Greater Rhea Research Articles

Time–activity budget of greater rheas (Rhea americana, Aves) on a human-disturbed area: the role of habitat, time of the day, season and group size

The aim of this study was to evaluate activity–time budget, habitat use and how seasonality and group size influence the expression of greater rhea behaviours. Greater rheas are threatened South American birds; habitat loss, predation and hunting are the main factors responsible for population declines. The study was conducted in farmlands within a matrix of commercial Eucalyptus plantation and remnants of natural habitats of cerrado vegetation (savannah-like) in southeastern Brazil. Rhea groups were located visually in different habitats visited monthly from January 2004 to December 2005. Time spent searching greater rheas in each habitat was equally distributed. Data were collected using scan sampling with instantaneous recording of behaviours every minute. The time–activity budget of greater rheas was influenced by habitat structure, time of the day, season and group size. Rheas spent more time in open areas than in forested areas (p < 0.001). Vigilance behaviours were more displayed in forested areas, in the dry season and by solitary and small groups of birds. Resting behaviours occurred more often in open lands and within groups with more than three rheas. Food availability, good visibility and low human presence are the possible factors for the preference of greater rheas for pasturelands. The results support the resource availability hypothesis, where it is expected that habitats with a higher food availability will be more used by the animals, group size hypothesis, where the scarcity of resources will lead to smaller groups of animals and that forestry modifies greater rheas habitat use and behaviours.

Reproductive characteristics of captive greater rhea (Rhea americana) males reared in the state of São Paulo, Brazil

Rheas (Rhea americana) belongs to the ratite group. Considering the commercial significance of this birds, some techniques, such as semen collection, were standardized. In this study, 107 male rheas (3 to 4 years of age) reared in commercial farms in the state of Sao Paulo, Brazil, were used. Semen was collected during the breeding and off-breeding seasons of 2001, 2002, and 2003. Bird hierarchical behavior was observed. Birds were restrained performed using a box and a black hood. Semen was collected by digital pressure on the base of the phallus, which size was measured, and the presence or absence of spiral shape was observed. Immediately after collection, semen samples were evaluated for volume, motility, sperm concentration, and morphology. In a limited number of birds, blood samples were collected to measure testosterone levels. Among the 69 birds studied during the breeding season, 44 presented large phalluses, out of which 26 showed spiral shape. The method of semen collection was efficient. The following semen parameter results were obtained: volume (0.68 ±0.14 ml), motility (61.11±11.54%), sperm concentration (3.29±1.33 x109 sptz/ml), and number of spermatozoa per ejaculate (2.40±1.38x109 sptz/ml). Morphological abnormalities were analyzed and recorded. Testosterone levels were statistically different (p = 0.0161) between the breeding and non-breeding season (53.28±18.41 ng/ml and 5:57±3.81 ng/ml, respectively). Variations in phallus size were also found between the breeding and non-breeding seasons. Larger phalluses and higher testosterone levels were correlated with dominant behavior. The results of the present experiment confirmed that it is possible to collect semen from rheas, allowing the future use of biotechnologies such as artificial insemination.

Comparative ossification sequence and skeletal development of the postcranium of palaeognathous birds (Aves: Palaeognathae)

Palaeognaths constitute one of the most basal lineages of extant birds, and are also one of the most morphologically diverse avian orders. Their skeletal development is relatively unknown, in spite of their important phylogenetic position. Here, we compare the development of the postcranial skeleton in the emu (Dromaius novaehollandiae), ostrich (Struthio camelus), greater rhea (Rhea americana) and elegant crested-tinamou (Eudromia elegans), focusing on ossification. All of these taxa are characterized by element loss in the appendicular skeleton, but there are several developmental mechanisms through which this loss occurs, including failure to chondrify, failure to ossify and fusion of cartilages prior to ossification. Further evidence is presented here to support a reduction in size of skeletal elements resulting in a delay in the timing of ossification. This study provides an important first look at the timing and sequence of postcranial ossification in palaeognathous birds, and discusses the influence of changes in the pattern of skeletal development on morphological evolution.

Comparative ossification and development of the skull in palaeognathous birds (Aves: Palaeognathae)

Ratites and tinamous are a morphologically diverse group of flightless and weakly flighted birds. As one of the most basal clades of extant birds, they are frequently used as an outgroup for studies discussing character evolution within other avian orders. Their skeletal development is not well known in spite of their important phylogenetic position, and studies have historically been plagued with small sample sizes and limited anatomical and temporal scope. Here, I describe the ossification of the skull in the emu (Dromaius novaehollandiae), ostrich (Struthio camelus), greater rhea (Rhea americana), and elegant crested-tinamou (Eudromia elegans). Skeletal development is remarkably consistent within palaeognaths, in spite of large differences in absolute size and incubation period. Adult morphology appears to play a role in interordinal differences in the sequence and timing of ossification of certain bones. Neither the timing of cranial ossification events relative to stage nor the sequence of ossification events provides any evidence in support of a paedomorphic origin of the palaeognathous palate. This study provides an important first look at the timing and sequence of skull development in palaeognathous birds, providing data that can be compared to better-studied avian systems in order to polarize ontogenetic characters. © 2009 The Linnean Society of London, Zoological Journal of the Linnean Society, 2009, 156, 184–200.

Trophic interactions among plains vizcacha (Lagostomus maximus), greater rhea (Rhea americana), and cattle in a wetland of the Paraná River Delta Region, Argentina

The plains vizcacha (Lagostomus maximus) and the greater rhea (Rhea americana) are considered to compete for forage with cattle in agroecosystems of South America. The aims of this research were to analyze the diet diversity and the trophic niche breadth of these three herbivores where they share a wetland area in Argentina, and to assess the extent of food niche overlap throughout the year. The three species all showed relatively narrow trophic niches in all seasons, which defines them as selective feeders. Vizcacha and cattle showed the highest (54.8%) mean food niche overlap throughout the year. A low overlap was observed between greater rhea and the other two herbivores, except in Winter (61.2% greater rhea and cattle). Vizcacha showed the highest mean diet diversity, and diet diversity was similar, but lower, in greater rhea and cattle. According to the results, if livestock raising increases and a scenario of competition is considered, the vizcacha is likely be the most affected species, because its foraging areas are restricted to the surroundings of its fixed burrows. On the other hand, greater rheas have an opportunistic foraging behavior and can move into areas where cattle are absent.

Scanning pattern of greater rheas, Rhea americana: collective vigilance would increase the probability of detecting a predator

Many models using vigilance to predict the probability of detecting an approaching predator assumes that prey scanning events should be produced at random. Consequently, the length of intervals among successive scans must follow a negative exponential distribution. We analyzed the scanning behavior of the greater rhea, Rhea americana, which is a gregarious, flightless bird, in eastern Argentina. We investigated whether individual and/or collective scanning departed from random and whether this departure varied with group size. We used two simulation models based on observed scanning sequences to assess the effectiveness of vigilance on the individual and collective level when faced with an opportunistic or stalking predator. The analysis of 59 behavioral sequences of wild greater rheas foraging solitary or in groups of two to six or more individuals revealed that the inter-scan length of individual sequences significantly departed from random. In contrast, inter-scan intervals for collective vigilance were shorter than individual ones, but only fit the random expectation for groups of two and five individuals. Models showed that collective vigilance could increase the probability of detecting a predator, thereby reducing their vulnerability, independent of whether the predator uses a stalking or opportunistic approaching strategy.

The molecular basis of chromosome orthologies and sex chromosomal differentiation in palaeognathous birds

Palaeognathous birds (Struthioniformes and Tinamiformes) have morphologically conserved karyotypes and less differentiated ZW sex chromosomes. To delineate interspecific chromosome orthologies in palaeognathous birds we conducted comparative chromosome painting with chicken (Gallus gallus, GGA) chromosome 1-9 and Z chromosome paints (GGA1-9 and GGAZ) for emu, double-wattled cassowary, ostrich, greater rhea, lesser rhea and elegant crested tinamou. All six species showed the same painting patterns: each probe was hybridized to a single pair of chromosomes with the exception that the GGA4 was hybridized to the fourth largest chromosome and a single pair of microchromosomes. The GGAZ was also hybridized to the entire region of the W chromosome, indicating that extensive homology remains between the Z and W chromosomes on the molecular level. Comparative FISH mapping of four Z- and/or W-linked markers, the ACO1/IREBP, ZOV3 and CHD1 genes and the EE0.6 sequence, revealed the presence of a small deletion in the proximal region of the long arm of the W chromosome in greater rhea and lesser rhea. These results suggest that the karyotypes and sex chromosomes of palaeognathous birds are highly conserved not only morphologically, but also at the molecular level; moreover, palaeognathous birds appear to retain the ancestral lineage of avian karyotypes.

Respostas comportamentais de emas cativas Rhea americana Linnaeus (Rheiformes, Rheidae) submetidas a treinamento anti-predação

Human activities have been diminishing greater rhea Rhea americana (Linnaeus, 1758) populations throughout their natural distribution. The reintroductions of captive-born greater rheas have been tried but without success; since the individuals reintroduced were killed by predators. Captive-born animals that have been isolated from predators for many generations can lose their predator recognition abilities. To enhance the survival rates of the reintroduced animals, researchers are now using antipredator training techniques. We studied the response of 15 zoo-borne greater rheas to antipredator training. The animals were divided into three groups: two test groups and one control group. We ran 15 antipredator tests and four control testes with each group. Antipredator tests consisted of pairing a taxidermized predator model or a real predator (domestic dog) with a simulation of a capture procedure. Control tests consisted of presenting the predator model (jaguar) to the birds, after training but not associating it with an aversive event and recording behavioural responses. All tests were video-recorded and analysed a posteriori. Results showed that the trained rheas responded appropriately to the predators, becoming more vigilant and that there was considerable individual differences in response to antipredator training. The results demonstrated that antipredator training is effective and therefore an invaluable tool for reintroduction projects involving greater rheas. Furthermore, the methods employed in this research project should be applicable to other species of flightless birds.

Home range of greater and lesser rhea in Argentina : relevance to conservation

In this work we report results of radiotracking studies on the movements and home range sizes of two near-threatened species, the greater rhea (Rhea americana) and the lesser rhea (Pterocnemia pennata pennata) in relation to different land use regimes. We radiomonitored greater and lesser rheas for 3 years in their respective habitats: the Pampas and the Patagonia regions. We chose two study areas in each habitat with similar agricultural activities and different hunting control. We did not find significant differences in movements and home range size between study areas of each species. This suggests that disturbance caused by human presence in the areas did not affect rhea spacing behaviors. Moreover, lesser rheas showed larger home range and movements than greater rheas, showing that the home range size is not an immutable property of body mass, and that abundance and distribution of food appears to be the main factor that influences the movements and home range size of these birds.

Comparative analysis of variables associated with germination and seedling establishment for Prosopis nigra (Griseb.) Hieron and Acacia caven (Mol.) Mol.

The purpose of this work was to compare different variables associated with the germination and growth of Prosopis nigra and Acacia caven seedlings. Fieldwork was carried out in 1999 on materials collected in Entre Rı́os province, Argentina. Germination percentages and rates were measured in order to determine the effect of immersion in water for different periods of time and of the ingestion of P. nigra fruits by the greater rhea. Seedling growth was compared for both species as a function of stem elongation, increase in volume, leaf production rate and survival percentage during the first 60 days following germination. Results indicate that, unlike A. caven, P. nigra seeds are negatively affected by immersion in water as seeds submitted to different immersion periods showed a significant decrease in final germination percentages with respect to untreated seeds. P. nigra seeds ingested by the greater rhea also showed lower final germination percentages as compared to those not ingested. Nevertheless, those that succeeded in germinating achieved significantly higher germination velocities. A. caven seedlings attained significantly higher heights than those of P. nigra from the 20th day onwards. Volume growth for A. caven was also higher, as well as leaf production and survival until the 60th day. Results suggests that in order to maintain P. nigra dominance, practices favoring prolonged waterlogging periods should be avoided, thus promoting a high seedling yield.

Characterization and chromosomal distribution of novel satellite DNA sequences of the lesser rhea (Pterocnemia pennata) and the greater rhea (Rhea americana).

Two different types of novel satellite DNA (stDNA) sequences were cloned from the lesser rhea (Ptercnemia pennata) and the greater rhea (Rhea americana) after digestion of genomic DNAs with a restriction endonuclease Pvu II, and characterized by filter hybridization and in-situ hybridization to metaphase chromosomes. These nucleotide sequences consisted of GC-rich 288-bp and 332-bp repeated elements in P. pennata and 288-bp and 336-bp repeated elements in R. americana, all of which were organized in tandem arrays in the genome. The 288-bp and 332-bp elements of P. pennata displayed strong sequence similarity with the 288-bp and 336-bp elements of R. americana, respectively. The 332-bp and 336-bp elements were located on almost all the microchromosomes in both the species. The other type of repeated elements, the 288-bp element, was located on four and nine pairs of microchromosomes in P. pennata and R. americana, respectively. All the stDNA sequences were not crosshybridized to genomic DNAs of another three ratite species, ostrich (Struthio camelus), cassowary (Casuarius casuarius) and emu (Dromaius novaehollandiae), suggesting that these stDNA sequences are conserved in the same family but fairly divergent among the different families of Struthioniformes.

Early Holocene Bone Technology at the La Olla 1 Site, Atlantic Coast of the Argentine Pampas

La Olla 1, in the Pampas of Argentina, is an open-air site located on the Atlantic coast in the Monte Hermoso District, southern Buenos Aires Province. Bones in lacustrine layers outcrop during very low tide exposed by longshore drift. Based on an initial analysis of the faunal assemblage, two species of sea mammal, guanaco, pampean deer, greater rhea, and a fish were represented in the almost 300 bones recovered during the rescue excavation. The lithic assemblage consisted of unifacially flaked tools, rounded cobbles reduced by bipolar technique, flakes, and artifacts with flat abraded surfaces. Radiocarbon determinations of c. 7300 and 6600 bp came from sea mammal femora. An informal bone tool recovered from the site is made from the left proximal tibia of an adult otariid. It is identified as a utilitarian bone tool on the basis of use-wear characters that are restricted in distribution, and as a fracture-based bone tool on the basis of technological characters. The element was dynamically impacted in the mid-diaphysis region. Use-wear characters are loss of edge angularity, microflaking, pitting, striae, and polish. Microflaking occurs along the posterior fracture surface and exterior adjacent cortical surface. Pitting of the fracture surface extends along the entire length of the worn edge, but is most concentrated along the posterior fracture surface. A multitude of very fine striae runs parallel to the fracture edge. The area of striations is limited to this edge with a well-demarcated boundary. Covering all of these characters is differential wear-polish. This high gloss polish is strongly reflective and occurs over very worn and rounded areas, providing a very bright, melted appearance. Based on these different use-wear patterns, the La Olla 1 bone tool is interpreted as a dual-purpose implement most likely used for carcass dismemberment and hide processing. The La Olla 1 tool is unusual in that it is made from pinniped bone. Biomechanical analysis of southern fur seal bone indicates, however, a strong suitability for impact-related tasks and, therefore, an appropriate choice for use as butchering tools.