Academic in the Department of Zoology, and one of our visitor engagement volunteers in the Museum, Dr Tony Fulford writes:

‘Swallows don’t quite do it for me.  Don’t get me wrong, they are wonderful birds, skimming the ponds and twittering in the sky, but it isn’t they who bring in spring.  They are up there if you look but they don’t fill the air with their song in the morning.  And, anyway, spring is well under way by the time they arrive.  For me that honour belongs to the warblers.  One by one they add their voices to the dawn as they arrive until late-April when all ten local species are singing and the riot of spring is unstoppable.  Almost any of them might turn up and sing, at least briefly, in your garden.  Most, however, like to be near water (for the insects) and won’t stay long.  The Chiffchaff and the Blackcap, however, may well settle down near you if there are few large trees around nearby.

‘Of our local warblers the Cetti’s Warbler is the only one that doesn’t migrate.  It’s a recent arrival having expanded its range northwards to encompass Cambridgeshire in the just last couple of decades.  They’ve become quite common and you can hear their strident song (a wolf-whistle followed by a couple of gabbled expletives) near water at any time of year.  But for a week or two in spring they don’t seem to sleep, belting out their song every 10 seconds or so throughout the night.  Oddly they stop just before the dawn chorus gets going.  They are quite wren-like in their behaviour and even appearance, if somewhat larger, though they aren’t related.  But don’t bother looking for them; they are impossible to spot deep in the vegetation and anyway a rather disappointing LBJ (little brown job).

‘The first migrant to arrive is the Chiffchaff.  They don’t migrate as far as most of the other warblers (mostly down to the Mediterratean, though some go as far as West Africa).  Actually, with the milder winters of late, a few have begun to stay all year round.  It’s such a relief to hear the male’s bright song (a simple rhythmic “chiff chaff chiff chiff chaff…”) in mid-March – the trees may still be bare but now we know that spring really is just around the corner.  Those familiar with this species will recognise the soft, characteristic “tirrip tirrip” sounds they utter between song phrases.  They don’t seem to do this when they first arrive, only later as the breeding season progresses – it’s a summery sound though I’ve no idea what it signifies.

‘Closely related to the Chiffchaff is the Willow Warbler.  You’d be hard pressed to tell them apart visually in the field.  Both are small green birds that flit about high in the trees hunting tiny insects among the leaves.  The Willow has longer wings because they migrate a lot farther. You shouldn’t have much trouble differentiating their songs.  The Willow’s is a silvery cascade of notes finishing with a flourish.  (In structure it is rather like that of a Chaffinch song, but far more delicate.)  A few decades ago this was the commonest warbler in the country and its gentle song the very sound of summer.  Sadly their numbers have decline dramatically recently; they aren’t rare but are now somewhere near the bottom of the warbler abundance table.  Given how visually similar Chiffchaff and Willow Warbler are it seems obvious that they have adopted very different songs to avoid confusion.  How odd, then, to hear a Willow Warbler including the Chiffchaff’s song within its own.  Nevertheless this is exactly what a proportion of them do, a phenomenon that seems to be particularly prevalent in the Cambridge area.  Is it a mistake or deliberate?  Did they learn it from Chiffchaffs or have they inherited the song after hybridisation?  We just don’t know.  It seems relatively common and Willow Warblers never seem to imitate other species.  By playing recorded songs to Willow Warblers I have managed to establish that, unlike normal Willow Warblers, all these “mixed singers” (N=20) react violently to Chiffchaff song.  So perhaps the singing is a spillover from the real purpose, which is to recognise Chiffchaffs and chase them out of their territories.

‘Often the next arrivals after Chiffchaffs are the Blackcaps.  You may be lucky enough to see Blackcaps at the bird table in winter but those birds are from Germany and don’t stay; they are replaced by our breeding population returning from the Mediterranean and West Africa.  Now spring has arrived!  His rapid jumble of pure musical notes is delivered with an exuberance that matches the hedgerow blossom. One way you can identify a Blackcap’s song is by his insertion of extra loud, fluty notes.  He has his own song but he’s also a prolific mimic.  I’ve heard them reproduce phrases from Blue Tits, Song Thrushes, Reed Warblers, Long-tailed Tits, Skylarks and even Blackbirds (this last quite a feat given the small size of the Blackcap and depth of the Blackbird’s song).  These are often given in rambling succession along with a lot of soft, non-descript warbling but listen long enough and he’ll burst into Blackcap to end his song.  Again, why?  Some have suggested that these are young birds learning their song but I’ve never heard one that didn’t already know how to sing a typical Blackcap song.  Perhaps a clue lies in the fact that he only does this early in the season; by May he pretty much sticks to his own song.  And by May he’s also likely to have found a mate.  Is the mimicry just to impress the girls?  Once they are paired it is all about defending the territory and she is as interested in that as he is.  Although she doesn’t sing – not a good idea when you’ve secret brood of eggs to incubate – I’ve often witnessed two neighbouring pairs, both male and female, engaged in violent territorial dispute.  These are smart little birds with their neat black caps (the female’s is brown) and there will be one singing not far from you right now.

‘Another extraordinary singer is the Blackcap’s close relative, the Garden Warbler.  They look very much like the Blackcap but without the cap, i.e. rather plain.  But don’t rush out looking for it in the garden; this is one of the least likely of the 10 warblers to be found there!  You will find it where there are tall trees and water and there it may well outnumber Blackcaps.  Some people have trouble differentiating the songs of Blackcap and Garden Warbler.  The Garden Warbler’s is faster, deeper and more sonorous and, unlike the Blackcap’s song arc, is delivered “by the yard” – it is often accurately compared to a babbling brook.  They will also incorporate mimicry to spice up their songs.  There are plenty of them in places like Wicken Fen, Paxton Pits or Woodwalton Fen.  If a site has Garden Warblers, it is usually quite special. They may not be lookers but they are up there with Nightingale and Blackbirds among the finest songsters in Europe.

‘Out in more open country along the hedgerows and scrubby vegetation you will often hear a scratchy song, like a poor, and often rather brief, rendition of a Blackcap’s song.  This is the Common Whitethroat, a bird with an ashy grey head, pure white throat and streaky, rusty wings and back.  It is a hyperactive little bird and will often ascend into the air and parachute back down singing all the while.  I’m always pleased to hear them because they have made a great recovery after a mysterious decline in their numbers a few decades ago.

‘The Whitethroat has a less well-know cousin, the Lesser Whitethroat, that lives in a similar habitat but is much more of a skulker and rarely seen.  However, when you are familiar with its song you realise that they are not uncommon.  Their song starts with a barely audible, Whitethroat-like warble then burst into a loud rattle – often the rattle is all you hear.  The Chaffinch and Yellowhammer also both incorporate a similar rattle in their song but the Lesser Whitethroat’s is quite characteristic, being all on one note and ending abruptly.  Occasionally, again especially earlier in the season, they will warble on and on producing some of the highest pitch notes of any bird.  While they do have a pure white throat, visually they would not be confused with a Common Whitethroat since they are rather smart shades of grey and white.  This is our only warbler that migrates down the east coast of Africa, guided by the River Nile.  In Britain it is on the westerly edge of its range and hasn’t yet learnt that there is a short cut via West Africa.  If it does work this out then the species is likely to split in two as has occurred with many other pairs of migrant species (e.g. Melodious & Icterine Warblers and Common & Thrush Nightingale).

‘Another early arrival is the Sedge Warbler.   What these birds lack in finesse they make up for with enthusiasm.  They have a problem in that they cannot learn their song from their father because he stops singing before they are old enough to learn from him and, unlike many other African migrants, they don’t have cause to sing on their wintering grounds.  So the males have to make it up as they go along, picking up what they can from what they hear around them.  The result is a lot of mimicry, a lot of buzzing and high-pitch squeaks, often getting “stuck” on one note for a while then burbling away with “jag”s and “ziz”s once they have detached themselves.  They sound so excited they it’s a wonder they don’t burst. At the height of their excitement they will sing all night (they are sometime referred to as the Scottish Nightingale – proper nightingales don’t get as far as Scotland).  Sometimes singing just isn’t enough and they take to the air in an arc singing furiously.  At dawn for a week or so shortly after they first arrive they shoot into the air over the reed beds one after another like fireworks.

‘Our warbler species seem to come in pairs and the Sedge Warbler’s pairing is the Reed Warbler.  They are the last of the Warblers to arrive in late April/early May.  While the Sedge is streaky yellowish brown, the Reed is rather uniform reddish brown. Reeds are even more attached to the reeds than Sedge Warblers and are seldom found far from them.  Their song is quite the opposite of the Sedge, being laid-back and soporific, a jumble of different note, each repeated 2 or 3 times, on and on apparently all summer long.  In our area the Reed Warbler is the major host to the Cuckoo.  The host-parasite interactions of these species have been the subject of extensive studies by Nick Davies and colleagues in the Zoology Department at Cambridge University.  Each female Cuckoo specialised in parasitising one host species while the male can mate with any type of female.  This works genetically because the Cuckoo’s host-specific genes (for instance, those mimicking the host’s egg pattern) are on the W chromosome, which is specific to females and only passed on from mother to daughter.

‘Finally, visit Wicken Fen or a similar spot at dusk or dawn in April or May and you may hear a prolonged, eerie rattling sound, like a fishing reel or an insect.  For a very long time people believed that it was, in fact, an insect and refused to countenance that it might be a bird.  It is, of course, the enigmatic Grasshopper Warbler.  You’d be luck to see it; it’s another real skulker but every now and then it will choose a song “post” (a tall reed) and deliver its song in full view, rotating its head in the horizontal plane so as to broadcast its song in all directions.

‘These are our ten local warblers. Most local wetland reserves will hold all ten.  Now is the time to get out there and discover them.  If you can recognise ten friends’ voice then, with a little persistence, you could recognise ten warblers.  Once you’ve got them you won’t forget them and a walk in the countryside will always be that much more rewarding.‘