Increasing variability and declining breeding success: A major challenge in the conservation of the critically endangered Ardea insignis (White-bellied Heron)

Understanding the ecological and demographic factors influencing reproductive success is essential for effective conservation planning. This is particularly critical for species like Ardea insignis (White-bellied Heron), which is critically endangered and survives in fragmented populations. We monitored 3–4 active breeding pairs in Bhutan from 2016 to 2025, focusing on the first egg-laying date and reproductive outcomes. Although all nests were spatially dispersed (7–70 km apart), pairs showed high site fidelity for multiple years. Nests were primarily built on broad-leaved trees near major river channels, at elevations of 280–540 m, often located in proximity to the confluence of the main river and a major tributary. The nests were in secluded areas with minimal disturbance, although not exclusively away from human settlement. Most nests were located on the opposite bank from human settlements, in narrow valleys where fast-flowing rivers serve as physical barriers to human approach. We observed variation in the first egg-laying dates from year to year, with this variability increasing in recent years. We also observed that some pairs consistently initiated early breeding and achieved higher success rates, while others experienced unpredictable outcomes. Overall, clutch sizes varied from 2 to 4 eggs with a mean of 3.10 ± 0.52 SD, hatchlings ranged from 0 to 4 with a mean of 1.55 ± 1.23 SD, and fledglings also ranged from 0 to 4 per nest with a mean of 1.12 ± 1.24 SD. We recorded re-nesting attempts following early clutch failures; however, all these attempts were unsuccessful. An extremely small population with increasing variability and unpredictable breeding output suggests that the population is at risk of extinction. We recommend management actions that prioritize the protection of all breeding pairs and critical habitats, as well as further research on breeding phenology and reproductive performance.