Winter can be a desolate season for the keen birder, but invading flocks of northern passerines cause excitement as they add their splashes of primary colour to our continually depleting berry bushes. Chief among these annual attractions has to be Waxwing, which in a good year occurs in liquidly trilling flocks even in the very heart of our cities, beautifully sinister looking as they jostle to feed on urban shrubs and trees.
With this winter’s sizeable invasion, these subtly coloured oscines (that is, true passerines) with their pale buffy-pink punk hairdos and candle-wax-red wing accoutrements are at the top of every birder’s wants list and show a fascinating array of behaviours and movements.
They are interesting taxonomically, too. The boundaries of the family and relationships between the close relatives of Waxwing have long been controversial, though the core genus Bombycilla consists of three closely related species. Waxwings are known to be allied with silky-flycatchers like the Nearctic Phainopepla, as well as the Middle Eastern Grey Hypocolius and Palmchat, a Hispaniolan endemic.
Common factor
A fairly comprehensive recent genetic analysis showed that the family Bombycillidae does indeed consist of all the descendants of one common ancestor, with Palmchat the most ‘primitive’. It also contains the enigmatic Olive-flanked Whistler of Sulawesi in Indonesia, formerly considered to be part of the Australasian whistler clade.
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Berries are Waxwings’ preferred food during the winter, and a flock will strip a rowan or Cotoneaster bare. The species is not wholly frugivorous, though, and it will eat insects, shoots,leaves, mosses and lichens, and spiders and snails. Photo by Jim Almond. |
This cryptic relationship also suggests that other obscure bombycillid relatives may be scattered around the globe. In fact, another recent paper has shown that the historically extinct Hawaiian honeyeaters are also derived from the same common ancestor as the bombycillids.
Clearly the group was widely distributed in prehistoric times, and true waxwings are still found throughout the Northern Hemisphere, with Cedar Waxwing distributed across North America below the tundra-line, wintering south to Central America, and Japanese Waxwing occupying part of north-east Asia, wintering in Japan, Korea and China.
Our familiar Waxwing has three generally accepted subspecies, ranging across the whole of temperate and boreal North America and Eurasia. The subspecies that annually arrives in Britain is the nominate Bombycilla garrulus garrulus, which breeds in northern Scandinavia east to the Urals. East of this zone it is replaced (possibly clinally) by B g centralasiae, which is greyer and has less orange around the loral area.
In North America is B g pallidiceps, which is the palest and brightest form with the most facial orange. This form is subtly distinctive and apparently not yet recorded in the Western Palearctic. However, the presence of a Cedar Waxwing in Noss, Shetland, on 25-26 June 1985 and another in Nottingham from 20 February to 18 March 1996 indicates that the American subspecies has the potential to occur in Britain as well.
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Waxwings can be quite acrobatic in tree branches. Photo by Steve Young (www.birdsonfilm.com). |
European invasion
The Eurasian breeding population is estimated at over one million pairs, with well over 100,000 in Scandinavia. Waxwing is notorious in Britain for being irruptive. It can be very scarce some years, with less than 100 birds on occasion, but seemingly everywhere in others. In a true ‘Waxwing year’ like this winter, birds will have evacuated a large part of their northern range due to favoured berry crops having run out or failed. They will arrive here in hordes, with single flocks numbering in their hundreds descending on neighbourhood rowans, Cotoneasters, Sorbus, hawthorns and rosehips.
Whether due to sheer hunger or a general fearlessness, these large flocks may become very approachable, leading to much popularity among photographers and the non-birding public. At the time of writing, several flocks of 200 or more have been reported this winter, including an astounding flock of over 1,400 at Pegwell Bay, Kent, on 17 December; historically, flocks of up to 3,000 have been observed.
The species is not wholly frugivorous, and relies on the plentiful midge and mayfly hatches of the open taiga forests during its short northern breeding season; it can often be seen flycatching. Other food items can include tree buds in spring, along with shoots, leaves, mosses and lichens, and spiders and snails. Early ripening fruits are also thoroughly exploited in summer.
Food colouring
The yellow and red parts of the plumage are derived from the physiological modification of berry pigments. A recent part-orange variant of Cedar Waxwing, however, was found to be probably solely the product of the ingestion of the red carotenoid rhodoxanthin from an unknown new food source.
Waxwing feeds almost continually, a habit probably due to the preferred berries that make up 84 per cent of its annual diet being relatively high in sugar but low in nutrients. Over winter, the birds are entirely frugivorous, but are known to specialise in flowers in late spring, the nectar of which is another source of what humans sometimes call ‘empty calories’. Birds also concentrate on petals and stamens, which provide vitamins and proteins for pre-breeding strength. As many of the berries and fruits eaten in winter are dried by the wind and sun, Waxwings drink a lot of water or eat a lot of snow to keep hydrated.
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In an irruption year, Waxwing flocks can number in their thousands. Superstores seem to be favourite sites, such as these birds photographed at B&Q in Folkestone, Kent. Photo by David Featherbe. |
Unlike most passerines, Waxwings do not possess a crop in which to store food. Instead they have a section of the oesophagus which is rapidly filled with undigested berries, and which can extend under the skin of the hind neck. This enables the birds to overeat their transient food source in anticipation of leaner times later, similar to a hamster’s cheek pouches (see Birdwatch 223: 10).
This feature is perhaps a primitive specialisation, as most true passerines have a crop and the bombycillids are generally understood to be basal in that group. At the other end of the digestive process, Waxwings also continue to extract fruit sugars even in the proximal part of their rectum, making sure that little goes to waste.
Birds of open woodland rather than dense forest, Waxwings nest in spruce, pine and birch, near rivers. Breeding tends not to occur much before June, owing to the lateness of the boreal spring and the adults’ and chicks’ need for berries in their diet. The birds are generally monogamous, with courtship beginning as early as March. Pair bonds are initiated by the passing of gifts of food from male to female, though possibly symbolic inedible objects may sometimes be used. Giftpassing is also a prelude to the species’ infrequent copulation.
Cedar Waxwings have been revealed to mate assortatively (that is, they select for the condition) according to the number and state of the red waxy tips to their secondaries. These are indicative of age and status, and also correlate with a larger clutch and brood size and number of fledged young. It is likely that this is also true of the Holarctic species.
Male and female birds co-operate in building a nest of thin twigs and grasses, lined with moss, feathers and fur. The nest is placed on branches close to a conifer or birch trunk at least one-and-a-half metres above the ground.
A clutch of around five eggs is laid in mid-June, though nests have been reported in use into October. The eggs are incubated by the female, while the chicks and female are initially fed by the male. Chicks fledge after about 15 days, despite the apparently low-protein diet.
Fight club
It is when the nest is occupied that male Waxwings show their rare instances of territorial aggression, with potential cuckolds threatening rivals at egg-laying by rearing up and opening the bill in an unmistakable posture of pugnacious defence. Chasing may also occur to drive off rivals, but all such violence is used only when a threat is close to the nest. No breeding territory is held, and nests can be fairly close to each other.
For a songbird, Waxwing is not known for its musical expressiveness, calling in a high-pitched liquid trill both in flight and when feeding. Their communal lifestyle probably means that males and females find mates with ease, negating the need for the prolonged and noisy overtures of courtship, and probably explaining the species’ lack of a clearly distinguishable song.
Arboreal by nature, Waxwing can be quite gymnastic in tree branches, but is somewhat ungainly on the ground, which it visits infrequently unless tempted by fallen fruit or to drink and bathe. Flight is fast and direct, reminiscent of Starling or Redwing, with occasional glides and bursts of shallow flapping.
Winter Waxwings will occur in coniferous or deciduous forests, or even in parks and gardens – anywhere that the berry crop is good. Notoriously, flocks are often seen around supermarkets, where rowan or Cotoneaster bushes are frequently planted as ornamental shrubs. Such a nomadic lifestyle is, of course, ideal for the spread of their food species, too, as birds spread seeds in their faeces.
Roosts are under-documented, but a preference for the denser conifers and hawthorns has been noted. There are also records of birds roosting in buildings or even underneath dense shrubs on the ground.
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Breeding only in the far east of Russia, and wintering from Japan through eastern China down to Taiwan, Japanese Waxwing has a small population, unknown in number, and is considered Near Threatened by BirdLife International. However, it seems to share its lifestyle and habits with Waxwing, breeding in coniferous forest and wintering in woods and gardens, in fact anywhere there is a good fruit and berry crop. Though a popular cagebird, a Western Palearctic record from Bialystok, Poland, on 4 January 2009 (pictured) may have involved a wild bird. Photo by Marcin Perkowski. |
Cedar Waxwing is the most well-known waxwing in North America, and has an increasing breeding population numbering about 15 million individuals. It is present all year round over much of its range, though the whole population moves southwards inwinter, reaching South America in irruption years. Its food is similar to the other members of the genus, but it has a particular fondness for the small cones of the Eastern Red-cedar, a kind of juniper from which it gets its name. There have been one Irish and two British records. Photo by Julian Hough. |
Flock together
Waxwings are gregarious and sociable, and wintering flocks appear to have little conflict, dominating berry-laden trees by overwhelming other species with sheer numbers. American Robins, for instance, have been shown to be able to defend crab-apple trees against fewer than 15 Cedar Waxwings, after which they are swamped. However, there is a record from North America of a Northern Mockingbird killing a Cedar Waxwing in a territorial dispute.
The alternative name for Waxwing, Bohemian Waxwing, underlines the species’ nomadic behaviour in its wintering areas, as small foraging flocks do not wander far in summer. Large movements are often observed in daylight, though night migration also occurs. Migration proper begins in September, though the distances involved are controlled by berry crops. Certainly, the first Waxwings are usually apparent in Britain from October, but an influx can happen at any time in the winter with the exhaustion of a food source. Movements seem to be uncorrelated with weather conditions, even though the major part of this season’s birds appeared to arrive with the snow and ice.
A real irruption year can sometimes be anticipated by an early arrival, but this wasn’t the case with the present invasion. Although spectacular, recent numbers are certainly not unprecedented, and the massive Europe-wide irruption in the winter of 1965-66 was bigger, with at least 34,000 birds in the Baden-Württemberg region, Germany, alone.
Birds have travelled as far south as North Africa, Cyprus and Iran. There appears to be no cyclical rhythm to irruptions, unlike those of Arctic predators, and periods between irruptions can be as little as one year or as great as 10 or more. Strangely for a species so anticipated and attractive, most of the research appears to have been in the United States on its congener, Cedar Waxwing. Clearly there is more to learn about this suave nomad with its bubbling calls and Starling-like flocking habits, but the mysteries only add to its attraction. As the berries drop, dry out or disappear, now is perhaps your last chance to try to find your own flock this winter before they fly back to Scandinavia.
References
- Fleischer, R C, James, H F, and Olson, S L. 2008. Convergent evolution of Hawaiian and Australo-Pacific Honeyeaters from distant songbird ancestors. Current Biology 18: 1,927-1,931.
- del Hoyo, J, Elliott, A, and Christie, D (eds). 2005. Handbook of the Birds of the World Volume 10: Cuckoo-shrikes to Thrushes. Lynx Edicions, Barcelona.
- Hudon, J, and Brush, A H. 1989. Probable dietary basis of a color variant of the Cedar Waxwing. Journal of Field Ornithology 60: 361-368.
- Johansson, U S, Feldsjå, J, and Bowie, R C K. 2008. Phylogenetic relationships within Passerida (Aves: Passeriformes): a review and a new molecular phylogeny based on three nuclear intron markers. Molecular Phylogenetics and Evolution 48: 858-876.
- Levey, D J, and Duke, G E. 1992. How do frugivores process fruit? Gastrointestinal transit and glucose absorption in Cedar Waxwings (Bombycilla cedrorum). The Auk 109: 722-730.
- Mountjoy, D J, and Robertson, R J. 1988. Why are waxwings ‘waxy’? Delayed plumage maturation in the Cedar Waxwing. The Auk 105: 61-69.
- Pietz, M A J, and Pietz, P J. American Robin defends fruit resource against Cedar Waxwings. Journal of Field Ornithology 58: 442-444.
- Snow, D W, and Perrins, C M (eds). 1998. The Birds of the Western Palearctic Concise Edition Volume 2: Passerines. Oxford University Press, Oxford.
- Spellman, G M, Cibois, A, Moyle, R G, Winker, K, and Barker, F K. 2008. Clarifying the systematics of an enigmatic avian lineage: What is a bombycillid? Molecular Phylogenetics and Evolution 49: 1,036-1,040.
- Studier, E H, Szuch, E J, Tompkins, E M, and Cope, V W. 1988. Nutritional budgets in free-flying birds: Cedar Waxwings (Bombycilla cedrorum) feeding on Washington Hawthorn fruit (Crataegus phaenopyrum). Comparative Biochemistry and Physiology 89A: 471-474.
