Reproductive Ecology of the Lesser Rhea (Rhea pennata) in the Peruvian Andes: Nesting Sites, Phenology, and Social Organization.

The suri, or lesser rhea (Rhea pennata), is a flightless Andean bird facing multiple anthropogenic threats. Despite these pressures, its reproductive ecology remains poorly documented near its distributional limits. This study provides the first comprehensive evaluation of the breeding ecology, nesting distribution, and threats for wild lesser rhea populations at their northern geographic limit in Moquegua, Peru. Across four consecutive breeding seasons (2021-2024), we combined systematic surveys, kernel density analysis, camera trapping, and micro-behavioral nest monitoring. We identified 14 nesting sites comprising 193 nests: 18 old with eggshells remains, 110 old without eggshells, 53 nests under construction, and 12 actives. Kernel density analysis indicated a total nesting area of 195.8 km2, with a low density of 0.15 nests/km2. Nests were primarily established on moderately sloping hillsides utilizing high-Andean desert vegetation for camouflage. The reproductive period extended from mid-July to mid-December, displaying marked interannual variation in breeding phenology. Camera trap records and field encounters confirmed nest predation and interactions by a native predator guild composed of mammals (Lycalopex culpaeus, Puma concolor) and raptors, while free-ranging domestic dogs act as localized anthropogenic disturbance factors and linear infrastructure represents potential movement constraints. These findings establish an essential ecological baseline, highlighting that the long-term persistence of this marginal population depends on standardized monitoring to detect subtle demographic shifts and on strategic connectivity conservation across high-Andean landscapes.