There’s still a lot we can learn about the aggressive Mistle Thrush – a bird you may struggle to find while you’re out birding…
By Dominic Couzens
This is the thrush that embarrasses birders. It’s the large, barrel-chested spotty-breasted one that ought to be simple to identify, but somehow isn’t.
It perches high on the branches of trees in early spring, seemingly always with its body angled away, or with a branch in front of it, so we cannot quite see its features properly. It is the thrush that sings, but never quite clearly or close enough for us to be sure. It isn’t the poet Robert Browning’s bird: “That’s the wise thrush; he sings each song twice over.” Instead it’s a wise thrush that makes fools of us all.
For a large, bold bird with seams of aggression stitched into its character, a bird of dominance which can scatter smaller beings when it lands nearby, the Mistle Thrush is a remarkably overlooked species. It is found almost all over Britain, yet is barely noticed. Who would have thought that the species was once involved in a large-scale, Collared Dove-like invasion of swathes of the country?
Admittedly, it was long ago; just before 1800, the Mistle Thrush was all but confined in this country to the south, but then something caused it very rapidly to spread all over northern England and Scotland over a few decades, until by 1850, it had conquered the whole realm.
The BTO’s Bird Atlas 2007-11 records breeding in 96% of the 10km squares covering the British Isles. While we conquered Napoleon, parts of our country were quietly being invaded.
Low density breeding
It would have been invasion-lite, however. It is not as if we readily see a Mistle Thrush at every street corner. It has long been recognised that British Mistle Thrushes breed at bewilderingly low density.
One well-studied suburban plot held 180 pairs of Blackbirds, 12 pairs of Song Thrushes and just one pair of Mistle Thrushes, while a broad estimate suggested that the density of Mistle Thrushes is only 10% that of Blackbirds. The impression is that there is plenty of room to expand, and the larger thrushes are not as numerous as they should be.
There are some explanations for the low density. In contrast to Blackbirds and Song Thrushes, Mistle Thrushes don’t tend to feed among leaf-litter, preferring open grassland, instead.
Furthermore, they generally eschew the patchwork of small gardens that make up suburbia, needing wider expenses of sward to feed comfortably. They also prefer tall trees for nesting. Despite these drawbacks, they still could be more abundant. And this is particularly odd when you bear in mind that, in some parts of the continent, Mistle Thrushes can be colonial.
Most pairs nest singly, but in countries such as Denmark, Germany and Russia, some do breed in close proximity. For some reason, this just doesn’t seem ever to happen here.
The low density of breeding pairs ensures that it is always a treat to hear the song of a Mistle Thrush percolating through the soundscape of a neighbourhood. Some consider it one of the finest of British bird songs, combining the Blackbird’s virtuoso content with the Song Thrush’s proclamatory style.
It does combine elements of the two, with a repetitive style redolent of Song Thrush but with tone closer to Blackbird. Listen long enough, however, and you can pick up its own unique flavour.
It has an unforgettable melancholy quite lacking in the other two species, and the singer also has a curious knack of sounding much further away than its actually is.
Invariably, it stays longer on its perch than the other thrushes, almost always close to the very top of a lofty tree.
Famously, it seems unperturbed by inclement weather, and will sing lustily in the rain and wind, when most other birds take shelter. I am not sure there are any statistics indicating that Mistle Thrushes sing more often than other thrushes in challenging meteorological conditions, nor indeed that they sing more frequently in the afternoon, as is claimed. Perhaps these impressions stem simply from the reality that Mistle Thrush phrases are easily drowned out by other songs? But it would take a hard heart not to be stirred by the wild, haunting utterances from the ‘Storm Cock’, fighting against an irksome wind on a stuttering spring day.
Another strange fact about Mistle Thrush songs is that, at least in some places, they apparently are given in flight. This isn’t an aberration but instead, in Germany and elsewhere, it is a routine phenomenon.
Personally, I have never seen this, and I don’t know anybody who has; neither do the usual bird books over here refer to it. Yet sometimes the bird evidently launches into the air and sings as it goes, as a Cuckoo often does. This aerial aria seems to be a continental oddity.
And what about their courtship-flight? Have you ever seen that? Again, though, it has been recorded in the literature many times. The choreography is similar to that of the Robin’s early courtship, the ‘song-and-following’; the male sings, the female darts away, the male follows and sings, and so on.
Sometimes the (presumed) male flies around the potential mate and shows off his gleaming white underwings. Usually concealed within tree branches, this ceremony is undoubtedly an early spring secret, unknown to most of us.
One piece of behaviour that is much easier to observe, however, is the Mistle Thrush’s aggression, coupled with its very loud, discordant calling, an angry and irritable rattle. While this is sometimes triggered by the presence of a bird of prey or other danger, or by the unwanted presence of rivals, look closely and you might see that it is frequently all about berries. You might have thought that squabbles over fruits might have finished by the end of autumn, but the fact that they can rage now, in late winter and early spring, unveils another interesting pastime of our largest thrush, the sequestration of fruity assets.
Half-understood bird species
While many thrushes, such as Redwings and Fieldfares, spend the winter passing nomadically from district to district feeding upon berries that they come across in serendipitous fashion, some singles and pairs of Mistle Thrushes take a different approach to foraging.
They select a tree or trees that have a crop of long-lasting fruits, such as Holly berries, and remain close by them, driving away any visitors that arrive to take advantage of the crop.
Such is the dominance and intimidatory manner of Mistle Thrushes that, for months on end, they can keep rivals of other species at bay, unless there is a sudden arrival of a large flock.
So long as that eventuality doesn’t occur, the birds can ensure the preservation of a significant, personal food-supply for them to pluck whenever they wish – and when it is mild, they can feed on soil invertebrates while keeping watch on their inheritance.
Their actions mean that Mistle Thrushes will often have a useful crop of berries available to feed themselves and their subsequent young well into the spring. It works so long as they are vigilant and suitably petulant when challenged. And yet, as so often with the Mistle Thrush, this isn’t the whole story.
Some individual Mistle Thrushes undertake long-term fruit-defence, while others don’t at all, but are nomadic. What causes some to be sedentary and others to move isn’t known.
And we don’t fully understand the song-flights, or the nest-dispersion, nor do we understand the nature of late-summer flocks. We don’t understand why Mistle Thrushes typically nest very early, with eggs in March, either.
True, the Mistle Thrush is often a half-seen and half-identified bird, of annoyance to many a frustrated birder. But, surely, to scientists, it is also a half-understood species.
Where to see Mistle Thrush
A bird widespread across the UK, it can be found almost everywhere but is absent from the highest, barest ground and also from the northern and Western Isles of Scotland. Look in gardens, woodland and parks.
Mistle Thrush factfile:
Scientific name: Tardus viscivorus
UK numbers: 170,000 breeding territories
Diet: Insects, berries, worms and slugs