Coal Tit — not so black-and-white
The more you look at birds, the more personality you see. If Coal Tit was a footballer, it would be Maradona — short, stocky and speedy. At a feeding station, nothing moves faster. Once a Coal Tit knows where food is located, it favours a smash-and-grab raid. The monochrome mite appears out of nowhere, extracts its prize and is gone. A few minutes later it is back for more. Or is there more than one? This is where the surprises begin. According to ‘The Birds of the Western Palearctic’ [1], the species has a monogamous mating system. Partners usually remain together in successive years if they survive from one breeding season to the next. In 82% of cases, both did. Two partners in one pair lasted six years, another couple lasted four. Such information bears out my hunch that often Coal Tits visit feeders in pairs. I say ‘hunch’ because, unlike Blue Tits and Great Tits that are usually individually distinguishable, Coal Tits look more-or-less the same, making it hard to tell one from another, especially when they whiz about like electrons in a nucleus.
For a tit, Coal Tit has a relatively slim, long bill. This is an adaptation for feeding among conifers, such as pine trees. Pine needles grow in clusters from a single base and a bird with a fine bill is better able to reach insects hidden among them. Differences in habitat preference were demonstrated in aviaries. Coal Tits searched diligently for food among coniferous foliage, whereas Blue Tits foraged among deciduous vegetation [2]. Blue Tit’s sharp stubby bill seems designed for picking and pecking, rather than probing. In addition, Blue Tit’s feet have opposable toes that allow more leaf surface to be grasped while feeding. Coal Tit takes the smallest prey items, from aphids to spiders, which helps explain why the bird is a busy-body.
There is another reason for all the industry. Coal Tits store food. The introduction of sunflower hearts in bird feeders must have come like a lottery win. Three of Coal Tit’s favourite seeds are pine, spruce and beech. A sunflower heart has much the same dimensions. Watch a Coal Tit extract one from a feeding port and the chances are it will let it drop; maybe the next one too. Third time lucky, it is off with the morsel. Why so fussy? The explanation is all to do with seed alignment in the bill. Spoiled by a feast, the bird pulls out individual seeds until it secures one pointing forwards, not sideways. Job done, it looks for somewhere to secrete the booty. This can be in the ground, a plant pot or — ingeniously — by sticking it to foliage by rolling the seed inside the mouth and coating it with, presumably, saliva. All the steps in this process are made easier if a seed is held lengthwise.
I do not know if food storing occurs throughout the year. But I regard it as an almost daily occurrence during autumn and early winter. Writing about the same habit among Coal Tits in Sweden, Lars Jonsson suggests that stockpiling is more prevalent in summer: ‘the birds store food during the summer months and hide it among the broomsticks of conifer needles and in dead male spruce flowers’ [3]. At times, storing seed — as opposed to eating it — is the main event in a Coal Tit’s working day. Statistics give an average storage rate of 26 items per hour, nearly one item stored per two minutes [4]. Probably, stored items (including insects, balled up as glupe) are eaten within days.
Based on plumage, how can you tell the sex of a Coal Tit? There are ways to do this but they are subtle. A study of museum specimens showed that bib size and coloration differed significantly between males and females [5]. Males have a larger bib. Looking at still photographs of Coal Tits coming to feeders, it is certainly feasible to distinguish those with more extensive black bibs that run like a ragged handlebar moustache onto the edge of the chest (sometimes reaching the flanks). With age comes a qualifier. Bibs become larger and darker in older birds of either sex. Moreover, in older males, bib colour darkens to deep black. It is possible to misidentify a Coal Tit for a Great Tit. The reason for this is the shared black helmet framing white cheeks. Because Great Tits are less hyper-active, it is easy to see that the crown on a male is glossy blue-black, whereas a female’s crown is matt black. In Coal Tit the same difference seems to apply — it is just harder to see.
Coal Tit has a vast breeding range encompassing Europe, Asia and parts of the Middle East as well as North Africa. Accordingly, it comes as no surprise that variation occurs. For those of us looking at Coal Tits in Western Europe, Britain or Ireland, the key areas to scrutinize are back colour, intensity of yellowish suffusion in white plumage on the head and nape, and bill size. The differences are not great, however. But because they are consistent they justify a few subdivisions (called subspecies) within the global brand. In other words, there is such a thing as ‘Continental Coal Tit’ that differs from ‘British Coal Tit’ which, in turn, differs (allegedly) from ‘Irish Coal Tit’. Let’s not get too excited. Some differences are ‘clinal’, meaning that they are gradual across a geographical range and may only be appreciated when specimens are spread along a museum bench.
This gives rise to the following situation: ‘although some Continental Coal Tits can be recognised by the clear grey back, this character is of less value for birds from parts of Europe adjoining Britain, in which the colour of the back becomes less pure blue-grey and more washed with olive southwards and westwards from Scandinavia, the Baltic and European Russia’ [6]. One way to see the wood from the trees is to compare Coal Tits from Scandinavia (ipso facto, ‘Continental Coal Tit’) with those we see in Ireland. Swedish artist Lars Jonsson paints a slimmer-billed bird than ours with a grey back (‘the back is grey without any green traces’) with a body colour described as grey-buff [7]. In contrast, Irish stock — and, by and large, British too — has an olive-grey back, buff-apricot underparts, a variable ‘butter yellow’ tint on the cheeks and a bill of variable size.
How can these traits be explained? Starting with variation in bill size, the heftier bill of some (or even many) in Ireland could be linked to habitat. The majority of Irish Coal Tits live in mixed woodland. Evidence confirming bill shape differences between Coal Tits in Killarney and Oxfordshire amounted to males in Ireland being larger-billed than females in Ireland. In Britain, bill dimensions in both sexes (and all ages) were homogeneous; those in Killarney showed a wider range in length and depth than their English counterparts, although some in each population had an identical bill [8].
Before running away with the notion that there may be consistent, albeit minor, bill shape differences between Coal Tits on either side of the Irish Sea, it should be remembered that, over the course of a year, bird bills can vary in size and shape. A bill is not fixed in shape. It is a part of the skeleton which is enclosed by a casing of keratin, the hard structural material that makes up, among other things, human fingernails and animal hooves. Researchers in England found that, in spring, Great Tits grew a larger bill [9]. Most likely, this was because of a demand to spend more time searching for food, especially when rearing chicks.
Food exerts another influence on titmice appearance. Depending on what the bird eats, carotenoids extracted from food affect the colour saturation of plumage [10]. For this reason, flamingos in captivity will turn whitish if they are not fed natural foods (certain small crustaceans) from which they extract carotenoids that allow them to develop pink feathers. In tits — not just Coal Tit but also Blue and Great Tits — differences in yellow pigmentation in plumage reflect the quantity of carotenoids consumed through eating yellow-green caterpillars. In deciduous woodland, more caterpillars are available as prey — or are preferentially eaten in comparison to, say, spiders and small insects favoured by Coal Tits foraging in conifer forest. Lars Jonsson, in comparing the appearance in Great Tits feeding in pure deciduous forest in Sweden versus those living in pure conifer forest in Finland, described the Finnish Great Tits as ‘colourless’ due to their plumage begin drained of yellow [11].
Another point needs to be made. This is the effect of air pollution on foliage and its influence on the chemical pathway of carotenoids through plants to birds. Anyone living in a built-up area and noticing the colour saturation of Blue Tits rearing a family in a garden next-box cannot fail to discern that, in comparison to Blue Tits living in clean-air rural woodland, urban and many suburban Blue Tits are drab. Here’s why. Research in Sweden demonstrated that foliage exposed to toxic compounds (basically, through air pollution) shows a decrease in carotenoid concentration. In turn, this is reflected in a lower content in caterpillars and, through the food-chain, to birds [12]. Sadly, even Blue Tits nesting in leafy suburbs fared no better, because foliage that absorbed pollutants was deficient in carotenoids, no matter how great the quantity of leaves.
Imagine that Ireland did not exist. Were it to magically emerge above the waves complete with its twenty-first century range of degraded habitat, what might its resident Coal Tit population look like? Sitting, geographically, at the species’ western extreme would mean that the cline of increased olive in the grey back is likely to be discernible. Given that most of the population breeds in mixed woodland — due to afforestation, pure coniferous habitats are now occupied, although this habitat was not available until, roughly, the 1950s — bill shape is also likely to be less ‘tweezer-like’ than among conifer-dwelling populations across northern Europe. Finally, the birds’ diet, depending on the range of yellow-green caterpillars that are consumed, is likely to influence the strength of yellow pigment in otherwise white plumage in the head pattern. The predictions are true; Coal Tits in Ireland exhibit these characteristics. Does this make them unique? After all, there is supposed to be such a thing as Periparus ater hibernicus, the Irish Coal Tit. Or, to be more precise, a subspecies of Coal Tit that is endemic to Ireland. When was this bird discovered?
The Irish Coal Tit was separated from the British Coal Tit by Mr W.R.Ogilvie-Grant in 1910. He exhibited examples at a meeting of the British Ornithologists Club and the following account was published in 1911 [13]. Because the article is somewhat difficult to locate, here is the text (minor, irrelevant details are not included):
‘Mr. W.R. Ogilvie-Grant exhibited and described examples of a new species of titmouse from Ireland. He said that it might seem almost incredible that an extremely distinct and well-marked species of Irish Titmouse should have escaped notice until the present time; nevertheless such was undoubtedly the case.
Of this new species, which he proposed to call Parus hibernicus, he had now examined twelve adult specimens from the following counties: Dublin, Wexford, Waterford, Westmeath and Sligo. Knowing that the Natural History Museum was extremely deficient in examples of Irish birds, Mr Collingwood Ingram had kindly forwarded a few specimens from Boyle, Co. Sligo, and, among them, two Coal Titmice, which Mr Ogilvie-Grant had at once recognised as belonging to a species quite distinct from P. britannicus. Mr Ingram was unaware that there was any particular interest attaching to the birds, and it seemed extraordinary that no one had hitherto noticed the striking characteristics of the Irish Titmouse.
The pale mustard colour of the patches on the side of the head and occipital spot [pale nape band], as well as of the breast and belly, also the clear cinnamon-coloured flanks and upper tail-coverts, rendered P.hibernicus distinguishable at a glance from P.britannicus.
The species might be characterised as follows: adult male differs from the male of P.britannicus in having the light patches covering the side of the head and neck, as well as the occipital spot, pale mustard-yellow, the back olive-grey washed with yellowish-cinnamon, the upper tail-coverts cinnamon, in marked contrast with the rest of the upperparts, the breast and belly whitish, washed with mustard-yellow, and the sides and flanks cinnamon …
There could be no doubt that the British Coal-Titmouse also occurred commonly in one locality at least in the north-east of Ireland, for Mr Ogilvie-Grant had himself obtained a number of specimens at Clandeboye, Co. Down, in January 1904. These differed in no way from examples of P.britannicus from England and Scotland. Mr W.R. Ogilvie-Grant was not aware whether these birds bred in Co. Down, or were merely winter migrants from the opposite coast of Great Britain.’
FOOL’S GOLD
Mmm. It is hard to know if Ogilvie-Grant was blind-sided by a few yellowish Coal Tits that he came across in various parts of Ireland, which he regarded as a previously undescribed species. Certainly, they fell outside his familiarity with the Coal Tit tribe. Some of the rhetorical gas in his published article — ‘extremely distinct and well-marked’ — reads like an attempt to create a novelty out of hyperbole. His contention that British Coal Tits occurred in northeast Ireland and that their presence there might be explained because the birds were winter visitors from across the Irish Sea, bears no relation to the sedentary behaviour of Coal Tits on both sides of the Irish Sea. According to the British Trust for Ornithology’s Migration Atlas [14], 170,000 Coal Tits were ringed in Britain and Ireland up to 1997. Of these a mere 227 moved more than 20km between the breeding season and winter. Even those that travelled more than 20km did not go far. The greatest distance appears to be just 51km. Of 11 Irish recoveries, none moved further than 20km from its place of ringing.
In the wake of Ogilvie-Grant’s discovery, the spotlight fell on Coal Tit populations across Ireland. His evidence of a uniquely Irish bird was undermined. Contemporary ornithologists looked afresh and none found his assertions convincing. By 1954, when Ruttledge et al. published Birds of Ireland, the jury had been out for over 40 years. That book’s summary [15] reads like a series of nails in the coffin: ‘in 1910 the Irish Coal Tit was first separated as a subspecies, but it was not very long before Nevin Foster showed that all specimens obtained in the Hillsborough district of Co. Down were referable to britannicus [that is, they matched Coal Tits in Britain]. Foster’s observations [Ir. Nat., XXXI, 12, and Proc. Belfast Nat. Hist. & Phil. Soc., 1920–21] have been confirmed by Mr. M.N.Rankin for Co. Antrim as well as for Co. Down. In both counties the birds are indistinguishable from the British form; Mr. H.T.Malcolmson writes: “the Irish Coal Tit does not seem to occur in the north” … in the west of Ireland, in spite of the fact that Co. Sligo provided one of the type specimens, examples can be seen from autumn to spring in widely separated places which are inseparable both in the field and in the hand from the British race. The same may be said of individuals in Co. Wicklow and Co. Tipperary.’
And so it goes on. Except that time has a habit of looping back on itself and a half-remembered ‘fact’ (that Coal Tits in Ireland are supposed to be different from those in Britain) gets repeated. A 2002 example comes from the BTO Migration Atlas [14], which states: ‘… the British Coal Tit (also found in northeast Ireland), and Irish Coal Tit have recently expanded their ranges.’ The crux of the debate has always rested upon the degree to which white plumage areas are suffused with yellow, thus indicating ‘Irish Coal Tit’. Not only do most Coal Tits in Ireland lack the requisite colour saturation to justify being called ‘Irish Coal Tit’, but some in Britain do: ‘difference between hibernicus [Irish Coal Tit] and britannicus [British Coal Tit] not always marked. 16% of 43 Irish birds from various counties show no yellow at all, while 12% of 279 from Wales and England and 8% of 209 from Scotland showed some yellow [1].
I hope that thirty years of looking at Coal Tits in Ireland (and elsewhere, especially in various parts of Scotland) stands me in good stead. My view is that almost all the Coal Tits I see in Ireland have a weak, butter-yellow wash on the rear half of the cheeks. In most, therefore, the front half of the cheek and the nape patch are white. Of course, I have seen the real McCoy too — the kind of individuals that caught the eye of Ogilvie-Grant in 1910. The yellowiest individuals were in the west of Ireland. But in the same places and at the same time, other ‘typical’ Coal Tits were present. These showed the usual pale butter-yellow on the rear cheek. I have, however, seen a few ‘classic’ wasp-headed examples in Co. Down.
By way of conclusion, I see variation and nothing that convinces me that Ogilvie-Grant stumbled into anything special. Nowadays, I am more interested in variation in Coal Tits in Scotland. In December 2022 I spent two mornings watching a blizzard of them attending feeders on Islay. Of course, as mentioned above, a ‘blizzard’ could mean a relatively small number constantly taking away food and hiding it. Although the majority were identical to Coal Tits in Ireland, one male had the ends of his black bib running deeper into the flanks than I recall on any Irish bird (see ‘1’ in plate). At times I also wondered if the range of back colour was wider than I am used to seeing in Ireland — meaning that some looked purer grey. I have thought the same for grey-backed individuals that I have seen in Edinburgh and Perthshire. Maybe, across Scotland, there is a cline in back colour? This might explain the grey-backed look of a few migrants noted at Copeland Bird Observatory during the last half century (Neville McKee, pers. comm.). In other words, the migrants might have come from Scotland?
Rathlin Island offers a chance to speculate on the origin of Coal Tits that arrived there, probably in the 1970s, and settled to breed among new conifer plantations on the island. Although the coast of Co. Antrim is closer, the Scottish coast is not too far away. Maybe the colonists came from Scotland, maybe Kintyre? Ric Else, resident on Rathlin since 2017, has noted groups of Coal Tits passing through the island in autumn. All moved from the north coast towards south-facing areas, suggesting they arrived from Scotland.
Before dismissing the notion that no trait is exclusive to Coal Tits in Ireland, a published note describes differences in bib feathering as a potential difference between Irish and British Coal Tits [16]. The starting point for this research was based on dissected specimens. So there was no possibility of confusing the birds’ provenance or, for that matter, age and sex. The conclusion? Although the outcome would appear to be applicable only to birds examined in the hand, I will let the researcher’s words speak for themselves: ‘the blackish bib feathering is significantly less extensive and rather browner in colour in male hibernicus [Irish Coal Tit] than in male britannicus [British Coal Tit] … as no such difference exists between females, the degree of sexual dimorphism [that is, difference between the sexes] is reduced in hibernicus.’ Does this mean that, watching a breeding pair, both adults look identical in Ireland whereas, across the water, the sexes can — with care — be told apart? I know it feels like we are splitting hairs, not Coal Tits. But if you do not look …
Acknowledgements
Many thanks to Ric Else on Rathlin Island for his perceptive observations of migrant and local birds. Neville McKee, because of years handling Coal Tits caught for ringing, always provides a back-stop reference for the birds’ range of variation. Thanks to John McClean for unlimited access to his feeding station and abundant Coal Tits on Clandeboye Estate lands in Co. Down — the same area where W.R.Ogilvie-Grant collected Coal Tits in 1904 that he pronounced to be similar in every way to Coal Tits in Britain.
References
1 Cramp, S. & Perrins, C.M. 1993. The Birds of the Western Palearctic, vol. 7, pp.207–225. Ox. Uni. Press.
2 Perrins, C.M. 1979. British Tits, pp.85–97. Collins, New Naturalist.
3 Lars Jonsson. 2017. Winter Birds, p.170. Bloomsbury.
4 Cramp, S. & Perrins, C. M. op.cit.
5 King, J.R. & Griffiths, R. 1994. Sexual dimorphism of plumage and morphology in the Coal Tit. Bird Study 41:7–14.
6 Cramp, S. & Perrins, C. M. op.cit.
7 Lars Jonsson op.cit. p.168
8 Gosler, A.G. & Carruthers, T.D. 1994. Bill size and niche breadth in the Irish Coal Tit Parus ater hibernicus. Journal of Avian Biology 25: no.3, 171–177.
9 Lars Jonsson op.cit. p.158
10 Definition in Chamber’s English Dictionary: ‘carotenoids are any of a number of naturally occurring reddish-yellow pigments found in plants and some invertebrates.’
11 Lars Jonsson op.cit. p.166
12 Isaksson, C. 2009. The chemical pathway of carotenoids: from plants to birds. Ardea 97(1):125–128.
13 Bulletin of the British Ornithologists Club. 1910–11. Vol. 17, pp.36–37.
14 Wernham. C. et al. 2002. The Migration Atlas, pp. 596–598. British Trust for Ornithology. T.&A.D. Poyser.
15 Ruttledge, R.F., Kennedy, P.G, Scroope. C.F. & Humphreys, G.R. 1954. The Birds of Ireland, p.328. Oliver & Boyd. London.
16 King, J.R. 1994. An undescribed plumage character of the Irish Coal Tit. Bull. B.O.C. 114: 173–175
