Reintroduction of a Key Apex Predator Species (Javan Leopard, Panthera pardus melas) Using the Local Conspecific ("Covalent") Species Method: A Four-Year Case Study from Gunung Halimun Salak National Park, Indonesia

1. Introduction

The Javan leopard (Panthera pardus melas) is the last remaining wild felid apex predator on the island of Java, Indonesia, and functions as an indicator of ecosystem integrity and food-web stability. The subspecies is currently listed as Endangered on the IUCN Red List, with a total population estimated at approximately 319–324 mature individuals across more than twenty fragmented subpopulations, each generally holding fewer than 50 mature individuals (Wibisono et al., 2021). The Government of Indonesia's 2016–2026 national action plan for the species prioritises population monitoring, habitat management, and enforcement (Kementerian Lingkungan Hidup dan Kehutanan [KLHK], 2016).

Within TNGHS, three species have been formally designated as landscape-level conservation priorities — the Javan leopard, Javan gibbon (Hylobates moloch), and Javan hawk-eagle (Nisaetus bartelsi) — based on a joint assessment conducted by Conservation International Indonesia and the TNGHS park authority (BTNGHS). Long-term camera-trap monitoring of these taxa within the SEGS operational landscape has been maintained since 2006 under a programme known internally as "Eye of the Forest," which has documented the continued presence of all three priority species alongside other native carnivores and ungulates in the operational area (SEGS Biodiversity Monitoring Report, 2025).

Rehabilitated wildlife reintroduction is one conservation tool available under this framework, but it carries well-documented risks. Global syntheses of large-carnivore translocations indicate that even under contemporary best practice, only around two-thirds of released individuals survive the first six months post-release, and roughly one-third go on to reproduce (Thomas et al., 2023). Orphaned or long-term captive-reared felids face additional challenges in hunting competence and predator-avoidance behaviour, making structured pre-release training and intensive post-release monitoring important components of rehabilitation programmes (Houser et al., 2011). Release-site selection is a further determinant of outcome: the presence of resident conspecifics at a release site has been examined as a factor in settlement and site fidelity for translocated leopards in southern Africa (Weilenmann et al., 2010), and recent multi-country carnivore reinforcement work shows that soft-release protocols combined with conspecific presence at the release site are associated with higher establishment probabilities than hard release without acclimation (Cerne et al., 2024).

Star Energy Geothermal Salak Ltd. (SEGS) operates a geothermal facility within the TNGHS landscape and, as part of its biodiversity management commitments, developed — in partnership with BTNGHS, the Natural Resources Conservation Agency (BKSDA), and the Cikananga Wildlife Center — a release-site selection approach referred to internally as the Local Conspecific ("Covalent") Species Method. The premise is that reintroduction success can be improved, and habituation time shortened, by releasing rehabilitated individuals into habitats where ecological suitability and the presence of resident conspecifics have already been confirmed.

This paper reports the first field application of the method — the release of a rehabilitated male Javan leopard ("Wahyu") at the AWI-6 site in May 2023 — and extends the evaluation reported at the 2026 Indonesia International Geothermal Convention & Exhibition (IIGCE) by incorporating a four-year (2022–2025) key-species monitoring time series. The objectives are to: (1) describe the method and its implementation; (2) report post-release outcomes across a longer observation window; (3) examine the associated four-year trend in a three-species key-taxa biodiversity index; and (4) critically discuss the strength of this evidence in relation to the broader carnivore reintroduction and biodiversity-monitoring literature, including appropriate caveats about what a three-taxon index can and cannot demonstrate.

2. Materials And Methods

The reintroduction was conducted at the AWI-6 forest area within TNGHS, covering approximately 10 hectares, at the coordinates recorded by SEGS at 6°44'19.3" S and 106°39'16.8" E (UTM Grid: 48S, E 682883, N 9254828). Pre-release habitat assessment, conducted jointly by BKSDA, BTNGHS, Cikananga Wildlife Center, and SEGS, identified the site as having well-preserved forest structure, adequate prey availability, suitable shelter, low anthropogenic disturbance, and a confirmed resident wild Javan leopard population. BTNGHS monitoring estimated leopard density in the vicinity at approximately 11.2 individuals per 100 km², reported as among the highest recorded densities for the species in Indonesia (BTNGHS, 2025).

The method combines standard ecological suitability screening (forest cover, prey base, shelter, disturbance level) with confirmation, via camera-trap survey, of resident conspecific individuals at the candidate release site. The working hypothesis is that conspecific presence indicates a habitat already capable of supporting the species' ecological requirements, potentially reducing the behavioural adjustment burden on a released individual and allowing the conventional minimum habituation period (approximately one month) to be shortened to one to two weeks. This is broadly consistent with, though not identical to, findings from soft-release carnivore studies elsewhere in which conspecific presence and acclimation period jointly influenced settlement outcomes (Weilenmann et al., 2010; Cerne et al., 2024).

The programme followed nine sequential stages: (1) identification of candidate individuals for release; (2) veterinary examination and health screening; (3) habitat suitability assessment; (4) camera-trap monitoring for resident conspecifics; (5) construction of the habituation enclosure; (6) sedation and transport; (7) habituation (7–14 days); (8) release; and (9) post-release monitoring. A 10 m × 10 m × 5 m enclosure was constructed at AWI-6, incorporating natural vegetation, climbing structures, a rain shelter, drinking facilities, and six continuous CCTV monitoring units.

Focal Animal

The focal animal, a male Javan leopard named Wahyu, was rescued in 2017 at an estimated age of six months after entering a community area in Tanggeung District, Cianjur Regency, West Java. At the time of rescue, the cub initially refused offered food, including live poultry, and required an extended period of veterinary and husbandry care before establishing a normal feeding pattern. Over the following approximately six years at the Cikananga Wildlife Center, the animal received continued care and behavioural conditioning intended to support the development of independent survival skills, and was released at an estimated age of six-and-a-half years in good body condition. Behavioural assessment prior to release indicated the animal was capable of independent survival in the wild. Pre-release camera-trap surveys confirmed the presence of a resident female leopard near AWI-6. Following a seven-day habituation period, the animal was released on 23 May 2023, in the presence of representatives from the Directorate of Forest and Ecosystem Conservation (KKH-KSDAE) of the Ministry of Environment and Forestry, SEGS, and Cikananga Wildlife Center.

Post-Release Monitoring

Seven camera traps were deployed within a 100-metre radius of the release point to monitor movement and foraging behaviour. Within the first few months following release, Wahyu was repeatedly recorded in healthy, well-conditioned body state, consistent with successful foraging in the wild.

Longer-term monitoring within the broader AWI-6 conservation grid subsequently recorded a third, previously undocumented wild leopard individual in June 2024 — distinct from both Wahyu and the resident female confirmed prior to release.

Key-Species Biodiversity Monitoring

Annual population counts of the three TNGHS priority ("key") species — Javan leopard, Javan gibbon, and Javan hawk-eagle — were recorded within the AWI-6 monitoring grid (10 ha) using a network of 30 camera traps, with 2022 serving as the baseline year and monitoring continuing through 2025 (partial-year data to June). For each year, the relative abundance (pi) of each of the three species was calculated as the ratio of that species' individual count to the combined count of all three species, and a Shannon-Wiener index was calculated as H′ = −Σ(pi × ln pi).

It is important to note that this index differs from a conventional community-level Shannon-Wiener diversity index, which is typically calculated across the full assemblage of species detected at a site (as SEGS itself does elsewhere in its biodiversity monitoring programme for birds and vegetation, discussed further below). Here, the taxon pool is fixed at exactly three pre-selected flagship species, so the index is better interpreted as a measure of relative evenness in the population trajectories of these three priority taxa over time, rather than as a general indicator of faunal community diversity at AWI-6.

Data Analysis

Descriptive trend comparison was used across the four-year (2022–2025) series of population counts and Shannon-Wiener values. Sub-annual (e.g., monthly or per-camera-trap) records underlying the reported annual counts were not available for this analysis; formal inferential statistics (e.g., time-series regression with variance estimation) were therefore not performed, and the four-year pattern is reported descriptively as a small, monotonic increase rather than as a statistically validated trend.

3. Results

The seven-day habituation period — substantially shorter than the conventional minimum of one month — was completed without reported adverse behavioural indicators, and Wahyu was released on schedule on 23 May 2023.

Camera-trap monitoring within a 100-metre radius of the release site recorded the released individual in apparently healthy, well-conditioned body state within the first few months following release, consistent with successful foraging. In June 2024, approximately 13 months post-release, a third, previously undocumented leopard individual — distinct from Wahyu and the resident female confirmed before release — was recorded within the broader AWI-6 conservation grid, indicating continued or increasing use of the area by the species.

Section

*2025 figures are based on data through June 2025.

Combined counts of the three priority species increased from 48 individuals at the 2022 baseline to 56 in 2025, and the corresponding three-species Shannon-Wiener index rose slightly and monotonically from 1.090 to 1.099 over the same period. All three taxa showed year-on-year increases or stable counts, with no observed decline in any species across the four-year window.

For comparison, SEGS's broader, community-level biodiversity monitoring at the same operational landscape — covering the full bird assemblage detected via transect survey rather than a fixed three-species pool — has recorded substantially higher Shannon-Wiener values, typically in the range of 1.3 to 3.8 across monitoring years and sites since 2013, reflecting a much larger species pool. This contrast underscores that the 1.09–1.10 range reported here for the three key species should not be interpreted on the same numerical scale as SEGS's own community-level bird diversity results, and is a function of the deliberately narrow three-taxon design of the key-species index (see Section 2.7).

Beyond the ecological indicators above, the programme generated several institutional and socio-economic outcomes relevant to its broader sustainability case. SEGS reports that shortening the habituation period from the conventional one month to approximately one week reduced enclosure, feeding, and volunteer-accommodation costs by an estimated IDR 89.25 million per release event. The programme also engaged 12 local community members in enclosure construction, transport support, and post-release monitoring, providing supplementary income (reported at approximately IDR 3 million per person per month during active phases). The programme has additionally been incorporated into SEGS's visitor education centre, and is complemented by a separate human-leopard conflict hotline and public-safety guidance materials distributed in partnership with BKSDA West Java.

4. Discussion

The four-year time series strengthens the evidence base compared to the two-point comparison reported in the original conference paper: population counts of all three priority species rose or held steady in every year from 2022 to 2025, and the composite index increased monotonically, from 1.090 to 1.099. Combined with continued post-release detections of the released individual and a subsequent leopard detection in 2024, these results are consistent with — though do not on their own prove — a positive association between the Local Conspecific Species Method and both short-term reintroduction success and longer-term key-species population trends.

Several considerations should nonetheless temper interpretation. First, the reintroduction evidence remains based on a single released individual; global reviews of large-carnivore translocation report that roughly one-third of released individuals fail to survive the first six months even under standardised protocols (Thomas et al., 2023), so a sample of one cannot establish whether the abbreviated habituation period generalises across individuals, sexes, or rehabilitation histories. Wahyu's own history — six years of captivity following rescue as an orphaned cub — falls into a category the literature associates with elevated risk of deficient hunting competence absent structured pre-release training (Houser et al., 2011); whether such training was provided is not documented in the materials available for this paper.

Second, Wahyu's own rehabilitation history — rescued as a roughly six-month-old cub that initially refused food and required extended husbandry care, followed by approximately six years of continued care and behavioural conditioning at Cikananga Wildlife Center before release at an estimated age of six-and-a-half years in good body condition — partially addresses concerns raised in the felid rehabilitation literature about hunting competence in long-term captive-reared, orphaned individuals (Houser et al., 2011). The qualitative account of sustained pre-release care and conditioning is reassuring, though quantitative veterinary records (body weight, body condition score, disease-screening results) and an explicit description of any live-prey or hunting-specific training protocol were not available for this manuscript and would further strengthen this section if the underlying Cikananga medical records can be located.

Third, and importantly, the three-species Shannon-Wiener index used here is not a general biodiversity metric in the sense typically implied by that statistic. Because the taxon pool is fixed at exactly three flagship species by design, the index captures the relative evenness of population counts among those three taxa rather than community-level species richness or diversity. This distinction matters: SEGS's own parallel bird-community monitoring at the same landscape, which surveys the full detected assemblage rather than a fixed three-species subset, reports substantially higher Shannon-Wiener values (typically 1.3–3.8) over a comparable multi-year period. Readers unfamiliar with the narrow construction of the key-species index could otherwise mistakenly interpret the 1.09–1.10 range as indicating comparatively low or stagnant ecosystem diversity, when in fact it reflects a deliberately narrow, flagship-species-only design. We recommend the manuscript explicitly distinguish this key-species evenness index from general biodiversity indices elsewhere in company reporting, both for accuracy and to pre-empt reviewer confusion.

Fourth, the population count methodology for a wide-ranging, largely solitary, cryptic carnivore such as the Javan leopard warrants clearer methodological description than is currently available. Camera-trap counts of individually recognisable animals (e.g., via unique rosette patterns) are the standard approach in leopard population monitoring, but the risk of double-counting or under-counting individuals moving between camera stations is well recognised in the broader carnivore-monitoring literature; a brief statement of how individual leopards were distinguished across the 2022–2025 series (e.g., photographic pattern-matching, spatial capture-recapture, or simple presence counts) — including how the newly detected June 2024 individual was confirmed as distinct from the two previously known animals — would substantially strengthen the credibility of the reported trend for a peer-reviewed audience.

Fifth, while the four-year trend is encouraging, the total change in the composite index (0.009 over four years) remains numerically small, and no measure of year-to-year variance or confidence interval is available to assess whether this trend differs meaningfully from a stable baseline. As in the original two-point comparison, causal attribution of the trend specifically to the leopard reintroduction — as opposed to, for example, general improvements in law enforcement, habitat management, or reduced poaching pressure across TNGHS over the same period — cannot be established from these data alone.

Finally, the reported institutional and cost outcomes (Section 3.4) provide credible evidence that the method offers an operational efficiency benefit — shorter habituation periods plausibly reduce cost, animal welfare burden during captivity, and logistical risk — independent of whether the ecological efficacy claims are fully established. We recommend the manuscript's central claim be reframed accordingly: the Local Conspecific Species Method is well supported as a cost- and time-efficient operational innovation, while its ecological efficacy — in terms of improved survival probability or genuine biodiversity gain attributable to the method — remains a promising but not yet statistically validated hypothesis, pending monitoring of additional released individuals, telemetry-based tracking, and a longer, methodologically transparent key-species and community-level monitoring programme.

5. Conclusion

This study extends an earlier two-point evaluation of the Local Conspecific Species Method for Javan leopard reintroduction with a four-year (2022–2025) time series of key-species population counts from the AWI-6 site within Gunung Halimun Salak National Park. Over this period, combined counts of the three TNGHS priority species (Javan leopard, Javan gibbon, Javan hawk-eagle) rose from 48 to 56 individuals, and the associated three-species Shannon-Wiener index increased monotonically from 1.090 to 1.099, alongside continued post-release detections of the released male leopard and a subsequent leopard detection in 2024. These results offer more consistent, if still modest and correlational, support for the method than previously available. However, because the underlying index reflects only three pre-selected flagship taxa rather than full faunal community diversity, and reintroduction evidence still rests on a single released individual, we recommend the method continue to be framed as a promising, cost-effective operational innovation warranting further testing — via telemetry, a larger number of released individuals, transparent individual-identification methodology, and statistically robust monitoring design — rather than as a fully validated reintroduction or biodiversity framework at this stage.

Acknowledgement

The authors thank Balai Taman Nasional Gunung Halimun Salak (BTNGHS), the West Java Natural Resources Conservation Agency (BKSDA), Cikananga Wildlife Center, and Jarmaskor community group for their partnership in this programme, and the Ministry of Environment and Forestry's Directorate of Forest and Ecosystem Conservation for facilitating the release. This programme's implementation record was formally endorsed by BTNGHS on 11 August 2025.