866 SHORT COMMUNICATIONS

The Condor 98:866-867 0 The CooperOrnithological Society 1996

FURTHER EVIDENCE OF PARASITISM OF CHOP1 BLACKBIRDS (GNORIMOPSAR CHOPI) BY THE SPECIALIZED (MOLOTHRUS RUFOAXILLARIS)’

ROSENKIM. FRAGA AsociacSn Ornitoldgicade1 Plats, 25 de Mayo 749, 2-6, 1002 BuenosAires, , e-mail: fragaQaorpla.org.ar

Key words: broodparasitism; specialization;Mol- between 26 November 1995 and 14 January 1996. In othrus rufoaxillaris; Gnorimopsar chopi; Argentina. the Iguazti area (mostly covered with subtropical hu- mid ), both Screamina Cowbirds and Chooi The Screaming Cowbird (Molothrus rufoaxillaris) is Blackbirds’were found onl; in extensive clearings the most specialized avian brood parasite within the around buildings, in particular in the airport and the New World icterineblackbirds (Friedmann 1929, 1963, nearby village where I made all the observations.I did Rothstein 1990). Throughout most of its range in Ar- not find Bay-winged Cowbirds, the regular hosts of gentina, ScreamingCowbirds parasitize a single host, ScreamingCowbirds, at IguazuAirport. A residentnat- the Bay-winged Cowbird Molothrus badius (Fraga uralist,A. Bosso(pers. comm.) hasnot seenBay-winged 1986).Chicks ofboth speciesshare a common plumage Cowbirds in the airport area since 1994. and similar calls (Fraga 1979, 1986, in press).Data on Vegetationin the village is mostly lawnsand gardens, mitochondrial DNA suggestthat host and parasiteare with planted youngpines and Ficus trees.At the airport not closerelatives (Lanyon 1992) and the resemblance village, ScreamingCowbirds foragedin lawns and gar- is probably mimetic. Screaming Cowbirds are some- bage dumps with Giant Cowbirds Scaphidura oryzi- times regardedas having a singlehost (Lanyon 1992). vora, or with Chopi Blackbirds.In two Ficus treesused Nevertheless,Sick (1985) showedthat ScreamingCow- for roostingI censused22 Chopi Blackbirdsand 6 adult at the northern (tropical) edge of their distribu- Screaming-Cowbirds(9 January 1996). tion in SoutheastBrazil parasitized another icterine, All Chopi Blackbird nestsin the village (n = 7) were the Chopi Blackbird (Gnorimopsar chop& Recently located in buildings, either under the eaves of roofs or Mermoz and Reboreda (1996) found evidence of in small windows, a habit reported since Spanish co- Screaming Cowbird parasitism of a third icterine lonial times (Azara 1802). The evidence for Screaming blackbird, the Brown-and-Yellow Marshbird (Pseu- Cowbird parasitism is as follows. On 26 November doleistesiirescens). Parasitism of this third host is rare; 1995 and 6 January 1996 I observed four visits of only a single ScreamingCowbird chick was reared out Screamme,Cowbirds to two Choui Blackbird nestsdur- of hundreds of nests examined by Mermoz and Re- ing 60 min of observations. bne or two pairs of boreda (1996) Screaming Cowbirds alighted on the roofs near the Sick (1985) believed that parasitism of Chopi Black- nests, and their behavior during the visits was noisy birds by ScreamingCowbirds evolved recently as the and conspicuous,as it is with their Bay-winged Cow- parasite invaded deforested areas of SoutheastBrazil hostselsewhere (Fraga 1986, in press).In all visits, and in the absenceof the usual Bay-winged Cowbird the ScreamingCowbirds were attacked and chasedby host. His data for Chopi Blackbirdssuggest a high fre- one or two Chopi Blackbirds.At least three other nests quency of ScreamingCowbird parasitism on this host: were visited by the parasites. in 1973 he found five Screaming Cowbird chicks in I checkedthe contentsof two nestsin January 1996 three Chopi Blackbird’s nestsin Rolandia. stateof Par- and found a brood of three feathered Chopi chicks in ana. Nevertheless,his record of parasitism lacked de- one, and two Chopi chicksand one ScreamingCowbird tailed information, was unique and could be regarded chick (all unfeathered, about 4 days old) in another. as having only local and transient importance, since This secondnest was revisited five days later when the Bay-wingedCowbirds invaded SoutheastBrazil by the three chickswere feathered.Unfeathered Chopi chicks early 1980 (Willis and Oniki 1985). Here I presentdata differ from Screaming Cowbird chicks in the hue of showing that Chopi Blackbirds are still effective hosts skin (yellowish vs. pinkish), and in bill color (blackish of ScreamingCowbirds in a locality in Northeast Ar- vs. pale pinkish, Fraga 1979). The plumage of Chopi gentina 4 10 km SW from the site reported by Sick, and chicks was entirely black, strikingly different from the comment on the importance and origin of this inter- brownish and rufous plumage ofthe ScreamingCow- action. bird chick. The beggingcalls of both speciesdid not Data were obtained at Iguazti Airport, Misiones differ as much (Fraaa 1986). consisting_ of reseated- se- Province, Argentina (25”45’S, 54’27’W) during 14 days ries of similar notes. I observed four groups of Chopi Blackbirds with fledgedchicks in the airport village; two were parasit- ized. One group consistedof a single Chopi adult and I Received 14 February 1996.Accepted28 June 1996. a ScreamingCowbird chick. The cowbird chick, still SHORT COMMUNICATIONS 867

in the mimetic Bay-wingplumage (Fraga 1986,in press), Blackbirds.This information would help to understand constantlyfollowed the adult Chopi, beggedfood from the evolution of host specializationin brood parasites. it and was fed four times in about 40 min. On 4 De- cember the ScreamingCowbird chick showed the first J. Anfuso shared information on Chopi Blackbirds. black blotches of the adult plumage in the scapulars A. Bossohelped in many ways during my study. Au- and back;this stageof postjuvenilemolt occursin chicks thorities at Iguazti Airport facilitated my work. Com- aged 3-4 days (Fraga, in press). The parasitic chick ments by J. C. Reboreda and S. Sealy improved the was fed by the single adult Chopi six times in 25 min. manuscript. On 7 January 1996 I observed a second parasitized LITERATURE CITED Chopi group with two ScreamingCowbird chicks and one Chopi chick, fed by 2-3 Chopi adults.The parasitic AZARA,F. DE. 1802. Apuntamientos para la historia chickswere seenduring the next week when they start- natural de 10spaxaros de1 Paraguayy Rio de la ed molting into black plumage. The non-parasitized Plata. Vol. 1. Imprenta de la viuda de Ibarra, Ma- Chopi groups consistedof two or three host chicks. drid. The observations confirm those of Sick and show FRAGA,R. M. 1979. Differences between nestlings that Screaming Cowbirds have been using Chopi and fledglingsof Screamingand Bay-winged Cow- Blackbirds as hosts in Southeast and extreme birds. Wilson Bull. 91:15 l-l 54. Northeast Argentina for more than 20 years. This in- FRAGAR. M. 1986. The Bay-winged Cowbird (Mol- teraction may also occur in nearby . When othrus badius) and its brood parasites: interac- read carefully, Azara’s (1802) account on the Chopi tions, coevolution and comparative efficiency. Blackbird suggeststhat parasitism occurredin Eastern Ph.D. diss., Univ. California, Santa Barbara. Paraguayduring Spanish Colonial times. Azara’s in- FRAGA, R. M. In press. The interactions of the par- formant (Father Noseda) described chicks obtained asitic Screamingand Shiny Cowbirds (Molothms from Chopi nests as having brown plumage with ru- rufoaxillaris and M. bon&iensis) with a shared fescent wing feathers, and molting in captivity into a host (Bay-winged Cowbird Molothrus badius). In glossy black plumage with rufous axillars. Only S. I. Rothstein and S. K. Robinson [eds.],Parasitic ScreamingCowbird chicks would fit this description, birds and their hosts.Oxford Univ. Press,Oxford. as realized by ornithologists commenting on Azara’s FRIEDMANN,H. 1929. The cowbirds. C. C. Thomas, work (Laubmann 1939, Pereyra 1945). Pereyra re- Springtleld,IL. garded Azara’s description as a mistake, but the data FRIEDMANN, H. 1963. Host relations of the parasitic presented here suggestotherwise. If correct, this old cowbirds. U.S. Natl. Mus. Bull. 223:1-276. recordargues against Sick ’s idea that parasitismof Chopi LAUBMANN, A. 1939. Die Vogel von Paraguay.Vol. Blackbirdsby ScreamingCowbirds evolved recently. 1. Streckerund Schriider, Stuttgart, Germany. Sick suggestedthat Screaming Cowbirds are para- LANYON, S. M. 1992. Interspecific brood parasitism sitizing Choui Blackbirds in the absenceof the usual in blackbirds(Icterinae): a phylogeneticapproach. Bay-wmgedCowbird host; this applies to his locality Science255~77-79. and my own. Nevertheless,Azara (1802) observedBay- MERMOZ, M. E., AND J. C. REBOREDA. New effective winged Cowbirds and Chopi Blackbirdsin EasternPar- host for the ScreamingCowbird. Condor 98:630- aguay;the first was scarce,and the second common. 632. In Northeast Argentina both hosts are often sympatric PEREYRA,J. A. 1945. La obra omit6logica de Azara. (pers. observ. at six localities in the provinces of For- Biblioteca Americana, Buenos Aires. mosa, Corrientes and Misiones). I saw Bay-winged ROTHSTEIN,S. I. 1990. A model system for coevo- Cowbirds (with ScreamingCowbirds) at Puerto Iguazti, lution, avian brood parasitism. Annu. Rev. Ecol. 15 km from the Iguazti Airport, in 1979; none were Syst. 21:481-508. observed there during this study. Further data would SICK, H. 1985. Omitologia brasileira, uma introdu- clarify whether the Screaming Cowbird-Chopi Black- cao. Universidade de Brasilia, Brasilia, Brazil. bird interaction occurs in the areas of sympatry with WILLIS, E. O., AND Y. ONIKI. 1985. Bird specimens Bay-winged Cowbirds. If so, data on the breeding suc- new for the state of Sao Paulo, Brazil. Rev. Brasil. cessof the parasitewith both hostsshould be obtained, Biol. 45:105-108. becauseSick ’s data and my own suggestgood survi- vorship of Screaming Cowbird chicks with Chopi