

I described the call notes as upward-inflected, and this becomes more apparent when the spectrogram is zoomed in. Each call note starts low and rises in frequency. Chris Batty described these as looking like the forward slash ( / ) character on a computer keyboard. They vary somewhat in length and slope, but they all rise in frequency. None of the notes begin with a descending part, and while some have a terminal drop in frequency, this is very small in comparison to the range of the rising part (e.g. penultimate note below). Overall they lack the characteristic reversed ‘N’ shape of Ortolan Bunting plik calls.

Goldfinch nocturnal flight calls
Goldfinch nocturnal flight calls (Portugal, 16/11/2017, Magnus Robb)

 

Conclusion

These recordings confirm that Goldfinches do, on occasion, migrate at night and call whilst doing so. The calls they give are identical to diurnal calls and both the pattern of calling and the structural of individual call notes are distinct from Ortolan Bunting plik calls. These results suggest it should be straightforward to eliminate Goldfinch as a potential confusion when identifying a nocturnal Ortolan Bunting.

Thanks to Tim Jones, Magnus Robb and Aat Schaftenaar for sharing their Goldfinch NFC recordings.

 

 

Redwing in flight by Tim Jones

Autumn thrushes

The first tseee calls of Redwings arriving into Britain and Ireland have been heard in recent nights and Song Thrushes have been on the move too, with more Continental immigrants soon to arrive to supplement our local breeders. As the BirdTrack reporting rate graph below shows, Fieldfares arrive a little more gradually and Blackbirds continue to arrive through November. If you’re lucky there’s always the chance of a Ring Ouzel. This blog summarises the main nocturnal flight calls of these species.

thrush_phenology_BT
Graph showing the percentage of BirdTrack complete lists in Britain & Ireland on which different thrush species were reported each week.

 

All the nocturnal flight calls described below are also given in daytime, during flight and sometimes when perched. They were all recorded as nocturnal migrants over Cambridge, UK.

 

Redwing

The characteristic tseee of an autumn evening. Calls vary a little in length and frequency but they all descend slightly in frequency. In the following recording you can also hear some soft puk calls too.

 

Blackbird

Blackbird srrri flight calls are a little like Redwing calls but are shorter and show less of a frequency drop. They also have a noticeable fluctuating or modulated quality, making it sound like the call is slower than a Redwing tseee call. In the following clip, a Blackbird call is followed by a Redwing call.

 

Blackbird sometimes pair these calls into a double call. The second note is often slightly lower pitch, as in the following example

 

Rarer still, Blackbirds will string together three of these calls into a triple call. The following example (apologies for quality) contains single, double and triple calls.

 

Song Thrush

A single high pitch zit call. A migrant might only give one of these calls as it passes overhead, but sometimes they can give two or three calls a few seconds apart. Very occasionally the zit call is repeated with almost no gap.

 

Fieldfare

At night, much scarcer than the previous three species. Main call a dry chattering, slightly chuckled schack-schack-schack, sometimes preceded by a wheezy rising eep call.

 

Ring Ouzel

Significantly rarer than the other autumn thrushes. Two main call types. The first, which is often heard from migrants in the day, is a very distinctive hard tac-tac-tac call.

 

The Ring Ouzel tac notes are shorter and sharper than corresponding tup notes of Blackbird, which can be heard in the following clip.

 

The second Ring Ouzel call is a rising squeaky bubbling call. It is superficially similar to Fieldfare calls, though it is faster and softer, with a rising quality.

(drake Teal calling in background)

Ring Ouzels also give a rolling prrrt call (e.g. here) though I have not yet recorded it myself.

© all recordings copyright Simon Gillings. Redwing photo by Tim Jones.

Ortolan Bunting by Jon Heath

Ortolan Buntings and Goldfinches

It’s peak season for migrating Ortolan Buntings in northwest Europe and in addition to several sightings and ringed birds, several have been recorded by the UK’s fledgling ‘nocmig network’. As well as the now regular locations of Portland/Weymouth and Poole Harbour area, birds have also been recorded (so far) over London, Surrey and Cambridge. They’re being recorded in several locations that don’t have any history of visual records of Ortolans, prompting lots of head-scratching about the likelihood of detecting such species and questions about identification criteria. The Sound Approach have produced two very detailed blog posts on the identification criteria (here and here), describing the common call types and their potential confusion species. With reference to the commonly used plik call they say:

European Goldfinch Carduelis carduelis has a call similar to Ortolan Bunting’s plik, although it normally uses this call in combination with others. Goldfinches usually move around in tight flocks, and we have never recorded one migrating at night, despite it being such a common species…Note the variation in pitch and rhythm, giving a bouncing effect. On odd occasions when a single goldfinch repeats only its most plik-like calls, these are likely to be given in twos as well as singly, and with much shorter gaps than an Ortolan Bunting

The suggestion that Goldfinch calls are a potential confusion for Ortolans has been raised as an issue, particularly in those counties where Ortolan Buntings have never been recorded in the daytime.

Setting aside for a moment how similar the calls are, it is helpful to quantify the potential for confusion from night flight calls of Goldfinches. I checked on the timing and reporting rate of diurnal and nocturnal Goldfinches and Ortolan Buntings on Trektellen. The many thousands of hours of day and night recording submitted there should give a good indication of the behaviour of these species.

Diurnal movements

First, here’s the timing of Goldfinch diurnal autumn migration (all countries, all years), showing a very low level of movement through late summer picking up in late September to a broad peak through October to November.

Trektellen_GO_diurnal
Figure 1. Timing of Goldfinch autumn diurnal migration, from Trektellen

For comparison, here’s the diurnal autumn phenology of Ortolan. Ortolans in daytime are clearly much earlier than Goldfinches and at the time when most Ortolans are moving, Goldfinches movements have barely got started. These results are largely driven by data submitted in the Netherlands, Germany and France where Ortolan passage is well understood.

Trektellen_OB_diurnal
Figure 2. Timing of Ortolan Bunting autumn diurnal migration, from Trektellen

Nocturnal movements

So now looking at the phenology of nocturnal movements of Goldfinch, here’s the corresponding plot.

Trektellen_GO_nocturnal
Figure 3. Timing of Goldfinch autumn nocturnal migration, from Trektellen

 

There’s no error in the graph. In 17,564 hours of nocturnal monitoring during autumn, no Goldfinches have been recorded. You might notice in the date range of the graph above that I have omitted 2011. That’s because there is a handful of sound-recorded Goldfinches submitted from Besh Barmag, Azerbaijan by Michael Heiss (note that totals here are currently numbers of calls, not numbers of birds). Michael records from sunset to sunrise, so includes civil twilight which most other nocturnal surveyors don’t consider. The handful of birds he has were all just pre-dawn (e.g. here) and represent the initiation of diurnal movements. More generally within Trektellen there are just two other “nocturnal” Goldfinches, recorded in March 2016 in the Netherlands, though I can’t tell what time of night they were.

For comparison here is the phenology of nocturnal Ortolans, which matches very nicely the timing of Ortolan diurnal migration as expected. Again, much of the data come from the Low Countries where Ortolan calls are well understood.

Trektellen_OB_nocturnal
Figure 4. Timing of Ortolan Bunting autumn nocturnal migration, from Trektellen

 

Possible interpretations

There are two ways of looking at these results – that nocturnal Ortolans are all/mostly misidentified Goldfinches, or that the identification of nocturnal Ortolans is all/mostly correct.

To take the view that all (or even some proportion) of the claimed nocturnal Ortolans are actually Goldfinches raises some tricky questions. Why are these nocturnal “Goldfinches” moving about a month or so before diurnal movements. Perhaps they are recently fledged juveniles? But if that is the case, why are they not apparent over a much wider window as juvenile Goldfinches can be around from late June onwards. Why are nocturnal Goldfinches not detected at any other time of year despite being present year-round at these locations. Further, these nocturnal “Goldfinches” would have to be giving only an unusual call and none of their more familiar calls at night. Otherwise in 17,500 hours of recording, nocturnal recorders would be picking them up more regularly and we would see Goldfinches on Figure 3. This all seems very implausible.

Alternatively, if we accept the identifications as being correct, the clear conclusion is that Goldfinches migrate at night extremely rarely (if ever), or they do not call while doing so. Hence they represent an extremely unlikely confusion species for nocturnal Ortolans. That’s not to say that Goldfinches should be ignored as a potential confusion species. It just means they should be weighed appropriately when considering putative Ortolans.  Nocturnal Goldfinches may in fact be rarer than Ortolans!

 

Thanks

Thanks to Jon Heath for the Ortolan photo and to the contributors to Trektellen on whose data this post is based.

Standardised Nocturnal Flight Call Monitoring

Recording nocturnal flight calls is seeing a big surge in interest in Europe and all this effort scrutinising hours of audio has the potential to generate invaluable data on a large scale for understanding movement patterns of birds. Witness the amazing nocturnal movements of Common Scoters through inland England recorded in April-May 2018, the tantalising records of nocturnal Ortolan Buntings in southern England and continental Europe, and the amazing breadth and magnitude of nocturnal movements through Besh Barmag, Azerbaijan. There’s much to learn if the data can be collected and collated in a consistent manner.

protocol_coverBTO, Sound Approach and Sovon have teamed up to produce a Protocol for Standardised Nocturnal Flight Call Monitoring (available here), and in parallel, significant improvements have been made to Trektellen for the submission and sharing of nocmig data. The protocol aims to highlight simple ways that recordings and the data extracted from them can be standardised whilst still allowing flexibility for local circumstances. It details aspects such as where and when to record, times of night to cover and which species to log. For example, we recommend that call logging starts no earlier than civil dusk and continues no later than civil dawn to exclude diurnal migrants. Ideally counts should be submitted in hourly blocks to allow future analyses of timing and weather, and all birds flying over should be logged whether they are considered to be migrants or local birds. These suggestions will be familiar to many seasoned recorders and should act as a guide for those just starting out.

Trektellen has been collecting nocturnal flight call data for several years and with the latest modifications it is now possible to submit numbers of individuals and numbers of calls, which will be invaluable for species where estimating bird numbers is problematic. It is now easier to indicate which records relate to flying versus stationary birds and sound files uploaded to xeno-canto can now be embedded within Trektellen lists, which will be especially useful for sharing recordings of unusual or unverified records.

trektellen_dayview
Alongside the advances being made by the Sound Approach and others in species identification, we hope this protocol promotes further interest in recording and submission of data from nocturnal flight call monitoring.

Nocmig recording in Cambridge

I started nocmig recording in March 2017 from my garden in Chesterton, one of the eastern suburbs of Cambridge. My garden is about 250 m from the River Cam but separated by a moderately noisy road and housing. In a birding sense it’s an uninspiring bit of the city and not somewhere you’d expect to have significant bird passage.

2017-03-28 08.07.36

My first recording gear was a very cheap USB microphone, the kind designed for Skype calls. For under £15 this gave me my first Moorhen and Water Rail for my nocmig garden list. In a bid to improve the quality of my recordings I upgraded to a Yeti USB mic but stubbornly stuck to using my computer to capture the audio. Spring 2017 was amazing for inland wader passage and I soon added Spotted Redshank and Grey Plover to a growing list of waders.

20170903 OBEarly September 2017 was a turning point – I was away with my family for the weekend and had taken the Yeti mic with me but on a whim decided to leave the mini USB running from Friday evening to Sunday. On my return I discovered that I had recorded not only a Sandwich Tern and a Tree Pipit but also an apparent plik call of an Ortolan Bunting – a potential first for Cambridgeshire. With hindsight, claiming an unseen county first based on a single call, when I was not even present, was asking for trouble. But it made me rethink my recording setup and invest in a proper microphone so that I’d be better prepared next time…

2017-10-17 21.11.41

Since October 2017 I’ve been using a Dodotronic Stereo parabolic microphone connected via a 10 m cable to a Zoom H4n Pro recorder. I recorded in Chesterton whenever I can and have so far recorded over 10,000 nocturnal flight calls of over 60 species, including highlights such as multiple Ring OuzelsCommon Scoter, Stone-curlew, Pied Flycatcher and Bittern.  I’ve just started putting these records onto Trektellen to add to the picture it is building of nocturnal migration in Europe.

This website came about when Nick Moran and I found we wanted to collate the answers to many of the questions we had as we were starting out. We’re keen to promote nocmig recording and especially interested to see useful counts generated and submitted to Trektellen for wider research uses.

Little Grebe

spectrogram_4s_LG_squealOne of the biggest surprises for me when starting nocmig recording was to learn that Little Grebes produce two night flight calls that are completely different to the familiar daytime song. Both these calls may be heard from March to October in UK.

The first is a clear, piercing rising squeal, given single or in pairs as in the example (right and below). The call can be heard from birds on water after dark. Xeno-canto examples here and here.

 

The second call is a series of pips followed by a rapid trill. The trill part is so reminiscent of a Whimbrel flight call I wonder if I have mistaken the two in the past. Both trills are at c. 2.5kHz; whereas Whimbrel trills may be constant pitch, rising or falling through the trill, Little Grebe trills are either constant or slightly falling in pitch. The key to distinguishing from Whimbrel seems to be the presence of the preceding pips, of which there may be as few as two. Little Grebe trills appear to be slightly slower, longer and sometimes less regularly spaced. Xeno-canto examples here and here. The example below is not the best – I have yet to record a really clear one – and the initial pips are unusually low. I’ll replace with a better example when I have one…

spectrogram_6s_LG_song

 

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