News Release

Indonesia’s national rare animal needs room to spread her wings

According to a new paper published in the Journal of Raptor Research, local stakeholders should prioritize protection of primary forest habitat in Java, Indonesia, to support the success of the endemic Javan Hawk-Eagle

Peer-Reviewed Publication

Raptor Research Foundation

Adult Javan Hawk-Eagle with prey


Adult Javan Hawk-Eagle with a black rat, Rattus rattus.

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Credit: Heru Cahyono


The endemic Javan Hawk-Eagle (Nisaetus bartelsi) depends upon primary tracts of forest to breed successfully. According to a new paper published in the Journal of Raptor Research, local stakeholders should prioritize protection of primary forest habitat in Java, Indonesia, to allow the remaining 511 pairs of this iconic species to thrive. 


The Javan Hawk-Eagle is currently listed as threatened by the International Union for the Conservation of Nature and was designated as Indonesia’s National Rare Animal in 1993 for reasons that are apparent once you lay eyes on the bird — they are beautiful, with auburn plumage and predatory grace. Like other raptors, they are difficult to study, selecting remote nesting sites and keeping to themselves. In their new paper, “Population Estimates of the Endangered Javan Hawk-Eagle Based on Habitat Distribution Modeling and Patch Occupancy Surveys,” a team led by Syartinilia, from the Department of Landscape Architecture of IPB University Indonesia, reevaluated population estimates for the Javan Hawk-Eagles using updated research methodology and painted an updated picture of their habitat use.


Accurate population estimates are important for conservation of wildlife generally, but here, especially so as the government of Indonesia issued a Ministerial Decree in 2015 stating that the population size of Javan Hawk-Eagles needed to be increased by 10% relative to the 2019 numbers.


The team analyzed habitat changes in West, Central, and East Java between 2008 and 2019 and assessed which patches were utilized by breeding pairs. Here, a patch refers to a piece of forest occupied by nesting Javan Hawk-Eagles. Importantly, they discovered that, although Javan Hawk-Eagles breed most successfully in large patches of forest, they will settle down in small patches if needed. These “stepping stone” habitats likely offer strongholds for nesting Hawk-Eagles in lowland forests where cultivated land is the norm.


Although the research team found a slight decrease in suitable habitat for these Hawk-Eagles between 2008 and 2019, they also determined that the species’ population is higher than previously thought. They attribute this to an improvement in study methods, including higher-resolution satellite imagery, which aids in the identification of suitable nesting habitat by filtering for factors such as slope, elevation, and vegetation cover.


These findings are important for several reasons. First, baseline information on threatened, endemic, and elusive wildlife species is essential in the creation of efficacious conservation policies. Next, these results demonstrate the importance of revisiting population estimate models and applying new technologies. Finally, these researchers conducted interviews with community members, raptor observers, government officials, site managers, and other locals with nuanced knowledge of the region’s realities. This approach to gathering information contributes depth to any long-term study and paves the way for locally relevant conservation. Syartinilia says their paper “will be used as a baseline for the latest information regarding population and distribution of the Javan Hawk-Eagle.”


Notably, the second-highest threat to Javan Hawk-Eagles, after habitat loss, is illegal trade. The number of young birds being sold online is high enough to verify that, prior to this study, published population estimates for the species were indeed inaccurately low.  


Raptors are bioindicators. This means that they offer clues about the health of the ecosystems in which they reside. Protecting raptor habitat benefits multitudes of other species, contributing to overall biodiversity and habitat resilience. Javan Hawk-Eagles are a key part of this ecosystem fabric.  


The authors suggest future studies to continue long-term patch occupancy surveys, field surveys to verify the presence of individual nesting Hawk-Eagles, habitat monitoring, and tracking studies to provide real-time information on the movement of individuals. “This research needs to be carried out because information on home ranges that correspond to the quality of habitat is important for estimating populations that are closer to existing conditions,” says Syartinilia.





Syartinilia, et al. (2023). Population Estimates of the Endangered Javan Hawk-Eagle Based on Habitat Distribution Modeling and Patch Occupancy Surveys. Journal of Raptor Research, 57(4): 1-14.

DOI: 10.3356/JRR-22-16



Notes to Editor:


1. The Journal of Raptor Research (JRR) is an international scientific journal dedicated entirely to the dissemination of information about birds of prey. Established in 1967, JRR has published peer-reviewed research on raptor ecology, behavior, life history, conservation, and techniques. JRR is available quarterly to members in electronic and paper format.


2. The Raptor Research Foundation (RRF) is the world’s largest professional society for raptor researchers and conservationists. Founded in 1966 as a non-profit organization, our primary goal is the accumulation and dissemination of scientific information about raptors. The Foundation organizes annual scientific conferences and provides competitive grants & awards for student researchers & conservationists. The Foundation also provides support & networking opportunities for students & early career raptor researchers.

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