Waxwings and silky flycatchers

(Bombycillidae)

Class: Aves

Order: Passeriformes

Suborder: Passeri (Oscines)

Family: Bombycillidae

Thumbnail description
Sleek, medium-sized, berry-eating songbirds, with plump bodies, short bills and crested heads

Size
5.9–9.4 in (15–24 cm); 1–2.1 oz (30–60 g)

Number of genera, species
5 genera; 8 species

Habitat
Forest, open woodland, semi-arid scrubland, and desert

Conservation status
Most species widespread and common, none are targeted for conservation efforts

Distribution
North and Central Americas, north temperate Eurasia, Middle East, and Indian subcontinent

Evolution and systematics

Despite the ubiquity of some members of the Bombycillidae, the taxonomic status of the waxwings, their relationship to the gray and silky flycatchers, and indeed the relationships among these flycatchers themselves, remains controversial. Most modern taxonomic treatments place the waxwings proper (Bombycillinae) within the order Passeriformes together with the silky flycatchers (Ptilogonatinae) and the palmchat (Dulidae). This classification is based primarily on coloration, nesting, skeletal features, musculature, and results of DNA-DNA hybridization studies. Here the consistency ends. Waxwings have also been allied with several other Passeriformes, including thrushes (Turdidae), Old World flycatchers (Muscicapidae), pipits (Motacillidae), and starlings (Sturnidae). More controversial is the placement of the gray hypocolius (Hypocolius ampelinus). This Middle Eastern bird is frequently allied with the other bombycillids, either as a sub-family or as a monotypic family closely related to the waxwings and silky flycatchers. However, Hypocolius has also been allied with the bulbuls (Pycnonotidae) and thrushes. Further research is needed to resolve these relationships.

This treatment recognizes three subfamilies. They are the waxwings: Bombycillinae, comprised of one genus and three species: the cedar waxwing (Bombycilla cedrorum), bohemian waxwing (B. garrulus), and Japanese waxwing (B. japonica). The silky flycatchers, subfamily Ptilogonatinae, with three genera and four species: the phainopepla (Phainopepla nitens), black and yellow silky flycatcher (Phainoptila melanoxantha), long-tailed silky flycatcher (Ptilogonys caudatus), and gray silky flycatcher (Ptilogonys cinereus). The latter is not to be confused with the only member of the third subfamily—the gray hypocolius (Hypocolius ampelinus) of the Hypocolinae.

Physical characteristics

Bombycillids are medium-sized songbirds with short bills, sleek plumage, head crests, and tails of varying length. The waxwings have fawn-gray bodies, and black chin and eye masks. Their wings have contrasting plumage with white, crimson, or yellow patches and their common name refers to the red, wax-like tips present on the secondary flight feathers. (These are absent however in the Japanese waxwing.) All have a bright band of orange or yellow at the base of the tail. The cedar waxwing's tail band is usually yellow, but in the past 30 years many have been sighted with orange tail bands, apparently due to pigments in the fruits of the invasive European honeysuckle (Lonicera spp.), which has successfully established itself in the United States and is eaten by the birds.

Silky flycatchers have longer tails than waxwings and their head crests (present in three of the four species) often appear as erect bristles. The plumage is black, gray, or brown, some species have brightly colored patches of yellow or white. The gray hypocolius is gray with a black tail band and face mask.

Distribution

The ranges of the three subfamilies are quite different. Waxwings, whose fossils have been reported from the Pleistocene in California, are distributed across the temperate Old and New Worlds; the cedar waxwing winters as far south as Guatemala. Silky flycatchers occur from the southern United States into Central America. The gray hypocolius is found in the Middle East and on the Indian subcontinent.

Habitat

The habitat preferences of the bombycillids vary, although all occur where they can find fruits and berries. Waxwings prefer open woodlands and hedgerows, and increasingly are found in suburban areas. Silky flycatchers and Hypocolius inhabit desert and arid scrub-land.

Behavior

All bombycillids are gregarious, social birds, although to varying degrees. Silky flycatchers nest in loose colonies and are somewhat territorial. Waxwings are non-territorial, and will form flocks of thousands, migrating erratically to areas of high fruit density. Bent (1950) wrote of the Bohemian waxwing "We never know when or where we may see these roving bands of gypsies. They come and they go, we know not whence or whither, in the never-ending search for a bounteous food supply on which to gorge themselves." Bombycillids are migratory, the phainopeplas moving altitudinally to moister habitats after breeding. They are quite vocal birds, their calls a mixture of chatters, warbles, and whistles.

Feeding ecology and diet

Bombycillids feed predominantly on small fruits, which are the mainstay of the diet for the north temperate species for seven months of the year. They also eat insects, plucking them off of vegetation and tree bark or swooping down from high perches and taking them in flight. The cedar waxwing can store ingested fruits in a portion of the esophagus, presumably to maximize the amount of food ingested while foraging. Unlike fruit-eating thrushes, they have the enzymes to digest sucrose. In recent years, waxwings have come to rely increasingly on crops and ornamental fruits planted in suburban areas. While it will eat a variety of fruits, the phainopepla specializes on mistletoe (Phoradendron spp.) berries and is closely associated with these plants that grow on the trunks and branches of mesquite.

Reproductive biology

Waxwings are socially monogamous and the same is believed of silky flycatchers, though their habits are less well known.

The breeding season of waxwings is one of the latest of North American birds, with eggs laid from early June through August. Adults tend to pair with similar-aged birds, and pairs of older birds nest earlier and raise more young than younger birds. Copulation in waxwings is preceded by courtship-hopping, which often involves passing a small item such as an insect or flower petal between male and female, and touching the bills together which results in a clicking noise. All bombycillids make a small, cup-shaped nest, usually at a strong fork in a tree. The female does most nest building in the waxwings, while the reverse is true for the phainopepla. Clutch sizes range from four to six in waxwings, from two to four in silky flycatchers. In both groups the young hatch naked and blind and are fed crushed berries and insects by both parents. The breeding biology of the gray hypocolius is not well known.

Conservation status

No conservation measures have been taken for the family, and none appear needed. According to Breeding Bird Survey data, cedar waxwing populations have increased across North America, and phainopepla populations remain stable. The status of populations of Middle Eastern and Central American species is not well known, but as of 2001, none are listed as Endangered or Threatened.

Significance to humans

The irregular mass invasion of Europe and temperate North America by waxwings has caused them to be considered pests at times. As they have become more prominent in suburban areas, more cedar waxwings are killed by flying into windows.

Species accounts

Resources

Grimmett, Richard, et al. Birds of the Indian Subcontinent. London: Christopher Helm Ltd., 1998.

Helle, Pekka, and Timo Pakkala. "Waxwing." In The EBCC Atlas of European Breeding Birds, edited by Ward J. M. Hagemeijer and Michael J. Blair. London: T. & A. D. Poyser, 1997.

Sibley, Charles G., and Burt L. Monroe. Distribution and Taxonomy of Birds of the World. New Haven: Yale University Press, 1991.

Witmer, M. C., et al. "Cedar Waxwing." The Birds of North America 309 (1997).

Witmer, M. C. "Consequences of an Alien Shrub on the Plumage, Coloration and Ecology of Cedar Waxwings." Auk 113 (1996): 735-43.

"Zoonomen Nomenclatural Data." Alan P. Peterson. 2000 (9 April 2002).

[Article by: Rachel Ehrenberg, MS]