There is serious concern for the future of a wide range of birds in Java and elsewhere in Indonesia due to both loss of habitat and trapping for the cagebird trade (the so-called “Asian Songbird Crisis”). Despite this concern, few data on presence and abundance of key species exist. We provide such data on 184 bird species from over two years of biodiversity surveys from 37 sites on 12 mountains in West and Central Java. Many of these species are heavily traded, endemic, and globally threatened. Several of the threatened endemics, notably Javan Trogon and Javan Cochoa, were often recorded, in terms of both geographical spread and numerical abundance. Rufous-fronted Laughingthrush, Spotted Crocias, and Orange-spotted Bulbul, believed to be threatened by trapping for the songbird trade, appear to remain fairly widespread. By contrast, Brown-cheeked Bulbul, Chestnut-backed (Javan) Scimitar-babbler, Javan Oriole, and especially Javan Blue-flycatcher, recorded on just a single occasion, and Javan Green Magpie, which we failed to record with certainty, now appear to be extremely rare. Our encounter rates, while not pinned to specific mountains for security reasons, represent an important baseline against which future changes in abundance can be gauged.

Many Indonesian, and in particular Javan, birds are suspected to have declined dramatically as a result of unsustainable trapping for the cagebird trade, but quantitative evidence of the scale of declines is lacking for the great majority of species. We conducted field surveys of the heavily traded Javan White-eye Zosterops flavus at 19 key sites in 2018–2019 matching the methods and personnel used in baseline surveys done around 10 years earlier. Overall numbers counted were 84% lower in the later survey, and while more white-eyes were recorded at three sites in 2018–2019, there was a significant decline in numbers across all sites. The three sites with highest numbers in 2006–2019 (502 birds counted) had 22 individuals counted in 2018–2019, but there was no overall trend for ‘declines’ to be greater at sites that held more birds originally. Declines in white-eyes were much steeper than those of several lesser-traded bird species at the sites, suggesting that trapping has been a more important driver of declines than habitat changes such as conversion of mangrove to shrimp ponds. Small numbers of white-eyes were recorded at several previously unvisited sites, but we suggest that the species, on Java at least, has shown declines in the region of 80% over the last 10 years. Although since 2018 Javan White-eye is legally protected, we urge that this protection is extended to all white-eye species, because of their similarity.

Designating protected areas remains a core strategy in biodiversity conservation. Despite high endemism, montane forests across the island of Java are under-represented in Indonesia's protected area network. Here, we document the montane biodiversity of Gunung Slamet, an isolated volcano in Central Java, and provide evidence to support its increased protection. During September–December 2018, we surveyed multiple sites for birds, primates, terrestrial mammals, reptiles, amphibians and vegetation. Survey methods included transects, camera traps and targeted searches at six sites, at altitudes of 970–2,512 m. We used species distribution models for birds and mammals of conservation concern to identify priority areas for protection. We recorded 99 bird species (13 globally threatened), 15 mammals (five globally threatened) and 17 reptiles and amphibians (two endemic). Our species distribution models showed considerable cross-taxon congruence between important areas on Slamet's upper slopes, generally above 1,800 m. Particularly important were records of the endemic subspecies of the Endangered Javan laughingthrush Garrulax rufifrons slamatensis, not recorded in the wild since 1925, the Endangered Javan gibbon Hylobates moloch and Javan surili Presbytis comata, and the Vulnerable Javan lutung Trachypithecus auratus and Javan leopard Panthera pardus melas. Recent forest loss has been modest, at least 280 km2 of continuous forest remain above 800 m, and our surveys show that forest habitats are in good condition. However, the mountain is widely used by trappers and hunters. Given its importance for biodiversity conservation, we discuss different options for improving the protection status of Gunung Slamet, including designation as a National Park or Essential Ecosystem.

The Short-tailed Green Magpie Cissa thalassina, a member of an Asian lineage of uniquely coloured corvids, is represented by two subspecies, thalassina and jefferyi, that occur on the islands of Java and Borneo, respectively. The distinct Javan nominate form is poorly described in the literature and next to nothing is published on its biology and occurrence in the wild. We here document the biology and distribution of this taxon based on hitherto unpublished historical data and on our own fieldwork. We also analyse vocal data of jefferyi, thalassina and two other Cissa species and show that jefferyi and thalassina are well-differentiated, and that thalassina is bioacoustically more similar to another Cissa species from the Asian mainland. We also demonstrate important and significant biometric differences between jefferyi and thalassina that may reflect divergent adaptations to the environment, as well as plumage differences that may serve signalling functions. Finally, the application of a novel species delimitation test to our data suggests that jefferyi and thalassina deserve to be classified as biological species because their phenotypic divergence exceeds that found in many sympatric species. The revised taxonomic status of Javan thalassina invites a reconsideration of its threat status. Based on its restricted range, extreme rarity and threats by bird trapping and habitat destruction, we consider the Javan Green Magpie as globally Critically Endangered.

The Javan Hawk-eagle Spizaetus bartelsi is endemic to the island of Java. Severe habitat fragmentation and small population size, aggravated by illegal hunting have put this rainforest species on the list of threatened bird species. Intensive searching since 1986 resulted in the discovery of a large number of localities additional to the historic ones. All known locality records of Javan Hawk-eagle have been scrutinized and are listed in the present paper. Confirmed post-1980 records are from 24 forest fragments of varying sizes: 10 (including 28 discrete localities) in west, seven (including 14 discrete localities) in central and seven (including 20 discrete localities) in east Java. The configuration of available habitat in forest clusters is evaluated. The co-existence with other threatened bird taxa, and the need for further field surveys and studies of the Javan Hawk-eagle are discussed.

In a manuscript written by August Spennemann in the 1930s, information is presented on display behaviour, vocalizations and habitat at two hitherto unknown localities of the Javanese Lapwing Vanellus (Hoplopterus) macropterus, a species last recorded in 1940. We provide a translation of the notes and give a summary of all information additional to what has already been published on the species. The Javanese Lapwing is historically known from two discrete areas on the island of Java: one in the west along the north coast, and one in the east along the south coast. Spennemann's observations, made in 1927 and 1928 at Poponcol and Tegallurung, represent the last documented sightings of the species along the north coast and are situated some 75 km east of the north coast's previous easternmost known locality, effectively doubling the species' known range in western Java. At this time, the Javanese Lapwing was observed daily, and unlike at most other localities from where the species is known, was common. Spennemann observed them in groups of up to six birds, the largest group size recorded. Some local movement or migration is suggested by its erratic occurrence and off-shore sightings.

Pink-headed Fruit-dove Ptilinopus porphyreus is a little-known, restricted-range species, endemic to the mountains of the Indonesian islands of Sumatra, Java and Bali. In the period 1981–2002 we conducted surveys throughout its range and compiled data on its presence and absence on 32 isolated mountain complexes. The fruit-dove appeared to be restricted to < 12,000 km2 of forest, scattered over 20 major mountain complexes on the three islands, i.e. three on Sumatra, 16 on Java and one on Bali. It occurred exclusively on mountains of > 2,000 m in altitude, where, depending on the size of the mountain, it reached its lower altitudinal limit between 500 and 1,000 m. The species was found mostly in singles or as pairs but occasionally in flocks of up to 17 individuals. It occurred almost exclusively in forest, feeding on figs and small berries in the upper-canopy. We documented three cases of breeding in the wild. From captive birds it is known that a single egg is laid which is incubated for 20 days, with fledging occurring after another 15–16 days. Based on a study of 104 skins, the breeding season peak in West Java is at the beginning of the dry season. Although Pink-headed Fruit-dove is found in scattered, ever-shrinking forest blocks of mostly < 200 km2, the scarcity of recent field records is more than likely due to its inconspicuous behaviour, and a threatened status is unwarranted as yet.

The Bali starling Leucopsar rothschildi is a passerine endemic to the dry monsoon forest of the island of Bali, Indonesia. Habitat conversion and excessive capture for the pet trade brought the species to the verge of extinction in the 1980s. The species is critically endangered because of 1) an extremely small population size, 2) restriction to a small area, 3) illegal trapping, and 4) diminishing suitable habitat left within its natural range. An intricate web of factors prevents the Bali starling from emerging from this precarious situation.

A faunal survey was conducted in May–September 1994 and June–July 1995 in the Dieng Mountains, one of the last remaining larger patches of forest in CentralJava province, Indonesia. All three primate species endemic to the Javan faunal region – Javan gibbon Hylobates moloch, grizzled leaf monkey Presbytis comata and ebony leaf monkey Trachypithecus auratus – were found to be present. Hylobates moloch occurs only in the lowland and hill forests in the western part of the study area, while the other two species were found throughout the area from lowland to montane forests. Although more research needs to be done onhabitat preferences and densities at which the primates occur, the available data suggestthat the Dieng Mountains may harbour the second largest populations of both H. moloch and P. comata in the same location. In order to safeguard these two endangered primates itis suggested that the reserve system in Java be expanded to include the Dieng Mountains.