j. Field Ornithol., 55(1):104-107

RANGE EXPANSION OF THE SHINY IN THE DOMINICAN

BY WAYNEJ. ARENDTAND TOMkS A. VARGASMORA Postand Wiley (1977a) have reviewed the spreadof the ShinyCowbird (Molothrusbonariensis) within the last 100 years from northern through the LesserAntilles and into the Greater as far westas .This speciesis an obligatebrood parasitewith a wide hostspecificity (Friedmann 1963). Its parasitichabits and tolerance for disturbedhabitats have facilitated populationincreases throughout its traditional (South American) range as well as its extended range (Friedmann1929, Johnson 1967, Postand Wiley 1977a).Here we doc- ument further dispersalof cowbirdsbanded in the DominicanRepublic. We observed and banded from October 1976 to October 1978. Additional observationswere made in Augustof 1981 and 1982. Cowbirdswere observed in a varietyof habitatsranging from mangroves and thorn scrubto the edgesof broadleafforests. Because they feed heavilyon rice and grains,most cowbirds were seenin disturbedareas at or near rice fields,pasturelands, and livestockmanagement facilities. We capturedcowbirds in mist netsat 3 pig farms within 30 km of Santo Domingobetween 10 March and 13 May 1978. In additionto a USF& WS metal band, we attachedan orange plasticleg streamerat the time of banding. Observationsand band returns document the spreadof the throughout the DominicanRepublic and westwardfrom its previouslyrecorded range limits (Fig. 1). By 1973 Dod (in Post and Wiley 1977a) found cowbirdsas far westas Najayo (22 km SW of )in the southand Santiagoin the north. In 1977 we observed a male cowbird on to the south and near Monti Cristi in the extreme northwest. Small- to medium-sized flocks were observed alongthe north coastin 1981 and 1982. The cowbird'scontinued spread westwardis suggestedby the band recoverysome 130 km west of the banding site. Moreover, the collaborator reporting the band conveyedthat he had been plantingrice in that for 10 yr and had not observedthe speciesbefore 1978. He shot the becauseit was new to him. Although yet unreported,cowbirds are probablyin . ShinyCowbirds inhabit open countrywhich may extend from coastal areasto high elevationsdepending on the extent of habitat alteration and husbandrypractices in suchareas (Friedmann 1929, Post and Wiley 1977b).Many of the DominicanRepublic's diverse life zones are beingaltered at an alarmingrate, mainlybecause the country'smore than 4 million inhabitantsdepend on a shiftingagriculture subsistence (Organizationof American States1964). We sawextensive clearings at elevationsexceeding 1000 m in the Cordillera Central, Sierra de Bao- ruco, and the Los Haitises limestone karst hills (Fi•. 1). As more and

104 Vol.55, No. ] Rangeof the Shin)' Cowbird [ 105

N

Central •- •1•'•• ' amana Bay LosHait ises•'•--•../•"•.•

/X SantoDomingo -'•' 'tSierradeBaoruco ) • • ,• '--'y CARIBBEANSEA SaonaIsland 0 15 30 45 60 75Km

FIGURE1. Rangeexpansion of the ShinyCowbird in the DominicanRepublic: sightings and reported range as of 1975 (/x) (after Postand Wiley 1977a);cowbird sightings from 1977-78 and 1981-82 (&)eastto west:Saona Island, Saman/•, S/•nchez, , Cabrera, Sos6a,Jos• E. Bison6, Punta R6cia, Villa Vasquez, Monti Cristi; banding sites(O) southto north: Engombe,Santa Marta, Panarama;recovery sites (•) eastto west: Cabreta, , 1 km E of the Capital, 13 km N of the Capital, , La Ci•naga (6 individuals),, , 10 km SE of Neiba.

more land fallsunder ,cowbirds may spreadinto the interior mountains. We banded 196 cowbirds, 78 females and 118 males. Fourteen in- dividuals(7.1%) were recoveredat distancesup to 130 km (R = 25.8 km) from the bandingsites (Fig. 1). A female captured5 yr after banding only about 5 km from the banding site constitutesour longestreported survival. The second longest reported survival was that of a female recaptured 2 yr after banding also within 5 km of the banding site. Three other were recaptured3, 3, and 18 monthsafter banding within 5 km of their respectivebanding sites, suggestingthat some individualsmaintain at least a regional tenacity. This is further dem- onstratedby a subadultmale banded at the Engombepig farm on 7 August1982 and releasedin SantoDomingo 7 km awaylater the same day. It was the first capture at Engombethe following day. Banded cowbirdsdispersed in a northeasternor southeasterndirection (Fig. 1). This is not surprisingsince large expansesof low-lyingmarshy areas, 106] w. J. Arend!and T. A. VargasMora j. FieldOrnithol. Winter 1984

conduciveto the growing of rice, exist both to the NE ( and SamantiBay districts)and to the SE (coastaland central lowlands). The plastic leg streamerswere durable. We found streameredcow- birds feeding in the La Ci•naga rice fields 5 months after banding. A male cowbird that was recovered 30 km from its banding site 1.5 yr later still retained its leg streamer, as did the male captured 3 months after bandingnear Neiba, some 130 km from the banding site. Observationsand bandingresults suggest that Shiny Cowbirdshave an extendedbreeding season in the DominicanRepublic. Although the mean weight of femaleswas 38.2 g (n = 54), after 4 April femaleswere capturedthat weighedas much as48 g and exhibited distendedcloacal areas. A 45-g female trapped on 14 April containeda developedegg lackingonly the shell, indicatingthat many femaleswere ovulatingby early April and probablybefore. We observedadults in associationwith potential hostsfrom March to August.We found singingmales accom- panying femalesat active coloniesof the introduced(African) Village Weaver (Ploceuscucullatus) on 22 March 1977 (Punta R6cia) and on 1 April 1977 (La Jina de ).On SaonaIsland on 16 1977 we sighteda singingmale at an active weaver colonywhile its residents were away foraging. In 1978 we observeda female cowbird moving through an active colonyof the endemic (Dulus dulus) at the Panaramapig styon 29 March and an adult Black-cowledOriole (Icterus dominicensis)feeding a fledglingcowbird at the Engombesty on 25 April. Later that same year, near Stnchez on 10 July, we observedjuvenile cowbirdsmixed within flocksof foraging weavers,while adult cowbirds fed separately.Near Nizib6n (Miches),on 12 August 1978, we sighted juvenile cowbirdsmixed in with foraging weaverswhile, once again, adult cowbirdsfed separately.Cowbird eggshave recently been found in the nestsof the Village Weaver, Palmchat, and the Black-cowled Oriole (A. Cruz, pers. comm.). The weaver is an opportunisticbreeder, synchronizingits nestings with maturing rice cropsand rainfall (Hall 1970, Da Camara-Smeets 1982). We found activeweaver colonies in every month of the year. It would be reproductivelybeneficial for the parasiticcowbird to extend its breeding seasonto take advantageof this host year around. Many other introducedbirds are now found on West Indian islands. The House Sparrow(Passer domesticus), for example,is well established in the DominicanRepublic and is spreadingrapidly (pers.obs.). I have found activenests of this speciesin mid-August.The presenceof these exotics,many of which have extended reproductive seasons,may be expeditingthe spreadof the cowbird.In ,cowbirds parasitize many speciesincluding the introduced Troupial (Icterusicterus) and the Bronze (Hooded) Mannikin (Lonchuracucullata) (Cruz, pers. comm.). As more is learned about the Shiny Cowbird's specifichost-parasite rela- tionsand its reproductiveecology, we will better understandthe mech- anismsbehind its rapid range expansionin the DominicanRepublic and elsewhere in the area. Vol.•, No.I Rangeof the Shiny Cowbird [ 107

SUMMARY Band recoveriesand observationsdocument the continuedrange ex- pansionof the ShinyCowbird (Molothrusbonariensis) in the . Its tolerance for disturbed habitats together with the introduction of exotic host specieswith extendedbreeding seasonsmay be expediting the spreadof this generalistand obligatebrood parasitein the Domin- ican Republicand throughout its northern range.

ACKNOWLEDGMENTS Our sincerethanks go to Alex Cruz for his encouragementin the initial writing of this paper. Angela Arendt and Guy Nakasuassisted in the field work. John Faaborg, William B. Robertson,Jr., Jared Verner, Jamesw. Wiley, and an anonymousreviewer provided many helpful suggestionson earlier drafts of the manuscript.The following institu- tionssupplied equipment and logisticand technicalsupport: U.S. , SmithsonianEnvironmental Program, and the Santo Domingo Natural History Museum.Annabelle Dod kindlyoffered her knowledge of specificsites of cowbird concentrations.

LITERATURE CITED

BONI•,J. 1979. Birdsof the West Indies.Fourth edition.Collins, St. James's Place, London. DA CAMARA-SMEETS,M. 1982. Nestingof the Village Weaver Ploceuscucullatus. Ibis 124: 241-251. HALL, J. R. 1970. Synchronyand socialstimulation in coloniesof the Black-headed Weaver Ploceuscucullatus and Vieillot's Black Weaver Melanopteryxnigerrimus. Ibis 112:93-104. FRmI•MANN,H. 1929. The cowbirds,a study in the biology of socialparasitism. C. C Thomas. Springfield,Illinois. 1963. Host relationsof the parasiticcowbirds. U.S. Natl. Mus. Bull. 233. JOHNSON,A. W. 1967. The cowbirdsof . Platt EstablecimientosGraffcos S.A., Buenos Aires. ORGANIZATIONOF AMERICANSTATES. 1964. America: problemsand perspectives of economicdevelopment. Pan American Union, Department of EconomicAffairs. Baltimore,Maryland. POST,W., ANDJ.W. WILEY. 1977a. The Shiny Cowbirdin the West Indies. 79: 119-121. --, ANI) --.. 1977b. Reproductiveinteractions of the Shiny Cowbird and the Yellow-shouldered Blackbird. Condor 79:176-184. U.S. Departmentof Agriculture,Forest Service, Institute of TropicalForestry, P.O. Box AQ.2 Rio Piedras,Puerto Rico 00928, and Departamentode Vida Silvestre,Secretaria de Agricultura,Santo Domingo, Repffblica Dominicaria. Received1 Dec. 1982; accepted7 Sept. 1983.