Stress in wild Greater Rhea populations: effects of agricultural activities on seasonal excreted glucocorticoid metabolite levels.

LECHE A.; BAZZANO G.; HANSEN C.; NAVARRO, J. L.; MARIN R. H.; MARTELLA M. B.

JOURNAL FUR ORNITHOLOGIE

WILEY-BLACKWELL PUBLISHING, INC

Año: 2015 vol. 155 p. 919 - 926

0021-8375

In recent years, wild populations of Greater Rhea (Rhea americana) have declineddrastically, due mainly to the conversion of grassland into cropland as a result ofintensive, specialized agricultural practices. In this study we test the potential stressfuleffects of agricultural activities on this ratite by assessing their adrenocortical response.Specifically, we compared fecal glucocorticoid metabolite (FGM) levels of rheas livingin two areas under very different land use: grasslands mainly used for cattle grazingand agro-ecosystems intensively used for crop production. Groups of rheas wereobserved during 45 to 50 min from a distance of approximately 1 km to avoid anypotential disturbance. Therefore, no matching of each fecal sample with a particularsex or individual within the group was possible. Radioimmunoassay of fecal samplesfrom 269 individuals indicated no significant differences in mean concentrations ofFGM from the two habitats sampled.. In the agro-ecosystem we found no overall effectof agricultural practices on the bird´s FGM levels. However, during the dry season FGMconcentrations were significantly higher, which may represent a stress response to thelow availability of food in the post-harvesting season. In contrast, no increase in theFGM levels was registered during the dry season in the grassland, where food wasavailable throughout the year. In this environment the highest increases in FGM levelscoincided with the reproductive period, likely due to the frequent agonist encountersbetween males at this time of the year. Our findings therefore suggest that theagricultural practices have to be viewed as chronic environmental stressors for GreaterRhea populations living under such conditions. The present results support earlierresearch showing detrimental impacts of agricultural activities on this species, whichinhabits the most productive regions of South America.