Juan Pablo Isacch

CONSERVATION STATUS OF THE BUFF-BREASTED SANDPIPER: HISTORIC AND CONTEMPORARY DISTRIBUTION AND ABUNDANCE IN SOUTH AMERICA

Abstract We present historic and contemporary information on the distribution and abundance of Buff-breasted Sandpipers (Tryngites subruficollis) in South America. Historic information was collated from the literature, area ornithologists, and museums, whereas contemporary data were derived from surveys conducted throughout the main wintering range in Argentina, Uruguay, and Brazil during the austral summers of 1999 and 2001. Variable circular plot sampling was used to estimate population densities. During 1999, the highest concentration of Buff-breasted Sandpipers in Argentina was in southern Bahía Samborombón (General Lavalle District) and areas north of Mar Chiquita coastal lagoon. During 2001, the highest concentrations in Brazil were at Ilha da Torotama and Lagoa do Peixe National Park. During 1999 and 2001, the highest concentrations of Buff-breasted Sandpipers in Uruguay were found along three lagoons (Laguna de Rocha, Laguna de Castillos, and Laguna Garzón) bordering the Atlantic Ocean. Population densities (birds/ha) of Buff-breasted Sandpipers were 0.11 (95% C.I. = 0.04–0.31) in Argentina, 1.62 (0.67–3.93) in Brazil, and 1.08 (0.37–3.18) in Uruguay. High turnover rates at survey sites, due to the formation of large, mobile flocks, contributed to moderately large confidence intervals around our population density estimates. Nevertheless, compared with historic accounts of Buff-breasted Sandpipers, our survey data indicate the population size of this species has declined substantially since the late 1800s and contemporary information suggests the species has continued to decline during the past three decades. Buff-breasted Sandpipers were found almost exclusively in pasturelands and appear to depend heavily upon intensive grazing by livestock, which maintain suitable short grass conditions. We discuss the need for protection of critical areas and proper range management to ensure appropriate habitat remains available for the species, and provide suggestions for future research needs.

Waterbird Response to Changes in Habitat Area and Diversity Generated by Rainfall in a SW Atlantic Coastal Lagoon

Abstract The rainfall regime of the Pampas region of Argentina shows a long-term cyclic behavior that has increased in intensity over the historical mean during the last four decades. In this paper we explored the effects of changes in monthly cumulative rainfall on lagoon and riparian habitat, and, in turn on the wetland waterbird community. We also explored the responses of waterbird morphofunctional groups to fluctuation in water level and habitat diversity caused by the change in rainfall at the Mar Chiquita Coastal Lagoon, Argentina (37°32’ to 37°45’S, 57°19’ to 57°26’W). Analysis of satellite images shows that increases in rainfall increased wetland water surface, but reduced riparian habitat area and habitat diversity. Increases in water surface negatively affected the abundances and species richness of waterbirds; habitat diversity did not explain a significant portion of total waterbird variability. Shorebirds (i.e., yellowlegs, plover, sandpiper) were the most affected by reduction in mudflats and habitat diversity. Other waterbirds (i.e., long-legged wading birds, waterfowls) were affected by increases in water surface (ducks, swans, long-legged waterbirds and gulls), decrease in mudflat availability (long-legged waterbirds and gulls), and decrease in habitat diversity (ducks). Our results show that the inter-annual variability in the rainfall pattern influenced the presence and abundance of most waterbirds, and species richness and composition. Fluctuation in water depth per se is known to be a key factor for habitat use of many waterbirds, but habitat diversity also needs to be considered.

Composition and seasonal changes of the bird community in the west pampa grasslands of Argentina

Abstract We studied the species composition and seasonality of the bird community in the semi-arid west pampa grasslands of Argentina. The study was carried out in natural grasslands with and without a history of cattle grazing (“mixed grassland” and “sorgastral,” respectively). We counted birds using the strip-transect method. We recorded a total of 22 bird species including only 12 grassland-dependent species. The more representative species of these grasslands were Chaco Pipit (Anthus chacoensis), Long-tailed Meadowlark (Sturnella loyca), and Grassland Sparrow (Ammodramus humeralis). Richness and abundance of birds were higher in mixed grasslands than in sorgastral in spring and summer, but not in winter. Inside habitats, richness and abundance were higher in spring and summer than in winter. We observed a seasonal change in guild dominance, with granivores dominant in winter, although bird density decreased during winter for all guilds. Despite the low richness recorded, the presence of certain rare species, such as the Chaco Pipit and the near threatened Greater Rhea (Rhea americana), add conservation value to west pampa grasslands.

Diversity and Habitat Distribution of Birds in Coastal Marshes and Comparisons with Surrounding Upland Habitats in Southeastern South America

We studied variation in bird assemblages with plant associations for three different coastal marshes from Southeastern South America (SESA) and assessed how marsh bird assemblages related to nearby upland bird assemblages. We surveyed bird species and plant structure along the tidal gradient of each locality from the low tide level to the upper habitats bordering coastal marshes. Twenty species frequently used coastal marshes, including relatively few migratory species. We found that birds occurring in SESA coastal marshes do not have distributions constrained to coastal marshes. Nonetheless, four bird assemblages were recognized in association with vegetation types and/or sites. Among the recorded coastal marsh species, the bay-capped wren-spinetail (Spartonoica maluroides) is both the most frequent and the most habitat constrained. Bird richness increases steadily along the tidal gradient associated with the increase in vegetation structure, suggesting that bird richness is directly explained by vegetation and indirectly by the physical conditions influencing vegetation structure. Results highlight the importance of SESA middle marshes as habitat for conservation of some threatened SESA grassland birds.

Breeding Biology of Spectacled Tyrant (Hymenops perspicillatus) In the Southeastern Pampas Region, Argentina

Abstract The Spectacled Tyrant (Hymenops perspicillatus) is a flycatcher that inhabits open lands, grassy areas near water bodies, marshes, fields and pastures in southern South America. Our aim was to describe the breeding biology of Spectacled Tyrants in native tall grasslands, specifically by studying their reproductive phenology and breeding success. The study was developed in the southeastern Pampas region, Argentina. We conducted nest searching and monitoring during the 2010–2011 and 2011–2012 breeding seasons. We found 88 nests. The breeding season was from mid-October to late January. Clutch size was 2–3 eggs, mode  =  2. Incubation and nestling periods were 15.8 ± 0.7 days and 14.7 ± 0.6 days, respectively. Nest predation was higher during the incubation period than during laying and nestling periods. The probability of nest success from egg-laying to fledging was 0.24. This species shows life-history traits in accordance with other South American temperate birds.

Year-Round Abundance, Richness and Nesting of the Bird Assemblage of Tall Grasslands in the South-East Pampas Region, Argentina

Summary. One of the most extensive grassland ecosystems in the Neotropics is located in the southeastern South America region. Here grasslands once dominated the Pampas but these are now mostly reduced to a mosaic of patches with different land-uses, largely croplands and pasturelands. Native Cortaderia selloana grasslands are widely distributed in the eastern Pampas region but relatively little is known of the bird assemblage inhabiting this habitat. We studied this bird assemblage addressing the overall richness and presence of species of conservation concern, seasonal variation in species composition, breeding phenology and the importance of C. selloana habitats for birds. Species richness was high: 54 species belonging to 22 families, including six species of conservation concern: three classified as vulnerable to extinction (dot-winged crake Porzana spiloptera, black-and-white monjita Xolmis dominicanus and pampas meadowlark Sturnella defilippii), and three near threatened (greater rhea Rhea americana, bay-capped wren-spinetail Spartonoica maluroides and Hudsons canastero Asthenes hudsoni). The highest species richness was observed in spring and summer, with peaks in spring and marked drops in autumn. The insectivore guild was the most numerous throughout the year. We identified 21 nesting species, four of which were of conservation concern, with a peak of reproductive activity during November. Owing to the high species richness and of the large number of threatened species, C. selloana grasslands should be considered of outstanding conservation priority in the Pampas region.

Shorebird Seasonal Abundance and Habitat-Use Patterns in Punta Rasa, Samborombón Bay, Argentina

Abstract. Shorebird assemblage composition and habitat-use patterns were characterized at Punta Rasa during the austral summer, autumn and winter. Compared to other sites within the region, this area showed high species richness, reflected by a total of 22 species recorded within a relatively short time frame. Differences in assemblage structure were driven by the use of estuarine mudflats and oceanic sandy beaches as feeding habitats. During low tide, more species used estuarine environments, achieving the highest total densities. Abundance patterns and assemblage composition also changed seasonally. Maximum total abundance occurred during the austral summer, and minimum total abundance during the austral winter. During the austral summer, the assemblage was dominated by Nearctic migrants such as American Golden-Plover (Pluvialis dominica), Hudsonian Godwit (Limosa haemastica) and White-rumped Sandpiper (Calidris fuscicollis). In addition, Two-banded Plover (Charadrius falklandicus) and American Oystercatcher (Haematopus palliatus) were abundant during the austral autumn. The Red Knot (Calidris canutus), a shorebird that dominated the austral autumn assemblage 25 years ago, was recorded in relatively small numbers during this study, probably reflecting the global population trend of a subspecies of the Red Knot (C. c. rufa) in the past two decades. During the austral winter, resident birds largely dominated the assemblage. However, it is noteworthy that some individuals of nine Nearctic migrant species remained in the area. In the case of the endangered Red Knot, Punta Rasa is, along with Lagoa do Peixe in Brazil, one of the sites in South America with the highest known abundances during the austral winter.

Variation in parental care in the spectacled tyrant Hymenops perspicillatus is associated with increased nest predation in grassland fragments

AbstractPredation risk on birds is often an important source of natural selection that shapes parental care and may promote behavioral changes. Parents can often estimate certain risks and adjust their behavior to reduce the likelihood of nest predation. The fragmentation of habitats is one of the main consequences of loss of habitats, and in general, for birds breeding in smaller patches, their daily nest-survival rate is lower due to increased nest predation. Since nest survival is an estimate of predation risk in the environment, we evaluated the daily survival rate (DSR) for nests of spectacled tyrants (Hymenops perspicillatus) and parental care behavior on fragmented and unfragmented grasslands. We conducted nest searching and monitoring during the 2012–2013 breeding season in small patches and in a continuous patch of grassland. In addition, parental activity was recorded using video monitoring. We found a lower DSR for the spectacled tyrant in fragmented grasslands, associated with increased nest predation risk; females showed a variation in parental care. This variation was evidenced by larger incubation bouts and lower visitation rate during the incubation period, and by a lower food delivery rate to nestlings, compensated by larger prey sizes. The results show that fragmentation not only reduces the fitness of individuals and impacts adversely on population, but individuals are also subjected to a strong selection pressure, and their reproductive success may depend to some extent on the ability of parents to estimate at least certain predation risk and adjust their behavior in this regard.ZusammenfassungUnterschiede in der Brutpflege beim Brillentyrann steht in Verbindung mit einer erhöhten Nest-Prädationsrate in fragmentiertem Grasland Das Prädationsrisiko ist für Vögel eine wichtige Quelle natürlicher Selektion, die die Brutpflege formt und zu Verhaltensänderungen führen könnte. Oft können Eltern bestimmte Risiken abschätzen und ihr Verhalten anpassen, um die Wahrscheinlichkeit für Nest-Prädation zu reduzieren. Die Fragmentierung von Habitaten ist die wesentliche Folge von Habitatverlust, und generell ist für Vögel, die in kleineren Habitatflecken brüten, die auf den Tag umgerechnete Überlebensrate eines Nests (daily survival rate, DSR) aufgrund von höherer Nest-Prädation geringer. Weil Nest-Überlebensraten ein Schätzer für das Prädationsrisiko in der Umgebung sind, erhoben wir die DSR für Nester des Brillentyrann (Hymenops perspicillatus) zusammen mit Brutpflegeverhalten in fragmentiertem und unfragmentiertem Grasland. Wir führten Nestersuche und Nestmonitoring in der Brutsaison 2012–2013 für kleine Flecken und in einem zusammenhängenden Stück Grasland durch. Außerdem wurde das Brutpflegeverhalten mit Videomonitoring aufgenommen. Wir fanden, dass der Brillentyrann in fragmentiertem Grasland eine geringere DSR hatte, und die Weibchen zeigten in Verbindung mit dem erhöhten Prädationsrisiko eine Änderung im Brutpflegeverhalten. Diese Änderung zeigte sich in längeren Bebrütungsphasen und verringerter Anzahl dieser Phasen, und in selteneren Fütterungen, die aber durch größere verfütterte Beute kompensiert wurden. Die Ergebnisse zeigen, dass Habitat-Fragmentierung nicht nur die individuelle Fitness herabsetzt und sich negativ auf die Population auswirkt, sondern auch einen Selektionsdruck auf Individuen darstellt, indem ihr Reproduktionserfolg teilweise davon abhängen könnte, wie gut die Elterntiere zumindest bestimmte Prädationsrisiken abschätzen und mit Verhaltensänderungen darauf reagieren können.

Microscale nest-site selection by the Burrowing Owl (Athene cunicularia) in the pampas of Argentina

ABSTRACT Habitat modifications have led many bird species to occupy areas with different characteristics, including human-altered landscapes. In this study, we analyzed how land use influences the nest-site selection at the microscale level by Burrowing Owls (Athene cunicularia) breeding in vegetated sand dunes, periurban areas, and agroecosystems in the Pampas of Argentina. We compared the characteristics of the nest site (percentage of open space) and the nest patch (distance to conspecific nests, tall vegetation and perches and number of perches) within and among the three land-cover types. In addition, we evaluated the breeding performance (nesting success and productivity) of owls nesting in these land-cover types. We found that nest microsite variables did not vary between owl-occupied and owl-unoccupied sites within nest patches, but they differed among land-cover types. Although nest patches differed in their availability of perches at each land-cover type, distance from the nest to the nearest perch did not vary between them. Distances to tall vegetation and to conspecific nests were highly variable and did not differ among land-cover types. Our results indicate that Burrowing Owls that inhabit the Pampas used a variety of land-cover types for nesting and showed little selectivity of nest sites and nest patches, thus reinforcing the idea that they are habitat generalists.

Conflict between the Greater Rhea and humans in agricultural landscapes: implications for conservation of the last large herbivore of the southern Pampas

Abstract South-eastern South America (SESA) hosts populations of a number of large herbivores, such as the Greater Rhea (Rhea americana). However, the natural grasslands of SESA have been subject to major transformation through agricultural development, primarily grazing, cropping and afforestation. Here, we assess the relative effects of environmental and anthropogenic predictors on the distribution of Greater Rheas in the southern Pampas at different spatial scales, and produce distributions maps of the species derived from habitat-suitability models. We undertook vehicle surveys in the southern Pampas over 2 years, surveying 4600 km of road each year, and recording a total of 146 sightings of 1353 individual Rheas. Generalised additive models were used to model the presence—absence of Greater Rheas in 250-m2 cells. The habitat suitability models suggest that preferred habitats included areas of high elevation supporting waterbodies and landscapes of grazing fields and native habitats, whereas centres of human activity negative affect the distribution of the species.