The first records of Swallow Tanager Tersina viridis in Uruguay were made in 2012 and 2022 in different regions of the country. Together with other observations in central-south South America outside its usual distribution, these data appear to support the hypothesis that the species makes erratic movements in search of food during the austral winter non-breeding period. Alternatively, the new records could reflect an expansion of the species' distribution.
Swallow Tanager Tersina viridis is a member of the Thraupidae. It is both insectivorous and frugivorous, with the proportion of these dietary components varying seasonally (Schaefer 1953, Hilty 2020). The species is widely distributed in the Neotropics, from southern Panama to north-east Argentina (Misiones) and southern Brazil (Ridgely & Tudor 2009; Fig. 1). Migratory movements have been documented (Schaefer 1953, Schulenberg et al. 2007) and presence in the south of its distribution appears seasonal, with the species moving north in the austral winter (Hilty 2020). Some authors consider Tersina to be nomadic because, outside the breeding season, it may make irregular and erratic movements (Zelaya et al. 2013, Dardanelli et al. 2020, Hilty 2020), with exceptional records of vagrancy to the Cayman Islands and Bonaire (Prins et al. 2009, Kirwan et al. 2019) as well as in the south of its range. In Chile there are just two records, in Antofagasta and Valparaiso (Barros & la Red de Observadores 2016, 2021). In Argentina vagrants have been recorded in the provinces of Buenos Aires (Bremer & Bremer 1987, Narosky & Di Giacomo 1993, Bodrati & Bodrati 2017), La Pampa (Darrieu 1994), Salta (Di Giacomo et al. 1995), Tucumán (Ortíz 2009), San Juan (Lucero 2013), Córdoba, Formosa (Zelaya et al. 2013), Entre Ríos (Dardanelli et al. 2020), and most recently in Jujuy in 2021 (L. Fernández, https://ebird.org/ebird/view/checklist/S87846418) and Mendoza in 2022 (A. Zarco & Q. Vandemoortele, https://ebird.org/checklist/S115612948). In southern Brazil there are also records outside its main range. In July 2008 the species was observed for the first time in Pelotas, Rio Grande do Sul (P. R. Santos, http://www.wikiaves.com/1343704). During May–August 2021, several observations were made in the same municipality, with a max. of 30–40 individuals (eBird 2022; F. Jacobs, http://www.wikiaves.com/4380737). Some were feeding on the fruits of Myrsine sp., as well as Tripodanthus sp. and Schinus terebinthifolius (F. Jacobs pers. comm.).
In Uruguay there are no published records of Swallow Tanager. However, an oral communication made on 20–21 October 2012 (II Jornadas sobre ‘Investigación y Manejo de Fauna Silvestre’, Córdoba, Argentina) reported the first record of the species in the country (J. Villalba Macías pers. comm.). In addition, a few records have been reported in a national ornithology forum (‘Ornitologiauy’). Below we provide details of several documented records, plus other recent reports, in Uruguay.
On 9 June 2012, E. Elgue observed an immature male Swallow Tanager (blotched green and blue; Fig. 2A) at Las Grutas, dpto. Maldonado (34°54′12″S, 55°02′10″W; Fig. 1). It was found in a small native forest feeding on fruits of Myrsine laetevirens (Primulaceae). The observation lasted a few minutes and the bird was very tame.
On 1 October 2012, J. Villalba Macías photographed an immature male (Fig. 2B) at M'Bopicuá Biopark, near the Uruguay River, dpto. Rio Negro (33°06′48″S, 58°12′21″W; Fig. 1). It was observed on a Ficus luschnathiana (Moraceae) and a Prosopis nigra (Fabaceae), and remained at the site for at least six days.
On 20 April 2022, L. Piñeyrúa, C. Crocce & E. Muñoz observed a female-plumaged individual (Fig. 2C) at the Botanic Garden, dpto. Montevideo (34°51′33″S, 56°12′08″W; Fig. 1). It was found in a sector of native flora with some fruiting trees that are often visited by other Thraupidae and Turdus spp.
On 14 May 2022 JM observed a female-plumaged individual (Fig. 2D) in a patch of psammophilous forest at Costa Azul, dpto. Rocha (34°37′45″S, 54°09′32″W; Fig. 1). It was seen for four minutes atop a Myrsine laetevirens, feeding on its fruits and vocalising.
There are other undocumented records. In winter 2010, a female-plumaged bird was observed at Barrio Prado, dpto. Montevideo (J. Mazzula pers. comm.) and in 2012, another female-plumaged individual was seen at Santa Teresa, dpto. Rocha (M. Rodriguez-Cajaraville pers. comm.).
The observations detailed here represent the first records of Swallow Tanager in Uruguay. The species seems to be an occasional visitor attracted to fruiting trees during the austral autumn and winter. The records in Uruguay appear to support the hypothesis that it makes erratic movements in search of food, mainly fruit (Zelaya et al. 2013, Dardanelli et al. 2020, Hilty 2020). More than half of the records involved individuals taking fruits, especially Myrsine laetevirens. Alternatively, the records could reflect an expansion of the species' range. The recent establishment of populations of numerous ‘subtropical’ bird species in Uruguay supports this hypothesis (Azpiroz et al. 2012, Menéndez 2020, Campaña et al. 2021), although more data are needed.
We are grateful to Ernesto Elgue, Juan Villalba Macías, Luis Piñeyrúa, Carlos Crocce and Eduardo Muñoz who kindly provided their records. We thank Fernando Jacobs for information on the species in Rio Grande do Sul, Brazil; Ariel de León Mackey for comments on the text; and Guy Kirwan and Chris Sharpe for their valuable comments and helpful suggestions that improved the submitted manuscript.