Peter Menkhorst

Uncertainty in population dynamics and its consequences for the management of the orange-bellied parrot Neophema chrysogaster

Abstract The population dynamics of a rare and dispersed species like the Orange-bellied Parrot Neophema chrysogaster include many uncertainties, especially concerning mortality. Taking these uncertainties into account we evaluated several options for management of the Orange-bellied Parrot habitat. Options were ranked by their effects on the viability of the population. There was considerable variability in the resulting rank orders. A few general features appeared to be rather stable with respect to all forms of uncertainty considered. It was found that survival of birds during the winter season was more important than their reproductive success in summer and qualitative features of the habitat, such as the composition of vegetation, were more important than quantitative features such as the habitat size.

Ecology of the Regent Honeyeater Xanthomyza phrygia

Data collected from archival material, literature surveys and responses to a questionnaire show that the Regent Honeyeater Xanthomyza phrygia is distributed mostly within 300 km of Australias south-east coast, from latitude 26°30′S (100 km north of Brisbane) to latitude 39°S (near Wilsons Promontory) and as far west as longitude 138°30′E (Adelaide). The species inhabits eucalypt woodlands and open-forest as well as treed farmland and urban areas. Regent Honeyeaters feed mainly on nectar and insects. Nectar is obtained chiefly from eucalypts and is clearly an important determinant of its lifestyle. The species aggressively defends nectar sources against other species of honeyeaters including larger species, although not always successfully. Other food is obtained mainly by foliage gleaning, although hawking and bark feeding are also important. Aggregations occur most often during autumn and winter and at nectar sources. Breeding occurs mostly from August to January. They may have adapted to the general unpredictability of eucalypt nectar flows by movements with two elements: semi-migratory longer-distance movement between regions where a supply of nectar is reliable and abundant; and local wandering in search of accessible nectar.

Fertility control in the koala, Phascolarctos cinereus: the impact of slow-release implants containing levonorgestrel or oestradiol on the production of pouch young

Two hormone-based fertility-control treatments were trialed on free-ranging female koalas. Either levonorgestrel or oestradiol-17β was administered in a cylindrical, silastic, sub-dermal implant. Levonorgestrel was administered in a commercially produced implant (Norplant 2, Leiras). Two different doses of oestradiol were administered via custom-made implants of different length (1 cm and 0.5 cm). Treatments were randomly applied to 58 females (each koala receiving a single implant) and a control group of 27 female koalas received no implant. Fertility, as determined by the presence of pouch young, was recorded following capture and examination during June 1998, 1999, 2000 and 2001. Fertility was reduced in all treatment groups but remained high (90%) in the untreated group. Fertility was lowest in koalas that received levonorgestrel (0%) and longer oestradiol implants (5%). The results demonstrate that slow-release implants containing either of these two steroid hormones have the ability to significantly lower fertility of wild koalas for at least four breeding seasons following treatment. No adverse side effects were apparent in any of the treated individuals. Compared with the cost of current management strategies for over-abundant koala populations, their deployment on a large scale should be cost-effective.

Status and conservation of the rodents of Victoria

Nineteen species of rodents, in two families, have been recorded from Victoria in the modern era. Eighteen are of the family Muridae, represented by 15 native and 3 introduced species. The other species, now extinct in Victoria, was the introduced Sciurus carolinensis. Six of the native species are extinct, one is classified Critically Endangered, one Endangered and four Lower Risk – near threatened. Four of the extinct species were restricted to the semi-arid far north-west; these were Leporillus apicalis, L. conditor, Pseudomys bolami and P. desertor. The two other extinct species, Conilurus albipes and Pseudomys australis, inhabited open forest/woodland, and grassy ecosystems. Extant species include Rattus fuscipes and R. lutreolus, both in the sub-family Murinae; both are widespread and common, particularly in southern Victoria. The remaining seven species are in the sub-family Hydromyinae. Hydromys chrysogaster is widespread in waterbodies throughout the state. Notomys mitchellii and Pseudomys apodemoides occur in dry habitats in the north-west of Victoria; they are uncommon, but most of their habitat is reserved. Mastacomys fuscus, found in higher-rainfall areas of southern and eastern Victoria, from coastal dunes to alpine snowfields, is uncommon. The distribution of Pseudomys fumeus is disjunct, in four widely separated areas. It is classified as Endangered. P. shortridgei is restricted to the Grampians and south-western Victoria, where it may be locally common. The most geographically restricted rodent species in Victoria, Pseudomys novaehollandiae, is Critically Endangered and is the subject of special conservation measures. The most critical threats to rodent populations in Victoria are considered to be (1) the lack of active habitat management for those species that require early seral stages in vegetation, (2) predation by introduced carnivores, and (3) the fragmentation of species into small genetically isolated populations.

The effects of climate on breeding in the Helmeted Honeyeater

Abstract Climate is known to influence the timing and success of breeding in many bird species. In the northern hemisphere, significant breeding changes have been associated with climate change, with warming temperatures, often, but not always, corresponding to earlier laying. For the critically endangered Helmeted Honeyeater (Lichenostomus melanops cassidix) of central southern Victoria, Australia, climate also plays a role in the timing and success of breeding. During the period 1989 to 2006, the timing of laying became earlier and there was a possible reduction in the mean number of eggs laid per breeding season. These changes correspond to a reduction in rainfall and mild warming. If these trends continue under projected climate-change regimes, there will be increased risk of further population decline.

Scope for genetic rescue of an endangered subspecies though re-establishing natural gene flow with another subspecies

Genetic diversity is positively linked to the viability and evolutionary potential of species but is often compromised in threatened taxa. Genetic rescue by gene flow from a more diverse or differentiated source population of the same species can be an effective strategy for alleviating inbreeding depression and boosting evolutionary potential. The helmeted honeyeater Lichenostomus melanops cassidix is a critically endangered subspecies of the common yellow‐tufted honeyeater. Cassidix has declined to a single wild population of ~130 birds, despite being subject to intensive population management over recent decades. We assessed changes in microsatellite diversity in cassidix over the last four decades and used population viability analysis to explore whether genetic rescue through hybridization with the neighbouring Lichenostomus melanops gippslandicus subspecies constitutes a viable conservation strategy. The contemporary cassidix population is characterized by low genetic diversity and effective population size (Ne < 50), suggesting it is vulnerable to inbreeding depression and will have limited capacity to evolve to changing environments. We find that gene flow from gippslandicus to cassidix has declined substantially relative to pre‐1990 levels and argue that natural levels of gene flow between the two subspecies should be restored. Allowing gene flow (~4 migrants per generation) from gippslandicus into cassidix (i.e. genetic rescue), in combination with continued annual release of captive‐bred cassidix (i.e. demographic rescue), should lead to positive demographic and genetic outcomes. Although we consider the risk of outbreeding depression to be low, we recommend that genetic rescue be managed within the context of the captive breeding programme, with monitoring of outcomes.

Demography of the Helmeted Honeyeater (Lichenostomus melanops cassidix)

Abstract Understanding the demography of threatened taxa is essential for formulating effective management strategies for their conservation and for making predictions about their long-term prospects. With fewer than 25 breeding pairs in the current wild population, the Helmeted Honeyeater (Lichenostomus melanops cassidix) is one of the most threatened birds in Australia. Demography of the sole wild population of the Helmeted Honeyeater was investigated by monitoring 526 nests between 1984 and 1996 and 324 colour-banded birds between 1984 and 2008. Throughout the study, the population was effectively closed, there being no evidence of immigration or emigration. Mean survivorship of nests from laying to fledging was 0.17, and mean survivorship of juveniles (from 40 days to 1 year of age) was 0.63. Weighted mean annual survivorship of adult females and males was 0.75 and 0.81 respectively. The population showed little between-year variation in annual productivity and survivorship, with sufficient recruitment for positive population growth. In general, the population dynamics of the Helmeted Honeyeater fit the pattern of an ‘old endemic’ Australian passerine, with low survival of eggs and chicks, extended parental care of juveniles and high survivorship of juveniles and adults. Eggs and chicks that would not naturally survive are a resource that may be used to assist recovery of the population.

Quantifying extinction risk and forecasting the number of impending Australian bird and mammal extinctions

A critical step towards reducing the incidence of extinction is to identify and rank the species at highest risk, while implementing protective measures to reduce the risk of extinction to such species. Existing global processes provide a graded categorisation of extinction risk. Here we seek to extend and complement those processes to focus more narrowly on the likelihood of extinction of the most imperilled Australian birds and mammals. We considered an extension of existing IUCN and NatureServe criteria, and used expert elicitation to rank the extinction risk to the most imperilled species, assuming current management. On the basis of these assessments, and using two additional approaches, we estimated the number of extinctions likely to occur in the next 20 years. The estimates of extinction risk derived from our tighter IUCN categorisations, NatureServe assessments and expert elicitation were poorly correlated, with little agreement among methods for which species were most in danger-highlighting the importance of integrating multiple approaches when considering extinction risk. Mapped distributions of the 20 most imperilled birds reveal that most are endemic to islands or occur in southern Australia. The 20 most imperilled mammals occur mostly in northern and central Australia. While there were some differences in the forecasted number of extinctions in the next 20 years among methods, all three approaches predict further species loss. Overall, we estimate that another seven Australian mammals and 10 Australian birds will be extinct by 2038 unless management improves.

Havens for threatened Australian mammals: the contributions of fenced areas and offshore islands to the protection of mammal species susceptible to introduced predators

Context Many Australian mammal species are highly susceptible to predation by introduced domestic cats (Felis catus) and European red foxes (Vulpes vulpes). These predators have caused many extinctions and have driven large distributional and population declines for many more species. The serendipitous occurrence of, and deliberate translocations of mammals to, ‘havens’ (cat- and fox-free offshore islands, and mainland fenced exclosures capable of excluding cats and foxes) has helped avoid further extinction. Aims The aim of this study was to conduct a stocktake of current island and fenced havens in Australia and assess the extent of their protection for threatened mammal taxa that are most susceptible to cat and fox predation. Methods Information was collated from diverse sources to document (1) the locations of havens and (2) the occurrence of populations of predator-susceptible threatened mammals (naturally occurring or translocated) in those havens. The list of predator-susceptible taxa (67 taxa, 52 species) was based on consensus opinion from >25 mammal experts. Key results Seventeen fenced and 101 island havens contain 188 populations of 38 predator-susceptible threatened mammal taxa (32 species). Island havens cover a larger cumulative area than fenced havens (2152 km2 versus 346 km2), and reach larger sizes (largest island 325 km2, with another island of 628 km2 becoming available from 2018; largest fence: 123 km2). Islands and fenced havens contain similar numbers of taxa (27 each), because fenced havens usually contain more taxa per haven. Populations within fences are mostly translocated (43 of 49; 88%). Islands contain translocated populations (30 of 139; 22%); but also protect in situ (109) threatened mammal populations. Conclusions Havens are used increasingly to safeguard threatened predator-susceptible mammals. However, 15 such taxa occur in only one or two havens, and 29 such taxa (43%) are not represented in any havens. The taxon at greatest risk of extinction from predation, and in greatest need of a haven, is the central rock-rat (Zyzomys pedunculatus). Implications Future investment in havens should focus on locations that favour taxa with no (or low) existing haven representation. Although havens can be critical for avoiding extinctions in the short term, they cover a minute proportion of species’ former ranges. Improved options for controlling the impacts of cats and foxes at landscape scales must be developed and implemented.

Taxonomic and nomenclatural implications of a review of the Pied Currawong Strepera graculina in southern Victoria

In a review of knowledge about subspecies of the Pied Currawong in southern Victoria and far south-eastern South Australia, Menkhorst & Morley (2017) hypothesised that the type specimen of Strepera graculina ashbyi Mathews 1913 might be an immature female of the population currently recognized as S. g. nebulosa Schodde and Mason 1999. If this hypothesis is correct, there are nomenclatural consequences, which we detail here. We also retract the suggestion that neotypes should be defined for the subspecies concerned.