I heard a dipper sing on Saturday. Incredible, really, that you can bird up and down the country for half a decade at least and still see or hear something new. I like to think I’ve developed a reasonable ear for bird vocalizations; I don’t claim wizardry – I can’t identify every last chirrup I hear, but what I can tell you is if I’ve never heard a sound before.
And when, on the first leg of our return walk from Rievaulx Abbey to Helmsley, in North Yorkshire (thoroughly recommended by the way), I heard a harsh, determined, somewhat wren-like song emanating right from the River Rye, I knew this was something not encountered on, say, the upper reaches of the Test near my patch in Hampshire. And sure enough, perched on a slaty rock centre-stream was a dipper, white throat and breast raised proudly as he bobbed up and down, cunningly using the surrounding banks as a sounding board so that his song echoed back to us all the louder.
The reason I haven’t heard it before is probably very simple: I don’t live alongside dippers! My dwelling has almost always been in lowland southern England; they prefer the rushing streams of the north and west, where you find wild, open hill country, fast rivers coming off the moors and feeding through narrow valleys. There the dipper lives, breeds, and feeds on aquatic invertebrates, aided by what are, for a passerine, remarkable adaptations to a watery habitat.
Actually, I rather feel my natural habitat is somewhat similar. I don’t mean that I regularly tuck into caddis fly larvae for lunch (I suspect you’d need to winkle them out of their little houses first or they’d be a bit crunchy), but that I like nothing better than a walk in the British hills – even better if accompanied by a musical mountain stream playing on pebbles and bouncing around boulders. The uplands aren’t the ‘birdiest’ of places, which has prevented me with something of a conundrum in recent years, as I try to simultaneously nurse both incurable bird fever and a magnetic attraction to anything resembling a mountain. But they undoubtedly harbour some very special ones, and so the few out-of-the-ordinary birds that I do encounter there are inevitably amongst my favourites. So it is with the dipper.
I could leave it there – a brief, lightweight reflection on a nice little bird. But is that all I think of dippers, when I see one? Cute, entertaining, a ‘nice’ little wildlife diversion on a pleasant walk? I actually think birds deserve somewhat better. So it was this morning that, in an investigative frame of mind, and seeking to do justice to Cinclus cinclus, I turned to a well-known professional research tool and expanded my intellectual horizons. Yes, I googled ‘dipper’.
Did you know that they are the state bird of Norway? That would be the nominate race, cinclus. Dippers in the British Isles are of the subspecies gularis, with a more red-brown belly (the old English name is ‘Water Ouzel’), an ‘important race’ according to the BTO. Which is, well, nice, and fortunately they are doing alright – they have a stable population of between seven and 20 thousand pairs. That’s a ‘best estimate’ from 2000 – a remarkable spread, really, which reminds one of how hard it is to number everything accurately, even in a country whose avian fauna is perhaps better known than anywhere else, and that for a species considered stable. I’d more than happily be paid to do a comprehensive, accurate and up-to-date ‘dipper stock take’, though they’ll be worth looking up in the 07-11 Bird Atlas next year to see if the range of estimates improves.
Whatever the subspecies, the bird’s biology is remarkable. They have nostril flaps! The better not to take in water when dipping under the surface. They are the only passerine with nictating membranes, a partially transparent ‘third eyelid’ which protects the eye underwater whilst still being able to see through it. Those sported by dippers are white, and they blink them rapidly as a signal or part of a courtship routine. For even better underwater vision, they have very strong focal muscles which enable them to change the shape of their lenses.
If you’ve seen one, you’ve probably noticed that they don’t just poke under stones and forage in very shallow water, but will actually dive and swim – aided by flipper-like short, strong wings, and weighed down by uniquely solid bones – and once down there, they can actually walk on the stream bed looking for food. Which leads me on to another amazing adaptation: high blood haemoglobin, which enables them to store more oxygen and stay underwater for longer. Even their song, like that of other species which live alongside swift rivers, is specially adapted: it’s pitched at between 4.0 and 6.5 kHz, much higher than the average ambient background of 2kHz from the rushing water.
As for threats, is it worth considering conservation, for a bird of apparently favourable status? I’d suggest yes – the cautionary tale of the starling or house sparrow at least teaches that complacency isn’t wise. And the more we know about common species biology, the better we can respond to future environmental threats. What dippers like best is not just a swift-flowing river, but one of the right pH. Too acidic, and the bird’s clutches and broods are smaller and later, nestling growth slower, and second broods entirely absent. Disappearing or declining dippers on a river could be a sign of deeper trouble, and researchers have raised concern about the effects of acid rain in Scandinavia.
They could, in fact, be highly sensitive to wider climate changes. Research in Norway found that 84% of population growth variation could be explained by the NAO (North Atlantic Oscillation), and a few winter weather factors to do with how soon and how extensively water bodies froze in the winter. In Spain, dippers’ wings and tails may be getting longer in response to global warming – possibly in response to a change in trophic niche as water flow reduces in the rivers. A fascinating example of how climate change might not just change the distribution of species, but also the morphology of the species itself.
I was bound to turn up a lot of dipper facts, since they are so obviously fascinating. But this simple exercise in internet procrastination shows, in minutiae, what a mind-alteringly, astonishingly wonderful amount of information there is out there, for the most part freely available*. There are still plenty of things I read on the subject of dippers that I don’t have time for in this already over-long piece. So I think I’ll repeat the exercise, with other species, more frequently – and just see what I learn. Thus I give you the inaugural Considering Birds ‘Species of the Week’: Dipper!
*I did cheat, and use my still functioning Athens login to download a few academic papers, but you can always just read abstracts or ask a friend with access to nicely email you the odd PDF…