Population Estimates of the Endangered Javan Hawk-Eagle Based on Habitat Distribution Modeling and Patch Occupancy Surveys
Syartinilia,1,2* Yeni Aryati Mulyani,3 Rofifah Aulia Suyitno,1 Aryo Adhi Condro,3 Satoshi Tsuyuki,4 and S. (Bas) van Balen5
1Department of Landscape Architecture, Faculty of Agriculture, IPB University (Bogor Agricultural University), Bogor 16680, Indonesia
2Center for Environmental Research (PPLH), IPB University, Bogor 16680, Indonesia
3Department of Forest Resources Conservation & Ecotourism, Faculty of Forestry and Environment, IPB University (Bogor Agricultural University), Bogor 16680, Indonesia
4Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan
5Basilornis Consults, Muntendampad 15, 6835 BE Arnhem, The Netherlands
ABSTRACT
Estimating the population size of threatened species is problematic and has biases because of a lack of validation data. The Javan Hawk-Eagle (Nisaetus bartelsi) is an endangered raptor endemic to the remnants of natural rainforests of Java, Indonesia. We aimed to improve the accuracy of population estimates through a combination of current habitat distribution modeling and patch occupancy surveys. Higher resolution data sources (improved from 250 m to 30 m) were used in a predicted probability model using logistic regression. Patch occupancy surveys were conducted in habitat patches identified from a predictive analysis and field validation results after 2008. We estimated population sizes only in occupied patches 20 km sq (size based on Javan Hawk-Eagle home-range size). The area of suitable habitats currently totaled 10,804 km sq, as calculated from the results of the 2019 predicted probability model (9106 km2) and field validation (1698 km sq ). The predicted area in 2019 decreased by 6.5% (638 km sq ) from that in 2008. We detected small suitable patches because of improvements in data resolution. The patch occupancy survey validated 44 of the 74 patches (59.5%) in the current habitat distribution. We confirmed that 38 patches (10,166 km sq ) were occupied by Javan Hawk-Eagles, and we estimated the population to be 511 6 3.1 (SE) pairs. This apparent population increase is attributable to improved methodologies in predicting habitat distribution and estimating population size.
KEY WORDS: logistic regression; occupied patch; patch occupancy; population size; suitable habitat.
CITATION : Syartinilia, Mulyani YA, Suyitno RA, Condro AA, Tsuyuki S, (Bas) van Balen S. 2023. Population estimates of the endangered Javan hawk-eagle based on habitat distribution modeling and patch occupancy surveys. Journal of Raptor Research. https://doi.org/10.3356/JRR-22-16