Bohemian waxwing

thumb|B. g. pallidiceps in Ontario, Canada

thumb|B. g. pallidiceps female in Saskatchewan Canada.

The Bohemian waxwing (Bombycilla garrulus) is a starling-sized passerine bird that breeds in the northern forests of the Palearctic and North America. It has mainly buff-grey plumage, black face markings and a pointed crest. Its wings are patterned with white and bright yellow, and some of the wing feathers have red tips, the resemblance of which to sealing wax gives these birds their common name. The two or three subspecies show only minor differences in appearance. Females are similar to males, although young birds are less well-marked and have few or no waxy wingtips. Although the Bohemian waxwing's range overlaps those of the cedar and Japanese waxwings, it is easily distinguished from them by size and plumage differences.

The breeding habitat is coniferous forests, usually near water. The pair build a lined cup-shaped nest in a tree or bush, often close to the trunk. The clutch of 3–7 eggs is incubated by the female alone for 13–14 days to hatching. The chicks are altricial and naked, and are fed by both parents, initially mostly with insects, but thereafter mainly fruit. They fledge about 14–16 days after leaving the egg. Many birds desert their nesting range in winter and migrate farther south. In some years, large numbers of Bohemian waxwings irrupt well beyond their normal winter range in search of the fruit that makes up most of their diet.

Waxwings can be very tame in winter, entering towns and gardens in search of food, rowan berries being a particular favourite. They can metabolise alcohol produced in fermenting fruit, but can still become intoxicated, sometimes fatally. Other hazards include predation by birds of prey, infestation by parasites, and collisions with cars or windows. The large numbers and very large breeding area mean that it is classified as being of least concern by the International Union for Conservation of Nature.

Taxonomy

The waxwings are a family, Bombycillidae, of short-tailed stocky birds with soft plumage, a head crest and distinctively patterned wings and tails. There are three species, the Bohemian, cedar, and Japanese waxwings. DNA studies and shared features such as a relatively large size, grey underparts and similar undertail patterns suggest that the Japanese and Bohemian waxwings are most closely related within the genus. Although only the cedar and Bohemian waxwings normally have red tips on their wing feathers, this feature is occasionally shown by the Japanese waxwing, suggesting that this was originally a whole-family characteristic that has been lost in one species, rather than an indicator of a close relationship. DNA analysis confirms that the cedar waxwing diverged early from the other members of the family. Outside the genus, the closest relatives of the waxwings are believed to be the silky-flycatchers, the palmchat, and the grey hypocolius, all of which have sometimes been included in the Bombycillidae.

The Bohemian waxwing was described by Carl Linnaeus in his 1758 10th edition of Systema Naturae as Lanius Garrulus. The waxwings were moved to their own genus, Bombycilla, by Louis Pierre Vieillot in 1808. Bombycilla, the genus name, is Vieillot's attempt at Latin for "silktail", translating the German name Seidenschwänze. Vieillot thought that motacilla, Latin for wagtails, was derived from mota for "move" and cilla, which he thought meant "tail"; however, Motacilla actually combines motacis, a mover, with the diminutive suffix -illa. He then combined this "cilla" with the Latin bombyx, meaning silk. the term is a reference to a supposed likeness to the Eurasian jay (Garrulus glandarius) rather than to the waxwing's vocalisations. The English name "waxwing" refers to the bright red tips of the secondary feathers on its wings, which look like drops of sealing wax, while "Bohemian" follows Gessner's usage, and may refer to the Romani, alluding to the bird's wanderings, or to its presumed origin from Bohemia. The spellings "Waxwing" and "Bohemian waxwing" were first recorded in 1817, the former as a reference to Vieillot's separation of this bird from the "chatterers".

There are two or three recognised subspecies:

B. g. garrulus (Linnaeus, 1758): the nominate subspecies, breeds in northern Europe from northern Norway east to the Ural Mountains.
B. g. centralasiae (Polyakov, 1915): breeds from the Urals eastwards across northern Asia. Included in B. g. garrulus by IOC.

The differences between these forms are small and clinal, and the species could be possibly considered as monotypic.

Description

thumb|alt= a spread wing with yellow white and red markings|right|The distinctive red wing tips

The Bohemian waxwing is a starling-sized bird in length with a wingspan, and an average weight of .

Compared to the nominate subspecies, eastern B. g. centralasiae is paler, greyer and has little reddish-brown behind the bill. The American subspecies B. g. pallidiceps has more colouring on the cheeks and forehead than the nominate form and is otherwise generally duller in appearance. All adult waxwings have a complete moult annually between August and January. Juveniles moult at the same time but retain their flight and some other wing feathers. The Japanese waxwing is easily distinguished from its relatives; it has a red terminal band to the tail, the black mask extends up the rear of the crest, and there is no yellow stripe and few or no red tips on the wings.

The Bohemian waxwing's call is a high trill sirrrr. It is less wavering and lower-pitched than that of the cedar waxwing, and longer and lower-pitched than the call of the Japanese waxwing.

thumb|alt=waxwings in a bare tree|A winter flock in Poland

In some years, this waxwing irrupts south of its normal wintering areas, sometimes in huge numbers. The fruit on which the birds depend in winter varies in abundance from year to year, and in poor years, particularly those following a good crop the previous year, the flocks move farther south until they reach adequate supplies. They will stay until the food runs out and move on again. In what may be the largest ever irruption in Europe, in the winter of 2004–2005, more than half a million waxwings were recorded in Germany alone. This invasion followed an unusually warm, dry breeding season. In 1908, an American flock wide was noted as taking two to three minutes to fly over. Outside the breeding season, the waxwing will occupy a wide range of habitats as long as suitable fruit such as rowan are available. It may be found by roads, in parks and gardens or along hedges or woodlands edges. It shows little fear of humans at this time. Older males have more red tips to the wings and are preferred by females. She is fed regurgitated berries by her mate, and rarely leaves the nest. The chicks are altricial and naked, and have bright red mouths; they are fed by both parents, although the male brings most of the food, mainly insects, in the first few days. The young are subsequently fed largely with fruit. The chicks fledge about 14–16 days after hatching. The average life expectancy is unknown.

Feeding

thumb|Eating a berry, [[Kenai National Wildlife Refuge, Alaska]]

Waxwings are primarily fruit eaters in the winter, and consume insects when available, particularly during the breeding season but also on any mild days in autumn and winter. Mosquitoes and midges are the most common prey, but many other insects and some spiders are eaten. They are caught mainly by flycatching from an open perch, but some, particularly aphids, may be picked off vegetation.

Fruit is rich in sugar but deficient in other nutrients, so it must be eaten in large quantities. sometimes fatally. and great grey shrikes. Merlins attack winter flocks, including those in cities. When alarmed, Bohemian waxwings "freeze" with bill and neck pointing upwards. If this fails, they fly, calling noisily.

Parasitic mites include Syringophiloidus bombycillae, first identified on this species, and the nasal mite Ptilonyssus bombycillae. Blood parasites include Trypanosoma species, and a Leucocytozoon first identified in this waxwing. Bohemian waxwings may carry flatworms and tapeworms, but levels of parasitic worm infestation are generally low.

Status

The global population of the Bohemian waxwing has been estimated at more than three million birds, and the breeding range covers about 12.8 million km2 (4.9 million mi2). Although this species' population, as of 2013, appears to be declining, the decrease is not rapid nor large enough to trigger conservation vulnerability criteria. Given its high numbers and huge breeding area, this waxwing is therefore classified by the International Union for Conservation of Nature as being of least concern. The woodlands used by this species are well to the north of major human populations, and the birds can use disturbed habitats, so there are no serious long-term threats to this species.