392 ShortCommunications [Auk,Vol. 105 The Relationship BetweenHylocichla and Catharus(Turdinae) KEVIN WINKER• AND JOHN H. RAPPOLE2 •BellMuseum of NaturalHistory, University of Minnesota,10 ChurchStreet SE, Minneapolis,Minnesota 55455 USA, and 2CaesarKleberg Wildlife Research Institute, Texas A&I University, Kingsville,Texas 78363 USA The relationshipof the Wood Thrush (Hylocichla vocalizationand the "upwar•t," "horizontal stretch," mustelina)to the Catharus thrushes has been debated and foot-quivering displays in H. mustelinacaused for well over 30 years (Table 1). Dorst (1950: 222) Dilger to consider the speciesseparate from the rest rejectedthe genusHylocichla and includedthe species of the Nearctic group. It appears,however, that most then in that group with Turdus.He called this the T. of these behavioral traits are held in common (Table mustelinusgroup, which, with Hylocichlamustelina, in- 2), and that continuedseparation on a behavioralbasis cludedthe North AmericanCatharus thrushes, C. gut- is no longer justified. tatus,C. fuscescens,C. minimus,and C. ustulatus(A.O.U. In placing Hylocichlamustelina closer to the genus 1983). His decisionwas basedlargely on the super- Turdusthan to Catharus,Dilger listed only one display ficial resemblance between the Wood Thrush and the held in common between the American Robin (Turdus EuropeanSong Thrush (Turdusphilomelos). As Ripley migratorius)and the Wood Thrush, and mentioned (1952: 17) pointed out, these similarities are not com- that these speciesboth use mud in nest construction pelling to those who are familiar with the different and vigorously defend their nests.The four Catharus behaviorsof the two species. speciestypically do neither. It is now recognized that Ripley (1952) further statedthat the entire group socialdemeanor can be widely different in closerel- of hylocichlids,which at the time included the North atives (McKinney 1978: 7). Dilger treated both body American Catharus thrushes, should be considered proportion and foraging differences between Turdus congenericwith the Neotropical group of Catharus andHylocichla lightly. His beliefthat the WoodThrush thrushes, and that the older name of Catharus should was more closely allied with Turduswas supported be usedfor the entire group.He basedhis reasoning by Bourns(1967), who, using serologicaldata, placed on the similarity in habitsand body proportionsof H. mustelinavery close to T. migratorius. the membersof the two groups. In contrast, Hendrickson and Yow (1973), using Dilger (1956a-c) made a strong casefor the sepa- electrophoresison blood proteins,concluded that H. ration of Hylocichlamustelina from the four speciesof mustelinais closely allied with the Catharusthrushes North American Catharusthrushes. His opinion was and quite distant from T. migratorius.Gibson et al. that it should remain provisionallythe type species (1976) criticized Bourns (1967) and Hendrickson and of its own monotypic genus, but that further work Yow (1973), citing the unproved value of each of the would probably ally it with the genus Turdus(Dilger two methods in showing evolutionary change and 1956c).This conclusionwas basedprimarily on be- the incompletenessof their data bases.Gibson et al. havioral posturesand callsthat distinguishthe Wood (1976) compared49 skeletalcharacters and found that Thrushfrom the four Catharusspecies (fuscescens, gut- the Wood Thrush formed a distinct group from both tatus,ustulatus, and minimus)on the breeding grounds. Catharusand Turdus.They concludedthat the Wood In the rain forest of southern Veracruz, Mexico, Thrush shouldretain its statusas Hylocichla. We ques- Wood Thrushes holding individual subsistenceter- tion whether the degree of distinctivenesswarrants ritoriesduring the winter monthsuse two of the ag- such a conclusion, however. gressivebehavioral postures and a call note that Dil- It is apparent from Gibson et al.'s (1976) principal get (1956a, b) found conspicuouslyabsent in the componentsanalysis and bivariate scatterplot that, specieson its breeding grounds in New York state. althoughH. mustelinaappears unique when compared The "upward" and "horizontal stretch" posturesare with the NearcticCatharus species, its relative distance both present on these wintering grounds, as is the from that group is no greater than the distance be- "zeep" vocalization (Rappole and Warner 1980, tween the Song Thrush and the Eurasian Blackbird Winker 1988; terminology follows Dilger 1956a).In (T. merula)in the samecomparison. We questionthe addition to these behaviors, Willis (1966: 199) record- separationof the Catharus-Hylocichlagroup, obviously ed in H. mustelinaboth a "sleeked posture" in a sub- closely related, basedsolely on the lack of interme- ordinate bird and a foot-quivering display on Barro diate forms. Other characteristics should be assessed Colorado Island, Panama. Neither of these behaviors in such a decision. was noted for the speciesby Dilger (1956a,b) on the We found that the display repertoiresof Hylocichla breeding grounds.The presenceand absenceof these and Catharuswere similar. Electromorphanalysis (Av- displaysvaries in H. mustelinaand the four Nearctic ise et al. 1980) indicatesthat the relationship is close Catharusthrushes (Table 2). The absenceof the "zeep" phenetically and cladistically, as well. Avise et al. April 1988] ShortCommunications 393 TAELE1. Summary of work on the generic alignment of the Wood Thrush. Author(s) Alignment Basedon Dorst (1950) Turdus External resemblance Ripley (1952) Catharus Similaritiesin proportionsand habits Dilger (1956a-c) Hylocichla-Turdus Behavioral differences from Catharus Bourns (1967) Turdus Serologicalwork Hendrickson and Yow (1973) Catharus Blood proteins Gibson et al. (1976) Hylocichla Osteologicalwork Avise et al. (1980) Catharus-Hylocichla Electromorphic proteins Corbin (in press) Catharus Statistical treatment of the data of Avise et al. (1980) (1980) useda much larger data basethan Hendrickson LITERATURE CITED and Yow (1973). They concluded that "data are now overwhelming in support of close evolutionary re- AMERICAN ORNITHOLOGISTS' UNION. 1983. Check-list lationshipsbetween Hylocichlamustelina and the Ca- of North American birds, 6th ed. Washington, tharusspecies examined" (Avise et al. 1980).They did D.C., Am. Ornithol. Union. not comment on whether Hylocichlashould retain AVISE, J. C., J. C. PATTON, & C. F. AQUADRO. 1980. separategeneric status.Corbin (in press)reanalyzed Evolutionary genetics of birds 1. Relationships these data with a multivariate statistical technique among North American thrushesand allies. Auk calledTaxon Cluster Analysis. He found a very strong 97: 135-147. relationship between the two genera and concluded BAIRD, S. F. 1864. Rev. Am. Birds 1: 12. that "the monotypic genus Hylocichla should be BOURNS,T. K. R. 1967. Serological relationships merged with Catharus." among some North American thrushes. Can. J. We believe that Hylocichlamustelina is not unique Zool. 45: 97-99. enough to warrant separategeneric status. The Wood CORBIN,K. W. In press. The use of genetic infor- Thrush should be considered Catharus mustelinus,and mation in avian systematics.In Proc. Segundo the genus Hylocichla(Baird 1864) should be laid to Congr. de Ornitologia Iberoamericana.Decem- rest with the other thrush genera abandoned since ber 1983. Xalapa, Mfixico, INIREB. their conceptionin the late 1800's (listed by Dorst DILGER,W. C. 1956a. Hostile behavior and repro- 1950: 217-218). ductiveisolating mechanisms in the avian genera The field observationsin this paper were collected (Catharusand Hylocichla.Auk 73: 313-353. while under the supportof the World Wildlife Fund, 1956b. Adaptive modificationsand ecolog- U.S., and the Instituto Nacional de Investigaciones ical isolating mechanismsin the thrush genera sobre Recursos Bioticos, Mexico. Catharusand Hylocichla.Wilson Bull. 68: 171-199. 1956c. Relationshipsof the thrush genera Catharusand Hylocichla.Syst. Zool. 5: 174-182. DORST,J. 1950. Considerationssystematiques BUr les TABLE2. Displays of Hylocichlaon wintering and grives du genre Turdus.Oiseau 20: 212-248. breeding grounds comparedwith those of Catharus GIBSON,A. R., M. A. GATES,& R. ZACH. 1976. Phe- on the breeding grounds. netic affinities of the Wood Thrush, Hylocichla Hylocichla Catharus mustelina(Aves: Turdinae). Can. J. Zool. 54: 1679- 1687. Behavior a Winter b Breeding½ Breedingc HENDRICKSON,H. T., & M. YOW. 1973. The relation- Wing/tail flicking x x x shipsof the Wood Thrush (Hylocichlamustelina): Crest raising x x someindications from the electrophoresisof blood Spread x x proteins. Condor 75: 301-305. Horizontal fluff x x MCKINNEY,F. 1978. Comparativeapproaches to so- Horizontal stretch x -- x cial behaviorin closelyrelated speciesof birds. Upward x -- x Adv. Study Behav. 8: 1-39. "Zeep" call x -- x Foot quivering x a _ x RAPPOLE,J. H., •r D. W. WARNER.1980. Ecological Sleeked posturea x -- aspectsof migrant bird behavior in Veracruz, M•xico. Pp. 353-393in Migrant birdsin the Neo- aDilger (1956a). bRappole and Warner (1980), Winker (1988). tropics:ecology, behavior, distribution, and con- ßDilger (1956a). servation (A. Keast and E. S. Morton, Eds.). Wash- dWillis (1966). ington D.C., Smithsonian Inst. Press. 394 ShortCommunications [Auk, Vol. 105 RIPLEY, $. D. 1952. The thrushes. Postilla 13: 1-48. racruz, Mexico. Master's thesis, Minneapolis, WILLIS,E.O. 1966. The role of migrant birdsat swarms Univ. Minnesota. of army ants. Living Bird 5: 187-231. WINKER, K. 1988. The Wood Thrush (Catharus mus- Received2 November1987,