The Saffron-cowled Blackbird, Xanthopsar flavus (Gmelin, 1788), is a globally vulnerable icterid endemic to grasslands and open areas, and a priority species for research and conservation programs. This contribution provides information on the population size, habitat, behavior, breeding biology and nest success of X. flavus in two conservation units (CUs) in Viamão, state of Rio Grande do Sul, Brazil: the Environmental Protection Area Banhado Grande, and the Wildlife Refuge Banhado dos Pachecos, classified as an “Important Bird Area”. Searches for X. flavus were carried out mainly in open areas, the type of habitat favored by the species. Outside the breeding season individual behavior was recorded by the ad libitum method; during the breeding season, selected X. flavus pairs were observed following the sequence sampling method. The research areas were visited once a month, totaling approximately 530 hours of observations (September 2014 to June 2016) over 84 days, which included two breeding seasons. The species was observed across all months (not necessarily within the same year) and several X. flavus flocks were encountered, some with more than one hundred individuals (range = 2-137). Additionally, the behavior and feeding aspects, habitat use and breeding information on X. flavus were recorded. Two breeding colonies were found, and eleven nests were monitored. The estimated nesting success was 10% in Colony 1, but zero in Colony 2, where all eggs and nestlings were predated. Saffron-cowled Blackbirds were recorded in mixed flocks, mostly with Pseudoleistes guirahuro (Vieillot, 1819), P. virescens (Vieillot, 1819) and Xolmis dominicanus (Vieillot, 1823), the last also a globally endangered species. The collected information highlights the importance of CUs for the maintenance of X. flavus populations in the region. Maintenance of proper areas for feeding and breeding is necessary and urgent. Information from current research is being employed in the management plan of the Wildlife Refuge Banhado dos Pachecos in which X. flavus is one of the conservation target-species.

Conservation, habitat degradation, natural history, vulnerable species

The Saffron-Cowled Blackbird, Xanthopsar flavus (Gmelin, 1788), is an endemic species of the grasslands of southern South America (Collar et al. 1992). The species is of high priority for conservation and research (Stotz et al. 1996, Fontana et al. 2013). This bird depends on heterogeneous areas of natural grassland, and uses different habitats for feeding and nesting (Fonseca et al. 2004, Fraga 2005, Azpiroz et al. 2012). It is currently listed as vulnerable at the regional, national and global levels (State Decree 51.797/2014, ICMBio/2014, IUCN 2016), largely due to the destruction and degradation of its habitat, and the consequent disruption of its biological cycle.

The geographical distribution of the Saffron-Cowled Blackbird includes southern Brazil (states of Santa Catarina and Rio Grande do Sul), southern Paraguay, Uruguay and northeastern Argentina (Collar et al. 1992, Azpiroz 2000, Dias and Maurício 2002, Fonseca et al. 2004, Fraga 2005, Birdlife International 2016). According to Collar et al. (1992), Saffron-Cowled Blackbird populations are decreasing throughout their distribution range, and for this reason it is important to protect the areas that still remains adequate to its life-cycle (Azpiroz 2000, Azpiroz et al. 2012). The world population of the species is estimated at 10,000 individuals, at the most (Birdlife International 2016).

In Brazil, information on the species’ natural history and conservation comes mainly from studies and observations carried out in the extreme north-eastern corner of the country (Belton 1994, Fonseca et al. 2004, Krüger and Petry 2010, Petry and Krüger 2010, Moura 2013) and on the southern coastal plain of the state of Rio Grande do Sul (Dias and Maurício 2002). Due to its status as a vulnerable species, new information on the species at other sites is both relevant and important. The current study provides data on the size of the Saffron-Cowled Blackbird population, habitat, behavior, breeding biology and nest success from an Important Bird Area (IBA) and its immediate vicinity, on the internal coastal plain of Rio Grande do Sul, Brazil.

The study area lies in the municipality of Viamão, within the coastal plain of the state of Rio Grande do Sul, southern Brazil (Fig. 1). It comprises the “Wildlife Refuge Banhado dos Pachecos (WRBP)” (30°05’45.43”S, 50°51’46.38”W), and the “Environmental Protection Area of Banhado Grande (EPABG)” and its immediate vicinity. The study areas lie within an ecotone zone between the Atlantic Rain Forest and Pampas biome. Sandbank vegetation, pioneer shrub-tree woods, swampy areas with Cyperaceae and high grass, flooded fields, dry marshes, pastures and areas with anthropic activities (mainly livestock and rice fields) occur within the limits of WRBP and EPABG (Accordi and Hartz 2006).

Figure 1. 

Map of study area, with the Wildlife Refuge Banhado dos Pachecos (WRBP) and, in its immediate vicinity, the Environmental Protection Area of Banhado Grande (EPABG), in the state of Rio Grande do Sul, Brazil.

EPABG, a Sustainable Conservation Unit of approximately 133,000 ha, was established in 1998 (State Decree 38.971/1998). WRBP is an Integral Protection Conservation Unit, with 2,543.46 ha, established in 2002. No environmentally degrading anthropic activity is allowed there (State Decree 41.559/2002). The preserved areas protect the region’s wetlands and water sources. The WRBP is classified as an “Important Bird Area” (IBA), highly relevant for bird conservation, particularly for species that depend on dense marshes and wet grasslands, including endangered species (Bencke et al. 2006). The research in the two protected areas was authorized by the Department of Environment (SEMA) of the state of Rio Grande do Sul (Authorization 01/2015).

The areas for the study of the Saffron-Cowled Blackbirds (SCB) were selected based on the results of Accordi and Barcellos (2006), Accordi and Hartz (2006), and on observations in the region during January 2014, when 12 SCBs and a bird couple with nest and two nestlings were reported in the EPABG. Monthly reports on SCB occurrences (from September 2014 to June 2016) were the result of research within the WRBP, and on the main and secondary roads in the area surrounding the EPABG. Roads were traversed by car at low speed (<10 km/h) and on foot. Research efforts focused on marshy areas and grasslands characterized by Eryngium sp. L. (Apiaceae), Cyperaceae and Asteraceae which may be used for breeding and in fields or pasturelands, with low vegetation, used for feeding.

When a SCB was detected, the number of individuals in the flock was counted, and the associated species, or species that interacted with SCBs, were identified. The birds were taxonomically identified and quantified by direct observation, or identified by their calls. Classification followed Piacentini et al. (2015). After the counting of individuals, each area was observed for 60 minutes to investigate individual arrivals and their behavior. Outside the breeding season, all SCB occurrences were noted, along with associated behaviors (Franchin et al. 2010). During the breeding season both ad libitum and sampling sequences methods were used (Franchin et al. 2010). In the latter case, selected pairs were monitored. However, whenever the birds seemed uncomfortable with the presence of the observer, monitoring was temporarily interrupted. Areas with SCB occurrences were visited once a month, totaling approximately 530 hours of field observations during 84 days (between September 2014 and June 2016), including two breeding seasons, across 22 months. Observations were conducted in the morning, during the day, and in the afternoon.

In the breeding seasons, two nesting areas were found and named “Nesting Colony 1” and “Nesting Colony 2”. After the first report of breeding activity, the colonies were assessed for four consecutive days, after which nests were visited every three days (with one exception in each area when four days had passed). Once the nesting areas were abandoned, each nest’s internal and external diameter, internal nest depth, external nest height and nest height from the ground were measured. All plant species supporting nests were identified and their heights were measured. All plants more than 60 cm high within a 1 m radius of the nest were also identified (Fonseca et al. 2004, modified), since they could support nests or predators. The tallest and the shortest plants (including leaves and inflorescences when present) were measured. Variables for each nesting colony were compared with a t-test using the statistical program Past 3.13 (Hammer et al. 2001).

Since no nest was found either under construction or during egg-laying, egg and nestling numbers are reported, but clutch size was not. To avoid research activities causing any reproductive loss, eggs and nestlings were not measured, and no specimens were captured or marked. To make comparisons possible, reproductive success was presented in two ways: first based on fledged chicks/eggs or nestlings rates so as to be comparable with some previous studies (Fraga et al. 1998, Dias and Mauricio 2002), and by apparent success (number of successful nests/total number of nests) to be comparable with others (Moura 2013). In the current study, nests were considered successful when at least one chick fledged.

SCBs in the WRBP mainly occupied a landscape characterized by fields and wetlands dominated by Eryngium sp. and Typha domingensis (Pers.) (Typhaceae). In the immediate vicinity of EPABG X. flavus was reported in dry field areas, mainly with Schizachyrium microstachyum (Desv. ex Ham.) Roseng., B.R. Arrill. and Izag. (Poaceae), in wet fields with Eryngium sp. occupied by livestock and horses, and in rice fields.

SCB were not encountered in the study areas in January and May, 2015, and in February, 2106. In the non-breeding season (during the austral autumn), the largest SCB flock (137 individuals) was reported in March 2015. Other sizeable flocks were reported in February 2015, January, April and May 2016, with 69, 96, 75 and 70 individuals, respectively. All reports occurred in areas close to the WRBP within the EPABG. During the first breeding season, the largest SCBs flock (16 individuals) was reported (November and December 2014) at a Nesting Colony 1 and a flock of 21 SCBs outside the nesting colony, on the edge of WRBP. In the second breeding season (November and December 2015) the largest flocks observed were 10 SCBs in Nesting Colony 2 and with 35 SCBs in a flock which was feeding within an adjacent area outside the Nesting Colony.

The habitats most commonly used by X. flavus for feeding were fields covered with short grasses and rice fields during the early maturation stages and post-harvest period. SCBs were mainly observed feeding on insects and insect larvae, usually foraging for them on the ground, while probing soil and vegetation. While some individuals were feeding on the ground, others took the role of sentinels, perched on eucalyptus Eucalyptus sp. L’Hér. (Myrtaceae) and maricá trees Mimosa bimucronata (DC.) Kuntze (Fabaceae). During the breeding season, two males, while acting as sentinels at the nest, were observed capturing flying insects and eating them in a manner similar to flycatchers.

In the non-breeding season, when SCBs were foraging in intraspecific flocks, two or three males took the role of sentinels and, through vocalization, appeared to warn off the other individuals to move away when researchers or possible predators came close. Sentinels rested on the ground and perched on trees (Eucalyptus sp. and M. bimucronata). In the non-breeding season, SCB individuals were seen in mixed flocks with Pseudoleistes guirahuro (Vieillot, 1819) (Icteridae), P. virescens (Vieillot, 1819) (Icteridae), Agelasticus thilius (Molina, 1782) (Icteridae), Sicalis luteola (Sparrman, 1789) (Thraupidae), Chrysomus ruficapillus (Vieillot, 1819) (Icteridae), Zenaida auriculata (Des Murs, 1847) (Columbidae) and Xolmis dominicanus (Vieillot, 1823) (Tyrannidae). Within these P. guirahuro and P. virescens acted as sentinels.

SCB were recorded with the Black-and-White Monjitas (BWM), X. dominicanus, only in the autumn and winter, in April, May, June, July and August. During these months, the largest BWM gatherings respectively comprised of 2, 15, 20, 15 and 15 individuals. Largest mixed flocks of SCBs and BWMs were, respectively, 14 and 36 in June 2015; 15 and 15 in July 2015; 70 and 15 in May 2016; and 30 and 12 in June 2016.

In October, during the two breeding seasons evaluated, and approximately one month prior to the discovery of nests, SCB males were displaying to females in aerial courtship flights. Females in Nesting Colony 1 were reported inspecting Eryngium sp., while males perched close by. In the breeding season, SCB individuals were reported close to Tyrannus savanna Daudin, 1802 (Tyrannidae), Progne tapera (Vieillot, 1817) (Hirundinidae) and Sturnella superciliaris (Bonaparte, 1850) (Icteridae). During territorial disputes and defense, SCBs attacked individuals of the same and of other species, including P. virescens and P. guirahuro, and each defended a territory some 3 m-radius around the nest. On one occasion, a nesting pair in Nesting Colony 2 joined a mixed flock of P. virescens and P. guirahuro to feed in a field area approximately 30 m from the colony. Several times, SCB gathered together with specimens of P. guirahuro, P. virescens, T. savanna, P. tapera to drive off such predators as Circus buffoni (Gmelin, 1788) (Accipitridae), C. cinereus, Vieillot, 1816 (Accipitridae), Milvago chimango (Vieillot, 1816) (Falconidae) and Falco femoralis Temminck, 1822 (Falconidae).

In the first breeding season assessed, there were six nests (1-6) in Nesting Colony 1, five of which were measured (Table 1). One nest was damaged by water, making it impossible to take the full set of measurements. It should be underscored that in the same area, in January 2014, a pair with a nest containing two nestlings was recorded. During the second breeding season, five nests (7-11) were found and measured in Nesting Colony 2 (Table 1). Colonies were separated by some 3 km from one another. Nesting Colony 1 was characterized by small, near-isolated, clusters of Eryngium sp., whilst Nesting Colony 2 was composed of isolated Eryngium sp. individuals and a small dense cluster of these plants, although the nests lay at the edge of the site, in a matrix of otherwise low-lying grazed grassland. All nests in Nesting Colony 1 were attached to Eryngium sp., the dominant plant in the region, and were, on average, 51 cm from the ground. Only one nest (Nest 1) was fixed on the tallest plant in the area, even though this was only 35 cm from the ground. In Nesting Colony 1, the closest nests were 5 m apart, whilst the most distant were 52 m apart. In Nesting Colony 2, the closest nests were separated by 4.5 m, and the most distant by 70 m. One nest was fixed only to a Scirpus sp. L. (Cyperaceae); three nests were fixed to Scirpus sp. and Eryngium sp. simultaneously, and one nest was attached only to grass. The latter was closest to the ground. No nest was fixed to the tallest plant within the area surrounding the nests. In Nesting Colony 2, nest diameters and depths were greater than those of Nesting Colony 1 (Table 1), but there was no significant variation in all nest measurements between the two colonies during the two breeding seasons under analysis (p > 0.05). Although the variables mean heights of the tallest plant and mean height of the shortest plant around the nests differed significantly between the two nesting colonies analyzed (p < 0.05 for both), the mean height of the plants supporting the nests were not significantly different between sites (p > 0.05).

Based on the number of eggs and nestlings observed in the two colonies (2-5), the average number of eggs per nest was calculated as 3.6 (± 0.84). One egg was laid per day and eggs hatched after 11-12 days (n = 1). Nestling lifespan (the time it took from egg-hatching to fledging) was analyzed following Azpiroz (2000). Nest 1 was discovered on November 28^th, 2014 with four nestlings, aged one or two days. The nestlings vanished between the 9^th and 12^th day of life: it is possible that they flew out of the nest, but not probable. Since those nestlings were too young and were unable to take long flights, it would be expected that, if they were alive and well, they would be found nearby, but this did not happen.

Nest 2 was discovered on November 28^th, 2014, with four one-day-old nestlings. They vanished during the night on the fourth day. This nest was the first monitored nest to be preyed upon. It was the farthest from the others, but the closest to the ground, on the edge of an irrigation canal. Paw tracks of the pampas fox Lycalopex gymnocercus (G. Fischer, 1814) (Canidae) were found nearby. Nest 3 was discovered on November 29^th, 2014 with two eggs. Then, on the following days, two more eggs were laid, one on each day. Nestlings were seen exiting the nest on the 9-10^th day. This was sooner than the 12^th day in the results of Azpiroz (2000). This accelerated fledging may owe to the intense heat on the nest, since it was exposed to the sun.

Nest 4 was discovered ready, but empty, on November 29^th, 2014. It remained empty and it was impossible to say whether there had been eggs and/or nestlings in it, or whether it was abandoned right after it was built. Nest 5 was discovered on November 29^th, 2014 with three nestlings, which were observed till the 9^th day. They were not seen after this, even though they could fly out of the nest, albeit not for long flights. They were not seen within the area close to the nest. Nest 6 was found on November 30^th, 2014 when it contained four eggs and a nestling aged one or two days. The latter was observed during the following eight days but was not seen after the 11^th day. It may have flown out of the nest since it was not seen in the immediate vicinity. The eggs were neither predated nor removed from the nest. They still had not hatched on the last day of observations, on January 14^th, 2015.

Based on the ratio of successful nests (at least one chick produced)/total number of nests evaluated for Nesting Colony 1, five out of six nests were successful (83%). On the other hand, only two fledgling birds at different stages of development were reported between December 10^th, 2014 and December 23^th, 2014 in the vicinity of Colony 1. Since they were only capable of hopping and short flights around the area, it is possible that they were the fledglings from Nests 1 or 5 and 3. If reproductive success is, following Fraga et al. (1998), calculated as the number of fledged chicks/eggs laid or nestling observed, then our estimates are close to 10%. In fact, out of the 20 possible individuals observed that could have developed in the Colony, only these two were observed.

Eight well-developed juvenile SCBs and two adult females were reported at another site, on the edge of the WRBP, on November 30^th, 2014. They were perched on M. bimucronata and then flew together to the interior of the WRBP. At another area, on the edge of the WRBP, a pair was seen feeding four well-developed fledglings accompanied by a male helper. While the male flew in search of food, the female and the helper attacked a low-flying C. buffoni together. The four fledglings hid among cattail brushes (T. domingensis). In addition, a male with two juveniles were seen close by.

Although two pairs of Shiny Cowbirds, Molothrus bonariensis (Gmelin, 1789) (Icteridae), had been seen in Nesting Colony 1 in October, they were not observed there during the breeding period. Also, parasitism by this species on SCB nests was not observed. During a two-hour morning observation on Nest 2, a SCB pair was observed feeding four nestlings every 12 minutes on average (range 4-30 min). During the observation period of one hour and fifteen minutes, in the late afternoon, the average interval of feeding the nestlings of X. flavus was 12.3 minutes (range 10–13), with only the female engaged in this activity. During this period, the male was seen engaging in territorial defense in the nesting area.

During the second breeding season, Nest 7 was found on November 13^th, 2015 with three eggs; the nest had two nestlings and one egg on November 21^th, 2015; there were three nestlings on November 22^th. Four days later, all the nestlings had been preyed upon. Nest 8 was discovered on November 13^th, 2015 with three eggs, but only two eggs remained on November 15^th. On November 21^th, there was a nestling in the nest, but it was not seen again after November 26^th. The pair associated with this nest was also not observed after this date. Nest 9 was seen between November 14^th and November 16^th with four eggs, but it was empty on November 18^th. Traces of eggshells were seen on the ground close to the nest. Nest 10 was recorded in the morning (10 a.m.) of November 15^th with four eggs, but it was empty in the afternoon (04:15 p.m.). The eggs were likely preyed upon during the day, but there were no traces of eggshells. Nest 11 was observed on November 15^th with two eggs; two nestlings were recorded on November 21^th; there was only one nestling on November 26^th, and the nest was empty on December 1^st. The fledgling may have flown out of the nest, but it was not seen in the vicinity.

Apparently, in Colony 2 there were two successful nests out of five (40%). However, we have almost certainly overestimated the reproductive success of the parent birds, since the fledged and juvenile offspring were not observed in the area close to the nests. It is possible that successful breeding did not occur at all in the colony. Beyond those attempts related above, the colonies were not observed making any new breeding endeavors during the study period.

We are grateful to Centro Universitário Univates and to Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) for the scholarship granted to Luciane Mohr. Thanks are also due to Enerplan Group and Logos/Bioimagens Consultoria Ambiental for subsidizing several practical activities undertaken; to the farmers of the Assentamento Filhos de Sepé who allowed us access to their farms; to André Osório, the manager of WRBP and to Cleberton Bianchini, Jonas John, Samuel Gaedke, Camila Schmidt, Rafael Dalssotto, Ricardo Stertz, Manfred Ramminger and Andrea F. Steffens for helping with data collection. Adrian Barnett helped with the English.