A small family of passerine birds, the Bombycillidae, has been selected for analysis in the present paper. By comparative study of coloration, nesting, food habits, skeleton and soft parts, an attempt is made to determine which of the differences and similarities between species are the result of habits within relatively recent geological time, and which differences are the result of inheritance from ancient ancestral stocks, which were in the distant past morphologically different. On the basis of this information, an attempt is made to ascertain the natural relationships of these birds. Previous workers have assigned waxwings alone to the family Bombycillidae, and a question to be determined in the present study is whether or not additional kinds of birds should be included in the family.

It has generally been assumed that the nomadic waxwings originated under boreal conditions, in their present breeding range, and that they did not undergo much adaptive radiation but remained genetically homogeneous. Also it is assumed that the species were wide ranging and thus did not become isolated geographically to the extent that, say, the Fringillidae did. The assumption that waxwings originated in the northern part of North America or Eurasia may be correct, but it is more probable that the origin was more southerly, perhaps, in northern Mexico, of North America (see p. 519.) Subsequent to the differentiation of this stock in the south, there was a northerly movement, while certain populations remained behind and underwent an evolution different from the northern group. Since the fossil record does not permit us to say when in geological time the family originated, we must rely on anatomical evidence and the distributional evidence of present-day species to estimate when the family stock had diverged from some unknown group sufficiently to merit the status of a separate family.

It is with pleasure that I acknowledge the guidance received in this study from Professor E. Raymond Hall of the University of Kansas. I am indebted also to Dr. Herbert Friedmann of the United States National Museum for the loan of certain skins, skeletons, and alcoholic material; to Mr. Alexander Skutch, for notes on certain Central American birds; and to Dr. Henry W. Setzer, Mr. George H. Lowery, Jr., Mr. Victor E. Jones, Mr. Victor Housholder, Mr. Alvaro Wille-Trejos, and Mr. Morton F. Davis, for gifts of specimens that have been used in this work. Suggestions and critical comments from Professors Worthie H. Horr, Charles G. Sibley and Edward H. Taylor are gratefully acknowledged. I wish also to thank Mrs. Virginia Unruh for the preparation of the drawings used in this work.

The following specimens, numbering 238, and representing each currently recognized species and subspecies, were used in the study, and were supplemented by observation in 1947 on specimens in the United States National Museum.

Diagnosis.—Rictus with conspicuous bristles; nasal fossa almost entirely exposed; tail long and rounded, graduated, or square; caudal muscles and pygostyle well developed; wings rounded and short, first primary a half to a third as long as second; second primary shorter than third; humerus long, with small external condyle; plumage soft and silky, less so in Phainoptila; sexes dissimilar, young like adult female; three genera, four species.

Diagnosis.—Without crest; tarsus longer than middle toe and claw, and booted or very slightly reticulate; tail shorter than wing, rounded; nostril exposed, ovate; rictal bristles distinct; first primary well developed; plumage normal, bill flared slightly at base.

Range.—Costa Rica and Panamá.

Diagnosis.—Coloration of adult males: Pileum, hindneck, back, scapulars, and upper tail coverts Black (capitalized color terms after Ridgway, Color Standards and Color Nomenclature, Washington, D. C., 1912), with Bluish Gray-Green gloss; rump Lemon Yellow tinged with Olive; lower breast and abdomen Gull Gray or Slate Gray; sides and flanks clear Lemon Yellow; lower chest, upper breast, and under tail coverts Yellowish Olive-Green, extending to patch on sides and flanks of same color; bill and feet Black or Blackish Brown. Coloration of adult females: Most of upper parts Olive-Green, with Yellowish Olive on rump; thighs Olive-Gray, as are sides of head; rest of coloration as in male. Coloration of young: As in adult female, but duller throughout.

Measurements.—Wing 99.0, tail 88.5, culmen 15.2, tarsus 28.4.

Range.—Highlands of Costa Rica and extreme western Panamá (Volcán de Chiriquí).

Diagnosis.—Coloration as in P. m. melanoxantha, but female with hindneck more extensively gray and of slightly darker shade; rump, upper tail coverts, and edgings to tail feathers slightly greener, less yellow; average size smaller than in P. m. melanoxantha.

Range.—Highlands of westeran Panamá (Cerro Flores and eastern Chiriquí).

Diagnosis.—Tail much longer than wing, even or graduated; head with bushy crest; nostril large, rounded and fully exposed, bordered by membrane; rictal bristles well developed; tarsus shorter than middle toe with claw; plumage soft, blended.

Range.—Southwestern United States to Costa Rica.

Diagnosis.—Coloration of adult male: Frontals, supralorals, malars, and chin White; orbital ring White; auriculars and nape grayish brown; rest of head smoke gray; back, scapulars, wing coverts, rump, and upper tail coverts plain Bluish Black; rectrices (except middle pair) with large patch of White midway between base and tip, rest plain Bluish Black; chest, breast, and anterior parts of sides plain Bluish Gray-Green, much lighter than back, and fading into paler Gray on throat; abdomen and thighs White; flanks and posterior part of sides Olive-Yellow or Yellowish Olive; under tail coverts Lemon Yellow; bill, legs and feet Black. Coloration of adult females: Head plain Smoke Gray, passing into White on frontals, malars, and chin; back, scapulars, wing coverts, and rump Hair Brown; upper tail coverts Dark Gull Gray; remiges and rectrices Black with faint Dusky Green gloss, edged with Gull Gray; chest Dark Grayish Brown lightening to Wood Brown on sides and flanks; abdomen White; under tail coverts Yellow Ocher. Coloration of young: As in adult female, but paler throughout.

Measurements.—In adult male, wing 94.0, and tail 104.2; in adult female, wing 93.3, and tail 94.8; both sexes, culmen 11.1, and tarsus 18.7.

Range.—Mountainous districts of central and southern Mexico, in states of Durango, Zacatecas, Hidalgo, México, Oaxaca, Colima, Morelos, Veracruz, San Luís Potosi, Guerrero and Michoacán.

Diagnosis.—Coloration of adult male: Upper parts darker bluish than in P. c. cinereus; venter paler; flanks Olive-Green rather than Olive as in P. c. cinereus. Coloration of adult female: Like female of P. c. cinereus but colors darker throughout; dorsum more olivaceous.

Measurements.—In adult male, wing 89.4, and tail 97.1; in adult female, wing 89.4, and tail 93.3; both sexes, culmen 11.7, and tarsus 17.3.

Range.—Western Guatemala, in subtropical and temperate zones.

Diagnosis.—Coloration of adult male: Forehead and crown Pale Grayish Blue, slightly paler anteriorly; orbital ring Lemon Yellow; rest of head and neck, including crest, Olive-Yellow; throat paler and tinged with Light Gull Gray; back, scapulars, rump, upper tail coverts and wing coverts uniform Bluish Slate-Black; chest and breast similar but paler; sides and flanks Yellowish Olive-Green; thighs, lower abdomen, and under tail coverts Lemon Yellow; remiges, primary coverts, and tail Black, glossed with Bluish Black and edged with Gull Gray; inner webs of rectrices (except two middle pair) with large middle patch of White; bill, legs, and feet Black. Coloration of adult female: Forehead and crown Pale Gull Gray, becoming paler anteriorly; rest of head, together with neck, back, scapulars, rump, and wing coverts plain Yellowish Olive Green; chest and breast similar but more grayish; lower abdomen and flanks White tinged with Yellowish Olive; under tail coverts Olive-Gray; remiges, primary coverts, and rectrices Black with Gull Gray edges. Coloration of young: Dorsum plain Light Grayish Olive; upper tail coverts Brownish Olive; underparts Grayish Olive anteriorly, becoming more Yellowish Olive on abdomen; under tail coverts pale Yellowish Olive with Grayish Olive base; bill and feet Brownish Drab.

Measurements—In adult male, wing 96.2, and tail 135.7; in adult female, wing 93.9, and tail 113.7; both sexes, culmen 12.6, and tarsus 19.1.

Range.—Highlands of Costa Rica and extreme western Panamá.

Diagnosis.—Tail almost as long as wing; head with pointed crest of narrow, separated feathers; rectrices without white; bill narrow, compressed terminally; conspicuous white patch under wing; nostril small, exposed; rictal bristles distinct; tail slightly rounded.

Diagnosis.—Coloration of adult male: Uniform glossy Bluish Black; inner webs of primaries except innermost pair with middle portion White; bill, legs, and feet Black. Coloration of adult female: Plain Olivaceous Black, longer feathers of crest Black, edged with Gull Gray; remiges and rectrices Dusky Drab to Black; rectrices and coverts margined by White; bill and feet Brownish Drab to Dusky Brown. Coloration of young: Like adult female but more Brownish Drab.

Measurements.—No specimens examined; larger than P. n. lepida (Van Tyne, 1925).

Range.—Central and southern Mexico, in states of Coahuila, San Luís Potosi, Durango, Guanajuato, México, Puebla, and Veracruz.

Diagnosis.—Coloration same as P. n. nitens; separated by smaller size.

Measurements.—Wing 91.0, tail 90.3, culmen 11.5, tarsus 17.6.

Range.—Southwestern United States, from central California, southern Utah, and central western Texas southward to Cape San Lucas in Baja California, and into northwestern Mexico (Sonora and Chihuahua).

Diagnosis.—Wings long and pointed, reaching almost to tip of tail; first primary spurious; second primary longest; tail short and even; rictal vibrissae few and short; secondaries generally, and sometimes also rectrices, tipped with red, corneous appendages; nasal fossa partly filled with short, antrorse, close-set velvety feathers; plumage soft, silky; tail tipped with yellow band (red in B. japonica); sexes alike; humerus short with large external condyle; caudal muscles and pygostyle not well developed; bill flared widely at base; one genus, three species.

Range of subfamily.—Holarctic breeding area; wanders nomadically south in winter to Central America and West Indies, southern Europe and Asia.

Diagnosis.—As described for the subfamily.

Diagnosis.—Coloration of adults: Shading from Saccardo's Umber on dorsum to Bister on top of head; upper tail coverts and proximal rectrices Gull Gray; underparts shade through pale Lemon Yellow wash on belly into White on under tail coverts; forehead, lores, and eye-stripe Black; chin same, soon shading into Blackish Mouse Gray and into color of breast; side of under jaw with sharp White line; narrow line bordering forehead, and lores, White; lower eyelid White; quills of remiges Dark Mouse Gray, darkening at tips; inner quills tipped with red horny wax appendages; tail feathers like primaries, but tipped with Lemon Yellow, and occasionally showing also red horny wax appendages; bill and feet Black. Coloration of young: Dorsum as in adult, but lightly streaked with White; head concolor with dorsum; forehead White; lores Black; eye stripe Black anterior to eye and White posterior to eye; throat Light Buff; belly with alternate streaks of Dresden Brown and light Ochraceous Buff but posteriorly White; tail tipped with Lemon Yellow bar; bill black at tip, shading to Sepia at base.

Measurements.—Wing 92.9, tail 55.5, culmen 10.9, tarsus 16.8.

Range.—Breeds from central British Columbia, central Alberta and Manitoba, northern Ontario, southern Quebec and Cape Breton Island south to northwestern California, northern New Mexico, Kansas, northern Arkansas, North Carolina, and northern Georgia. Winters south to Louisiana, Mississippi, Texas, Arizona, Colorado, Florida, Honduras, Costa Rica, Jamaica, Little Cayman Island, Haiti, and Panamá.

Diagnosis.—Coloration of adults: General color Olive-Brown, shading insensibly from clear Smoke Gray of upper tail coverts and rump to Cinnamon-Drab anteriorly, heightening on head and forehead to Hazel; narrow frontal line, lores, broader mask through eye, chin, and upper throat, Sooty Black; under tail-coverts Cinnamon-Brown; tail Smoke Gray, deepening to Blackish Mouse Gray distally, and tipped with Lemon Yellow; wings Blackish Mouse Gray; primaries tipped with sharp spaces of Lemon Yellow or White, or both; secondaries with White spaces at ends of outer web, shafts usually ending with enlarged, horny red appendages; primary coverts tipped with White; bill Blackish Slate and paler at base; feet Black. Coloration of young: Much like adult, but general color duller; some streaking on venter and back; chin, throat, and malar region dull White. Three subspecies.

Diagnosis.—Coloration: As described for the species, but darkest of the three subspecies; tending to be more Vinaceous dorsally than either pallidiceps or centralasiae.

Measurements.—Wing 113.5, tail 63.1, culmen 12.5, tarsus 20.7.

Range.—Europe; breeds north to northern Russia and Norway, south to about 65° N latitude; winters south to England and Ireland, southern France, northern Italy, and Turkey.

Diagnosis.—Coloration: As described for the subspecies garrula, but less Vinaceous dorsally, and more Cinnamon; venter lighter gray than garrula, and much paler than pallidiceps.

Measurements.—Wing 114.7, tail 63.0, culmen 12.2, tarsus 21.0.

Range.—Asia; breeds northern Siberia south to Vladivostok; winters to Turkestan and central eastern China and Japan.

Diagnosis.—Coloration: As described for the species, but more grayish above and below than B. g. garrula; darker gray than in centralasiae.

Measurements.—Wing 115.1, tail 71.7, culmen 12.6, tarsus 21.1.

Range.—Breeds from western Alaska to northern Mackenzie and northwestern Manitoba south to southern British Columbia, southern Alberta, northern Idaho, and possibly Colorado (Bergtold 1924) and Montana (Burleigh 1929); winters east to Nova Scotia and irregularly over much of Canada, and south irregularly to Pennsylvania, Ohio, Michigan, Indiana, Kansas, Colorado, California, Arizona, and Texas.

Diagnosis.—Coloration: Dorsum generally Brownish Drab shading to Light Brownish Drab on lower back, rump, and upper tail coverts; secondary and tertiary coverts Pale Brownish Drab, washed on outer web with Carmine; primary coverts Blackish Slate, with White edging; tail feathers Slate-Gray, broadly tipped with Carmine, bordered anteriorly by subterminal Black bar; head crested, forehead Chestnut; lores, frontals, and stripe extending around eye and nape, Black; throat Black, narrowing on lower throat; breast, sides of flanks Light Drab; venter pale Sulphur Yellow; thighs Brownish Drab; under tail coverts Carmine; bill, legs, and feet Black.

Measurements.—Wing 108.3, tail 53.6, culmen 11.2, tarsus 19.4.

Range.—Breeds eastern Siberia, northern China; winters south in China, and to Japan (Hokkaido, Kyushu), Taiwan, and Korea.

Diagnosis.—Bill deep and compressed, culmen strongly depressed; nostrils circular, wholly exposed; tail even, and shorter than wing; tenth primary less than half length of ninth; under parts streaked; plumage hard and harsh; rictal bristles minute; wing rounded; humerus long and with small external condyle; pygostyle and caudal muscles not well developed; one genus, one species.

Range of subfamily.—Islands of Haiti and Gonave, Greater Antilles.

Diagnosis.—Like the subfamily.

Diagnosis.—Coloration: Dorsum Olive, back, scapulars, and wing coverts more Brownish Olive; lower rump and upper tail coverts Olive-Green; pileum and hindneck with indistinct streaks of Brownish Olive; tail Brownish Drab, edged with Light Olive Gray; lores, suborbital region, and auricular regions Dusky Brown; malars Dusky Brown and streaked with Sooty Black, streaks narrower on abdomen, broader and paler on under tail coverts, bill Light Brownish Drab; legs and feet Brownish Drab.

Measurements.—Wing 85.0, tail 68.8, culmen 15.0, tarsus 24.7.

Range.—Island of Haiti, Greater Antilles.

Diagnosis.—Coloration: Like D. d. dominicus, but averaging more Grayish Olive; rump and tail coverts with less greenish wash.

Measurements.—Wing 90.1, tail 71.3, culmen 16.2, tarsus 25.1.

Range.—Gonave Island, off Haiti, Greater Antilles.