Trapping method and quota observance are pivotal to population stability in a harvested parrot

Wildlife trade is currently regulated mainly in terms of ‘volume’, i.e. the number of individuals taken from the wild or numbers appearing on the market in a given year. To explore the possible effects of other factors such as capture methods, variability in annual harvest, and habitat, we built and validated a demographic model for a closed population of Grey Parrots Psittacus erithacus on Príncipe, and ran 50-year simulations for the population under different harvest scenarios. There was a fine line between capture volumes being robustly sustainable (11% harvested) and dramatically unsustainable (15%). Population trajectories were highly sensitive to changes in adult survivorship, such that the inclusion of even a small number of adults among the harvest had a far greater impact than a similar number of juveniles. High annual variation in capture rate (reflecting poor national management of trade) could make the difference between sustainability and non-sustainability if quotas were set around critical harvest volumes. While these patterns may be common to large traded parrots generally, sufficient habitat and secure nest sites exist on Príncipe to render the effects of habitat loss on the island less important than in most other situations. If trade in parrots is to continue sustainably it will require reliable demographic and harvest data and must eliminate instability in quota observance (exceeded quotas are not compensated by shortfalls in other years) and, especially, the indiscriminate capture of adults

Spatial and seasonal variation in abundance within an insular grey parrot population

© 2017 John Wiley & Sons Ltd. Populations of Psittacidae are endangered by habitat loss and the international pet market. The grey parrot (Psittacus erithacus) is among the most traded species, yet little is known about densities and their variability in time and space. The population of grey parrots on the island of Príncipe (Gulf of Guinea) was estimated with distance sampling, in both pre- and postbreeding seasons. Abundance was related to a range of habitat features using generalized additive models. Densities averaged 48 ± 3 (SE) individuals km-2 in the prebreeding and 59 ± 4 in the postbreeding season, both extremely high compared to elsewhere in Africa and to other parrot species. Despite a population of 6000-8000 individuals over only 139 km2, parrots were patchily distributed, being unrecorded in ~25% of surveyed areas. Abundance varied seasonally, with densities being significantly higher in secondary compared to primary forest in the post- but not in the prebreeding season. Abundance was most tied to the presence of nest-tree species prior to breeding and to feeding-tree species and lightly sloping ground after breeding. These results highlight the need to preserve a matrix of habitat types to provide resources for parrots across seasons and ensure that surveys recognize seasonality in habitat use as a potential bias

Productivity constraints on Citron-crested Cockatoos in a rich community of large hole-nesting birds

Knowledge of breeding success and its limiting factors is crucial in assessing species’ conservation needs. As cavity-nesters, parrots are particularly influenced by the availability of suitable cavities and low breeding output, whether due to natural processes or trapping. On the island of Sumba, Indonesia, the Critically Endangered Citron-crested Cockatoo (Cacatua citrinocristata) has the added problem of co-existing with an unusually rich hole-nesting bird community in a forested environment much constrained by habitat loss. We monitored 95 nesting cavities of cockatoos and their competitors and potential nest-predators, over one to four breeding seasons, using a combination of camera-traps, direct checks on nest contents, and observations from the ground. Competition for suitable cavities was intense among three large parrot species, two owls and a hornbill. Visitation rates by potential competitors were higher at unoccupied cavities than at those containing active nests, reflecting the guarding behaviour of the occupants. The Endangered Sumba Hornbill (Rhyticeros everetti) dominated observed direct confrontations and was the most frequent visitor to active parrot nests, suggesting a further role as a potential nest-predator. Cockatoos prospected many cavities but rarely then attempted to nest: instead the sites were usually occupied by other cavity-nesters, or by bees. At the few cavities where cockatoos did breed, predation pressure was likely low, and observed success rate high (10 successful of 15 nests), although the low number of nests found early in the breeding cycle suggests that some may have failed before detection. Intense competition for cavities suggests a shortage of suitable nest-sites, the need for preservation of old hole-bearing trees and a role for nestboxes. Accessible, known, safe artificial nest-sites would also provide opportunities to assess the scale of nest-site shortage, allow camera placements to study productivity, exclude some competitors and predators, and prevent illegal trapping. Especially given continued trapping pressure, the species would benefit from targeted local awareness-raising and law enforcement, with the whole endeavour backed up by longer-term forest restoration

Performance of a points-based scoring system for assessing species limits in birds

Species are fundamental to biology, conservation, and environmental legislation; yet, there is often disagreement on how and where species limits should be drawn. Even sophisticated molecular methods have limitations, particularly in the context of geographically isolated lineages or inadequate sampling of loci. With extinction rates rising, methods are needed to assess species limits rapidly but robustly. Tobias et al. devised a points-based system to compare phenotypic divergence between taxa against the level of divergence in sympatric species, establishing a threshold to guide taxonomic assessments at a global scale. The method has received a mixed reception. To evaluate its performance, we identified 397 novel taxonomic splits from 328 parent taxa made by application of the criteria (in 2014‒2016) and searched for subsequent publications investigating the same taxa with molecular and/or phenotypic data. Only 71 (18%) novel splits from 60 parent taxa have since been investigated by independent studies, suggesting that publication of splits underpinned by the criteria in 2014–2016 accelerated taxonomic decisions by at least 33 years. In the evaluated cases, independent analyses explicitly or implicitly supported species status in 62 (87.3%) of 71 splits, with the level of support increasing to 97.2% when excluding subsequent studies limited only to molecular data, and reaching 100% when the points-based criteria were applied using recommended sample sizes. Despite the fact that the training set used to calibrate the criteria was heavily weighted toward passerines, splits of passerines and non-passerines received equally strong support from independent research. We conclude that the method provides a useful tool for quantifying phenotypic divergence and fast-tracking robust taxonomic decisions at a global scale

On the edge: habitat restoration priorities for three critically endangered bird species on Sangihe, Indonesia

Remnant forests on the small Wallacean island of Sangihe north of Sulawesi hold the entire ranges of more critically endangered (CR) bird species than any other comparable area on earth. We develop habitat association models for three of these CR species to identify critical habitat features as well as areas where habitat falls slightly short of suitability, and to determine whether another area of forest away from the largest block might be suitable as an insurance site for a translocated population. Hopes for all three species appear almost totally pinned to forest within a 13 km2 area of the Sahendaruman crater, with virtually no near-suitable habitat away from this site. There is, however, little overlap in habitats between one CR species and the other two: cerulean flycatcher Eutrichomyias rowleyi is associated with mature streamside forest with full canopy cover, lianas, and mid-level growth, while Sangihe whistler Coracornis sanghirensis and Sangihe golden bulbul Hypsipetes platenae are restricted to ridgetop forest with full canopy cover and large trees. We pinpoint small areas (around 5 km2) of forest in the crater that are already suitable or can be made so with habitat management, and these are absolute priorities for conservation action. We show how habitat characteristics identified within models might be enhanced, and how features, especially certain tree species, can be used as indicators of future habitat improvement

Protected by dragons: Density surface modeling confirms large population of the critically endangered Yellow-crested Cockatoo on Komodo Island

Intense trapping of the critically endangered Yellow-crested Cockatoo (Cacatua sulphurea) for the international pet trade has devastated its populations across Indonesia such that populations of >100 individuals remain at only a handful of sites. We combined distance sampling with density surface modeling (DSM) to predict local densities and estimate total population size for one of these areas, Komodo Island, part of Komodo National Park (KNP) in Indonesia. We modeled local density based on topography (topographic wetness index) and habitat types (percentage of palm savanna and deciduous monsoon forest). Our population estimate of 1,113 (95% CI: 587-2,109) individuals on Komodo Island was considerably larger than previous conservative estimates. Our density surface maps showed cockatoos to be absent over much of the island, but present at high densities in wooded valleys. Coincidence between our DSM and a set of independent cockatoo observations was high (93%). Standardized annual counts by KNP staff in selected areas of the island showed increases in cockatoo records from <400 in 2011 to ∼650 in 2017. Taken together, our results indicate that KNP, alongside and indeed because of preserving its iconic Komodo dragons (Varanus komodoensis), is succeeding in protecting a significant population of Indonesia's rarest cockatoo species. To our knowledge this is the first time DSM has been applied to a critically endangered species. Our findings highlight the potential of DSM for locating abundance hotspots, identifying habitat associations, and estimating global population size in a range of threatened taxa, especially if independent datasets can be used to validate model predictions. LAY SUMMARY Yellow-crested Cockatoos are threatened by extinction due to illegal trapping for the pet trade. Komodo Island in Indonesia supports one of the largest remaining populations. The island is part of Komodo National Park, famous for its Komodo dragons. A 2006 survey indicated cockatoo numbers might have been declining. In contrast to previous surveys we sampled the whole island instead of focusing on coastal valleys, which are known to harbor the highest cockatoo densities. We used distance sampling and density surface modeling, which allowed us to estimate how many cockatoos remained undetected and to produce a map of predicted cockatoo densities. We estimate there are between 600 and 2,100 cockatoos on Komodo, most likely ∼1,100. Komodo National Park authorities also reported an increase in their annual counts of cockatoos from below 400 in 2011 to around 650 in 2017. Thus, the cockatoo population on Komodo Island is large and stable; Komodo National Park is successfully protecting its cockatoos

Correlates of persistence in remnant populations of two Critically Endangered cockatoos

A challenge with species that have disappeared from most of their range is to identify the correlates of local persistence. With species decimated by trade, site-specific trapping risk is hard to capture by remotely accessed predictors. The recently split yellow-crested cockatoo Cacatua sulphurea and citron-crested cockatoo C. citrinocristata have undergone catastrophic declines due to habitat loss and especially trapping, and are now extinct in much of their former range across Indonesia. Of 144 sites on 30 islands known to contain the species in 1950, only 76 on 27 islands did so in 2017–2019, with many of the other 68 experiencing extinctions between 1985 and 2000. We compared socio-ecological conditions such as forest cover and loss, human population density and infrastructure, and protected area status between the occupied and unoccupied sites, using ‘random forests’ within decreasing time intervals 1950–2015. Populations on Sulawesi and West Nusa Tenggara were more likely to become extinct than those on Sumba, Timor-Leste and small remote islands. Sites retaining cockatoos had high proportions of tree cover, low road density and low human densities. The relative importance of these factors changed little over time, but road density and human density became respectively more and less important in recent years. The examination of local conditions at ‘false negative’ sites (where cockatoos survived contrary to model predictions) showed that, particularly in recent years, cockatoo survival has been promoted by site-specific protection due to traditional beliefs, NGO activities, dedicated individual residents and local topographic barriers. Some of these local influences add complexity to the task of conserving cockatoo strongholds, but also offer exciting possibilities for low-cost conservation prescriptions tailored to individual sites. Studies combining field and remotely sensed data, and examining false negative sites for beneficial location-specific conditions, have broad application for the conservation of taxa with once-large ranges

Street-level green spaces support a key urban population of the threatened Hispaniolan parakeet Psittacara chloropterus

While urbanisation remains a major threat to biodiversity, urban areas can sometimes play an important role in protecting threatened species, especially exploited taxa such as parrots. The Hispaniolan Parakeet Psittacara chloropterus has been extirpated across much of Hispaniola, including from most protected areas, yet Santo Domingo (capital city of the Dominican Republic) has recently been found to support the island’s densest remaining population. In 2019, we used repeated transects and point-counts across 60 1 km2 squares of Santo Domingo to examine the distribution of parakeets, identify factors that might drive local presence and abundance, and investigate breeding ecology. Occupancy models indicate that parakeet presence was positively related to tree species richness across the city. N-Mixture models show parakeet encounter rates were correlated positively with species richness of trees and number of discrete ‘green’ patches (> 100 m2) within the survey squares. Hispaniolan Woodpecker Melanerpes striatus, the main tree-cavity-producing species on Hispaniola, occurs throughout the city, but few parakeet nests are known to involve the secondary use of its or other cavities in trees/palms. Most parakeet breeding (perhaps 50–100 pairs) appears to occur at two colonies in old buildings, and possibly only a small proportion of the city’s 1500+ parakeets that occupy a single roost in street trees breed in any year. Our models emphasise the importance of parks and gardens in providing feeding resources for this IUCN Vulnerable species. Hispaniola’s urban centres may be strongholds for populations of parakeets and may even represent sources for birds to recolonise formerly occupied areas on the island