Part 2: Put it all together and what have you got?

Simple calls

This first sonagram shows huit calls of a Common Chiffchaff (CD1-13), regularly used by adults. Each call has three layers, and all of them start low to the left and end high to the right, so the call rises in pitch. The three layers are, from the bottom up, the fundamental, first harmonic and second harmonic. These add a little ‘colour’ to the sound, a slight impurity which is very hard to describe, but very easy to hear and see.

The corresponding call of a Willow Warbler P trochilus in the next sonagram was recorded when Magnus and Roy Slaterus were looking for a Hazel Grouse Tetrastes bonasia beside the Siemianowka reservoir in north-eastern Poland (CD1-14). This sonagram shows a single, weak harmonic; compared to the chiffchaff’s call this is a purer-sounding whistle. Look at the sonagram and listen for the sudden rise in pitch at the end. This is the best way to tell a Willow Warbler’s from a Common Chiffchaff’s call.

Next comes the sonagram of the equivalent calls of wintering Siberian Chiffchaff P tristis recorded at Bharatpur in India (CD1-15). You won’t see any clear inflection in pitch: the sound is flat. These distinctive calls are quite high-pitched, and their harmonics are much less prominent, so when you listen to the recording, you will hear that the tone is a much purer-sounding whistle. 

These typical calls of Iberian Chiffchaff P ibericus (CD1-16) were recorded in a beautiful pine forest along the ancient pilgrim’s path to Santiago de Compostela in north-western Spain. They are distinguished from calls of other chiffchaffs occurring in western Europe by their smooth downward inflection. These calls start at a higher pitch, more or less where the others finish, then drop to where the Willow Warbler starts.

Simple song

The first time I realised that I could make my own sonagrams on a lap-top computer I had this shown to me by Swedish birders, Lars Jonsson and Urban Olsson, at the 1993 conference on English bird names organised by Birding World at Swanwick in Derbyshire, England. Urban took his Mac from the hotel safe and Lars whistled the song of a Common Rosefinch Erythrina erythrina (CD1-17) into its mic, and then Urban produced a sonagram. In this case, we’ve had to make do with a real Common Rosefinch as we can no longer afford Lars and Urban. The simple traces on the sonagram are typical of the way song phrases show up on a page. 

Inspired by this, I bought a Mac lap-top, and was producing my own sonagrams a short time later. I won’t pretend I found it easy, but it was very satisfying. It meant I could make sound recordings in the field, analyse them at home, and compare them with published recordings and sonagrams. Difficult identifications could be confirmed within hours. If you have a go, don’t forget to use the same scale when comparing any two sonagrams. Once I had started to learn how to use the computer to produce sonagrams, I wanted to use it to answer all the other birding mysteries. What was the difference between Richard’s A richardi, Blyth’s A godlewskii and Tawny Pipit A campestris flight calls? What about Blyth’s Reed A dumetorum, Marsh A palustris and European Reed Warbler calls? Siberian Stonechat Saxicola maurus? Semipalmated Plover C semipalmatus? How did the different gulls sound, and what could I see in their sonagrams? I can’t quite remember how I first started talking to Paul Holt about it all, but I do remember that he had quite a few of these precious recordings that weren’t available on ‘Teach yourself bird sounds’. Blyth’s Pipit flight calls and a variety of Yellow-browed Warbler P inornatus sounds come to mind. But even he didn’t have most of the desired recordings, and we started to talk about a new project, dreaming about collecting all these exciting sounds and publishing something. He came up with the name ‘The Sound Approach’, which with his Burnley vowels seemed to have a w where the u is. Then he went birding in China and hardly came home again.

Now The Sound Approach has many of the recordings Paul and I craved back then, and Magnus and I have chosen a few of our favourites, some intriguing and some just rare examples that illustrate different types of sonagram and, I hope, take bird sound identification a little further. Being able to see small features you hadn’t noticed just through listening is one of the advantages of looking at sonagrams. 

‘Curlews’ and proportions in sonagrams

Sitting out at dusk drinking red wine and listening to Stone-curlews Burhinus oedicnemus on a Mediterranean island in the spring, has to be one of the great pleasures in the world. Even more so for sound buffs, for whom noises of the night are always an attraction. The secretive Stone-curlews are often hidden in an orchard or deep grass during the day, and surprise when they call to each other straight after darkness falls. They have varied repertoires and at home, before I had as much experience, I mistook them for Eurasian Oystercatchers Haematopus ostralegus, Eurasian Curlew Numenius arquata and Little Owl Athene noctua. The first call they usually give after sunset is the one that gave them their name. Comparing these two sonagrams shows you the difference in proportions between the commonly heard and sometimes confused sounds of Eurasian Curlew with those of the unrelated Stone-curlew. You can see (and hear) that Eurasian Curlew starts with a long, low note and ends with a short high one (CD1-18), whereas Stone-curlew is the opposite, starting with a short lower one and with a longer, high note at the end (CD1-19). 

Kite and pipit calls illustrate modulation

Red Kite Milvus milvus are migrants in Schwaben, Bayern, Germany, and the locals look forward to their return in the way other Europeans wait for Common Cuckoo Cuculus canorus. I stayed with Diana Krautter who can whistle the ‘Milan’ into circling her as she watches from her garden. This bird was following the plough and calling to passing birds. The modulation in this Red Kite’s call (CD1-20) is very slow and easy to hear (aye aye aye) and visible in the sonagram.

This Black-eared Kite M lineatus (CD1-21) was recorded in the north of Japan where in winter many roost on the edge of frozen lakes. Japanese fishermen carve fishing holes in the ice and the kites hope for scraps. They often mob the Steller’s Sea Eagles Haliaeetus pelagicus and White-tailed Eagles H albicilla as they all look for fish remains. This note has a much faster modulation that sounds like a neigh of a horse.  

The flight sounds of Richard’s, Tawny and Blyth’s Pipits are like three quizzes with beginner, intermediate and advanced: Richard’s Pipit has a diagnostic call used in flight that makes it very good to learn. Let’s call it squonk. The great thing about Richard’s Pipit is that when it passes overhead you can hear it coming a long way off and disappearing for quite a while so you can get your mind around the sound (CD1-22). This sound doesn’t vary much; it can be given singly or in twos or threes, and most of the variation you hear is caused by distance. As you can see, sonagrams give us several additional characters to look and listen for. In this case, how ‘buzzy’ it sounds is a reflection on the modulations in the call: much faster than either of the kites. The buzzy quality is especially coarse and obvious in Richard’s, where this has pronounced modulation, showing as ‘shark’s teeth’ on a sonagram. 

Tawny Pipits can be a little trickier, as they show a lot more variation (CD1-23). The next two recordings were made by Killian whose field notes describe the equivalent call of Tawny as “a strongly downslurred tsleeuu, a fuller, slightly longer note than a similar call of House Sparrow, reminiscent of Yellow Wagtail but not really confusable with it”. This is the call he associates most with birds in full flight; “flushed birds may give it too, but it is often preceded or interspersed with a rapid series tchilp-tchelp-tchilp.. notes, not unlike the usual take-off call of Short-toed Lark”. Now check the sonagram; first notice the variation in sounds, the downslurred shape of the sound, then the pitch compared to Richard’s Pipit. In Tawny’s tsleeuu the modulated bits are so brief that they have very little bearing on the timbre of the call as a whole, leaving the sound slightly musical as an attractive note, or as Killian referred to it “a real call”. 

One of the reasons Blyth’s Pipit counts as advanced is that it’s extremely rare throughout the Western Palearctic, and conse-quently much sought after. Like Tawny Pipit, Blyth’s has a variety of sounds it uses in flight (CD1-24). Comparing Blyth’s to Tawny, Killian added: “most of the time it’s just an unobtrusive and extremely Tawny Pipit-like typp typp typp typp every half second or so. If you are lucky enough to hear the full call, when it gets into its stride, its squonk equivalent is an emphatic speuu, a little higher-pitched than Richard’s”. You can see this on the sonagram and that the modulation is so rapid and fine that it results in a wheezing quality, or as Killian describes “not so throaty as Richard’s, cleaner, more like Yellow Wagtail”. 

Broadband and Trumpeter Finches

Having looked at modulations, time for some fun. In the first sonagrams of the book, we already noted that adding layers of harmonics to a simple, pure-sounding linear whistle changes the timbre, but what happens when this is taken to extremes? When we started The Sound Approach, one of the most exciting prospects was to make recordings of Western Palearctic species that had never been included in audio publications before. Mongolian Finch Bucanetes mongolicus was one of these. It has various songs, and the most lyrical one recorded at the ruined Ishak Pasha palace in eastern Turkey near the border with Iran (CD1-25) sounds like a cross between a Common Linnet Linaria cannabina and a Common Rosefinch. In the sonagram you can see several layers of harmonics, giving it a somewhat squeaky timbre, but this is nothing compared to the amazing timbre of a Trumpeter Finch B githagineus, its desert counterpart (CD1-26). This was recorded in India in January 2002, close to the Pakistani border, with the two countries on the brink of war and Magnus trying to look unobtrusive, despite the parabola in hand, every time a military vehicle passed by. The Trumpeter Finch sounds as if he saw the funny side of all this. Look at the incredible profusion of layers in the sonagram: this cool little desert creature has been into ‘broadband’ for thousands of years. 

Shapes and Yellow-browed
comparisons

Few people get Yellow-browed Warblers in their garden, so Arnoud was lucky when he recorded this one in a Bird Cherry Prunus padus in his garden at Santpoort-Zuid, the Netherlands (CD1-27). Compare the sonagram with one of a Coal Tit Periparus ater recorded at nearby IJmuiden, as it perched briefly before continuing on a migration flight (CD1-28). These two sounds are commonly confused; both are high-pitched and show a V-shape in sonagrams. As you can see, however, the Coal Tit’s calls are a shorter, more rounded V-shape and it tends to double its calls, whereas the Yellow-browed does not. Now compare both to a Pallas’s Leaf Warbler P proregulus recorded by Arnoud, surrounded by curious children, in the middle of town near Rotterdam (CD1-29). The harmonics you can see in the sonagram create a similar quality to chiffchaff, but the rapid descent at the start, gives it a more of a t– or ch– sound. Both these qualities also separate it from Yellow-browed and Coal, and it is also lower-pitched. All a bit technical? Try Anthony’s and Killian’s more artful description, dreamt up when they first heard Pallas’s Leaf Warbler in China; they compared Pallas’s calls to “the twang sound when you skid a piece of ice across a frozen pond”.

M shapes in Common Ringed and Semipalmated

In the summer of 2004, we sent Magnus to Siberia, Russia. He liked it so much he missed his plane home and had to wait five days for the next one. This gave him the opportunity to make lots of Common Ringed Plover recordings. A few weeks earlier, Arnoud travelling with René Pop through Alaska, USA, found, photographed and sound recorded a Semipalmated Plover sitting beside the old road from Nome to the Eskimo village of Teller. Look at the sonagram as you listen to the sounds. These Common Ringed calls (CD1-30) have a simple rising inflection as you can see. In Semipalmated, the equivalent call is higher-pitched, has stronger inflections, and is M-shaped with a downward dip in the middle (CD1-31). Looking at the sonagram and listening to the CD does really help in understanding these differences but it is hard to put them into words.

Separating stonechats by inflection

European Stonechat S rubicola has a variety of calls, and the most common are a chat, often compared to the sound of two stones being tapped together, and a whistled weet with an upward inflection (CD1-32). These are easy to see on a sonagram: the chats are vertical lines and the weets diagonal. The two are often given in alternation, with chat tending to take over from weet in the autumn. While in Kazakhstan, Magnus thought he noticed that the whistled sound in Siberian Stonechat had a downward inflection: wiu (CD1-33). The sonagram confirms the point nicely and the recordings support these observations. You can see the vertical trace produced by chat sounds interspersed with upward and downward inflected weet and wiu calls, respectively

Rattles of Red-breasted Flycatchers

Rattles show in sonagrams as a series of the vertical chat or tick traces you’ve just learnt. These three sonagrams show the differences between rattling calls of Eurasian Wren Troglodytes troglodytes, Red-breasted Flycatcher Ficedula parva and Taiga Flycatcher F albicilla. In Red-breasted Flycatcher (CD1-34), the individual ticks are very evenly spaced; in Eurasian Wren (CD1-35), the ticks are not evenly spaced, but closer together at the start of each rattle. The flycatcher’s rattle is also slower, in other words its ticks are spaced further apart. We can also use sonagrams to separate Red-breasted from Taiga Flycatcher (CD1-36), its recently split counterpart breeding from the Urals eastwards and occurring as a vagrant in Europe. In both flycatchers, the rattle is of roughly similar length, but in Taiga it contains many more ticks with much shorter gaps between them, and it slows down slightly towards the end. The resulting rattle is so different from that of Red-breasted that, as you can see in the sonagrams, Eurasian Wren fits in between.

Gull long calls

Gull sounds are always with us, at least in western Europe, and for me living by the sea they can change a rather boring meeting into something quite bearable. Male and female Herring Gulls Larus argentatus stand on the roof opposite my office in Poole, Dorset, and pass opinion on every bird flying overhead. The most helpful sound to listen for is the long call, effectively the song of a gull. It can be heard at any time of the year, but particularly from adults and near-adults in late winter and during the breeding season. This one was recorded in March at a quiet spot in the Netherlands (CD1-37). These sonagrams are more complex than any you have tried so far. Cut them into pieces and they are much easier to understand. There are three separate stages to the long call, each with the gull adopting a different stance, and I hope that visualising these will help when reading the sonagrams. First, there are a few fairly low, short notes as the bird stretches its head a little forward. Then some longer, comparatively high-pitched notes are produced with the head pointing downwards. Finally the head is jerked upwards (in Herring Gull around 45º above the horizontal) and a long, loud series of fairly short, trumpeting notes are belted out.

In April 2003, Jacek Betleja took a group of us with him as he checked the breeding colony of Caspian Gulls L cachinnans at Babice in southern Poland (CD1-38). Having criticised field guide authors earlier on for their use of adjectives, I am going to have a go at describing something most of them ignore: Caspian Gull sounds. Caspian is the tenor to Herring Gull’s alto and as you can see in the sonagram Caspian’s long calls have the same three stages but the notes are deeper and richer in harmonics. After a few introductory calls, the long screamed notes of the second part sound as if it is straining for the Herring Gull’s higher pitch while bowing much deeper. Next, the head is thrown all the way up to the vertical as it ‘laughs’ (cachinnans means ‘laughing’). After the screamed middle, this diabolical cackling adds to the call’s grotesque character. This is because of the speed of the notes, which you can compare with sonagrams of Herring and Yellow-legged Gulls L michahellis. Unlike both, a standing Caspian often opens its wings in an albatross-like posture while performing the long call. The recording was an adult giving two long calls while flying over its breeding colony. Long calls sound the same whether they are given in flight or on the ground.

Apart from cheering up a dull meeting, another reason for listening to the gulls at work is that there is always a chance that I’ll hear a Yellow-legged Gull, as Poole is its only British breeding site. In summer we get a good influx here; the local pie factory and surroundings are home to over a hundred, and they substantially outnumber Lesser Black-backed Gulls L fuscus. Yellow-legged (CD1-39) has a long call that is uniformly deeper than that of Caspian Gull, with softer introductory notes and a far slower delivery, replacing all the maniacal qualities with sounds delivered at a pace you would expect from a bird that sits around eating pies all summer. The long call gestures are similar to Caspian but less exaggerated. Again, the sonagram gives you an impression of the speed of delivery. The length of long calls varies considerably in all gull species, while the speed of delivery and pitch do not. 

Finally, here is a sonagram of a long call from a Lesser Black-backed Gull (CD1-40) for you to practice.

Loudness and intensity

The final measurement of bird sounds that we will consider is their loudness or quietness. In the same way that pitch relates to frequency, loudness is a word for how we perceive intensity, which is measured in decibels or dB. How loud a sound seems depends not only on the effort put into making it, but also on its pitch, and the prevalent acoustics, including any other sounds audible at the same time. 

Loudness is shown in a sonagram by the depth of black in the tracing. When the sonagram is set to ‘greyscale’, a quiet whistle will show as a narrow, light grey line, whereas a loud one will be thicker and blacker. When judging loudness in a sonagram, it is wise to use the darkness of the tracing comparatively – and thus judge the louder parts of a song or call only in comparison with other parts of the same sonagram. A sonagram from another recording may not have been made from the same distance, or with the same equipment.

A helpful graph for illustrating loudness and timing is an oscillogram. It measures the sound waves. Their size above or below the horizontal axis tells us how loud the sound is. As usual, their change over time is read from left to right. Because a 1 kHz sound has 1000 waves per second, you have to zoom in a very long way to see that kind of detail. We don’t need to see the individual waves; we can use oscillograms to see how the patterns of loudness change over time, and the rhythm or timing of the sounds.

Comparing woodpecker drums by oscillogram

Listen to typical drums of male Great Spotted Woodpecker Dendrocopos major (CD1-41) and male Lesser Spotted Woodpecker D minor (CD1-42). Compare what you hear: the differences in duration, the way loudness changes or stays the same over the course of the drum (the envelope), and the strike-rate in the individual drums. Now check these elements against the oscillogram. An additional difference not visible on these oscillograms is the length of the pauses between drums, which is much longer in the Great Spotted. 

Baillon’s Crakes’ emotions

Birds produce strong and weak sounds depending on the distance their message is intended to travel and the meaning they want to convey. Most birds produce weak, short-distance sounds when subsinging, copulating or comforting young, for example. Stronger, long-distance sounds are used to advertise for a mate, defend territory, contact others or mob a predator. Emotion always plays a part in this and many bird sounds increase in strength and change pitch depending on the emotional state. Listen to the recording of an adult Baillon’s Crake Porzana pusilla (CD1-43), leading its young along a ditch. The continuously repeated weak tuc… tuc… tuc… calls it uses to keep the brood together gradually morph into louder (from 0:31) tak! calls as it senses danger (in this case the danger was Magnus). These louder calls are presumably not only intended for its young less than a metre away, but also for its mate about 10 m further along the ditch. 

The power of a Thrush Nightingale

How loud a given sound seems to be depends on the acoustic conditions and the distance from the bird, as well as the  direction the bird is facing. Describe each sound separately, and try to avoid unqualified use of the words ‘loud’ and ‘soft’. Powerful, moderate and weak are more meaningful words to describe the power at which sound is produced. A flock of Greater Canada Geese Branta canadensis, with their low-pitched calls, flying over a house at dawn could wake the inhabitants, whereas the loud, high-pitched calls of a large flock of Redwings T iliacus would not, even if they were much closer. The calls of both species in flight can be described as loud, but only Greater Canada calls can be described as powerful. Listen to this Thrush Nightingale Luscinia luscinia as it sings from a small island in a pond in the town park of Białowieza, Poland (CD1-44). The power of the song dominates over even closer songs of Eurasian Wryneck Jynx torquilla, Common Wood Pigeon C palumbus, Eurasian Collared Dove Streptopelia decaocto, Great Reed Warbler A arundinaceus and Common Chaffinch Fringilla coelebs. It held my attention so well I didn’t notice the Icterine Warbler Hippolais icterina song that you can hear in the recording.

It is also worth noting that sounds learnt from published tapes and CDs can often give the wrong impression regarding the loudness of the sound; the birds invariably seem weaker when heard in the field. Previous bird sound publications have often been ‘mastered’ by people who did not have any field experience of the sounds, and set them all to play at the same volume.