Chapter I: Part 1

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Phylogeny of the Waxwings
and Allied Birds

BY

M. DALE ARVEY

University of Kansas Publications
Museum of Natural History

Volume 3, No. 3, pp. 473-530, 49 figures in text, 13 tables
October 10, 1951

UNIVERSITY OF KANSAS
LAWRENCE
1951

UNIVERSITY OF KANSAS PUBLICATIONS, MUSEUM OF NATURAL HISTORY

Editors: E. Raymond Hall, Chairman, Edward H. Taylor,
A. Byron Leonard, Robert W. Wilson

Volume 3, No. 3, pp. 473-530, 49 figures in text, 13 tables
Published October 10, 1951

University of Kansas
Lawrence, Kansas

PRINTED BY
FERD VOILAND, JR., STATE PRINTER
TOPEKA, KANSAS
1950

23-1019

Phylogeny of the Waxwings
and Allied Birds

by
M. DALE ARVEY

CONTENTS

PAGE Introduction 476 Acknowledgments 476 Nomenclatural History 477 Materials 478 Diagnoses 478 Coloration 485 Courtship 489 Nest Building 491 Food 493 Skeleton 494 Skull 494 Humerus 499 Pygostyle 502 Sternum 505 Relative Lengths of Bones 505 Leg-trunk Percentages 509 Arm-trunk Percentages 511 Musculature 514 Caudal Muscles 514 Pectoral Muscles 517 Hind Limb Musculature 517 Digestive Tract 517 Origin of the Species 519 Conclusions 521 Summary 524 Bibliography 525

INTRODUCTION

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.

ACKNOWLEDGMENTS

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.

NOMENCLATURAL HISTORY

The oldest name available for any species of the waxwings is _Lanius garrulus_ Linnaeus (1758). _Lanius garrulus_ and _Lanius garrulus_ variety B _carolinensis_ were described as conspecific. The description has been associated with the first of the two names. The latter name is a _nomen nudum_ since it was not accompanied by a separate description. The generic name _Lanius_ was originally applied to both shrikes and waxwings by Linnaeus. Since that name is applied to the shrikes only, the next available generic name that may be applied to the generically different waxwings must be used. This is _Bombycilla_, a name originally proposed by Brisson (1760) for the Cedar Waxwing. In the 12th Edition of the Systemae Naturae (1766) Gmelin proposed the generic name _Ampelis_ for the Bohemian Waxwing, and combined it with the specific name _garrulus_, the Cedar Waxwing being termed variety B. Vieillot (1807) proposed the generic name _Bombycilla_ and combined it with a new specific name, _cedrorum_, for the Cedar Waxwing. Vieillot has been cited as the author of _Bombycilla_ since that time, although Brisson used _Bombycilla_ 33 years before. Oberholser (1917) did not cite Brisson's work in his discussion of the proper generic name for the waxwings, and _Bombycilla_ should be ascribed to Brisson and not Vieillot, since Opinion 37, rendered by the International Zoological Committee on Nomenclature, states that generic names used by Brisson (1760) are valid under the Code. In consequence, the specific name available for the Cedar Waxwing, since Brisson is ruled not to be a binomialist, is _Bombycilla cedrorum_ Vieillot (1807).

Most workers prior to 1900 utilized the family name Ampelidae to include waxwings, silky flycatchers, and palm-chats. Ridgway (1904:113) elevated the silky flycatchers to family rank under the name Ptilogonatidae, and assigned the palm-chats to a separate family, the Dulidae.

MATERIALS

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.

====================================================================
Species or Subspecies | Skin | Skeleton| Alcoholic
----------------------------------------+------+---------+----------
_Phainoptila melanoxantha melanoxantha_ | 8 | 1 | 2
_Phainoptila melanoxantha minor_ | 2 | |
_Ptilogonys cinereus cinereus_ | 13 | 3 | 4
_Ptilogonys cinereus molybdophanes_ | 6 | |
_Ptilogonys caudatus_ | 16 | 3 | 4
_Phainopepla nitens nitens_ | | 1 | 5
_Phainopepla nitens lepida_ | 12 | 5 | 4
_Bombycilla cedrorum_ | 53 | 27 | 8
_Bombycilla garrula garrula_ | 4 | 3 |
_Bombycilla garrula centralasiae_ | 9 | 2 |
_Bombycilla garrula pallidiceps_ | 7 | 3 | 2
_Bombycilla japonica_ | 10 | |
_Dulus dominicus dominicus_ | 9 | 5 | 2
_Dulus dominicus oviedo_ | 4 | 1 |
|---------------------------
Totals | 153 | 54 | 31
--------------------------------------------------------------------

DIAGNOSES

Family Bombycillidae

_Diagnosis._--Bill short, flat, somewhat obtuse, minutely notched near tip of each maxilla, flared at base; gape wide and deeply cleft; culmen convex; nasal fossa broad, exposed, or filled with short, erect or antrorse, close-set velvety feathers; nostril narrowly elliptical; rictal vibrissae long, short, or absent; lacrimal bone free, articulating at two points; wings long and pointed, or short and rounded; primaries ten, tenth reduced in some species; tail short, narrow, even, two thirds or less length of wing, or much longer and forked or rounded; feet weak (except in _Dulus_ and _Phainoptila_); tarsus generally shorter than middle toe and claw, distinctly scutellate with five or six divisions, the lateral plate subdivided (except in _Phainoptila_); lateral toes of nearly equal length; hallux approximately as long as inner lateral toe, or shorter; basal phalanx of middle toe more or less united to that of outer and inner toes; body stout; head generally conspicuously crested; plumage soft, smooth and silky (except in _Dulus_); eggs spotted; nest in trees; three subfamilies, five genera, eight species.

Subfamily Ptilogonatinae

_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.

Genus =Phainoptila= Salvin

_Phainoptila_ Salvin, Proc. Zool. Soc. London, 1877:367, April 17,
1877. Type _Phainoptila melanoxantha_ Salvin.

_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 Panama.

=Phainoptila melanoxantha melanoxantha= Salvin

Phainoptila

_Phainoptila melanoxantha melanoxantha_ Salvin, Proc. Zool. Soc.
London, 1877:367; April 17, 1877.

_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 Panama (Volcan de Chiriqui).

=Phainoptila melanoxantha minor= Griscom

Phainoptila

_Phainoptila melanoxantha minor_ Griscom, Amer. Mus. Novitates,
141:7, 1924.

_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 Panama (Cerro Flores and eastern Chiriqui).

Genus =Ptilogonys= Swainson

_Ptilogonys_ Swainson, Cat. Bullock's Mex. Mus., App. 4, 1824.
Type _Ptilogonys cinereus_ Swainson.

_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.

=Ptilogonys cinereus cinereus= Swainson

Ashy Ptilogonys

_Ptilogonys cinereus cinereus_ Swainson, Cat. Bullock's Mex. Mus.,
App. 4, 1824.

_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, Mexico, Oaxaca, Colima, Morelos, Veracruz, San Luis Potosi, Guerrero and Michoacan.

=Ptilogonys cinereus molybdophanes= Ridgway

Ashy Ptilogonys

_Ptilogonys cinereus molybdophanes_ Ridgway, Man. N. American Birds,
464 (footnote), 1887.

_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.

=Ptilogonys caudatus= Cabanis

Costa Rican Ptilogonys

_Ptilogonys caudatus_ Cabanis, Jour. fuer Orn., 1866:402, Nov. 1866.

_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 Panama.

Genus =Phainopepla= Sclater

_Phainopepla_ Sclater, Proc. Zool. Soc. London, 26:543, 1858. Type
_Phainopepla nitens_ (Swainson).

_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.

=Phainopepla nitens nitens= (Swainson)

Phainopepla

_Phainopepla nitens nitens_ (Swainson), Anim. in Menag., 1838:285,
Dec. 31, 1837.

_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 Luis Potosi, Durango, Guanajuato, Mexico, Puebla, and Veracruz.

=Phainopepla nitens lepida= Van Tyne

Phainopepla

_Phainopepla nitens lepida_ Van Tyne, Occ. Pap. Bost. Soc. Nat.
Hist., 5:149, 1925.

_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).

Subfamily =Bombycillinae=

_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.

Genus =Bombycilla= Brisson

_Bombycilla_ Brisson, Orn. ii, 1760:337. Type _Bombycilla garrula_
(Linnaeus).

_Diagnosis._--As described for the subfamily.

=Bombycilla cedrorum= Vieillot

Cedar Waxwing

_Bombycilla cedrorum_ Vieillot, Hist. Nat. Amer., 1:88, Sept. 1, 1807

_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 Panama.

=Bombycilla garrula= (Linnaeus)

Bohemian Waxwing

_Bombycilla garrula_ (Linnaeus), Syst. Nat., 10th Ed., 1758:55.

_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.

=Bombycilla garrula garrula= (Linnaeus)

Bohemian Waxwing

_Bombycilla garrula garrula_ (Linnaeus), Syst. Nat., 10th Ed.,
1758:55.

_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 deg. N latitude; winters south to England and Ireland, southern France, northern Italy, and Turkey.

=Bombycilla garrula centralasiae= Poljakov

Bohemian Waxwing

_Bombycilla garrula centralasiae_ Poljakov, Mess. Orn. vi:137, 1915.

_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.

=Bombycilla garrula pallidiceps= Reichenow

Bohemian Waxwing

_Bombycilla garrula pallidiceps_ Reichenow, Orn. Monats. 16:191, 1908.

_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.

=Bombycilla japonica= (Siebold)

Japanese Waxwing

_Bombycilla japonica_ (Siebold), Nat. Hist. Jap., St. No. 2:87, 1824.

_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.

Subfamily _Dulinae_

_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.

Genus _Dulus_ Vieillot

_Dulus_ Vieillot, Analyse, 1816:42.

_Diagnosis._--Like the subfamily.

=Dulus dominicus dominicus= (Linnaeus)

Palm-chat

_Dulus dominicus dominicus_ (Linnaeus), Syst. Nat., 12th Ed.,
1766:316.

_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.

=Dulus dominicus oviedo= Wetmore

Palm-chat

_Dulus dominicus oviedo_ Wetmore, Proc. Biol. Soc. Wash., 42:117,
1929.

_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.

COLORATION

The general coloration of waxwings is cryptic, that is to say, concealing or blending. The lighter color of the venter, especially of the belly, contrasts with the duller, darker vinaceous color of the dorsum. Several ruptive marks tend to obliterate the outline of the body. The crest of the head, when elevated, tends to elongate the body, making the outline less like that of a normal bird. The facial mask effectively breaks up the outline of the head, and conceals the bright eye, which would otherwise be strikingly distinct. The white spots on the distal ends of the secondaries of _B. garrula_ and the yellow color on the distal ends of the rectrices (red in _B. japonica_) are also ruptive. These ruptive marks on an otherwise blending type of plumage might be important to waxwings, and probably are more effective when the birds remain motionless in either a well-lighted area or in one that is partly in shadow, rather than in one that is wholly in shadow.

The red wax tips on the secondaries of the flight feathers, and sometimes found on the ends of the rectrices in _Bombycilla_, are puzzling and no wholly convincing reason has been suggested for their occurrence. Two instances are known of yellow instead of red-colored wax tips in _B. cedrorum_ (Farley, 1924). It is well known that many individuals, especially of _B. cedrorum_, do not possess these tips; they are absent in a smaller proportion of individuals of _B. garrula_. Of the 53 skins of _B. cedrorum_ available in the University of Kansas Museum of Natural History, which might be taken as a sampling at random of the general population of this species, only 17 possess wax tips. A few specimens are unilateral, and the tips are of varying sizes in different individuals. Of these 17 birds, 6 are female and 7 male, the others being unsexed at the time of skinning. This proportion is, roughly, half and half. Of the seven skins of _B. garrula pallidiceps_ in the same Museum, five possess the tips, and two that are females have no trace of the red tips at all. Of the five which do have the tips, two are males, two are females, and one is unsexed. In a series of 13 specimens of the three subspecies of _B. garrula_, loaned by the United States National Museum, all but two individuals possess the tips on the secondaries, and, in addition, four specimens, equally divided between the two sexes, have color on the rachis of some rectrices, and small appendages of pigment extend beyond the feathers. Stevenson (1882) found that among 144 specimens of _B. garrula garrula_ killed by storms in England in the winter of 1866-67, 69 individuals had wax tips. Of these, 41 were males and 27 were females; the remaining one was of uncertain sex. Among 38 definitely sexed _B. garrula pallidiceps_ in the California Museum of Vertebrate Zoology, Swarth (1922:276) lists tips in 22 males and 16 females. These data indicate that the proportion of birds with the wax tips is higher in _B. garrula_ than in _B. cedrorum_. The potentiality for wax tips is possibly inherited according to Mendelian ratio.

_Bombycilla japonica_ is of interest in that the adults, at least, seldom have the waxy appendages. Nevertheless, in the specimens observed, the entire distal ends of the feathers normally possessing the tips in other species are suffused with red color. This may be the original condition of all waxwings, or perhaps, instead, this species is in a transitional stage in the development of the tips. Swarth (1922:277) says concerning the probable derivation of the wax tips in _B. garrula_ (and in _B. cedrorum_): "the ornamentation, in fact, may well have begun with the coloring of the shaft, spreading later over adjoining feather barbs. The last stage would have been the coalescing of the barbs, forming the waxlike scale as is now seen. Various steps of this hypothetical development are supplied in the wing and tail feathers of different birds of this series." _Bombycilla japonica_ thus may be close to the ancestral condition in the waxwing stock in the development of the waxy appendage.

The rectrices of all three species of waxwings seldom possess the wax tips, unless the secondaries have the maximum number of tips. In these individuals, the pigment seems to "spill over" onto the tail feathers. Eight is the maximum number of tips found on the secondaries. Rectrices with wax tips are more frequently found in _B. garrula_, and only occasionally in _B. cedrorum_. The pigment in the tip of the tail of _B. japonica_ is red rather than yellow as it is in the other two species, and some individuals of the Japanese Waxwing show a slight amount of coalescence of wax in the tail feathers as well as in the secondaries.

If the tips were present in all members of the two species, it could be postulated, in line with recent investigational work by Tinbergen (1947), that the tips are in the nature of species "releasers," facilitating species recognition. Such recognition is now regarded as of prime importance in the formation of species. It is improbable that sex recognition may be aided, as there is no evidence to indicate that the tips are found predominantly in either sex.

The wax tips are not limited to the adult birds in the species _B. garrula_. Swarth (_op. cit._) mentions the capture of several young Bohemian Waxwings, and describes them as "possessing all the distinctive markings of the most highly developed adult." This includes wax appendages, and several citations are given (Wolley 1857, Gould 1862) to indicate that this is the rule rather than the exception, not only for the American subspecies _pallidiceps_, but at least for the European subspecies _garrula_ as well. On the other hand, the young of _B. cedrorum_ lack the wax tips, at least as far as available data show.

Some characteristics of living animals are of the "relict" type; that is to say, they were developed in ancient times when some unknown ecological factor was operative which is no longer demonstrable, and the characteristic is now neutral or at least not detrimental, although of no positive value to the organism. Possibly the wax tips of waxwings are thus to be explained. I am more inclined to the opinion that the wax tips are adaptations to present-day ecological conditions for the birds.

The wax tips are ruptive in effect, since the birds, especially in winter, are habitues of bushes and trees that have berries, and the tips, on the otherwise dull body, suggest berries. The red tips tend further to disrupt the body outline at the midline, or slightly posterior to this. Perhaps the wax tips on the rectrices emphasize the end of the tail, the region of the body that is the least vital and that may be expendable in times of pursuit by an enemy.

Any characteristic is of survival value to an organism if in any way the characteristic enhances the chances of survival up to the time when the organism can successfully raise even a few young to maturity. If that character, as for example, the red wax tips on the secondaries, helps to maintain the individual until it can raise to independence a greater number than merely a few young, such a character can be said to be of greater survival value. The character may be effective for a brief period of time and may be uncommon; it might be effective for a split second in time, and only at a particular stage in the life history.

The winter period probably is the most hazardous for waxwings, in that they then depend at times upon long flights to find food. The food is vegetable, and thus is comparatively low in food value; the birds must ingest large quantities of berries or dried fruits to maintain themselves. In winter, in northern latitudes at least, predators are more apt to prey upon those species which, like waxwings, do not migrate south. The winter months are those in which waxwings frequent berry bushes, and it may well be that in these months, the wax tips that appear like berries, are especially valuable to the birds, and operate selectively.

It is suggested, therefore, that the wax tips are of positive value to waxwings, rather than being relict characters. Coalescence of pigment has taken place in the formation of the wax tips. _B. japonica_ is closer to the ancestral stock insofar as wax tips are concerned, and generally lacks the tips. _B. cedrorum_ has the tips in approximately half of the adults, and not at all in the young. _B. garrula_ has the tips in almost all the adults, and in a like proportion of the young, and probably has evolved further in the development and retention of the wax tips than has either of the other two species.

The streaked plumage of _Dulus_ is decidedly generalized, and is probably more nearly like the color of the ancestral stock. In this connection it is notable that young Cedar Waxwings are streaked, and young Bohemian Waxwings are streaked to a lesser degree. This streaking is apparently a recapitulation of the feather color of the stock. Perhaps the color of _Dulus_ has not changed, as the streaking would not be a disadvantage to the birds in their environment of light and shadow. In joining together in groups and in the construction of large communal nests, _Dulus_ has evidently gained sufficient protection against predators; other birds solve this problem by modifying their coloration.

_Ptilogonys_ is ruptively colored, but in a different fashion than _Bombycilla_. The tail markings, the distinct yellow on the under tail coverts, the sharply marked pileum, are all examples of ruptive coloration. The generally lighter venter (especially under tail coverts), the crest that may be elevated, and the generally drab bluish dorsum, are cryptic and serve to hide the animal insofar as is possible considering its habits. The very conspicuous coloration of the male, in contrast to the more drab color of the female, however, would lead one to believe that in _Ptilogonys_, following the pattern of many passerine birds, the male leads a predator from the nest, leaving the drab female to incubate the eggs, and thus preserve the young.

It is difficult to suggest reasons for the brilliant coloration of the male _Phainopepla_, unless it is for decoying predators away from the nest. Possibly some birds survive not because of, but in spite of, their coloration, and _Phainopepla_ may be a case of this sort. Anyone who has observed _Phainopepla_ in life will agree, certainly, that the male makes no attempt at concealment, and flaunts his color to all comers.

The coloration of _Phainoptila_, in contrast to _Phainopepla_, is much more plain, and is suited to its habits of brush dwelling; in a brush habitat the drab coloration is difficult to detect. The Yellowish Olive under tail-coverts and the Olivaceous dorsum are all evidences of cryptic coloration, and undoubtedly, this bird depends upon hiding for escape from its enemies, since it is a bird of the dense forest cover.

Coloration, which varies relatively rapidly in response to differing ecological conditions, has become more different in the species of Bombycillidae than is true in many other families of passerine birds. The explanation lies in early geographical isolation of the three subfamilies, with consequent radiation in three directions. Waxwings have become adapted by possessing a thick protective layer of feathers and drab coloration broken by ruptive marks. They still retain the streaked plumage, which is probably ancestral, in the juveniles; this is lost at the first molt in the fall. In its evolution, _Dulus_ has developed large feet, heavy decurved beak, and the large communal nest that affords protection from enemies; as a consequence, perhaps _Dulus_ did not need a plumage different from the primitive and streaked one. The survival of _Dulus_ may not have depended on either ruptive marks or on brilliant and outstanding plumage. The large feet and large bill seem to be responses to particular ecological requirements, as will be shown later.

The Ptilogonatinae, with habits paralleling those of the flycatchers, probably are considerably modified from the ancestral stock; the coloration probably is more brilliant and conspicuous. Perhaps this type of coloration and the habit of capturing insects from a perch are correlated. Some amount of territoriality is characteristic of this subfamily and dimorphism in color--the plumage of the male is outstandingly conspicuous--possibly is of selective value to the race. In a tropical forest community, a duller pattern possibly would be more visible and thus would be selectively disadvantageous.

COURTSHIP

Waxwings are gregarious birds and individuals establish no well-defined territories as do many birds. The nest itself is the only defended territory, and as Crouch (1936) has shown, the Cedar Waxwing will nest in close proximity to others of the same species. Swarth (1932:275) mentions that the Bohemian Waxwing is tolerant of the nests of other pairs near by. The extreme condition is that found in _Dulus_, in which the territory is not limited even to the nest, but to the individual compartment of the community nest. _Phainopepla_, a less gregarious bird than _Dulus_ and waxwings, has a much more definite territory, although individuals of _Phainopepla_ are tolerant of others of the same species; no feeding territory is established, and small flocks of birds feed together at any time of the year.

In birds whose territories lack well-defined boundaries, it would be expected that elaborate song would not have evolved, and that most of the recognition of kind and sex would be dependent upon the behavior of the birds. This is the fact; song, as such, is lacking in the three subfamilies Bombycillinae, Ptilogonatinae, and Dulinae. Waxwings utter (1) notes that serve to keep the flock together, (2) calls used by the young in begging for food, and (3) some low notes that Crouch (_op. cit._:2) considered as possibly concerned with courtship. _Phainopepla_ has various call notes, and in addition, a succession of notes which are run together. _Ptilogonys_ utters a note which Skutch (MS) characterizes as a loud, not unmusical "tu-whip" that is used as the birds "fly in straggling parties which keep in contact by their constant chatter." _Dulus_ is described by Wetmore and Swales (1931:349) as having only a variety of rather harsh chattering notes in chorus.

The most notable behavior pattern associated with courtship in Waxwings, in the absence of song, is the so-called "mating dance" described by Crouch (1936), and observed by me in Lawrence, Kansas, in the spring of 1948. This consists of one bird of a pair (presumably the male) hopping along a branch toward the other bird (the female), then away again, repeating the procedure for some little time. The female remains motionless until, as the male approaches, mutual fondling of the head and neck feathers takes place, or the birds may peck at each other's bill. A berry may be passed from bill to bill, although generally the berry is not utilized for food, and this can be interpreted as a nervous reaction of the birds. It may be an instance of "false feeding" as is seen in many birds, in which the female begs for food, as a nestling would beg, as a preliminary to the sexual act. I am of the opinion that these reactions are in the nature of behavioristic patterns that bring the birds into the emotional balance for copulation, as copulation follows the "dance." Sometimes, however, copulation is preceded by a "nuptial flight" around the nesting area, at which time the birds utter loud calls. Armstrong (1924:183) is of the same opinion, citing numerous instances in which nuptial flights and elaborate displays have evolved for just this purpose. The birds are then in the proper physiological balance to initiate the complicated sequence of copulation, nesting, incubation, feeding, and brooding of the young.

It would be valuable to know more concerning the life histories of the other birds considered in this paper, since behavior is inherent, and probably can be cited as evidence of close relationship or the opposite. All that I have been able to learn is that _Phainopepla_ has a nuptial flight in which the male chases the female, and that _Dulus_ (Wetmore and Swales, 1931:347) seeks the company of others of its kind at all times, and that two birds, presumably paired, will sidle up to one another when they are perched.

NEST BUILDING

There are numerous papers concerning the nesting of waxwings. _B. garrula_, owing to its nesting in the far north, where observers are few, has received less attention than _B. cedrorum_. There is, on the other hand, no literature that deals with the nesting habits of the majority of the Ptilogonatines, with the exception of _Phainopepla_, on which there is considerable literature (Merriam, 1896; Myers, 1907, 1908). No detailed study of the nesting of _Dulus_ has been reported, although Wetmore and Swales (1931) have described carefully the large communal nest of this genus.

In _Bombycilla_, both members of a pair apparently aid in the construction of the nest (Crouch, 1936; Swarth, 1932). Although the sexes are alike in plumage and general appearance, most students of the nesting of waxwings agree that one bird, assumed to be the female, does most of the arranging of the material, and does the shaping of the nest, whereas both birds carry materials to the nest site. As is characteristic of many passerine birds, both members of the pair gather materials and fly back to the nest site, where the female takes the more active part in the construction of the nest itself.

Both species of American waxwings build bulky nests, with the base or platform composed of a large amount of twigs and sticks, from which there often trails a mass of sticks and moss or string. Softer materials such as moss, plant fibers, and string, are placed inside the platform; moss is readily available to, and preferred by, _B. garrula_ according to Swarth (_op. cit._:271), and various plant fibers and string are used by _B. cedrorum_. The inner lining consists of soft plant fibers or down, dry grasses, and feathers. The nest is usually unconcealed in a tree either adjacent to a trunk or on a main side branch, but sometimes in a fork. Nest building by both Cedar and Bohemian waxwings is rapid, taking from three to five days, and is followed immediately by egg laying.

Nesting by waxwings is late in the season; June is the month in which the nest is usually started. This is readily explainable in Bohemian Waxwings, since adverse weather would prohibit earlier nesting in the area in which they spend the summer. Crouch (_op. cit._:1) remarks that _B. cedrorum_ possibly evolved in the far north where it was impossible for it to start nesting earlier, and that the habit has been retained. Perhaps, on the other hand, nesting is delayed until the berry crop is ripe, to insure sufficient food for the young.

Desertion of the nest is not uncommon in waxwings, despite the tolerance to other animals that is shown by the birds. A new nest may suddenly be begun before the first one is finished, and all the materials from the first nest may be removed, or the nest may be abandoned before it is completed. The eggs may be left at any time up to hatching, and the young may be deserted, especially in the earlier stages of development.

The very large and bulky communal nest of _Dulus_ is not radically different from the nest of waxwings. In the absence of sufficient nesting sites, a pair of gregarious birds such as _Dulus_ could combine their nest with those of other pairs, retaining for their own territory only the nest cavity, and in this way communal nests might have evolved. The nest of _Dulus_ is communal probably because of the lack of suitable trees for nesting sites, and only incidentally does this type of nest afford better protection from natural marauders. Large numbers of Palm-chats work together in the construction of the nest platform, and both sexes probably take part in the work.

In _Phainopepla_ the nest is built mostly by the male (Merriam, 1896; Myers, 1908), although the female does some of the work, especially in the shaping and lining of the nest. In this genus, the nest is usually a compact structure, but exceptional nests are of considerable bulk. The nest is commonly placed in a fork near the main trunk of a tree, in a conspicuous location, and generally is 10 to 20 feet from the ground. In shape and location, the nest closely corresponds to that of _Bombycilla_, but the materials used for a base are stems of annual plants, whereas _Bombycilla_ uses more woody twigs. The finer materials used by _Phainopepla_ are more readily obtainable in the ecological association inhabited by _Phainopepla_ than would be heavier twigs such as _Bombycilla_ uses.

FOOD

Waxwings are typically frugivorous; berries are the staple food. The birds are known to catch insects, especially in the spring and summer, and their insect gathering technique has been likened to that of Tyrannid flycatchers. Nice (1941) experimented with a young captive Cedar Waxwing and found that it had a decided preference for red or blue berries, and that meal worms were utilized as food only when the birds became educated by other captive birds of other species as to the food value of the worms. Post (1916) indicates that the food given to the nestlings of Cedar Waxwings is entirely animal for the first three days, and that a mixed diet of berries and insects is subsequently offered.

In feeding of the young, regurgitation of partly digested food does not take place, according to Wheelock (1905). Rather, the adults "store" food in the form of berries in the expanded esophagus or crop, feeding them whole to the young. Digestion is an unusually rapid process, involving merely minutes for the passage of berries and cherries. This is correlated with a short intestinal tract, which is unusual for a frugivorous bird. Nice's (1940) experiments with Cedar Waxwings revealed that cherries would pass through the digestive tract in 20 minutes, blueberries in 28 minutes, and chokecherries in 40 minutes. Heinroth (1924) states that berries pass through the digestive tract of Bohemian Waxwings in the space of a "few minutes." This rapid digestion is obviously adaptive, since the value of the food is slight and therefore large quantities of it must be ingested; the large seeds would hamper further ingestion until they were eliminated, since they seem not to be regurgitated.

Members of the subfamily Ptilogonatinae are both insectivorous and frugivorous insofar as available data show, although again there is relatively little information available concerning them. Skutch (MS) has found that the Guatemalan _Ptilogonys cinereus_ catches insects by repeated sallies into the air from a perch, after the manner of flycatchers. He notes also that the birds feed on berries of _Eurya theoides_ and _Monnina xalapensis_. It is well known that _Phainopepla_ catches insects when these are available, and its liking for berries is so apparent that in parts of its range, it is known as the "pepper bird," since it frequents pepper trees (_Schinus molle_) and feeds on the small red berries. The preserved specimens of _Ptilogonys_ and _Phainoptila_ available for this study contain only berries in the digestive tract. _Dulus_ feeds mostly, if not wholly, on plant food. According to Wetmore and Swales (1931:349), berries, fruits, and parts of flowers are eaten.

SKELETON

A critical analysis of the skeletons provides evidence that aids the student in estimating which differences are merely the result of habits developed in relatively recent geological time as opposed to those which owe their existence to more ancient heritage. Stresses caused by the action of different sets of muscles can apparently stimulate changes in bones to meet new needs, and the evidence from genetics is that such mutations in wild birds are minute and cumulative, rather than of large degree and of sudden appearance. Once adaptive mutations have occurred, if genetic isolation from one source or another accompanies it, a new population different from the parental stock may become established. Study of the skeleton of any species of living bird may indicate those characters identifiable as modifications fitting it to a particular environment. If no distinguishing characters are discovered that may be attributed to environmental factors, such a species can be spoken of as generalized; the inference then is that such a species is not modified for a single, particular ecological niche.

Some parts of the skeleton, obviously, are more adaptable or plastic than others. The beak seems to be the most adaptable part. Probably this results from its frequent use; it is the part of the bird to capture the food. The long bones, meeting the environment as legs which serve as landing mechanisms or as locomotory appendages, and as wings which provide considerable locomotion for most birds, probably come next in order as regards plasticity. In these parts, then, one may look for the most change in birds, which, within relatively recent geologic times, have been modified to fit a particular set of conditions. From the beak and long bones of a species in which habits are unknown, one can infer the habits and habitat from a comparison with the skeletal features of species of known habits.

_Skull._--The skulls in all three subfamilies have essentially the same general appearance and structure, the most marked differences being, as would be expected, in the bills and associated bones.

The most specialized bill is to be found in _Dulus_; its bill is decurved, and the associated bones are correspondingly changed for support of the bill. For example, the palatines and "vomer" are much wider, the palatines are more concave from below and have longer posterior processes than the corresponding bones in _Bombycilla_. Moreover, the "vomer" in _Dulus_ and in _Phainoptila_ is larger and heavier than in _Bombycilla_, and the quadrate and pterygoid bones are relatively large for support of the beak. The palatines, however, are weak in _Phainoptila_. In the Ptilogonatinae, with the exception of _Phainoptila_, the wings of the palatines flare more than in _Bombycilla_, but not to the extent that they do in _Dulus_, nor does the palatine bone present a concave appearance in the Ptilogonatinae. The premaxilla is a relatively weak bone in _Bombycilla_ and _Phainopepla_, stronger in _Ptilogonys_, and is notably heavy in _Phainoptila_ and _Dulus_, and in these latter two genera shows a sharply-ridged tomium. The maxillae connect to somewhat widened nasal and naso-lateral processes in all the genera, and the premaxillae narrow abruptly from this point forward. In the family, _Phainopepla_ and _Phainoptila_ show the least flaring in this region.

1. _Phainoptila m. melanoxantha_, sex?, MNH no. 26493, 15 mi.
SE Cartago, Costa Rica.

2. _Ptilogonys caudatus_, male, MNH no. 24492, 15 mi. SE Cartago,
Costa Rica.

3. _Phainopepla nitens_, male, MNH no. 24752, Pima Co., Arizona.

4. _Ptilogonys cinereus_, female, Louisiana State University
no. 297, Xilitla Region, San Luis Potosi, Mexico.

5. _Dulus dominicus_, female, USNM no. 292652, Don Don, Haiti.

6. _Bombycilla cedrorum_, male, MNH no. 15331, Bexar Co., Texas.

7. _Bombycilla garrula_, sex?, USNM no. 223895, Bozeman, Montana.]

8. _Phainoptila m. melanoxantha_, sex?, MNH no. 26492, 15 mi.
SE Cartago, Costa Rica.

9. _Ptilogonys caudatus_, male, MNH no. 24492, 15 mi. SE Cartago,
Costa Rica.

10. _Phainopepla nitens_, male, MNH no. 24754, Pima Co., Arizona.

11. _Ptilogonys cinereus_, female, Louisiana State University
no 297, Xilitla Region, San Luis Potosi, Mexico.

12. _Dulus dominicus_, female, USNM no. 292652, Don Don, Haiti.

13. _Bombycilla cedrorum_, male, MNH no. 15331, Bexar Co., Texas.

14. _Bombycilla garrula_, sex?, USNM no. 223895, Bozeman, Montana.]

15. _Phainoptila m. melanoxantha_, sex?, MNH no. 26493, 15 mi.
SE Cartago, Costa Rica.

16. _Ptilogonys caudatus_, male, MNH no. 24492, 15 mi. SE Cartago,
Costa Rica.

17. _Phainopepla nitens_, male, MNH no. 24752, Pima Co., Arizona.

18. _Ptilogonys cinereus_, female, Louisiana State University
no. 297, Xilitla Region, San Luis Potosi, Mexico.

19. _Dulus dominions_, female, USNM no. 292642, Don Don, Haiti.

20. _Bombycilla cedrorum_, male, MNH no. 15331, Bexar Co., Texas.

21. _Bombycilla garrula_, sex?, USNM no. 223895, Bozeman, Montana.]

This flaring, immediately lateral to the antorbital plate, is common to all Bombycillids and constitutes a major skeletal characteristic useful for recognition of the members of the family, since the swelling is easily discernible both externally and on the cleaned skulls. In _Phainopepla_ there is much variability in this character; some specimens have a narrower antorbital bridge than others. Only one skeleton of _Phainopepla n. nitens_ was available. The flaring in the skull of this specimen is identical with that in _Ptilogonys_. Among the skulls of _P. n. lepida_ in the University of Kansas Museum of Natural History, is No. 19228, a juvenile, taken 5 miles south of Tucson, Arizona. In this specimen, the flaring in the antorbital region is clearly evident and equal in amount to that in skulls of _P. n. nitens_, but the bird had not attained full skeletal growth. However, the flaring of the antorbital region appears to be common in the nestlings of many species of passerine birds. Other specimens of the subspecies _lepida_ show a varying amount of flaring, the least (in the series available) being in No. 24754, MNH, in which the proportion of the skull (length divided by width) closely corresponds to that in _Phainoptila_; the skull of No. 24754 is long and thin, and the base of the bill is only slightly swollen. The skull of _Phainopepla nitens lepida_ is more generalized than that of _Phainopepla n. nitens_, having a longer and narrower bill like the generalized _Phainoptila_. In _Phainopepla n. nitens_ and in members of the genus _Ptilogonys_, more flaring occurs in the antorbital region.

_Phainoptila_, as noted above, has no great amount of flaring in the antorbital region. When more specimens of _Phainoptila_ are examined, the base of the bill probably will be found to flare more in some individuals than in others; this would be expected if we may judge by the data on _Phainopepla_. The premaxilla and maxilla of _Phainoptila_ are similar to the same bones in _Dulus_, and there is a well-marked ridge on the tomium (possibly for cutting flower parts). In _Phainoptila_, the palatines are narrower than in any other genus of the family and abut the lacrimals. The entire skull appears to be modified along different lines from those of the skull of _Dulus_; the skull of _Phainoptila_ seems to be modified for a frugivorous rather than an insectivorous diet. The skull of _Phainoptila_ probably is more nearly similar to the ancestral skull than is that of any other living species in the family. The wide gape characteristic of some members of the family is undoubtedly a modification for aiding in the capture of insects, and _Phainoptila_ has progressed less in this direction than have other species in the family.

The mandibles vary somewhat in the shape and proportionate size of the bones. The mandible is proportionately, as well as actually, highest in _Dulus_. The medial condyle varies to some extent, being slightly flattened mediad in _Bombycilla_, and less so in the other genera. The mandible of _Bombycilla_ narrows to the symphysis much more gradually than it does in the other genera.

The antorbital plate is large and divides the orbital chamber from the nasal chamber. The small lacrimal bone anterior to the plate articulates with the maxilla and the premaxilla. Shufeldt (1889) states that the free lacrimal ossicle might be of some taxonomic importance in the passerines, since it is found in the generalized Corvids and in nestling Turdids. I find it well developed and identical, with a double articulation and free ends, in all the Bombycillids. There is no significant variability in the family, and this is more evidence of close taxonomic relationship between the members of the family.

The size of the crania is somewhat variable, although the differences seem to be primarily those of proportion. Ptilogonatinae have long crania, whereas the crania of the Bombycillinae and Dulinae are shorter but deeper. I regard the longer cranium as primitive, and it is longest in _Phainoptila_. In order of decreasing relative length of the cranium, _Phainoptila_ is followed by _Ptilogonys caudatus_, _P. cinereus_, and _Phainopepla_. _Bombycilla garrula_ has the deepest cranium in the family.