Chapter 14: A flock of birds forever in flight

The first Sound Approach CD was a freebie of flight calls for Dutch Birding subscribers called Out of the blue (van den Berg et al 2003). At the time, Magnus taught me a sound I had been missing. This is the Ring Ouzel’s basic flight call (CD1-61). Nick and I heard one of the birds using this as it continued its journey. Since Out of the blue, Magnus spent an autumn living in Poole, and many of the migration recordings in this chapter were made by the two of us locally.

Chaffinches were flying north along a narrow front, maybe 100 m across. The line drifted a little as they flew into the wind. Finding local migration corridors is a fieldcraft exam in itself. This one happened to be half way along a high ridge, and we could have missed it, had the wind been from another direction. The best weather to hear the glory of migration on Ballard is when the wind is northeasterly.

These migration corridors are three dimensional with birds like swallows and wagtails happy to fly low over Swanage Bay, while the layers of migration can reach unseen up to 4 km high, depending on weather conditions.

On this typical autumn morning, Scandinavia’s Blackbirds were arriving for winter, literally tumbling out of the sky from great heights before disappearing into cover. Joining the flocks of finches flying into the wind, they headed up to our ridge from where Hamish was counting on Long Meadow. They gained height over Swanage Bay to skim just over our heads on top of Ballard Down, before descending over the fields to Studland village and on past Little Sea to South Haven.

There must be hundreds of these migration corridors. It wasn’t until 2005 that Hamish discovered the magic of Long Meadow. Having walked across it thousands of times, he had been blissfully unaware of its true potential over 27 years of intensive Durlston birding. At present, it has to be one of the finest migratory corridors in Britain. We can scope it from where we are sitting. Running north-south for 300 m and up to 70 m wide, it has woodland along one side and a double running hedge bordering a quiet access road along the other.

The finches and buntings flying past on migration have a couple of predictable types of call. In Chaffinches the same calls are heard overhead from females, males and first-winters. One call type is described in the Collins bird guide as yupp. Here is an example of it from a Chaffinch that was recorded on a day when the migration was southbound. It had already passed over Ballard and was heading across Long Meadow (CD1-62).

The other Chaffinch call heard on migration flights, more noticeably though actually less frequently, is described as fink. It is more powerful than the flight call, and more strongly associated with perched Chaffinches. Here is a solitary female that has paused to perch on a bramble and is calling while looking skywards, presumably to try to attract another Chaffinch (CD1-63). Now listen to another female Chaffinch mixing the two calls as she flies north past us (CD1-64).

Using the example of migrating Chaffinches and Bramblings, we can illustrate a basic guideline that helps in identifying a range of other species. Single migrants often use different call types than birds migrating in groups. The more common the migrant, the more likely that they will be giving ‘flight calls’ as the flocks pass. These are often not very striking calls, and en masse they may at first sound like anonymous chattering. Many of the following examples feature single birds giving flight calls, but this is to help you learn them. Chaffinch and Brambling seldom use flight calls while perched, but in other species they may signal an intention to fly. In the Collins bird guide, Lars Svensson suggests yupp for Chaffinch and yeck for Brambling.

Fortunately for us, the scarcer the migrant the more likely it is to be alone and using different, far-carrying calls in the hope of attracting friends of the same species. For convenience, let’s call these ‘social calls’. These are designed to stand out from the general background of hundreds of other finches migrating together using their flight calls. On the breeding grounds, the same sounds are often repeated from prominent perches, and in most finches and buntings you hear them routinely all year round. Sometimes given when a bird is in danger from a predator, they may seem to be used as alarm calls, but in fact the idea is to attract reinforcements to help with mobbing. In different species, these calls have been given different names. In crossbills for example, they are usually called ‘excitement calls’.

Back on Ballard a little later in the morning, and a single Brambling was passing by. You can hear its flight calls and one distinctive social call in CD1-65. It is mainly the social calls that alert us to Bramblings passing, but to count them, it is better to listen for flight calls. In years where there are a lot of Bramblings, they can sneak past high on southerly winds in poor light and in mixed flocks. If they don’t use their social calls, we risk misidentifying them as Chaffinches. Here are some Bramblings that Magnus recorded at migration watchpoint de Nolledijk in the Netherlands (CD1-66). On this occasion, they passed by without giving any social calls.

Another bird that I tend to identify mainly by its social call is Siskin. This is how I like my Siskins (CD1-67): all alone and giving plenty of descending piercing whistles. What you normally get can be heard from a little flock passing Nick and me that Monday morning on Ballard (CD1-68). First a few high frequency descending whistles which make you look round for Siskin, then as the birds get closer, surge after surge of six or seven flight calls that are superficially like muted Goldfinch flight calls.

Here is a flock of Goldfinches from Durlston. One individual has been left a little behind and is rushing to catch up. These twittering flight calls are musical, and seem easy to recognise on that quality alone. The pitch bounces up and down, creating a sparkling effect (CD1-69). Siskins seem to mutter indistinctly by comparison. Flocks of Goldfinches are something of a speciality on the British south coast, andw this massive Goldfinch migration would be glorious even without anything else. Here is a larger flock heading towards the harbour from Durlston (CD1-70). In Goldfinch and the next species Linnet, we have not noticed much difference between the calls uttered by single migrants and those within migrating flocks.

Linnets have a duller plumage and duller flight calls (CD1-71). A tight flock of Linnets sounds a little like a flock of Goldfinches, but their twittering averages lower-pitched, and has far less range between the higher and lower notes. They often deliver their flight calls in pairs, mixed in with singles and triplets. Migrating Siskin, Goldfinch and Linnet can occasionally throw in bits of song, and call types other than flight calls. Here is an example of Linnets singing a little as they pass by on migration (CD1-72). Juveniles have a different call (CD1-73), which can occasionally be heard in migrating flocks early in the autumn.

Lesser Redpolls migrating are fun to learn and identify. They have distinctive harsh but not deep che che che flight calls, delivered in rapid-fire bursts of two or three notes, interspersed with the occasional social call. The combination sounds like a steady repeated flat dot-dot dot-dot dash of morse code. This lone Lesser Redpoll flying over Long Meadow gave no social calls (CD1-74), but now listen to a single migrant in the dunes at IJmuiden in Holland, and you can hear the typical pyuee (CD1‑75). A little like a cat’s meow, it resembles the Siskin’s whistled social call but always has a question-like rise in pitch.

The flight calls of Greenfinch, the last of Dorset’s commoner finches, are one of the more familiar sounds on migration along the south coast of England (CD1-76), although we no longer hear them as often as we used to. Delivered in rapid-fire bursts faster than Linnet calls, faster even than Lesser Redpoll flight calls, they can almost sound like a trill. Greenfinches have a social call too, but interestingly, autumn migrants don’t seem to use it in flight. Juvenile Greenfinches can be mistaken for crossbills, but generally give an almost continuous series of identical calls (CD1-77).

Crossbills come in various vocal types, and in The Sound Approach to birding (2006) we explained how Parrot and Scottish Crossbill, widely regarded as species, just happen to be two of the best known. Neither type has occurred in Poole Harbour, but we do receive visits from other vocal types, which we believe are no less, or more, worthy of species status. Once learnt, crossbill vocal types are far easier to separate than some other closely related migrants, such as Rock Pipit and Water Pipit.

Many birders know when they are hearing a crossbill, but only the attentive know which vocal type. As a group, they have powerful, incisive, metallic-sounding flight calls. Glip Crossbills are the common crossbill from Finland to Poole (cf Lindholm 2011). Here you can hear a flock of 11 passing Nick and me. Nick suspects that I am not taking my exam very seriously (CD1‑78).

It turned out to be a record day for Glip Crossbills with 212, and a further 451 passing during two subsequent visits that week (CD1-79).

Bullfinches migrate past regularly and give themselves away with social calls. The migrant in CD1-80 was resting between flights. Bullfinches also have an insignificant-sounding, soft bit flight call that is mainly used as a precursor to flight, although attentive listeners may occasionally hear it from passing birds too, in between the more noticeable social calls.

One of the most sought after migrants for my Poole Harbour list used to be Hawfinch. I had a blind spot, although it really wasn’t so much a blind spot as a deaf spot. I’m not very good on anything that sounds vaguely like a Robin. As this recording illustrates (CD1-81), the Hawfinch’s social and flight calls are both fairly Robin-like and quite unlike any of the other finches. The highly distinctive social call is much lower-pitched than the flight call, a stony fwit that is often doubled. However, this is not the usual migration call. Instead it is a very high-pitched, lisping flight call that should alert you to Hawfinches more often. I eventually saw one migrating as I was waiting for the ferry at North Haven, on 30 October 2005. The ferry chains drowned any finer sounds, so hearing one as it passes overhead is a treat still to come.

Twite tend to migrate from late October to early November and being hardy birds, most winter further northeast, stopping anywhere from the Thames estuary northwards. They are extremely rare in Poole Harbour, although the occasional bird must be overlooked. So we assume our Twite will be travelling alone and are listening out for its extremely distinctive social call, a nasal, rising keet (CD1-82). Twite flight calls are like Linnet notes delivered in the style of a redpoll. They show almost no variation in pitch, so they sound rather flat by comparison with Linnets. None of us has managed the equally rare Serin yet on migration through Poole (CD1‑83), though Durlston has managed four autumn migrants. Serins have a high-pitched jangle with the sparkling quality of a Goldfinch, but delivered as a rattle-like burst of identical notes.

Snow Bunting’s flight calls are more musical than Serin’s, their lower pitch creating a more rippling effect. Experienced observers have been known to confuse the two. Fortunately, Snow Bunting has a highly distinctive social call that typically alternates with its flight calls (CD1-84). Lapland Bunting’s flight calls are also a rapid succession of about 3 or 4 notes, delivered at a similar speed to Serin and Snow Bunting. In Lapland, each note is a hard staccato tic, and the combination of several results in a rattle (CD1-85). It has a social call similar to Snow Bunting, but contrasting so strongly with its rattle that a single migrant passing overhead can create the illusion of two entirely different species.

None of the buntings are common migrants in Poole, so many of these recordings were collected by Magnus as he stood in the dunes of IJmuiden on the Dutch coast. Nick is very proud of a Lapland Bunting he managed to record flying over his Stoborough house in the dark, not least because he was lying in bed at the time. He had put his microphone on the roof and connected it to a very long cable, which he runs to his machine and earphones in the bedroom.

In October and early November, Reed Buntings shoot past South Haven daily in ones and twos, but in IJmuiden there may be up to 100 in a morning. Reed Bunting has a very odd, low-pitched and nasal-sounding flight call quite unlike anything else (CD1-86). This is probably an adaptation to living in reedbeds, where rustling reeds could easily obscure shorter and higher-pitched flight calls on windy days.

The social calls of Reed, Lapland and Snow Bunting are all short descending whistles. Reed Bunting’s social call is much higher pitched and purer-sounding than the other two (CD1-87). Lapland and Snow Bunting’s social calls are very similar and easily confused, but Lapland has some lower-pitched, shorter and more nasal variants that are missing in Snow Bunting.

Corn Buntings on migration flights only use their flight call: an electric, fairly low-pitched click described in the Collins bird guide as bt… bt… (CD1-88). They are surprisingly rare here on migration, and only the occasional one or two pass over South Haven towards the end of October. Yellowhammers breed locally but are only occasionally seen as passing migrants. Their flight calls are dry ticking notes, given singly or in twos or threes, in which case the first note is higher than any that follow (CD1‑89). Yellowhammer’s social call is a dry buzzing sound (CD1‑90), very different from the whistled social calls of Reed, Lapland and Snow.

Ortolans are probably overlooked in Poole Harbour. Nick heard one calling when walking at the top of Glebelands, close to the track. He followed the call to the hedge thinking that since he was in Poole Harbour it really couldn’t be one. The call moved and then an Ortolan popped its head up. He was really chuffed. There it was right in front of him, a first for Poole Harbour. The call Nick heard was a repeated single note something like this (CD1-91). Ortolans on migration use similar flight calls, but usually showing much more variation in pitch (CD1-92). The calls are typically single notes spaced well apart, plucked from different strings of the same instrument.

Magnus recorded this Little Bunting migrating through IJmuiden (CD1-93) when he was still learning his flight calls. I was quite sceptical when he claimed it, but now I believe him. We’ve had just the one record here in Poole, the bird that flew past Graham and James at South Haven. Superficially, the tic call sounds like a Robin, but when they combine the flight call with a chup that is probably the social call, we can only confuse them with Yellowhammer.

Leaving behind finches and buntings and their penchant for social and flight calls, the other big group of passing birds is the pipits and wagtails. As with all lessons, things get a little tougher the further you get into the course. Imagine you are attending a wedding in a rural Dorset church, and that the organist is hard of hearing. The bride and her father have arrived and are waiting to walk up the aisle, accompanied by strains of Hear comes the bride. The organist is blissfully unaware, and various people including the groom are trying unsuccessfully to attract his attention. Pssst… pssih… ist ist ist… spibz… viisst… psit…

This descriptive ‘birdie talk’ is from the Collins bird guide’s descriptions of various pipit and wagtail sounds. It prepares you for flight calls of Meadow Pipit, Rock Pipit and Water Pipit, which can all overlap. Meadow Pipit’s ist ist ist is extremely varied in pitch and delivery, but these calls are among the easier to identify as every note is short and rises in pitch (CD2-01). The calls in this recording have been brought into close focus by the recording equipment. You can hear the way variations grade into one another, with the sounds varying in length, pitch and intensity. The next recording is more representative of the real experience, with varied calls coming from several directions, and other species trying to confuse the issue (CD2-02). Meadow Pipit is the most common pipit through the harbour, with 100 passing Ballard Down on a reasonable day and a record 372 on 7 October 2009.

Now listen to viisst calls of a Rock Pipit, this time recorded on Tory Island in Ireland (CD2-03). Compared to Meadow Pipit flight calls these are higher-pitched, longer and shriller.

If you look at the sonagram you can see that Water Pipit is similar to Rock Pipit but lower-pitched and coarser (CD2-04). These examples illustrate distinctive variants of their calls, and this is how we’d like to hear them all the time, but unfortunately they can sound extremely similar. Both Rock and Water Pipit can sometimes even sound very Meadow Pipit-like when migrating in groups. Rock Pipit is occasionally recorded migrating in Poole but not Water Pipit. Both overwinter along the bays and edges of the harbour.

Tree Pipit is a far easier bird to identify when flying over on migration. The pitch sounds even or slightly descending, and not rising as in the last three species. There is some variation, especially in length and intensity, most obvious when Tree Pipits migrate in small groups. This first example is of just two individuals migrating in Bulgaria, one after the other, making the detail easier to hear (CD2-05). They are using flight calls and a very short sip note, which may be equivalent to the social calls of finches and buntings. This example is followed by one from Durlston, showing the greater variety of calls heard in a flock (CD2-06). The high pitch and sibilance makes it difficult for some people to hear them.

Arguably, the flight call of Richard’s Pipit is the strongest and most attention grabbing of any pipit (CD2-07). You normally hear them when they’re still a long way off, and you can look forward to watching a big pipit bounding your way. Tawny Pipits have flight calls with a very different, chirruping quality, something like a cross between a sparrow and a Pied Wagtail (CD2-08).

White and Pied Wagtails both migrate through Poole, and their flight calls are not really separable. I don’t know where I learnt that their calls are a ‘disyllabic’ chis-ick, but like a good boy, when they fly past that’s what I hear. When I listen to our recordings, I realise that in reality migrants frequently give monosyllabic and trisyllabic calls too. Magnus points out that the chis-ick is really chichik because the second syllable isn’t that different from the first. We both find this type of birdie talk exasperating. Here is a very typical recording of White Wagtail flying past (CD2-09), which we used in a recent paper comparing these calls in Dutch Birding (Robb et al 2010), followed by a recording of a large flock (CD2-10). Compare them with a smaller flock of Pied flying over Durlston (CD2-11). Although White and Pied Wagtails’ chichik calls are not safely distinguishable, Pied Wagtail often uses a rasping call while migrating that we have never heard from a White Wagtail (CD2-12).

Grey Wagtails look like darts when they hurtle past high overhead. Their flight calls often sound like a more piercing version of the disyllabic call of White Wagtail, with shorter, higher-pitched notes and slightly longer gaps between them.

Listening to this recording of a single migrant passing at close range, it is apparent that they also have monosyllabic and trisyllabic calls (CD2-13).

To me, a flock of of migrating Yellow Wagtails is a sound of late summer. They move through in August and September and are rare by October. The monosyllabic flight call is a wedge of sound, thick at the front and narrowing to a whistle at the end. In autumn, there is a possibility that some of our yellow wagtails may be Blue-headed Wagtails from the continent, which have indistinguishable flight calls. The migrant in the recording was certainly of the British taxon flavissima, although it was actually recorded in Holland in spring (CD2-14).

If pipits and wagtails are the bread and butter of learning flight calls, larks are the jam. Every time I hear a Skylark migrating, it’s a treat. We usually recognise them by a fruity chirrup. There are so many variants of this call that it often seems as if each one could be a fragment of song. Here is one calling beautifully on the day of my exam (CD2-15). If Skylark is a treat, a migrating Woodlark’s musical calls can make a morning (CD2-16). As for Horned Lark, we keep a defibrillator besides the toilet block at South Haven just in case we hear this very special bird flying up the beach (CD2-17). 

It may come as a surprise to some that we see woodpeckers migrating. In October, one or two Great Spotted Woodpeckers can be seen undulating past in a single day. They sometimes pass silently, but here in Poole most of them give this call (CD2-18).

Hirundines pass a little later in the day than most migrants, and their calls are constantly in the air as the birds migrate. Barn Swallow flight calls are liquid, rising notes, on a background of cheerful song fragments (CD2-19). One evening when thousands were passing through the harbour, Mo and I saw a Red-rumped Swallow near Higher Bushey farm. Sadly, no one else got there before it moved on. Red-rumped Swallows can be picked up on call. The rippling quality and double length help to separate them from Barn Swallows if you are lucky enough to come across one (CD2-20). Flight calls of House Martin are hard, little two-part rattles (CD2-21), while Sand Martin flight calls are similar, but softer and more gravelly (CD2-22).

Migrating Song Thrushes have very short calls. Their extreme brevity and high pitch make them difficult for some of us to hear. If it hadn’t been for the calls of the birds migrating on the morning we saw 6,000, though, we might have assumed they were Redwings. In CD2-23, a recording of birds migrating along the Dutch coast, they have been brought closer by using a parabolic dish. While many arrive to spend the winter in Britain, others winter much further south. In the next recording (CD2‑24), you can hear Song Thrushes starting the sea crossing to Africa from the southwest corner of Europe. Their tiny flight calls are a little more varied than usual here, perhaps because they have just noticed that a Long-eared Owl is migrating along the same route. The whole scene was illuminated as the birds passed a floodlit fortress.

Redwings have flight calls that are equally high pitched, but long, descending and rapidly modulated, which gives them their characteristic zzzzz quality. In this recording (CD2-25) you can hear a mass exodus from Helgoland in the southern North Sea. After crossing the Low Countries and the English Channel, some of these birds could have reached Poole a day or two later. Blackbird’s migration call is more like a slow cicada. They are less descending in pitch than Redwing, and have a slower modulation. In this dish recording (CD2-26), you can hear natural-sounding calls at a distance, followed by a couple of very close ones that are not how we usually hear them.

The latter three thrushes are mainly nocturnal migrants, and Redwing in particular can often be heard at night, but there are two thrushes that are more often heard migrating during the day. Both have different, much lower-pitched flight calls. Mistle Thrushes have a short harsh rattle, a bit like the sound of drawing one’s finger across a comb (CD2-27), while Fieldfares give a great variety of goblin-like chuckles and queep calls as they fly above the Redwings in small flocks (CD2-28).

In the past, Starlings roosted in large numbers at South Haven. In recent winters they have preferred to collect around the Royal National Lifeboat Institute along Holes Bay and around Selsdown Bridge, sometimes in tens of thousands. These giant roosting flocks come and go in smaller groups, often leaving in giant concentric circles as they spread out to forage (see chapter 13). Small flocks pass South Haven looking a bit like Redwings. When migrants pass you at close range, you are more likely to hear their wings than the low-pitched flight call (CD2-29). 

Tree Sparrows are rare in the harbour, but we occasionally get the odd one or two migrating. A variety of calls can be heard as they fly past, most of which are higher-pitched than the equivalent calls of House Sparrow. The one to listen out for is the main flight call, a relatively deep, wooden-sounding tuv (CD2-30). House Sparrows are resident here, and they could pass a migration watch point at any time. Their flight call is a much longer, disyllabic and nasal-sounding chuwiv (CD2-31). In flocks, the length of individual birds’ flight calls influences the collective sound. The Tree Sparrows’ shorter calls leave gaps in the flock sound, whereas House Sparrows, with longer calls, can attain a saturated flock sound with fewer birds. 

Bearded Reedlings are always entertaining to watch, especially when they migrate. Magnus often saw them attempting this along the Dutch coast. When they finally get going, after many false starts, their progress seems painfully slow on short, unsuitable wings. Their calls are unmistakable, and we once had a troop take off from the reed bed at South Haven sounding just like these ones in the Netherlands (CD2-32). Each note is a ping with a buzzing ‘tail’. 

Hearing a good bird before you see it is a common experience for a birder. This was best summed up for me when Ewan, Shaun, Graham Armstrong and Iain Prophet were at Lytchett Bay, standing on the bank looking into the field for Jack Snipe. Graham heard a sound he recognised, turned round, pointed into the sky calling “Waxwing”, and then they all watched it fly over towards the water works. “You could even see the yellow band on its tail when it flew off, calling as it went,” said Shaun (CD2-33).

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