The Relationships of the Silky Flycatchers

THE RELATIONSHIPS OF THE SILKY FLYCATCHERS CI-IARLES G. SIBLE¾ THE silky flycatchersinclude the generaPtilogonys, Phainopepla, and Phainoptila,which are usuallytreated either as a family, Ptilogonatidae (e.g. Wetmore 1960), or as a subfamily of the waxwing family Bomby- cillidae (e.g. Greenway1960). Someauthors have includedthe Palm Chat (Dulus dominicus)of Hispaniola and the Grey Hypocolius (Hypocolius ampelinus) of Iraq and Iran in the Bombycillidae (Arvey 1951, Mayr and Amadon1951). Othershave consideredsome of theseallocations to be tentative or unproved and have recognizedseparate families for some or all of these groups (e.g. Wetmore 1960, Greenway 1960). The silky flycatchersare confinedto North and Central America. The Phainopepla(Phainopepla nitens) occursin the arid and semiaridregions of the southwestern United States and in Mexico south to Puebla and Vera Cruz. The Gray Silky Flycatcher (Ptilogonyscinereus) is a montane speciesranging from northwesternand easternMexico to Guatemala. The Long-tailedSilky Flycatcher(P. caudatus)and the Black-and-yellowSilky Flycatcher (Phainoptilamelanoxantha) are eachendemic to the highlands of Costa Rica and western Panama. This paper reviews some of the taxonomichistory and charactersof the silky flycatchersand presentsnew evidencefrom studies of the egg- white proteins indicating that they are closely related to the genus Myadestes,the solitaires,of the thrushfamily Turdidae. The two species of the genusEntomodestes of northwesternSouth America may be part of this natural cluster,but their egg whites have not been available for comparison. TAXONOMIC H•STOR¾ or THE S•LK¾ FLYCATCHERS AND A•;L•ES Ptilogonyscinereus, the first of the group to be discovered,was described by Swainsonin 1824. Swainsonalso describedthe Phainopepla (1837), which he placed in Ptilogonys. From the time of their discovery these birds were consideredto be closelyrelated to the waxwings. Gray (1846) placedthem near the waxwingsbecause of similaritiesin bill shape,tarsal scutellation,plumage texture, and the possessionof a crest. But there also are differences. Phainopepladiffers from Bombycilla in having a long tenth primary (vs. a rudimentaryone), a roundedwing (vs. a long, pointedwing), long rictal bristles(vs. the obsoletecondition), unfeathered nasal fossae (vs. denselyleathered), downy nestlings (vs. naked), and unstreakedjuvenal plumage (vs. streaked). Thus those who advocated placementin separatetaxa alsohad a basisfor their opinion. 394 The Auk 9o: 394410. April 1973 April 1973] Silky FlycatcherRelationships 395 Baird (1858) proposedthe genusPhainopepla for Swainson'sPtilogonys nitens, an arrangementthat has since been acceptedwithout debate. The associationof Myadesteswith the waxwingsand silky flycatchers was apparently first challengedby Baird (1864-72: 417-433) who advocated the tranfer of Myadestes from its "usual associationwith Ptilogonys,among Ampelidae [= Bombycillidae],to, or at least very near, the Turdidae." Although Baird noted the "close resemblancein generalappearance" between Myadestes and Ptilogonyshe traceda series of links that showedthe alliance of Myadestes to the typical thrushes. Baird proposedthe subfamily"Myiadestinae" to include "Myiadestes... Cichlopsis...Platycichla...the latter genus is so closelyrelated to Cichlopsisas almost to be the same; Platycichla forming the link with with Turdinae through Planesticus,while such speciesas Myiadestes unicolorshow the affinities of Cichlopsisto Myiadestes." Coues'treatment of the problemprovides an indicationof the transition of taxonomic opinion from the older view of Myadestes as a relative of Phainopeplato the new alliance with the thrushes. In the first edition of his "Key" Coues(1872) includedPhainopepla and Myadestesin the waxwing family (Ampelidae), but noted that Baird had separatedthem and that this coursewas possibly correct. In the "Birds of the Colorado Valley" (1878) Couesadopted Baird's arrangementand placedMyadestes with the thrushes.Then, in later editionsof the "Key" (e.g. 1887), he recognizedthe subfamily"Myiadestinae" but placedit in the "Ampelidae," followingthe Ptilogonatinae,and stated that althoughMyadestes townsendi "was formerlycalled 'Ptilogonys', it has nothingto do with the foregoing subfamily. The Myiadestinae are in fact nearly related to the Turdidae." Seebohm(1881) left Myadestescompletely out of the Turdidae and Sharpe(1883) includedthe genusin the Timaliidae,noting (p. 368) that this was an unsatisfactoryarrangement but that he "placed them near the Mocking-Thrushes[= Mimidae], which they resemblein the power of song."Seebohm defined the Turdinae primarily on the basisof the booted tarsus and spotted juvenal plumage, a definition relied upon to the present day. Stejneger (1883) praised Seebohm'sdefinition of the Turdinae, but was "provoked by the arrangementproposed." As a reply Stejneger presenteda reviewof the systematicsof the American thrushesin which he adoptedBaird's proposalconcerning Myadestes. But one speciesdid not fit the definitionand Stejnegerdecided that "the groupwill not, however, be naturally limited or clearly defined without removing the species Myadestesleucotis (Tschudi), which is widely different, from the Mya- destinae, being a true member of the Ptilogonatidae." Stejneger then 396 C•^•z•s G. Smz• [Auk, Vol. 90 proposedthe new genus Entomodestesfor M. leucotis and assignedit to the silky flycatchers. An important factor in this decisionseems to have beenthat Stejnegerhad found the tarsusof leucotisto be faintly scutellate anteriorlywhereas Baird had thoughtthat it was "without distinctscutellar divisionsanteriorly, except below" (Stejneger 1883: 457). Thus by applying Seebohm'sdefinition, Stejnegerfelt obliged to separateleucotis from the thrushes. Although Entomodesteslater was replacedin the thrushes (Ridgway 1904, Ripley 1964), Myadesteswas not again consideredto be a relative of the silky flycatchers. The Seebohmdefinition, supportedby Baird, Coues,Stejneger and others,precluded the associationwith the thrushesof a specieswith a scutellatetarsus. But that a relationshipexisted between the waxwingsand silky flycatcherswas not challenged,and they continued to be placedtogether. Lucas (1894) noted that Phainopeplaand Ampelis (= Bombycilla) are alike "in the palatal regionand both possessa large, free, swollen lachrymal,this last beinga point of muchimportance, since such a lachrymal is of rare occurrenceamong birds." According to Beecher (1953) freelachrymals are alsopresent in (at least) somecorvids (Cissa), Oriolus, Paradisaea, Ailuroedus, Callaeus, Pericrocotus, .Cracticus, Artamus, Laniarius, Vanga, Prionops,Aegithina, and Sitta. Lucas (1894) alsofound that "the quadratesof Ampelisand Phainopepla agreewith eachother in minute as well as generalcharacters, as do also the pneumatic maxillo palatines." This last point is of special interest becausethe thrushes,including Myadestes, also have maxillo-palafines with inflated ("pneumatic") tips. Lucas noted further that Phainopepla and the waxwingsagree in the general contour of the dorsal feather tract, but this has little or no taxonomicsignificance for Mary H. Clench tells me that nothing in their pterylosesdistinguishes between thrushes, waxwings, silky flycatchers,and several other passerinegroups. Lucas (1894: 310) also stated that "the skull of Myadestesis rather short,and on its superioraspect bears a considerableresemblance to that of Ampelis." It follows that the skulls of Myadestes and Phainopepla shouldbe similar,and examinationshows that they are. It is curiousthat Lucas stated (p. 311) that "Myadestes . has a flat non-pneumatic maxillo-palatine." This is certainly incorrect for I have examined these bonesin Myadestes,Phainopepla, and Bombycillaand all three have an inflated,hollow, i.e. "pneumatic"tip. Thoseof Myadestesand Phainopepla are more alike than either is like that of Bombycilla. It is possiblethat Lucas' specimenof Myadestes was damagedand that this similarity there- fore escapedhis notice. His Figure 10 (p. 311) showsthe palatal region April 1973] Silky FlycatcherRelationships 397 of Myadesteswith the tip of one of the maxillo~palatinesmissing, but the otherseems to be intact. Lucasconcluded (p. 311) that although Myadestes"has someleanings toward the Ampelidaeit seemsto have more decidedaffinities with the thrushes,although it is by no meansa typical thrush." Ridgway (1904) recognizedthe families Ampelidae,Ptilogonatidae, and Dulidae and consideredthem allied to one another. Concerningthe silky flycatchershe stated(pp. 113-114) that "they are relatedto the Waxwings(family Ampelidae),and have usuallybeen placed with them; but they differ in their roundedwings, with well-developedtenth and short- enedninth primaries,their well-developedrictal bristlesand differentchar- acter of the frontal feathers.Their habits,however, are said to be very similar." The statementabout similar "habits" presumably referred to the fact that both groupseat fruit and insectsand have somewhatsimilar nests. In his diagnosisof the PtilogonatidaeRidgway (1904:113) noted that in adultsof Phainoptila(Salvin 1877) the acrotarsiumis not distinctly scutellateand that "the genusPhainoptila is doubtfullya memberof this group,and as far as the adult is concernedmight easily be referredto the Turdidae without materially affectingthe diagnosisof the latter family; but the younghave the plumageabsolutely plain-colored and the acro- tarsium distinctly scutellate." Ridgwaywas not consistentin his applicationof the Seebohmdefinition

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