An annotated checklist of birds of Paraje Tres Cerros, Corrientes province, Argentina

We provide an updated checklist of birds of a unique landscape in northeastern Argentina, which is characterized by three isolated, rocky outcrops and their surrounding agroecosystem. We recorded 188 bird species, including nine that are globally or nationally threatened. We highlight the presence of several grassland-specialist birds of conservation concern. Of the species recorded, 80.6% are residents and 17.7% are migrants. The heterogeneity of the landscape and its structural complexity accounts the existence of a high avian species diversity, which includes both generalists and specialists. This study confirms the conservation value of this ecosystem, due both to the rocky outcrops and grassland matrix. Grasslands are one of the most threatened biomes in the world.


Introduction
Corrientes is among the provinces with the greatest avian richness in Argentina (Capllonch et al. 2005;Chate llenaz et al. 2010). Its high avian diversity is related to the convergence of three phytogeographic provinces (Cabrera 1971): Chaqueña, Paranaense, and Espinal. Among the most representative and threatened formations in the province are grasslands (Di Giacomo 2011). Grasslands are highly disturbed worldwide, as a large proportion of the biome has been replaced by crops or is subject to cattle grazing (Hannah et al. 1995). Until recently, the protected areas of Corrientes covered only areas of the Chaqueña and Paranaense phytogeographic provinces (i.e., Parque Nacional Mburucuyá, Parque Provincial San Cayetano, Reserva Natural Iberá, Reserva Rincón Santa María, and Reserva Natural Apipé). Recently, the Reserva Natural Privada Paraje Tres Cerros (RNPPTC) within Paraje Tres Cerros was created. It is the first private protected area of the Espinal province. The purpose of this nature reserve is to protect two of the three rocky outcrops of Paraje Tres Cerros, which are part of a remarkable and unique landscape. Rocky outcrops, or inselbergs, are defined as geological features consisting mainly of granitic and gneissic rocks that protrude above the surface of the surrounding land (Bremer and Sander 2000). The difficulty of accessing the outcrops has hindered their exploitation. For this reason, their natural habitats are generally well preserved and may act as a refuge for wildlife, including many endemic species (Porembski and Barthlott 2000;Fredericksen et al. 2003).
Although the nature reserve protects 117 ha of rocky grasslands and forests that grows on the outcrops, the rest of the landscapes of Paraje Tres Cerros, including the surrounding grassland matrix, forest patches, marshes and the third outcrop, are unprotected. Studies of its fauna have focused on herpetology, arthropods, and bats (Cajade et al. 2013;Ojanguren-Affilastro et al. 2017;Nadal et al. 2018). However, despite the site's notable characteristics, studies on its avifauna are scarce, with the exception of a study by Fandiño et al. (2017), who studied the grasslands and forests avifauna and recorded 107 species. No study has focused more broadly on the avifauna of Paraje Tres Cerros and the grassland matrix. Species inventories are an important for a better understanding of the regional distributions of species, data which are essential for management plans and species conservation.
Our goal in this study is to report data from six years of monitoring at Paraje Tres Cerros, including both natural and anthropogenic environments. We update the previously published avifaunal inventory (Fandiño et al. 2017) and compare our data to this previous inventory. Our data fill a knowledge gap in the avifauna of the Espinal region. As Fandiño et al. (2017) did not include the grassland matrix or anthropogenic environments in their study, and because we undertook a larger sampling effort, we expected to find a greater diversity of bird species, including threatened grassland species.

Study Area
The study was carried out at Paraje Tres Cerros located in the San Martín Department, central-west Corrientes Province, northeastern Argentina (Fig. 1). Phytogeographically, Paraje Tres Cerros is within the Ñandubay District, corresponding to the Espinal Province in the Chaco Domain (Cabrera 1971). The topography of the site presents three rocky outcrops or inselbergs ( the hills is 1.86 km 2 . The northern slope, with more sunshine and exposed to the warm northern wind, has sparse shrub and herbaceous vegetation among the rocky outcrops. The southern slope, with less incidence of the sun, greater retention of moisture, and protection from the north wind, has developed a primary hygrophilous forest. The floristic elements of these forests are associated with the Atlantic Rainforest biome, but with less species richness (Parodi 1943). The surrounding matrix is mostly represented by savannas dominated by grasses of genus Elyonurus (Humb. & Bonpl. ex Willd.) (Fig. 2), flooded grasslands dominated by Andropogon (L.), temporary marsh areas locally known as malezales (Parodi 1943), forest patches composed of species of the Chaqueña ecoregion (Parodi 1943), and approximately 5 km 2 of exotic Pinus elliottii (Engelmann) plantations. In addition to these plantations, there are also areas used for livestock and rice cultivation. On the edge of Cerro Capará there is a 50 km 2 reservoir which was built to provide water to the rice fields. To characterize the avifauna, we defined six macrohabitat types. These included four natural habitats (Cerro Nazareno, Cerro Chico, Cerro Capará, Cerro Pelón) and two exotic habitats: the reservoir and the exotic pine plantations. As all the hills have the same vegetation cover (i.e., rocky grassland, rocky forest, and matrix forest), we considered all hills as one habitat type to simplify comparisons. Thus, records at each hill correspond to the birds seen or heard both in the outcrops and in its surrounding matrix. The surrounding matrix was considered in a 1 km radius around the hills.

Methods
Data were collected from 2012 to 2018 using three different methods in all seasons and in all natural and exotic environments. We conducted 120 point-count surveys (Bibby et al. 2000), which were separated 200 m from each other; during the point-count surveys, we recorded all birds heard or seen in 10 minutes within a defined radius of 50 m. We also conducted 136 MacKinnon lists (MacKinnon and Phillipps 1993) of 10 species. During each survey, we recorded the first 10 species encountered, which constitute one MacKinnon list. Sample effort per site is shown in Table 1. We also carried out nonsystematic observations to detect silent or inconspicuous species. We did not survey during strong winds and rains. We only carried out diurnal bird surveys. We recorded the season and the site where each individual was encountered. Birds were detected and identified using 8 × 42 binoculars, a 20 × 60 spotting scope, and field guides (Narosky and Izurieta 2010). We compared the number of species recorded in only one habitat (non-shared species). Species nomenclature follows Remsen et al. (2019). Observations (Table 2) are stored on eBird (http://www.ebird.org). Birds were categorized according to their phenology following Mazar- Barnett and Pearman (2001), Fandiño et al. (2017), and into three categories based on our own data: year-round resident; winter or non-breeding visitor; and summer visitors that migrate north for the autumn-winter. For conservation status, we follow Ministerio de Ambiente y Desarrollo Sustentable de la Nación and Aves Argentinas (MAyDS and AA, 2017) and IUCN (2019).  We recorded 188 species from 49 families and 21 orders ( Table 2). The most diverse family was Tyrannidae (26 species) followed by Thraupidae (21 species). Within non-passeriformes the richest family was Accipitridae (11 species). The highest species richness was recorded at Cerro Nazareno (139 species), which represents 75.5% of the total, followed by Cerro Chico (105), Cerro Capará (99), the reservoir (83), pine plantations (65), and finally Cerro Pelón (50). Of all species, 33 were found in all four hills, 50 in at least three of hills, and 39 in only one. The number of non-shared species was greater in the reservoir and Cerro Nazareno (23 and 24 species, respectively). According to their migratory status, 146 species (80.6%) are residents in the area and 32 (17.7%) are migrants. We could not assign any status to the remaining nine species due to the low number of records. Among migrant species, 28 are summer visitants and only three are winter visitants: Euphonia cyanocephala (Vieillot, 1818), Knipolegus cyanirostris (Vieillot, 1818), and Mi mus triurus (Vieillot, 1818). According to our data, 60 species were recorded in all seasons, and the highest proportion occurred in spring (73%).

Results
Of all recorded species, five are globally threatened (IUCN 2019): Sporophila palustris (Barrows, 1883) and Gubernatrix cristata (Vieillot, 1817)  Below, we describe some aspects of the observations of some species recorded in Paraje Tres Cerros. Figure 3A Observations. ARGENTINA • Multiple (♂, ♀ and juveniles); Corrientes, La Cruz, Paraje Tres Cerros; 29° 06′55′′S, 056°55′09′′W. Several adults and chicks recorded foraging in the grasslands of PTC during all seasons. We recorded this species in systematic and nonsystematic observations since the beginning of our study. Identification. Unmistakable. Often in groups. Long and powerful legs, small head. Three toes. Plumage is gray with black around the neck and head. Males are darker than females.
Identification. Similar in shape to T. caerulescens¸ but differs by its rufous cap and neck.
Identification. Identified by its distinctive bill shape. Plumage mostly bright pink.
Identification. Similar to Yellow-headed Vulture (C. bur rovianus Cassin, 1845) and Black Vulture (Coragyps atratus Bechstein, 1783). It was identified by head and neck reddish and whitish ventral surface of remiges.   Figure 4F New records. ARGENTINA • Multiple (no sexual dimorphism); Corrientes, La Cruz, Paraje Tres Cerros; 29° 06′38′′S, 056°55′50′′W. Highly social birds and very common in the study site. We recorded several individuals in mixed flocks, usually soaring on thermals above rocky outcrops. Identification. We identified this species by its bare black head and white wingtips, which are easily recognized in flight. Identification. Light morph identified by its relatively small size; upperparts bluish; finely rufous barred underparts, iris orange-yellow. Figure 4G New records. ARGENTINA • 5 (no sexual dimorphism); Corrientes, La Cruz, Paraje Tres Cerros; 29°09′33′′N, 056°50′26′′W. Five individuals recorded in different surveys perching or flying near water. Identification. Mostly cinnamon-brown. Wings with all remiges broadly edged black. Black tail with median band and tip white. Figure 4H Observations. ARGENTINA • 1 (no sexual dimorphism); Corrientes, La Cruz, Paraje Tres Cerros; 29°05′39′′S, 056°56′08′′W. We saw one individual flying in the grassland near water. Identification. Almost entirely black. Tail is mostly black with a broad white band.
Identification. Head and upperparts dark, with contrasting underparts white. Forehead white. Wing-tips reach tail tip on perched birds.

Identification.
Resembles an Ibis. Identified by its long neck, large size, bill yellowish and feathers with white markings.

Rostratulidae
Nycticryphes semicollaris (Vieillot, 1816) Observations. ARGENTINA • 1 (no sexual dimorphism); Corrientes, La Cruz, Paraje Tres Cerros; 29°06′ 34′′S, 056°55′23′′W. Hard to detect. We recorded one individual after a rain, foraging in a short-grass wetland near the reservoir.  Figure 5H Observations. ARGENTINA • 10 (no sexual dimorphism); Corrientes, La Cruz, Paraje Tres Cerros; 29°06′ 22′′S, 056°55′31′′W. We recorded 10 individuals vocalizing or perching on the trees. Identification. Differs from other large pigeons by its wing-coverts dark with white spots in each feather, giving spotted effect.    Figure 6D New records. ARGENTINA • 1 (sex: unknown); Corrientes, La Cruz, Paraje Tres Cerros; 29°06′34′′S, 056°55′ 49′′W. We recorded an individual during the morning, perched on a rock in Cerro Nazareno. Identification. Little nightjar. It was identified by its conspicuous rufous collar on the sides and back of the neck. It has a thin, white stripe from the base of the bill through the cheeks and white throat patch. Hylocharis chrysura (Shaw, 1812) Figure 6F New records. ARGENTINA • 7 (no sexual dimorphism); Corrientes, La Cruz, Paraje Tres Cerros; 29°06′21′′S, 056°56′05′′W. Individuals of this species were recorded several times during the surveys in different macrohabitats. Common and widespread hummingbird in the study site. Identification. It was identified by its iridescent goldengreen plumage and bronzy tail, which differs from that of C. lucidus, which is blue. Figure  Identification. Relatively small woodpecker. Above olive. Conspicuous supercilium and malar witish. Head dark with a red crown in males. Figure 6H Observations. ARGENTINA • 4♀ 2♂; Corrientes, La Cruz, Paraje Tres Cerros; 29°06′27′′S, 056°55′54′′W. We recorded a nest in a dead tree in November 2016, with three cheeks or nestlings. Identification. Identified by its red semi-crest on nape and white face. Figure 7A Observations. ARGENTINA • Multiple ♂ and ♀; Corrientes, La Cruz, Paraje Tres Cerros; 29°09′20′′S, 056°51′43′′W. We observed several individuals foraging on the open grounds and grasslands and perching on tree branches. Identification. Fairly terrestrial woodpecker. Identified by its both sides of the head, breast and neck, yellow. Crown black and malar red in male. Figure 7B Observations. ARGENTINA • 1♀ 2 unidentified; Corrientes, La Cruz, Paraje Tres Cerros; 29°06′45′′S, 056° 56′01′′W. Three individuals observed between 2015 and 2017. One individual flew from the plantation towards the forest of Cerro Nazareno. The other two individuals were in the hygrophilous forest on the southern slope. A female was foraging in a dead tree.   Identification. Supercilium and coronal stripe white coronal stripe; body grayish above, with belly and lower abdomen yellowish. Figure 7D Observations. ARGENTINA • 1♀; Corrientes, La Cruz, Paraje Tres Cerros; 29°09′33′′S, 056°51′51′′W. A male observed in August and October 2014 in grasslands of Cerro Capará. Identification. Rare in the study area. Crown grey to blackish, finely striped with white; breast and flanks cinnamon; bill and legs black. A small bird; similar in size to Culicivora caudacuta (Vieillot, 1818), but this species has a conspicuous, white supercilium.
Identification. Similar to P. chalybea (Gmelin, 1789), but with a contrasting blackish throat and breast, and lighter brown underparts. Identification. Similar to P. tapera, but it has a shiny, blue back.
Identification. Rump, and loral line white.

Identification.
Tail long and deeply forked; throat rufous.
Identification. In males, mask and tail black; females lack a mask.
Identification. Head, bill, and tail black; iris yellow; each side of throat with yellowish patch; underparts yellowish; back dark brown.

Basileuterus culicivorus (Swainson, 1838)
Identification. Small. Males with yellow forehead; underparts bright yellow, and the rest bright blue. Females mainly olive and grayish.

Discussion
Our data increase the number of known bird species in forests and grasslands at Paraje Tres Cerros to 188 (Fandiño et al. (2017) had only reported 107 species). This richness represents 36% of the known avifauna in Corrientes province (Capllonch et al. 2005;Chatellenaz et al. 2010), which shows the importance of the Espinal region for regional biodiversity.
As expected, in contrast to Fandiño et al.'s (2017) study that did not survey wetlands, we recorded orders associated with water (i.e. Ciconiiformes, Pelecaniformes, Anseriformes, Suliformes). Among the species we observed in wetlands is Amblyramphus holosericeus, which is listed nationally Vulnerable (MAyDS and AA, 2017).
An important find was the presence of several grassland-specialist species which are globally threatened, such as Sporophila palustris; this species is one of the most threatened seedeaters and a summer visitor, which nests in grasslands and marshes of northeastern Argentina (Silva 1999;Areta 2008). Another threatened and sympatric seedeater is S. cinnamomea. Seedeaters are specialists of these environments and indicators of sites having high conservation interest (Devenish et al. 2009). Another species of conservation interest that breeds in the area is Gubernatrix cristata. It is typical of the Espinal Province (Reales et al. 2019). Its populations are declining due to the extraction of individuals from the wild and to habitat loss (BirdLife International 2018). The continuous degradation of natural grasslands in the area due to anthropogenic activities and the absence of natural reserves to protect these environments (Di Giacomo et al. 2011) threatens the viability of bird populations, especially of species with restricted ranges and small population sizes. We also found populations of Near Threatened species. One of the most abundant is Rhea americana, which has undergone declines in Argentina mainly due to habitat loss, hunting, and egg collecting (Martella and Navarro 2006). Rhea ameri cana inhabits grasslands and savannas, but has adapted to agricultural and livestock areas, although in low densities (Giordano et al. 2010).
There are two threatened species, known from nearby areas that were not found by us in the study area. These include Buteogallus coronatus (Vieillot, 1817) and Alectrurus risora (Vieillot, 1824) (Fandiño et al. 2017). Although not found there by us, these species could potentially use the resources available in the habitats of Paraje Tres Cerros. Our new records of threatened species are important contributions to the knowledge of these species' distributions, and such data has potential use for proposing Paraje Tres Cerros as an important bird area (BirdLife International 2014).
Cattle ranching is the main activity in Paraje Tres Cerros and its surroundings. In some farms, the high grazing pressure hinders the growth of natural grasslands, which are necessary for the existence of several threatened species. Indeed, there were species found in protected sites without the presence of livestock. For example, Culicivora caudacuta (Vieillot, 1818) inhabits tall grasslands in the lowlands that are rarely disturbed and Xanthopsar flavus (Gmelin, 1788) and Xolmis domi nica (Vieillot, 1823) occurs in marshes and wet natural grasslands. Although these species can use short grasslands for feeding, they need tall grasslands for nesting and shelter.
The greatest number of non-shared species and species richness among hills was recorded at Cerro Nazareno. This could be partly because it was where the greatest sampling effort was made. However, the presence of an important continuous primary hygrophilous forest on the southern slope, with floristic elements of the Atlantic Forest (Parodi 1943), provides resources for many forest-dependent species, for example, Acci piter striatus (Vieillot, 1807), Dryocopus lineatus, and migrants like Coccyzus melacoryphus (Vieillot, 1817), a summer visitant that feeds on seeds and insects (Beltzer and Quiroga 2008). Although we made no nocturnal surveys, we recorded three species of nightjars at Cerro Nazareno. It has been suggested that these species are relatively abundant in rocky outcrops because they may feed on the numerous insects that fly at dusk among the rocks (Fredericksen et al. 2003). Additional studies on the abundance and diversity of insects in rocky outcrops and nocturnal surveys are needed to corroborate this.
Despite the fact that the surroundings of the rocky outcrops include anthropogenic habitats, the heterogeneity of the landscapes and the structural complexity of the different environments favors the existence of a great number of both generalists and specialists species. It has been suggested that a greater complexity of habitat structure may provide a wider variety of resources for birds than less complex habitats (Codesido et al. 2013;Brandolin and Blendinger 2016). The forests that cover the slopes of the hills also play an important role for birds, providing food and shelter for both resident and migrant species. The difficulty of access to these forests impedes logging, which favors their conservation.
The small size of outcrops studied here does not act as a barrier to the free movement of birds, but the ecological relationships between birds and rocky outcrops may be acting at another level. Our future goal is to determine the specific role of rocky outcrops for birds (nesting, foraging, and shelter). We found several species nesting among the rocks. Interestingly, we recorded the three species of vulture nesting in the hills: Cathar tes aura, C. burrovianus, and Coragyps atratus. We also found species, such as Colaptes campestris, Lep totila rufaxilla (Richard & Bernard, 1792), and Elae nia spectabilis (Pelzeln, 1868) nesting among the hill vegetation.
We consider that Cerro Capará and its grassland matrix offers conditions to support a greater number of species than we report here; hence, future studies with increased sampling effort should focus on this habitat. As on Cerro Nazareno, the south-facing forest of Cerro Capará may offer food resources to frugivorous bird species. Despite its small area, the presence of a rocky environment in a grassland-dominated landscape may increase the regional avifaunal diversity by providing different resources for foraging, roosting, nesting, or shelter.
In conclusion, our study confirms and highlights further the conservation value of Paraje Tres Cerros, both because of the importance and uniqueness of the rocky outcrops and because of the grassland matrix, one of the most threatened environments in the world. .

Comparison with the rocky outcrop avifauna of southern Brazil and Uruguay.
Several bird studies have been conducted on rocky outcrops in Brazil. These habitats, known as the High-Altitude Complex, support a high biodiversity and several endemic species (Vasconcelos 2008;Freitas et al. 2012). In general, these studies reported a high species richness. For example, Vasconcelos and Neto (2009), recorded 209 species in Serra da Mantiqueira, and Nunes et al. (2013) recorded 413 species in Serras de Maracaju. Endemic bird species include Scytalopus petrophilus (Whitney, Vasconcelos, Silveira & Pacheco, 2010) in Espinhaco and Serra da Mantiqueira, and Neopelma chrysolophum (Pinto, 1944) in forests of Serra do Mar, among many others. The greater species richness and the presence of endemic birds in rocky outcrops in Brazil compared to the rocky outcrops in Corrientes is likely explained by the area covered by the rocky outcrops. In southeastern and northeastern Brazil, these geological features can be as large as 500 to >1500 km 2 , and the dominant vegetation occurs at 900-1500 m a.s.l., depending on the type of vegetation. Thus, conditions and habitat complexity offer many more resources and a larger area to support endemic species than the relatively small outcrops in Corrientes. However, as in Paraje Tres Cerros, the largest proportion of bird species in these rocky habitats is composed of non-endemic wide-ranging species (Vasconcelos and Rodrigues 2010). We did not find any studies on the avifauna of rocky outcrops in Uruguay, nor any records of endemic species. However, we highlight the presence of Knipolegus lophotes (Boie, 1828), a small tyrant flycatcher which is also found in Brazil and occurs in rocky grasslands and savannas with scattered trees in Uruguay (Arballo 1990).