Foraging habitat preferences of a selective herbivorous bird, the Puna Rhea Rhea tarapacencis in the desert Puna, midwestern Argentina

Abstract

In herbivores, habitat preference is influenced by resource availability, which is most evident in desert ecosystems. The desert puna is a South American environment dominated by grassy steppes with local grassy cushion plants associated with moist soil conditions, which form the habitat called 'vegas'. In this environment, Puna Rhea Rhea tarapacencis has a strongly selective foraging strategy towards plant species that are in low abundance but that exhibit low contents of secondary compounds, fiber, or both. This contrasts with other generalist herbivores of arid environments, which prefer plant species with high fiber content and are highly abundant. We determined habitat use by Rheas in three habitat types: foothills, valley and vegas; and provided evidence of their feeding habitat preferences. From 2011 to 2014, we estimated density of birds and environmental variables such as total plant cover and abundance of total food, preferred foods and non-preferred foods. In particular, the density was estimated indirectly based on counting and collecting feces of the birds in transects. We analyzed the effect of the habitat type and environment variables on bird density; and compared the environmental variables among habitats. Puna Rheas used the three habitats, but fecal records were very scarce in vegas. The density was higher in foothills than in the valley (0.45 and 0.01 inds/km2, respectively), increased with higher abundance of the preferred foods and declined with increased non-preferred foods. The foothills were preferred as they had the highest abundance of the preferred foods and the non-preferred foods were similarly abundant in foothills and valley. The vegas had the highest total plant cover and the lowest abundance of all food species consumed by the Rheas. Therefore, the abundance of preferred foods, which have the best nutritional quality, represents a good predictor of habitat preference and, possibly, an essential resource during the life cycle of the Puna Rhea.