Study maps lesser rhea breeding ecology in Peru’s high Andes
Bottom line
A new study in Animals offers what the authors describe as the first comprehensive look at the reproductive ecology of wild lesser rheas, or suris (Rhea pennata), at the northern edge of the species’ range in Moquegua, Peru. Across four breeding seasons from 2021 to 2024, researchers identified 14 confirmed nesting sites within a broader set of 20 candidate areas, documented breeding timing from late June through January, and described a social system built around solitary males, female groups, reproductive harems, and male-led family groups. The work also details nest placement, clutch characteristics, incubation behavior, and threats including predation, trampling by wild and domestic ungulates, livestock activity, and human land use. (preprints.org)
Why it matters: For veterinary and wildlife professionals, the study adds baseline reproductive and behavioral data for a species with limited field evidence in Peru, where Rhea pennata has been reported as Critically Endangered nationally even though its global IUCN status has been listed differently. The authors report average clutch size of 14.8 eggs, an incubation period of about 43.5 days in the nests followed from laying to hatching, and 71% hatching success in two monitored nests, while camera data confirmed predation by culpeo foxes, Andean caracaras, variable hawks, and pumas. Those details can help inform nest monitoring, ex situ and in situ conservation planning, rehabilitation protocols, and discussions about how grazing, infrastructure, and predator pressure shape reproductive success in marginal populations. (preprints.org)
What to watch: The next question is whether Peru’s ongoing census, monitoring, and conservation efforts in Moquegua, Puno, and Tacna translate these breeding-ecology findings into site-level protection and measurable population gains. (gob.pe)
Key facts
- Study type
- Reproductive ecology study
- Species
- Lesser rhea, or suri (Rhea pennata)
- Location
- Moquegua, Peru
- Study period
- Four breeding seasons, 2021 to 2024
- Confirmed nesting sites
- 14
- Candidate areas
- 20
- Average clutch size
- 14.8 eggs
- Average incubation period
- 43.5 days
- Hatching success
- 71% in two monitored nests
A newly published study in Animals sheds light on the breeding ecology of the lesser rhea, or suri (Rhea pennata), in Peru’s high Andes, filling a long-standing evidence gap for one of the country’s most vulnerable wild birds. Working in Moquegua over four consecutive breeding seasons, the research team mapped confirmed nesting areas, tracked reproductive timing, described social organization, and documented threats affecting nests and chicks at the northern edge of the species’ distribution. (preprints.org)
That matters because reproductive ecology for wild Andean lesser rhea populations has been poorly documented, even as conservation concern has grown. A 2024 population viability analysis from Peru noted that the species occurs in the southern highlands of Puno, Moquegua, and Tacna, and cited declines between earlier national counts, along with pressure from poaching, egg collection, habitat fragmentation, and mining-related disturbance. That paper also noted a disconnect between the bird’s international and Peruvian conservation classifications, underscoring why local data are so important for management decisions. (scielo.org.pe)
In the new study, the authors report 14 confirmed nesting sites and a nesting kernel area of 195.8 km², with estimated nest density of 0.15 nests/km². Nests were typically placed on moderately sloping hillsides in mixed grassland and shrub habitats, but the team also found use of sparsely vegetated high-Andean desert sites more than 1 km from wetlands, suggesting local flexibility in nest-site choice. The breeding cycle began with pre-laying behavior from late June into October, followed by egg-laying from the last week of August to the third week of October, incubation from early September to mid-December, and hatching from mid-October to mid-December. (preprints.org)
The reproductive details are especially useful. Across monitored nests, clutch size averaged 14.8 eggs, with individual nests ranging from 5 to 19 eggs. Eggs averaged about 499 g, and the two nests followed from laying through hatching showed an average incubation period of 43.5 days and hatching success of 71%. The male handled incubation and brood care, with observed behaviors including egg shifting, rotation, retrieval, vigilance, resting, and nest maintenance. Chicks became mobile within three days of hatching and stayed with the male for months, sometimes more than a year. Over 2020 to 2024, the researchers recorded 48 family groups and 357 chicks, with first chick sightings shifting earlier over time, from December 7 in 2020 to October 17 and 18 in 2024 and 2023, respectively. (preprints.org)
The paper also adds practical threat data. Camera traps and direct monitoring linked active nest and egg predation to culpeo foxes, Andean caracaras, variable hawks, and pumas. Nest damage was reported less often than predation, but when it occurred it was mainly associated with trampling by vicuñas, followed by llamas and taruca, leading to egg breakage, abandonment, and secondary predation. Several nesting areas were also associated with livestock grazing, private property, mining claims, or solar energy projects, pointing to the layered pressures facing this remnant population. (preprints.org)
There does not appear to be substantial outside expert commentary on this specific paper yet, but the broader conservation response in Peru suggests the findings land in an active policy context. Peruvian authorities have announced and carried out additional census and monitoring efforts for suri populations, including national census work and satellite-supported monitoring in Moquegua. Taken together with the recent population viability analysis, the new field data provide a more operational picture of where breeding happens, when it happens, and which threats are most immediate on the ground. (gob.pe)
Why it matters: For veterinary professionals, especially those working in wildlife medicine, conservation programs, zoological collections, or rehabilitation, this study is less about clinical intervention and more about decision-grade biological context. Knowing the timing of laying, incubation, chick rearing, and male parental investment can shape handling protocols, nest surveillance windows, rescue thresholds for displaced eggs or chicks, and coordination with land managers. It also reinforces that reproductive success in this species is tied not just to disease or individual health, but to habitat structure, disturbance, predator guilds, and human use of breeding landscapes. (preprints.org)
What to watch: The next step is whether these findings are folded into targeted protection of confirmed nesting areas in southern Peru, and whether future monitoring shows improved recruitment or stabilization in a population already flagged as vulnerable in national conservation planning. (scielo.org.pe)