Using species distribution models to direct nest surveys for the Critically Endangered Philippine Eagle on Luzon and the Eastern Visayas

The Philippine Eagle (<i>Pithecophaga jefferyi</i>), a Critically Endangered apex forest raptor, faces severe threats from habitat loss, fragmentation, and human disturbance. While most research and confirmed nesting sites are from Mindanao, knowledge of distribution and nesting ecology on Luzon, Samar, and Leyte remains limited due to challenging terrain and logistical constraints. We applied species distribution models (SDMs) integrating nest locations, GPS tracking data, and high-resolution remotely sensed habitat covariates to predict suitable nesting habitats on these understudied islands. We fitted models using penalized logistic regression and evaluated via Continuous Boyce Index (CBI), yielding high predictive accuracy (CBI: Luzon = 0.873; Eastern Visayas = 0.709). For Luzon, habitat suitability was most strongly associated with intermediate Leaf Area Index values (peak ≈ 3.0), reflecting dense canopy cover and potential prey abundance. In the Eastern Visayas, suitability was best predicted by intermediate vegetation structural homogeneity (peak ≈ 0.4), indicative of diverse forest structure. Predicted high-suitability habitat accounted for 10 % of the total landscape in both regions, with medium-to-high suitability comprising 25 % of the total landscape. Core high-suitability habitat was scarce (Luzon = 3 %, Eastern Visayas = 2 %), emphasizing the fragmented nature of remaining optimal habitat. On Luzon, the largest contiguous high suitability habitat occurred in the northern Sierra Madre, with smaller patches in the Cordillera and Zambales ranges. In the Eastern Visayas, high suitability zones were concentrated along Leyte’s central mountain spine, with smaller, fragmented patches on Samar. Our outputs provide spatially explicit priorities for targeted nest surveys and broader conservation action, including habitat protection, threat mitigation, and monitoring. By directing limited resources toward high probability areas, our SDMs offer an efficient, data-driven approach to address key knowledge gaps and advance the objectives of the Philippine Eagle conservation. Our methodology also has wider applicability for range-restricted forest raptors in similar tropical landscapes.