View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by CONICET Digital SHORT COMMUNICATIONS ORNITOLOGIA NEOTROPICAL 19: 299–303, 2008 © The Neotropical Ornithological Society NOTES ON THE NESTING OF CHOPI BLACKBIRDS (GNORIMOPSAR CHOPI) IN ARGENTINA AND PARAGUAY, WITH DATA ON COOPERATIVE BREEDING AND BROOD PARASITISM BY SCREAMING COWBIRDS (MOLOTHRUS RUFOAXILLARIS) Rosendo M. Fraga CICYTTP, Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Matteri y España, (3105) Diamante, Entre Ríos, Argentina. E-mail: [email protected] Notas sobre la nidificación del Chopí (Gnorimopsar chopi) en Argentina y Paraguay, con datos de cría cooperativa y de parasitismo de cría por el Tordo Pico Corto (Molothrus rufoaxillaris). Key words: Chopi Blackbirds, Gnorimopsar chopi, nesting, cooperative breeding, Screaming Cowbird, Molothrus rufoaxillaris. The Chopi Blackbird (Gnorimopsar chopi) is an northeastern Argentina (Corrientes and Mis- icterid endemic to South America (Jaramillo iones provinces) and Paraguay, between 1995 & Burke 1999) and a member of the South and 2007. My data show this icterid to be a American quiscaline clade, a monophyletic cooperative breeder (Brown 1987), as individ- group defined by DNA data (Johnson & uals other than a single pair aid in chick care. Lanyon 1999, Cadena et al. 2004). This icterid Also, I add further information on its host- is found from northeastern Brazil and south- parasite interactions with Screaming Cow- eastern Peru to northern Argentina and Uru- birds (Molothrus rufoaxillaris) in Argentina and guay (Jaramillo & Burke 1999). It is usually Paraguay (Sick 1985, Fraga 1996). subdivided into three subspecies with consid- I obtained most of my information on erable variation in body size (Jaramillo & Chopi Blackbirds while carrying field research Burke 1999), but only the nominate subspe- on endangered grassland birds from eastern cies occurs in eastern Argentina and Paraguay. Argentina and Paraguay (Fraga 2005). Chopi Few first hand reports on the natural history Blackbirds were easy to detect by their loud and breeding behavior of Chopi Blackbirds songs and other vocalizations, and nested in exist (Azara 1802, de la Peña 1987, Sick 1993, the open habitats I surveyed. Observation Fraga 1996, Di Giacomo 2005), and only two times for each breeding pair or group ranged nests have been described from Paraguay from 45 to 180 min, but subsequent visits to (Dalgleish 1899). I present here new informa- the nests were often impossible. Chopi Black- tion obtained from 12 nests observed in birds are sexually monomorphic in plumage. 299 FRAGA Body mass data from two male and two 2005). None of my nests were in palm groves, female specimens (American Museum of and all were apparently solitary, with a mini- Natural History, New York) collected in mal distance of 60 m between simultaneous Puerto Valle (Corrientes) give values of 73.8 nests (Appendix 1). Moreover, nests 1 and 9 and 74.1 g (mean 73. 9 g) for males, and 68.5 were located in isolated trees in extensive pas- and 70.8 g (mean 69.6 g) for females. Because tures or agricultural fields. of this small size dimorphism the sexes could I observed agonistic interactions between not be separated in the field. As no individu- nesting pairs and other conspecifics at four of als were banded, the group size I report for the nine nests found before egg hatching. The each nest was the maximum number of indi- interactions involved some chasing and sup- viduals simultaneously observed. The planting, with most individuals singing. My exposed location of most nest sites facilitated observations suggest that Chopi Blackbird behavioral observations, supplemented with nests were attended by single pairs during the the help of tape recordings. earlier stages of the nesting cycle. Chopi Blackbirds avoid dense unbroken By contrast, group size in the three nests forests, being found in large clearings, open containing chicks ranged from five to six indi- woodland, savannas and palm groves. viduals. Group members often perched in the Although locally common, this icterid has a same branch and no intraspecific aggression rather patchy distribution in Argentina, and is was observed. At nest 10, only two individu- more evenly distributed in eastern Paraguay. als brought food simultaneously but, because Chopi Blackbirds foraged mostly on the of the small size of the delivered prey (green ground, and were usually found in groups of carterpillars), possibly the chicks were 5–22 individuals. Chopi Blackbirds showed recently hatched. Other three individuals usu- conspicuous sentinel behavior, with one or ally perched within 20 m of the nest without two individuals perching on lookouts (trees, any visible antagonism, and on two occasions poles or buildings) while the group foraged. the five blackbirds attacked a Yellow-headed As in Baywinged Cowbirds (Agelaioides badius) Caracara (Milvago chimachima) that flew above a descending high-pitched whistle was used as the nest tree. a hawk-alarm call by the sentinels (pers. The five individuals observed at nest 11 observ.). Groups of Chopi Blackbirds were brought insects and spiders to the nest, and at often seen mobbing and chasing avian preda- least three removed fecal sacs. All scolded vig- tors, even during the non-breeding season. orously while I inspected the nest. The five Basic information on all the blackbird individuals also chased and mobbed Crested nests can be found in Appendix 1. My nest Caracaras (Caracara plancus) and parasitic locations mostly agree with published reports Screaming Cowbirds. At nest 12, at least four (Azara 1802, Dalgleish 1899, de la Peña 1987, of the six individuals carried insects and spi- Sick 1993, Fraga 1996, Di Giacomo 2005), ders to the chicks, while others scolded me, or but the use of nests built by Rufous Horneros mobbed Crested Caracaras and Screaming (Furnarius rufus) (three of the five nests found Cowbirds. in Corrientes) had not been reported for In a previous study at the Iguazú Airport Argentina. Chopi Blackbirds should be village, Misiones, Argentina (Fraga 1996), included among the few hole nesting icterids fledged Chopi Blackbird chicks were escorted (Orians 1985). by up to three adults, but I obtained no good Chopi Blackbirds sometimes breed in evidence of helping behavior at this stage of small colonies in palm groves (Di Giacomo the breeding cycle. Besides, this village popu- 300 SHORT COMMUNICATIONS lation was subject to a high incidence of 1972, Orians et al. 1977, Fraga 1991). Chopi Screaming Cowbird parasitism, and some par- Blackbirds also resembled Baywinged Cow- asite fledglings were fed by only one adult birds in nesting in cavities, palm trees and the blackbird (Fraga 1996). During a later visit to covered nests built by other birds (Fraga this site (18 December 2000) I found a mini- 1988). mum of nine adult Chopi Blackbirds, but the Most cooperative breeding icterids are only fledglings I saw were five Screaming members of the South American quiscaline Cowbirds, escorted by one or two adult black- clade, (Johnson & Lanyon 1999, Cadena et al. birds. The other adult Chopi Blackbirds in the 2004, Fraga 2008). Chopi Blackbirds become area were seen attacking and chasing the another cooperative species in this remarkable young cowbirds three times, rather than feed- group. ing them. One parasite chick uttered repeated distress calls when pecked by an adult black- ACKNOWLEDGMENTS. bird. This observation may be compared to the few reports of host discrimination or My travels in Argentina and Paraguay were aggression against the parasitic chicks of hon- financed by American Bird Conservancy, eyguides (Short & Horne 1985) and cuckoos Asociación Guyrá Paraguay and the World (Langmore et al. 2003). Screaming Cowbird Bank. I thank all the landowners that allow chicks do not mimic Chopi Blackbird chicks me to visit their properties. My visit to the in plumage, and are conspicuously different in AMNH was financed by a collection study coloration (Fraga 1996, 1998). Chopi Black- grant from the same institution. Comments bird fledglings have uniform blackish plum- by reviewers improved the MS. age and bare grayish facial areas, whereas Screaming Cowbird chicks closely resemble REFERENCES chicks of Baywinged Cowbirds (Fraga 1998). Two of the five Screaming Cowbird chicks Azara, F. de. 1802. Apuntamientos para la historia attacked by Chopi Blackbirds had a few black natural de los páxaros del Paraguay y Río de la blotches in the upperparts, the others appar- Plata. Volume 1. Imprenta de la Viuda de Ibarra, Madrid, Spain. ently not (the molt sequence is described in Brown, J. L. 1987. Helping and communal breeding Fraga 1998). in birds. Princeton Univ. Press, Princeton, New Details of the social organization of Chopi Jersey. Blackbirds in the nonbreeding season (senti- Cadena, C. D., A. M. Cuervo, & S. M. Lanyon. nel behaviour, group mobbing) closely resem- 2004. Phylogenetic relationships of the Red- ble those of other cooperative breeding South bellied Grackle (Icteridae: Hypopyrrhus pyrohypo- American quiscalines (e.g., Orians et al. 1977, gaster) inferred from mitochondrial DNA Fraga & Di Giacomo 2004). Begore egg sequence data. Condor 106: 664–670. hatching single Chopi Blackbird pairs attend Dalgleish, J. J. 1889. Notes on a collection of birds nests, and show agonistic behavior against and eggs from the Republic of Paraguay. Proc. conspecifics. After egg hatching, however, Royal Phys. Soc. Edinburgh 10: 73–88. de la Peña, M. R. 1987. Nidos y huevos de aves other individuals (three to four) may perform argentinas. Imprenta Lux, Santa Fe, Argentina. as helpers, bringing food and defending Di Giacomo, A. G. 2005. Aves de la reserva El nests and chicks against potential predators. Bagual. Pp. 201–465 in Di Giacomo, A. G., & Although my results are preliminary, a similar S.F. Krapovickas (eds.). Historia natural y pattern occurs in cooperative breeding paisaje de la reserva El Bagual, provincia de Baywinged Cowbirds in Argentina (Fraga Formosa, Argentina. Temas de Naturaleza y 301 FRAGA Conservación N°4, Aves Argentinas, Buenos 671–673.