Nocturnal flight calls of flycatchers, robins and chats

Author: Magnus Robb

European Pied Flycatcher, Spotted Flycatcher, European Robin and Bluethroat

With the current surge in popularity of night flight call (NFC) recording in Europe, many people are struggling to identify one group of passerines in particular: flycatchers, robins and chats, which are nowadays considered to belong to the family Muscicapidae. The challenge is compounded because some members of this group appear to have no NFCs at all, while those that do rarely if ever use flight calls during the day. So far I have made night migration recordings mostly in Portugal, so I can only guess what are the NFCs of species occurring elsewhere in Europe. This is very much work in progress. In future I hope to post updates and any corrections that prove necessary. Here is what I have learned so far.

The members of this group that I have recorded most often at night are European Pied Flycatcher Ficedula hypoleuca (hereafter Pied Flycatcher) and European Robin Erithacus rubecula (hereafter Robin). I have only a handful of NFCs that I believe can be attributed to Spotted Flycatcher Muscicapa striata, and one recording of a migrating Bluethroat Luscinia svecica. I have also recorded a couple of calls of Northern Wheatears Oenanthe oenanthe that appeared briefly near floodlights during nocturnal migration flights, but I don’t regard these as true NFCs. If any of the other commoner flycatchers or chats that migrate through my area have NFCs (eg, Common Nightingale Luscinia megarhynchos, Common Redstart Phoenicurus phoenicurus or Whinchat Saxicola rubetra) then I have yet to recognise them.

What we usually think of as the Old World flycatchers and chats, family Muscicapidae, can be divided into subfamilies but there is more to it than just ‘flycatchers’ and ‘chats’. It has become clear that Spotted Flycatcher Muscicapa striata and Mediterranean Flycatcher M tyrrhenica (both in subfamily Muscicapinae) are not so closely related to European Pied Flycatcher and other Ficedula flycatchers as the English name suggests. The latter flycatchers can be grouped with, eg, Bluethroat, Northern Wheatear and redstarts Phoenicurus in subfamily Saxicolinae. Robin is often listed in another subfamily, Cossyphinae, while ‘true thrushes’ such as Zoothera and Turdus are either separated in subfamily Turdinae, or as a family by itself, Turdidae. The dust has not settled in revealing these birds’ relationships.

Before I became really interested in night migration recording, I didn’t even know that some Muscicapidae have flight calls. When you see them flying any longer distance during the day, there is usually no particular call associated with flight in the way that there is in the true thrushes. As it turns out, however, a large proportion of the NFCs that I record in autumn belong to Pied Flycatchers and Robins, the former mainly in September and the latter peaking in October.

Although these species do not appear to use specific calls to say “I’m taking-off” or “I’m flying” during the day, they do use calls very similar to their NFCs for other purposes, and I believe that studying their daytime call repertoire is the key to working out what is going on at night. We need not look further than the limited set of calls that they use during the migration period.

 

Pied Flycatcher


European Pied Flycatcher Ficedula hypoleuca, Griend, Friesland, Netherlands, 10 September 2005 (Magnus Robb)

In Portugal where I live, Pied Flycatcher is sometimes the commonest migrant at headlands and other hotspots in early autumn. Migrants may hold feeding territories for a few days, defending them from neighbours and giving birders opportunities to hear a range of their calls.

During the last glacial maximum, the breeding range of Pied Flycatcher was restricted to a small area in Iberia (Sætre et al 2001). When Europe warmed up, the species took the opportunity to spread north and east until its breeding range stretched through boreal forests as far as 93˚E. Birds find it very difficult to change migration routes (Newton 2008), and as a result, most of the world’s Pied Flycatchers still return to Africa via Iberia each autumn. They are rewarded for the long east-west leg of their journey. In the west of the Iberian peninsula the prevailing wind in September is northerly, offering fast track migration south past the Sahara to their wintering grounds in western Africa.

The three most important calls that Pied Flycatchers use in autumn are a slightly metallic-sounding wit, a sharp tak and a high-pitched zzz that sounds very similar to one of the main calls of Spotted Flycatcher. Here is a short recording of an interaction between territorial autumn Pied, with all three calls in action.


European Pied Flycatcher Ficedula hypoleuca, Cabo Espichel, Setúbal, Portugal, 09:22, 13 September 2009 (Magnus Robb). Wit, tak and zzz calls of autumn migrants defending feeding territories during the day, with a scuffle at 0:22.

Calls very similar to two of these three feature heavily in my night migration recordings from August until early October. The commonest by far is a high-pitched buzzing zzz, while the other sounds similar to the wit that Pied Flycatchers use during the day. Both are highly variable, especially wit. Often it is possible to hear both in loose association in the same recording, not necessarily from the same individual. The following recording illustrates one of the busiest moments during a night of strong Pied passage over the lighthouse of Berlenga island, Leiria, Portugal in September 2012.


European Pied Flycatcher Ficedula hypoleuca, Berlenga, Leiria, Portugal, 04:03, 16 September 2012 (Magnus Robb). Wit and zzz calls of nocturnal migrants flying past a lighthouse on an overcast night.

Zzz calls of Pied Flycatcher are as variable as snowflakes. However, all sound buzzy and most are distinctly high-pitched. On sonagrams we can see that the many different variations share certain features in common:

  • at least two frequency bands that are not harmonically related and may show slightly different inflections (in Tree Pipit calls, by contrast, a second weaker band often appears at exactly half of the strongest frequency: these are harmonically related)
  • fine zig-zag modulations that show on both of the main frequency bands, at a rate of up to 120 modulations/sec; often more marked in daytime
  • mean duration 135 ms at night (range 77-188 ms, n = 46) and 181 ms by day (range 141-242 ms; n = 29)
  • frequency range 4-9 kHz

 

Now listen to some recordings of Pied Flycatcher zzz calls and compare them on the sonagrams below. First hear are three examples recorded by day.


European Pied Flycatcher Ficedula hypoleuca, Cabo Espichel, Setúbal, Portugal, 09:01, 12 September 2009 (Magnus Robb). Zzz calls of two autumn migrants during the day, defending feeding territories.


European Pied Flycatcher Ficedula hypoleuca, Cabo Espichel, Setúbal, Portugal, 09:18, 13 September 2009 (Magnus Robb). A territorial interaction between two autum migrants during the day, with many zzz calls.


European Pied Flycatcher Ficedula hypoleuca, Faia, Guarda, Portugal, 07:52, 31 August 2013 (Magnus Robb). Zzz calls of autumn migrants during the day, defending feeding territories.


European Pied Flycatcher Ficedula hypoleuca. Five variations of zzz calls recorded during the day. 1) Cabo Espichel, Setúbal, Portugal, 09:32, 3 September 2010 (Magnus Robb), 2) Sagres, Vila do Bispo, Portugal, 09:05, 16 September 2011 (Magnus Robb), 3) Cabo Espichel, Setúbal, Portugal, 09:18, 13 September 2009 (Magnus Robb), 4) Sagres, Vila do Bispo, Portugal, 13:10, 15 September 2011 (Magnus Robb), 5) Ponta da Erva, Benavente, Portugal, 09:28, 6 September 2011 (Magnus Robb)

 

Zzz calls recorded at night are not only around 25% shorter; they also have slightly shallower modulations making them sound a little less harsh, and they show an even wider range of shapes. Given the very different behaviour when daytime and night time versions are used (territorial confrontation versus migration flight) it may be stretching credibility to regard them as essentially the same call type. At the very least, strong similarities suggest that Pied Flycatcher is responsible for both.


European Pied Flycatcher Ficedula hypoleuca, Berlenga, Leiria, Portugal, 01:20, 16 September 2012 (Magnus Robb). Zzz calls of at least two nocturnal migrants in flight.


European Pied Flycatcher Ficedula hypoleuca, Berlenga, Leiria, Portugal, 03:24, 16 September 2012 (Magnus Robb). Zzz calls of at least one nocturnal migrant in flight.


European Pied Flycatcher Ficedula hypoleuca, Cabriz, Sintra, Portugal, 04:08, 20 September 2012 (Magnus Robb). Zzz calls of several nocturnal migrants in flight.


European Pied Flycatcher Ficedula hypoleuca. 10 variations of zzz calls given by nocturnal migrants in flight. 1) Berlenga, Leiria, Portugal, 01:20, 16 September 2012 (Magnus Robb), 2) Cabriz, Sintra, Portugal, 05:24, 20 September 2012 (Magnus Robb), 3) Cabriz, Sintra, Portugal, 04:43, 20 September 2012 (Magnus Robb), 4) Berlenga, Leiria, Portugal, 04:03, 16 September 2012 (Magnus Robb), 5) Berlenga, Leiria, Portugal, 03:24, 16 September 2012 (Magnus Robb), 6) Cabriz, Sintra, Portugal, 23:06, 14 October 2015 (Magnus Robb), 7) Cabriz, Sintra, Portugal, 02:36, 9 September 2015 (Magnus Robb), 8) Cabriz, Sintra, Portugal, 05:04, 2 September 2015 (Magnus Robb), 9) Cabriz, Sintra, Portugal, 03:48, 30 August 2014 (Magnus Robb), 10) Cabriz, Sintra, Portugal, 03:23, 30 September 2012 (Magnus Robb)

 

Wit calls are if anything even more variable, especially at night. All sound ‘sharp’ and have audibly rising intonation. Sonagrams show that their features include:

  • at least two frequency bands that are not harmonically related
  • generally lacks fine modulation, although there may be a hint of it
  • at closer range the strongest band may be seen to start as low as 2 kHz or below and to rise rapidly to around 5 or 6 kHz where it forms a kind of arch, leaning towards the right; final descent rapid but not descending as far as starting point; slightly weaker band follows similar course but top of the arch sits left of the stronger arch (this weaker arch does not lean to the right). Maximum frequency of weaker band typically slightly higher than stronger band (especially in night examples), but occasionally lower.
  • mean call duration 62 ms (range 54–78 ms; n = 12 daytime examples)

 

Here are some examples of Pied Flycatcher wit calls. First three recordings by day, followed by a sonagram of five individual calls with a corresponding sound track.


European Pied Flycatcher Ficedula hypoleuca, Sagres, Vila do Bispo, Portugal, 08:28, 17 September 2008 (Magnus Robb). Wit calls of a perched first-winter migrant during the day.


European Pied Flycatcher Ficedula hypoleuca, Cabo Espichel, Setúbal, Portugal, 09:59, 19 September 2008 (Magnus Robb). Wit calls and tak calls of a perched first-winter migrant during the day, in the presence of an Iberian Grey Shrike Lanius meridionalis.


European Pied Flycatcher Ficedula hypoleuca, Cabo Espichel, Setúbal, Portugal, 09:16, 13 September 2009 (Magnus Robb). Wit calls during a territorial interaction between two autumn migrants during the day.

European Pied Flycatcher Ficedula hypoleuca. Five variations of wit calls recorded during the day. 1) Cabo Espichel, Setúbal, Portugal, 09:58, 19 September 2008 (Magnus Robb), 2) Cabo Espichel, Setúbal, Portugal, 09:15, 12 September 2009 (Magnus Robb), 3) Cabo Espichel, Setúbal, Portugal, 10:28, 28 September 2009 (Magnus Robb), 4) Kaamanen, Lapland, Finland, 24 May 2014 (Killian Mullarney), 5) Cabo Espichel, Setúbal, Portugal, 19:57, 1 October 2015 (Magnus Robb)

 

Now listen to three sequences recorded at night, followed by a sonagram showing five individual calls, with a corresponding sound track.


European Pied Flycatcher Ficedula hypoleuca, Berlenga, Leiria, Portugal, 03:01, 16 September 2012 (Magnus Robb). Wit and zzz calls of more than one nocturnal migrant in flight. The very last call, at 0:19, is a European Robin Erithacus rubecula.


European Pied Flycatcher Ficedula hypoleuca, Berlenga, Leiria, Portugal, 03:08, 29 September 2011 (Magnus Robb). Wit call of a nocturnal migrant in flight.


European Pied Flycatcher Ficedula hypoleuca, Cabriz, Sintra, Portugal, 23:52, 11 October 2012 (Magnus Robb). Wit and zzz calls of nocturnal migrants in flight.


European Pied Flycatcher Ficedula hypoleuca. Five variations of wit calls given by nocturnal migrants in flight. 1) Berlenga, Leiria, Portugal, 03:08, 29 September 2011 (Magnus Robb), 2) Cabriz, Sintra, Portugal, 03:42, 27 September 2012 (Magnus Robb), 3) Cabriz, Sintra, Portugal, 04:43, 20 September 2012 (Magnus Robb), 4) Berlenga, Leiria, Portugal, 04:03, 16 September 2012 (Magnus Robb), 5) Berlenga, Leiria, Portugal, 03:01, 16 September 2012 (Magnus Robb)

 

Every now and then in my night recordings I find the two call-types combined into a zzz-wit. This does not happen very often but I am grateful when it does, since this is good circumstantial evidence clarifying which zzz calls belong to Pied Flycatcher.


European Pied Flycatcher Ficedula hypoleuca. Three variations of zzz-wit calls given by nocturnal migrants in flight. 1) Cabriz, Sintra, Portugal, 04:40, 7 September 2017 (Magnus Robb), 2) Cabriz, Sintra, Portugal, 03:12, 26 August 2012 (Magnus Robb), 3) Cabriz, Sintra, Portugal, 23:58, 11 September 2012 (Magnus Robb)

 

It is worth mentioning here that some of the Pied Flycatchers I record in autumn are presumably Iberian Pied Flycatchers F hypoleuca iberiae, a subspecies that breeds in neighbouring Spain and has a distinctive plumage in spring. With only a few recordings of calls from on the breeding grounds to refer to, I am currently unable to identify this taxon’s NFCs with any confidence. Its zzz calls appear to overlap with those of Pied, and while its wit calls differ subtly during the day (personal observation), the greater degree of variation at night means that it would be highly risky to try to pick out those of Iberian Pied. In order to make progress it will be necessary to record autumn calls of positively identified Iberian Pied, but at present there is no literature explaining how to identify this taxon in immature and non-breeding plumages. In short, there is still much work to be done.

 

Spotted Flycatcher


Spotted Flycatcher Muscicapa striata, Muntasar, Dhofar, Oman, 15 April 2010 (René Pop)

When I first started recording flycatchers at night, I was already aware that some of the zzz calls could belong to Pied Flycatcher. Nevertheless, I assumed that many would be Spotted Flycatchers, since they use their own kind of “zzz calls” in a wider range of situations than Pied during the day. Over the years, however, as I sharpened up my criteria for telling them apart, I came to the conclusion that almost all of the zzz calls I was recording could be attributed to Pied. Again, this has been as a result of studying the characteristics of calls that both species use during the day.

When I think of migrant Spotted Flycatchers at my favourite headlands in autumn, there are two main call-types that come to mind. One is a high-pitched zzz call that would be almost impossible to separate from Pied Flycatcher were it not that, by day, it is nearly always given in combination with the other call-type, a short, sharp tzak. Typical sequences sound like zzz-tzak… zzz-tzak-tzak, as you can hear in the following example.


Spotted Flycatcher Muscicapa striata, Sagres, Vila do Bispo, Portugal, 10:59, 16 September 2011 (Magnus Robb). Zzz and tzak calls of an autumn migrant during the day. Also a European Goldfinch Carduelis carduelis.

I have never heard this combination of zzz and tzak at night, which makes the challenge of separating Pied Flycatcher and Spotted Flycatcher all the more difficult. In three recordings of Spotted actively migrating by day, shared with me by Aat Schaftenaar from the Netherlands, tzak calls are also absent.

Note that in spring, Spotted Flycatcher has a song-type that involves spacing out many different-shaped, high-pitched units that sound roughly similar to zzz calls, often having two frequency bands but showing a much greater range of shapes. In one of Aat’s recordings of a bird migrating by day (all three were in spring), there are several of these followed by a more typical zzz call. It is not unusual for passerines to give snatches of song during migration flights in spring, but I would be surprised to hear this from a flycatcher on migration flight during the autumn.

If we restrict ourselves to Spotted Flycatcher’s zzz call, the type usually combined with tzak during the day, it shares most of its basic characteristics with the zzz of Pied Flycatcher. I have been studying sonagrams of these calls over a period of nine years, and for much of that time I tried, and failed, to identify a particular shape, frequency or relationship between the two bands that would separate the two species for me. In the end I concluded that almost all variants of Spotted can be closely matched by certain variations of Pied. Here are the main characteristics of zzz calls of Spotted.

  • at least two frequency bands, sometimes more, occasionally just one visible when distant
  • fine and often shallow modulations, often so fine as to be difficult to see, requiring adjustment of sonagram parameters. Typically around 130-180/sec, but sometimes fewer, ie, within the range of Pied Flycatcher
  • shape variable, but typically descending in a convex curve; bands usually near-parallel but sometimes converging
  • mean duration 131 ms (range 103-174 ms, n = 24 daytime)
  • frequency range 4.5-8.5 kHz

 

Eventually I worked out that the best feature for separating zzz calls of the two species during the day is the rate of modulation. This requires looking at magnified sonagrams and adjusting the parameters in favour of time resolution. In Raven Pro I set the ‘window size’ to 240 samples and the ‘hop size’ to 30. With these settings, modulations may appear that were previously too ‘smudged’ to see. If they are very shallow I stretch the sonagram vertically to make them more visible. To measure the rate of modulation, I count the number of modulations during a 100 ms stretch and multiply this by 10 to give a rate per second. If there is not a full 100 ms stretch with modulations I count the waves during 50 ms and multiply by 20. If the rate changes markedly, it is the fastest 50 ms that counts.

Spotted Flycatcher zzz calls usually vibrate at around 130-190 modulations/sec (occasionally fewer), but in hundreds of calls of visually identified Pied Flycatchers in daytime, I have still not measured modulations faster than around 120/sec. At night, very few of the 200 or so zzz calls I have measured went beyond this mark, but a handful that did went well beyond it, up to 180/sec. I believe that those few were Spotted, since this rate is normal in their daytime calls. Perhaps musculature or bone structure limits the rate at which flycatchers can modulate their calls, with Spotted being able to do this up to 50% faster.

By using this criterion I may be misidentifying some Spotted Flycatcher calls that fall within the range of Pied Flycatcher, and I must remain alert to the possibility that Pied may be able to exceed the range I have so far measured. But I suggest this as a working hypothesis: where only these two species of flycatcher occur, up to 120/sec is presumably Pied. 130/sec is unsafe but possibly Spotted, and 140/sec or more should be Spotted.

Here are three recordings of zzz calls of Spotted Flycatcher by day, followed by a sonagram showing five examples, and a corresponding sound track in which the tzak calls that follow most daytime examples of zzz calls have been removed to help us focus on the zzz calls.


Spotted Flycatcher Muscicapa striata, Cabo da Roca, Sintra, Portugal, 08:35, 9 September 2011 (Magnus Robb). Zzz and tzak calls of an autumn migrant during the day.

Spotted Flycatcher Muscicapa striata, Sagres, Vila do Bispo, Portugal, 12:39, 15 September 2011 (Magnus Robb). Zzz and tzak calls of at least two autumn migrants during the day.


Spotted Flycatcher Muscicapa striata, Ifrane, El Hajeb province, Morocco, 08:22, 11 June 2015 (Arnoud B van den Berg). Zzz and tak calls of an adult on breeding territory during the day.

Spotted Flycatcher Muscicapa striata. Five variations of zzz calls recorded during the day. Note that here the tzak calls that followed most of these zzz calls have been edited out. 1) Muntasar, Oman, 06:59, 15 April 2010 (Magnus Robb), 2) Cabo da Roca, Sintra, Portugal, 07:58, 9 September 2011 (Magnus Robb), 3) Cabo da Roca, Sintra, Portugal, 08:35, 9 September 2011 (Magnus Robb), 4) Sagres, Vila do Bispo, Portugal, 12:39, 15 September 2011 (Magnus Robb), 5) Sagres, Vila do Bispo, Portugal, 10:59, 16 September 2011 (Magnus Robb)

 

Now listen to a nocturnal recording in which a presumed Spotted Flycatcher gives three calls in a row, with long gaps, flying closer towards the end. The modulation rate here is 180/sec, and indeed these zzz calls have a timbre very similar to the examples recorded by day. Below this is a sonagram showing five examples, with a corresponding sound track.


Spotted Flycatcher Muscicapa striata, Cabriz, Sintra, Portugal, 03:49, 26 September 2011 (Magnus Robb). Three zzz calls of a nocturnal migrant in flight, coming closer.


Spotted Flycatcher Muscicapa striata. Five variations of zzz calls given by nocturnal migrants in flight. 1) Cabriz, Sintra, Portugal, 03:49, 26 September 2011 (Magnus Robb), 2) Portland, Dorset, United Kingdom, 23:27, 5 September 2016 (Nick Hopper), 3) Sagres, Vila do Bispo, Portugal, 02:35, 19 October 2016 (Magnus Robb), 4) Sagres, Vila do Bispo, Portugal, 22:08, 19 October 2016 (Magnus Robb), 5) Sagres, Vila do Bispo, Portugal, 23:51, 15 October 2015 (Magnus Robb)

 

Robin


European Robin Erithacus rubecula, Julianadorp, Netherlands, 21 October 2003 (René Pop)

I now find it amazing that I could have gone so many years without hearing Robins at night. How could I have picked up so many Redwings T iliacus and Song Thrushes T philomelos without noticing the robins usually that accompany them on the same nights? In fact their migration starts earlier that the thrushes. I have recorded them migrating in Portugal as early as 8 September, and I would not be surprised to pick up dispersing juveniles much earlier still.

Although Robins have a rich repertoire of calls, we only need to learn one call type and variations in the context of nocturnal migration. This is the call described in the Collins Guide (Svensson et al 2009) as a thin, hoarse tsi. I often hear the same or a very similar call from migrant and wintering Robins perched in bushes during the day, especially in the early morning after a fall of migrants. At such times their tsi is usually combined with irregularly spluttered ticking calls.

Robin’s tsi call shares some characteristics with the zzz calls of the two flycatchers, such as being high-pitched and normally having two frequency bands, but it is slightly shorter and differs strikingly from them in lacking a ‘zzz’ timbre. In sonagrams we can see the following features:

  • usually at least two frequency bands, roughly 1 kHz apart, although sometimes one is vestigial or even absent completely
  • usually unmodulated (although occasionally a few deep modulations, especially in daytime)
  • bands may run up or down approximately in parallel, be more or less flat, or slope in entirely different directions
  • mean duration 87 ms (range 53-149 ms; n = 18 nocturnal examples)
  • frequency range between 6 and 9 kHz, higher than the two flycatchers on average

 

Here are three examples recorded from migrant and wintering individuals during the daytime, followed by a sonagram showing five examples, with a corresponding sound track.


European Robin Erithacus rubecula, IJmuiden, Noord-Holland, Netherlands, 09:15, 8 October 2006 (Magnus Robb). Tsi calls of a presumed autumn migrant during the day.


European Robin Erithacus rubecula, Serra da Arrabida, Setúbal, Portugal, 06:49, 2 October 2009 (Magnus Robb). Tsi calls (eg, at 0:01, 0:14, 0:30, 0:35, 0:48) and ticking calls during the day, with other species including Sardinian Warbler Sylvia melanocephala.


European Robin Erithacus rubecula, IJmuiden, Noord-Holland, Netherlands, 7 November 2005 (Magnus Robb). Two tsi calls and some unusual low, quiet, harsh calls given during the day.


European Robin Erithacus rubecula. Five variations of tsi calls recorded during the day. 1) São Miguel, Azores, Portugal, 8 April 2002 (Magnus Robb), 2) IJmuiden, Noord-Holland, Netherlands, 10:41, 3 November 2004 (Magnus Robb), 3) IJmuiden, Noord-Holland, Netherlands, 7 November 2005 (Magnus Robb), 4) IJmuiden, Noord-Holland, Netherlands, 8 October 2006 (Magnus Robb), 5) Serra da Arrabida, Setúbal, Portugal, 2 October 2009 (Magnus Robb)

 

Now listen to three examples recorded from nocturnal migrants in flight, followed by a sonagram showing five examples, with a corresponding sound track.


European Robin Erithacus rubecula, Cabriz, Sintra, Portugal, 04:47, 30 October 2011 (Magnus Robb). Several tsi calls of nocturnal migrants in flight. Also a flight call of a Song Thrush Turdus philomelos.


European Robin Erithacus rubecula, Bialowieza Forest, Podlaskie, Poland, 00:22, 3 October 2012 (Magnus Robb). Several tsi calls of nocturnal migrants in flight.


European Robin Erithacus rubecula, Sagres, Vila do Bispo, Portugal, 21:57, 15 October 2015 (Magnus Robb). Several tsi calls of nocturnal migrants in flight. Also a few ticking calls of one that had presumably landed briefly.


European Robin Erithacus rubecula. Five variations of tsi calls given by nocturnal migrants in flight. 1) Cabriz, Sintra, Portugal, 04:47, 30 October 2011 (Magnus Robb), 2) Bialowieza Forest, Podlaskie, Poland, 00:22, 3 October 2012 (Magnus Robb), 3) Bialowieza Forest, Podlaskie, Poland, 00:22, 3 October 2012 (Magnus Robb), 4) Sagres, Vila do Bispo, Portugal, 21:57, 15 October 2015 (Magnus Robb), 5) Sagres, Vila do Bispo, Portugal, 21:57, 15 October 2015 (Magnus Robb)

 

Bluethroat


Bluethroat Luscinia svecica, Gun Galuut, Tuv Aimag, Mongolia, 21 May 2008 (René Pop)

While I was learning the NFCs of Pied Flycatcher, Spotted Flycatcher and Robin I started speculating which other Muscicapidae might have nocturnal flight calls. By studying their daytime repertoire I was able to make a few predictions about what to listen for in a few other species. For example, Mediterranean Flycatcher, Red-breasted Flycatcher F parva, Semicollared Flycatcher F semitorquata, Collared Flycatcher F albicollis and Atlas Flycatcher F speculigera seem likely to have NFCs in the same genre as Spotted Flycatcher and Pied Flycatcher, but I have yet to record convincing NFCs of any of them. In fact the only prediction so far that I consider to be proven has been the NFC of Bluethroat Luscinia svecica.

Bluethroat is a localised wintering species here in Portugal, and given its skulking behaviour, the best way to find one is often by listening. During the non-breeding season it is a buzzing bzui that helps me to find them most often. Sometimes they use this call in long sequences, but I have also heard it associated with plastic song. Given its buzzing timbre and the way it is used in territorial interactions, like the zzz of Pied Flycatcher, I guessed that this might also be used as a NFC. In sonagrams we can distinguish the following features:

  • two or more frequency bands running approximately parallel but hard to see because overal appearance is often smudged
  • deep modulations speed up dramatically about a third of the way in
  • pitch rises noticeably towards the end of the call
  • accented at the start, weakening towards the end
  • mean duration 155 ms (range 112-220 ms; n = 14 diurnal examples)
  • energy distributed from 1.5-8.5 kHz, ie, over a much wider range and including much lower frequencies than the NFCs of the two flycatchers and Robin

 

Here are three examples recorded from migrant and wintering individuals during the day.

Bluethroat Luscinia svecica, Eilat, Israel, 07:00, 3 December 2001 (Killian Mullarney). Bzui calls of an adult female during the day.


Bluethroat Luscinia svecica, Ponta da Erva, Benavente, Portugal, 11:44, 14 November 2009 (Magnus Robb). Bzui calls of two or more wintering individuals during the day.


Bluethroat Luscinia svecica, Ponta da Erva, Benavente, Portugal, 08:03, 22 September 2010 (Magnus Robb). Bzui calls and subsong of a wintering individual during the day.

Now listen to a recording with two flight calls given by a nocturnal migrant while passing the fortress of Sagres in the southwest corner of Portugal. This followed by a sonagram showing four daytime examples and then my only nocturnal one, all of which you can hear in the corresponding sound track.


Bluethroat Luscinia svecica, Sagres, Vila do Bispo, Portugal, 04:36, 16 October 2015 (Magnus Robb). Two bzui calls of a nocturnal migrant in flight. The first call is followed by an echo from a fortress wall.


Bluethroat Luscinia svecica. Variations of bzui calls; four given during the day and one given by a nocturnal migrant in flight. 1) Eilat, Israel, 07:00, 3 December 2001 (Killian Mullarney), 2) Ponta da Erva, Benavente, Portugal, 08:03, 22 September 2010 (Magnus Robb), 3) Ponta da Erva, Benavente, Portugal, 11:44, 14 November 2009 (Magnus Robb), 4) IJmuiden, Noord-Holland, Netherlands, 17 August 2005 (Magnus Robb), 5) Sagres, Vila do Bispo, Portugal, 04:36, 16 October 2015 (Magnus Robb)

 

Conclusions

Although it may seem very precise to measure the modulation rate of night flight calls on specially adjusted sonagrams, this belies the reality that these are still tentative first steps. My method relies on deriving characters from calls that flycatchers, robins and chats use while perched during the day, and using them to identify similar-sounding calls given while flying long distances at night. So we have to admit that there are uncertainties, and patience will be required to take these ideas further.

Assuming that this method has some validity, I am hopeful that dedicated recordists in appropriate locations may eventually identify NFCs of Mediterranean Flycatcher, Red-breasted Flycatcher, Semicollared Flycatcher, Collared Flycatcher and Atlas Flycatcher. It’s about time we sorted them out. Naumann actually described nocturnal calls of Pied after listening to caged migrants as long ago as 1822 (Glutz von Blotsheim & Bauer 1993), but this knowledge never became mainstream. Now we have the technology to help investigate calls obtained without imprisonment, and patience is the thing we need most.

Finally, a word of caution. It is simply not possible to be sure of the identity of all flycatcher/robin-type flight calls recorded during the hours of darkness. A high proportion will have to remain unidentified, and not just the ones too distant and degraded to give clear shapes on sonagrams. I strongly recommend not to agonise over every last call, some hardly more audible than mosquitos colliding, as a good friend likes to remind me, others clear but simply ambiguous. I often get no further than ‘flycatcher sp.’, and this is nothing to be ashamed of. On other nights I obtain many clear identifications and feel confident to be making some progress. Once in a blue moon I have a valuable new insight or record something genuinely new. Those are the magic moments that make all the other sessions worthwhile.

 

Acknowledgments

I would like to express my gratitude to Aat Schaftenaar and Nick Hopper for sharing their recordings of migrating Spotted Flycatchers, and to Lukas Pelican for telling me about Naumann’s early description of Pied Flycatcher calls at night.

 

References

Glutz von Blotsheim, U N & Bauer, K M 1993. Handbuch der Vögel Mitteleuropas 13. Wiesbaden.
Newton, I 2008. The migration ecology of birds. London.
Sætre G-P, Borge T, Lindell J, Moum T, Primmer C R, Sheldon B C, Haavie J,Johnsen A & Ellegren H 2001. Speciation, introgressive hybridization, and nonlinear rate of molecular evolution in flycatchers. Molecular Ecology 10: 737–749.

 

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