Joaquín L. Navarro

MODELING HABITAT SUITABILITY FOR GREATER RHEAS BASED ON SATELLITE IMAGE TEXTURE

Many wild species are affected by human activities occurring at broad spatial scales. For instance, in South America, habitat loss threatens Greater Rhea (Rhea americana) populations, making it important to model and map their habitat to better target conservation efforts. Spatially explicit habitat modeling is a powerful approach to understand and predict species occurrence and abundance. One problem with this approach is that commonly used land cover classifications do not capture the variability within a given land cover class that might constitute important habitat attribute information. Texture measures derived from remote sensing images quantify the variability in habitat features among and within habitat types; hence they are potentially a powerful tool to assess species-habitat relationships. Our goal was to explore the utility of texture measures for habitat modeling and to develop a habitat suitability map for Greater Rheas at the home range level in grasslands of Argentina. Greater Rhea group size obtained from aerial surveys was regressed against distance to roads, houses, and water, and land cover class abundance (dicotyledons, crops, grassland, forest, and bare soil), normalized difference vegetation index (NDVI), and selected first- and second-order texture measures derived from Landsat Thematic Mapper (TM) imagery. Among univariate models, Rhea group size was most strongly positively correlated with texture variables derived from near infrared reflectance measurement (TM band 4). The best multiple regression models explained 78% of the variability in Greater Rhea group size. Our results suggest that texture variables captured habitat heterogeneity that the conventional land cover classification did not detect. We used Greater Rhea group size as an indicator of habitat suitability; we categorized model output into different habitat quality classes. Only 16% of the study area represented high-quality habitat for Greater Rheas (group size > or =15). Our results stress the potential of image texture to capture within-habitat variability in habitat assessments, and the necessity to preserve the remaining natural habitat for Greater Rheas.

Diet of greater rheas in an agroecosystem of central Argentina

Using microhistological analysis of feces, we studied the diet of wild greater rheas (Rhea americana) by comparing plant species frequency in feces with availability. Green material composed 90% of the diet of rheas, followed by seeds (9%), fruits, and fragments of invertebrates and vertebrates. Wild and cultivated gramineous plants were eaten in low quantity throughout the year (11% of the green material), and were not preferred by rheas. Alfalfa and wild dicots were frequent in the diet (89%) and preferred in some seasons. Rheas consume alfalfa in higher proportions during the winter when this plant is not available to large domestic livestock. Therefore, greater rheas would probably compete more with sheep and goats than with horses and cattle. So the conservation and management of rheas for sustainable use could be compatible with traditional cattle ranching.

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.

Abundance and spatial distribution of Greater Rhea Rhea americana in two sites on the pampas grasslands with different land use

Summary In Argentina the original landscape structure of the pampas grasslands has changed rapidly due to intensified and specialized agricultural practices. The conversion of grasslands into croplands has been suggested as a threat to Greater Rhea Rhea americana populations. The main goals of this study were to estimate the abundance of Greater Rheas and to analyse the species’ spatial distribution at two sites of the pampas region with different land use: agro-ecosystem and grassland. The former was mainly devoted to crop production whereas the latter was mostly used for livestock grazing. Data were collected through 14 aerial surveys from 1998 to 2001, and in 2004. Each survey consisted of six strip-transects per site, spaced at regular intervals. The total area surveyed represented 4% of each study site (113 km 2 in the grassland and 95 km 2 in the agro-ecosystem). Greater Rhea density (iSE) was significantly higher in the grassland (from 0.22 i0.11 to 0.86 i 0.24 ind. km 22 ) than in the agro-ecosystem (from 0.05 i 0.05 to 0.12 i 0.08 ind. km 22 ). Greater Rheas occupied 51% of the study area in the grassland but less than 5% in the agro-ecosystem. They showed a wide and uniform spatial distribution in the former area, whereas in the latter individuals occurred in small and isolated clusters. These results raise concern about the future of the species because, over recent years, land has been increasingly used for crop production. Hence, if the current rate of change in land use continues, the conservation status of this species will be seriously affected.

Habitat use by wild and captive-reared greater rheas Rhea americana in agricultural landscapes in Argentina

From 1998 to 2000 we used radio telemetry to study habitat use by greater rheas Rhea americana in rural areas. Captive-born greater rheas preferred pastures to grasslands and did not use crops. No differences in habitat use were found between wild and captive-born greater rheas. Wild individuals preferred pastures, showed less preference for grasslands, and did not use crops. Rheas used pastures and grasslands for nesting but they did not use crops. No differences in nesting success was detected between these habitats. Our results show that agroecosystems that include grasslands and pasture production would strongly contribute to the conservation of this species. However, poaching must be controlled to ensure long-term persistence of wild populations of greater rheas.

Physiological stress in captive Greater rheas (Rhea americana): Highly sensitive plasma corticosterone response to an ACTH challenge

Up to the present no studies have been conducted either on baseline concentrations of adrenal hormones or on hormonal responses to stress in Greater rhea (Rhea americana) and most ratite species. The aims of this work were to assess the presence of corticosterone in plasma of Greater rhea, to validate a corticosterone (125)I-radioimmunoassay for determining corticosterone levels in plasma samples and to study the activation of the adrenal gland after an adrenocorticotrophic hormone (ACTH) challenge. Six captive Greater rhea juveniles of 10 months of age received an intravenous ACTH injection. Blood samples were taken at 0min (baseline pre-ACTH levels), and post-injection at 15, 30, 60min and at 24 and 48h. The high pressure liquid chromatography (HPLC) analysis of pooled plasma showed that corticosterone is the glucocorticoid found in the plasma of Greater rhea. Biochemical assays of standard validation (e.g., parallelism, exogenous corticosterone recovery) showed that measurements of corticosterone present in the plasma of the Greater rhea provided by commercial corticosterone (125)I-radioimmunoassay were accurate and precise. ACTH challenge induced a more than 40-fold increase in plasma corticosterone at 60min post-ACTH (from 4.0 to 166.5ng/ml, on average). The corticosterone response to ACTH in Greater rhea was higher than is usual in birds, an apparently typical characteristic of ratites.

Carcase and component yields of rheas

1. Three Greater Rheas (Rhea americana) and 5 Lesser Rheas (Pterocnemia pennata) were slaughtered, using the procedures conventional for ostriches in South Africa, in order to determine the expected yield of by-products and saleable lean meat, fat and bone of rheas. 2. Differences (P < 0.05) between species were found in the proportional weight of the wings, feet, skin and liver. The wings, feet and head of rheas form a higher proportion of the carcase than in ostriches, whereas the skin of the former represents a lower percentage of body weight. 3. Lean meat production from rheas (64% on a carcase weight basis) is in the same order as for ostriches, broilers, turkeys and beef.

Corticosterone stress response of Greater Rhea (Rhea americana) during short-term road transport

The effect of transport stress on blood corticosterone levels in captive Greater Rheas was investigated. Twelve adult individuals (7 males; 5 females) were loaded in pairs inside wooden crates and transported along a paved road for 30 min. Blood samples were taken before the individuals were introduced into the crate (baseline value) and immediately after they were unloaded (30 min after capture). To assess whether corticosterone levels were affected by the blood sampling procedure per se, another 6 (nontransport) control birds (3 males; 3 females) were also captured and sampled at the same times as their transported counterparts. Plasma corticosterone concentrations were measured using a commercially available corticosterone (125)I radio-immunoassay kit. Baseline corticosterone levels were similar in the control and transported birds (9.0 ± 1.6 and 10.4 ± 0.8 ng/mL, respectively). Transportation induced a highly significant (P < 0.001), more than 40-fold increase in the corticosterone levels (433.6 ± 35.4 ng/mL) that was about 5 times higher (P < 0.001) than in their nontransported counterparts (88.4 ± 14.8 ng/mL). The present findings suggest that Greater Rhea is a species highly sensitive to stressful manipulations. Both blood sampling and transportation induced highly significant adrenocortical responses. Considering that transportation is one of the unavoidable common practices in the management of Greater Rheas and, as shown in the present study, that it induces a significant 40-fold corticosterone stress response, efforts should focus on helping to generate management transport standards for optimization of the welfare of this ratite.

Effects of hunting, egg harvest and livestock grazing intensities on density and reproductive success of lesser rhea Rhea pennata pennata in Patagonia: implications for conservation

Wild lesser rheas were studied during two re- productive seasons (2004-2005 and 2005-2006) in three adjacent ranches in Argentine Patagonia. These ranches differed in hunting pressure and egg harvest (protected, moderate and intensive use of the species), and livestock grazing conditions (with and without overgrazing). Density of individuals and nests, clutch size, brood size, hatching success, chick survival and recruitment rate were estimated in each area. At the ranch with intense hunting pressure, egg harvesting and livestock grazing, density of lesser rheas was the lowest and reproductive events were not recorded. None of the recorded demographic parameters differed signifi- cantly between the ranch where the species is protected and there is low livestock grazing intensity and the ranch where there is moderate use of the species and intensive grazing. Our work suggests that intense hunting and egg harvesting would have stronger effects than overgrazing on the density and reproductive success of wild lesser rhea populations in

Microbial contamination of artificially incubated Greater Rhea (Rhea americana) eggs.

1. This paper is a report of biological agents that contaminate Greater Rhea (Rhea americana) eggs during artificial incubation. 2. The cleanliness of eggs when collected, and the period of storage prior to incubation, were investigated to assess their effects on microbial contamination and hatchability. 3. A total of 14 bacteria and 4 fungi species were isolated within the egg in the laboratory. 4. Microbial contamination was higher (24%) in very dirty eggs than in eggs which were clean or dirty (16%). Hatching success was lower (30%) for very dirty eggs, compared with 42% for clean or dirty eggs. 5. The percentage of microbial contamination of stored eggs (10%) did not differ significantly from that of non-stored ones (5%). 6. The extreme lower and upper limits of infection rate estimated for artificially incubated Greater Rhea eggs were 4% and 40%, respectively, being higher than in poultry species. 7. It is concluded that collecting eggs soon after laying will reduce the risk of microbial contamination.