Recently, the Flores Hawk-eagle was downgraded on the IUCN Red List from Critically Endangered to Endangered. While this may initially appear to be a positive step for the species, it doesn’t necessarily reflect an improvement in their overall conservation status. The population estimate, previously believed to be fewer than 250 individuals, has been revised upward to a range between 320 and 1,500 individuals. This revision simply brings the species’ population above the threshold for Critically Endangered status (which is 250 individuals), but the truth is, the species’ situation on the ground hasn’t improved. The increased population estimate is still very much an “estimate” and empirical data on population size are lacking. Approximate numbers of nesting pairs have been given per island based on habitat suitability, how much space each pair needs (i.e. home range estimates) and limited knowledge of the species distribution. One of the problems is that this is a lot of guesswork.
Estimating the Home Range: What We Know So Far
Accurately estimating home range size is important for understanding the overall population size because if you know how much space an animal needs and how much habitat is available, then you can infer how many animals there could be. But if you underestimate home range size, you might overestimate the population estimate and vice versa.
Until now, our understanding of the space needs of Flores Hawk-eagles has come from observational studies. By recording sightings of eagles around two known nest sites, researchers Kuspriyangga et al. (2025) estimated that the eagle’s home range spans between 1.6 – 8.4 km². However, these estimates are likely to underestimate the eagle’s actual space requirements due to limitations on collecting sightings data in areas further away from the nest. The same team also looked at the distance between the two nesting sites, and assuming circular, non-overlapping home ranges, came up with a larger home range estimate of around 23.1 km².
Insights from Our Year of Tracking
In May 2024, HawkWatch International placed a transmitter on a Flores Hawk-eagle for the first time in collaboration with the Raptor Conservation Society (RCS) in Indonesia. Now, a year since that momentous occasion, we have our first insights into the amount of space they require throughout the year.
From tracking data, we can derive accurate monthly estimates of the eagle’s movements, revealing significant variation depending on the time of year. While incubating, the eagle’s home range was estimated at as little as 4.2 km². During non-breeding months, the home range expanded to as much as 29.1 km². Overall, during the first year of tracking, the tracked eagle’s annual home range, containing 95% of the eagles movements, was estimated at 21.8 km².
What Does This Mean for Conservation?
These new data provide crucial insights into the habitat needs of the Flores Hawk-eagle. The significant increase in home range size during non-breeding periods indicates that the species requires large, undisturbed tracts of forest to meet its needs throughout the year.
The annual range size of 21.8 km² is much larger than the estimates based solely on sightings, highlighting the importance of accurate data for developing effective conservation strategies. We can also see from the data that the eagle is heavily dependent on undisturbed forests in a protected area, and makes use of forest patches which have been fragmented by habitat loss. However, the extent of this forest is being continually reduced by agriculture and land occupation. If we aim to protect this species, we need to ensure that sufficient areas of preferred habitat are conserved, so that both breeding and hunting grounds are protected.
Looking Forward
As we continue to track and study the Flores Hawk-eagle, we will gain even more insight into how they use their environment throughout the seasons, and between different areas or individuals. This will be essential for refining conservation strategies to protect one of Indonesia’s most iconic raptors.
Acknowledgements
This research is being led by our project partner, Usep Suparman, at Raptor Conservation Society in Indonesia. Trapping and tagging of this Flores Hawk-Eagle was done in collaboration with Forest Management Unit (KPH) Maria Donggomasa, Sindikat Wildlife Photography Bima-Dompu, and the local community in Kaowa.
This blog was written by Dr. Meg Murgatroyd, HWI’s International Programs Director. You can learn more about Meg here.
References
- BirdLife International. 2024. Nisaetus floris. The IUCN Red List of Threatened Species 2024: e.T22732096A229714191. https://dx.doi.org/10.2305/IUCN.UK.2024-2.RLTS.T22732096A229714191.en. Accessed on 23 June 2025.
- Kuspriyangga, A., Mulyani, Y. A., Syartinilia, & Hidayat, O. (2025). Home range and habitat use of the endangered Flores Hawk-eagle (Nisaetus floris) in Ende, Flores, East Nusa Tenggara. Journal of Tropical Forest Management, 31(May), 133–144. https://doi.org/10.7226/jtfm.31.2.133
