Symposium Participants
Rosendo Fraga
Manomet Center for Conservation Sciences
Guyra Paraguay
Cnel. Franco No. 381 c/ Leandro Prieto
Asunción, Paraguay
Telefax: (59521) 227.777/229.097
Icterid Blackbirds as Austral Migrants
The scale of icterid migration within South America seems modest, involving mostly a few species in the Southern Cone ( particularly those breeding in Chile and Argentina). There is no seasonal withdrawal of any such species from most of their breeding ranges, suggesting partial migration. The small scale of the seasonal movements implies that evidence for movements is difficult to obtain. The only official program of bird banding in the region (Instituto Miguel Lillo, Tucumán, Argentina; see Lucero 1982) has not been as extensive as desired.
SHINY COWBIRD Molothrusbonariensis
Hudson (1870) and H. Friedmann (1929) regarded Shiny Cowbirds as partially migratory in Central Argentina. During a study of Shiny Cowbirds at Estancia La Candelaria (35º15´S, 59º13´W), Buenos Aires Province, I censused cowbirds at major roosting sites (clumps of bamboo and other evergreens) during seven years (1972-1979) (Fraga 1985). I found a regular seasonal change in numbers. The local breeding season (based on the dates were eggs were first observed) covered the period from 26 September to 7 February. Almost no adult cowbirds were seen at La Candelaria (roosts or everywhere) from mid-February to the first week of March. By mid-March there was a marked increase in numbers, and throughout fall and winter up to about 500 cowbirds were using the roosts. Numbers declined again to 30-40 individuals in late September and early October, at the start of the breeding season. The data suggest a pattern of seasonal population replacement. I also color-banded 53 adult Shiny Cowbird at La Candelaria, and those banded in winter were not observed during the breeding season.
The Shiny Cowbird populations breeding along the Andes in southern Argentina (Neuquén and Chubut provinces) dissapear duing the austral winter (H. Matarazzo, pers. com.) A Shiny Cowbird banded in winter in Córdoba province (Tigre Muerto) was recovered 700 km. southward in spring (Mainque, Río Negro Province, ) giving additional support to the hypothesis of seasonal movements (Lucero 1982).
YELLOW-WINGED BLACKBIRD Agelasticusthilius
The best evidence for partial migration in this icterid comes from records obtained in northeastern Argentina and Paraguay. Hayes et al. (1994) mentioned that thee few sight records from Paraguay are all from the austral winter (July to the first week of September). The same applies to the few records from the Argentinian provinces of Chaco and Formosa (e.g. Wetmore 1926), and the extreme north of Corrientes. The northern limits of the blackbird´s breeding range in Argentina are not well known; available data suggests northern Santa Fe province (De la Peña 1997), and perhaps the Iberá marshes in Corrientes (Fraga 2001) and the Bañados de Figueroa in Santiago del Estero (Nores et al. 1991). Much more information on the seasonality, numbers and breeding status of this blackbird in northern Argentina is needed.
In western and southern Argentina populations of Yellow-winged Blackbirds show either a marked decline in winter (Blendinger and Alvarez 2002, Laguna Llancanelo, southern Mendoza) or even dissappear (Santa Cruz province, S. Imberti com.pers.).
The Yellow-winged Blackbird has a distinctive and isolated subspecies (alticola) breeding in the highlands of Bolivia and Peru (Jaramillo and Burke 1999); this population may have evolved from austral migrants.
SAFFRON-COWLED BLACKBIRD Xanthopsarflavus
Two old sources suggested that some extinct populations of this species in Buenos Aires province (Argentina) could be migratory: Barrows (1883) and Holland (1893). The evidence presented by both authors is very weak. Barrows interpreted an April flock observed during one day at Pigué (SW Buenos Aires) as pre-migratory. Holland also suggested that the populations at Estancia Santa Elena, in W Buenos Aires, could migrate to the region of the Río de la Plata. All surviving populations of this icterid are resident (Fraga et al. 1998).
MEADOWLARKS (Sturnellaloyca and S. defilippi).
I could not find convincing evidence of partial migration for the Long-tailed Meadowlark S. loyca, although this icterid has breeding populations as far south as the Falklands/Malvinas and Tierra del Fuego (Jaramillo and Burke 1999). The Pampas Meadowlark S. defilippi has been considered a migrant mostly by Hudson (1870, 1920), who witnessed large flocks traveling north-south across the pampas. Recent evidence (Tubaro and Gabelli 1999) shows, however, that migration in this icterid is partial.
Altitudinal and Irregular Movements
Mountain populations of Long-tailed Meadowlark S. loyca (breeding range up to 3100 m) appear to have regular altitudinal movements (Nores 1996). J. Mazar Barnett (pers. comm.) observed flocks of Golden-winged Caciques Cacicuschrysopterus performing altitudinal movements at Parque Nacional Calilegua, Jujuy, Argentina.
Partial migration in response to regular dry seasons occur in the Scarlet-headed Blackbird Amblyrhamphusholosericeus, a very specialized marsh icterid that finds food mostly by gaping into the stems of green marsh plants. During the dry season (austral winter) only a few remain in the dessicated wetlands of the Western Chaco. Irregular movements in response to unusual and severe ambiental changes occur in sthis and other marsh icterids. During severe draughts (e. g. the fall of 1997, during a La Niña episode) only a few Scarlet-headed Blackbirds remained in one of its strongholds, the Paraná River Delta in Argentina. During that period most of the vegetation in the delta remained parched and dry. Conversely, during wet El Niño episodes icterids breeding in marshes or wet meadows may occur out of their regular ranges.
References
Barrows, W. B. 1883. Birds of the lower Uruguay. Bulletin Nuttall Ornithological Club 8:82-143.
Blendinger, P., and M. E. Alvarez. 2002. Ensambles de aves de los bañados de Carilauquen (Laguna Llancanelo, Mendoza, Argentina): consideraciones para su conservación. Hornero 17:71-83.
De la Peña, M. R. 1997. Lista y distribución de las aves de Santa Fe y Entre Ríos. Literature of Latin America, Buenos Aires.
Doering, A., and P. G. Lorentz. 1939. La conquista del desierto: diario de los miembros de la Comisión Científica de la expedición de 1879. Comisión Nacional Monumento al Tte. Gral. Julio A. Roca, Buenos Aires.
Fraga, R. M. 1985. Host-parasite interactions between Chalk-browed Mockingbirds and Shiny Cowbirds. Neotropical Ornithology, Ornithological Monograph 36: 829-844, American Ornithologist's Union.
Fraga, R. M., H. Casañas and G. Pugnali. 1998. Natural history and conservation of the endangered Saffron-cowled Blackbird Xanthopsarflavus in Argentina. Bird. Conservation International 8: 255-267.
Fraga, R. M. 2001. The avifauna of Estancia San Juan Poriahú, Iberá Marshes, Argentina. Cotinga 16:81-86.
Friedmann, H. 1929. The cowbirds. C. C. Thomas, Springfield, Illinois.
Holland, A. H. 1893. Letter on migration in the Argentine Republic. Ibis 1893: 483-488.
Hayes, F. E., P. A. Scharf and R. S. Ridgely. 1994. Austral birds migrant in Paraguay. Condor 96: 83-97.
Hudson, W. H. 1870. Letters on the ornithology of Buenos Ayres. Reprinted (1951) by D. Dewar. Cornell University Press.
Hudson, W. H. 1920. Birds of La Plata. J. M. Dent, London, UK.
Jaramillo, A., and P. Burke. 1999. New World blackbirds. The Icterids. A. & C. Black Publishers, London .
Lucero, M. M. 1982. El anillado de aves en la República Argentina. Miscelánea No. 74, Fundación M. Lillo, Tucumán, Argentina.
Nores, M., D. Yzurieta and S. Salvador. 1991. Lista y distribución de las aves de Santiago del Estero, Argentina. Boletín Academia Nacional Ciencias (Córdoba) 59: 157-196.
Nores, M. 1996. Avifauna de la Provincia de Córdoba. Pp. 255-337 in I. E. Di Tada & E. Bucher, (eds.) Biodiversidad de la Provincia de Córdoba, Voumen 1. Universidad Nacional de Río Cuarto, Río Cuarto, Argentina .
Tubaro, P. and F. Gabelli. 1999. The decline of the Pampas Meadowlark: difficulties of applying the IUCN criteria to Neotropical grassland birds. Studies in Avian Biology 19: 250-257.
Wetmore, A. 1926. Notes on the birds of Argentina, Paraguay, Uruguay and Chile. Bulletin of the United States National Museum 133: 383-388.
