Habitat structure and association with ungulates drive habitat selection and grouping behaviour of lesser rhea (Rhea pennata subsp. pennata)

Social prey species respond to predation risk by modifying habitat selection and grouping behaviour. These responses may depend on both actual predation risk (predator probability of occurrence) and/or on perceived predation risk associated with habitat structure. Other factors like food availability and co-occurrence with other species may also affect habitat selection and group formation. We analyse habitat selection and grouping behaviour (group size and cohesion) of lesser rhea (Rhea pennata subsp. pennata), a ratite endemic of South America inhabiting steppe shrublands and grasslands, in relation to actual (puma probability of occurrence) and perceived (habitat structure: openness, visibility) predation risk, co-occurrence with other herbivore species and forage availability in the Chilean Patagonia. We used data from 9 sampling seasons in 5 years. Results show that habitat selection, group size and cohesion in lesser rhea were mainly driven by variables associated with perceived predation risk and by co-occurrence with other herbivores both during breeding and non–breeding season. As expected, lesser rhea preferred open habitats (vegas and grasslands) that allow a behaviour of ‘watch and run’ to avoid predation and formed larger groups in them. Moreover, lesser rhea positively selected year-round habitats where livestock occur, forming large groups during non–breeding season there. Group size and co-occurrence with other herbivores significantly decreased group cohesion, suggesting a reduction of perceived predation risk. Therefore, lesser rhea seems to take advantage of forming mixed interspecific groups to reduce predation risk. These results suggest that lesser rhea habitat selection and grouping behaviour are preferentially driven by factors related to perceived predation risk than by actual predator occurrence or food availability.