Matthew Webb

Ground-based survey methods both overestimate and underestimate the abundance of suitable tree- cavities for the endangered Swift Parrot

Abstract Most cavity-dependent species select tree-cavities with a narrow range of characteristics so that only a small subset of available cavities may be suitable for any species. Most surveys for tree-cavities are done from the ground using binoculars to reduce effort, but this technique is prone to error. These errors are likely to contribute to the loss of the cavity resource when used to inform conservation efforts for cavity-dependent species. The Swift Parrot (Lathamus discolor) is an endangered migratory bird threatened by ongoing removal of cavity-bearing trees by production forestry. We climbed trees with cavities used for nesting by Swift Parrots and determined that they prefer cavities with small entrances, deep chambers and wide floors. Such cavities are rare and occur in large trees that support higher than average numbers of tree-cavities. Importantly, cavities used by Swift Parrots were also likely to be both overestimated and underestimated using ground-based surveys, and without calibration by climbing, the size and direction of survey error could not be determined. We conclude that the most effective way to gain detailed information about the characteristics and abundance of tree-cavities is to climb a representative sample of trees to calibrate ground-based methods for a specific ecosystem.

Nesting requirements of the endangered Swift Parrot ( Lathamus discolor )

Abstract Declines in avian biodiversity are being reported worldwide. A better understanding of the ecology of many species is fundamental to identifying and addressing threatening processes and developing effective mitigation measures. The Swift Parrot (Lathamus discolor) is listed as endangered and is an obligate migrant that breeds only in Tasmania, wintering in mainland Australia. The species nests in tree-hollows and forages primarily on flowers of the Tasmanian Blue Gum (Eucalyptus globulus) and Black Gum (Eucalyptus ovata) during the breeding season. Surveys for Swift Parrot nests conducted over three consecutive breeding seasons identified 130 Swift Parrot nests in 117 trees. Sites were between 12 and 130 ha in area with up to 49 nests found at an individual site. Swift Parrot nest-trees were characterised as being large eucalypts (mean diameter at breast height = 105 cm) with five or more potential hollows (mean = 8.6) and showing clear signs of senescence. Reuse of nests was uncommon over the 3 years and the infrequency of reuse was most likely related to poor flowering of Tasmanian Blue Gums around nesting sites in years following recorded nesting. To protect the species, conservation actions need to account for the spatiotemporal variation in the availability of Swift Parrot breeding habitat and recognise there may be several years between the use of a particular site. Given the number of nests found at individual sites this will require the management or reservation of suitable forest stands with old-growth characteristics across the landscape, rather than focussing on individual trees or historical nesting sites.

Exploiting the richest patch has a fitness pay‐off for the migratory swift parrot

1. Unlike philopatric migrants, the ecology of nomadic migrants is less well understood. This life-history strategy reflects responses to spatiotemporal variation in resource availability and the need to find resource rich patches to initiate breeding. The fitness consequences of movements between regions of patchily distributed resources can provide insight into ecology of all migrants and their responses to global change. 2. We link broad-scale data on spatiotemporal fluctuation in food availability to data on settlement patterns and fitness outcomes for a nomadic migrant, the endangered swift parrot Lathamus discolor. We test several predictions to determine whether facultative movements are adaptive for individual swift parrots in an environment where resources are patchily distributed over time and space. 3. Variation in the availability of swift parrot food resources across our study period was dramatic. As a consequence, swift parrots moved to breed wherever food was most abundant and did not resettle nesting regions in successive years when food availability declined. By moving, swift parrots exploited a variable food resource and reproduced successfully. 4. Exploiting the richest patches allowed swift parrots to maintain stable fitness outcomes between discrete breeding events at different locations. Unlike sedentary species that often produce few or lower quality offspring when food is scarce, nomadic migration buffered swift parrots against extreme environmental variation. 5. We provide the first detailed evidence that facultative movements and nomadic migration are adaptive for individuals in unpredictable environments. Our data support the widely held assumption that nomadic migration allows animals to escape resource limitation.

The importance of incorporating functional habitats into conservation planning for highly mobile species in dynamic systems

The distribution of mobile species in dynamic systems can vary greatly over time and space. Estimating their population size and geographic range can be problematic and affect the accuracy of conservation assessments. Scarce data on mobile species and the resources they need can also limit the type of analytical approaches available to derive such estimates. We quantified change in availability and use of key ecological resources required for breeding for a critically endangered nomadic habitat specialist, the Swift Parrot (Lathamus discolor). We compared estimates of occupied habitat derived from dynamic presence-background (i.e., presence-only data) climatic models with estimates derived from dynamic occupancy models that included a direct measure of food availability. We then compared estimates that incorporate fine-resolution spatial data on the availability of key ecological resources (i.e., functional habitats) with more common approaches that focus on broader climatic suitability or vegetation cover (due to the absence of fine-resolution data). The occupancy models produced significantly (P < 0.001) smaller (up to an order of magnitude) and more spatially discrete estimates of the total occupied area than climate-based models. The spatial location and extent of the total area occupied with the occupancy models was highly variable between years (131 and 1498 km2 ). Estimates accounting for the area of functional habitats were significantly smaller (2-58% [SD 16]) than estimates based only on the total area occupied. An increase or decrease in the area of one functional habitat (foraging or nesting) did not necessarily correspond to an increase or decrease in the other. Thus, an increase in the extent of occupied area may not equate to improved habitat quality or function. We argue these patterns are typical for mobile resource specialists but often go unnoticed because of limited data over relevant spatial and temporal scales and lack of spatial data on the availability of key resources. Understanding changes in the relative availability of functional habitats is crucial to informing conservation planning and accurately assessing extinction risk for mobile resource specialists.

Further knowledge and urgent action required to save Orange-bellied Parrots from extinction

ABSTRACT Only three wild-bred female Orange-bellied Parrots returned from migration in the 2016/17 breeding season, representing the lowest point of a long-term decline. In this context of imminent extinction risk we (i) update knowledge of population parameters, (ii) critically evaluate current recovery actions, and (iii) identify new management options. We present new data from the 2016/17 breeding season. Orange-bellied Parrots were only observed at the last known breeding site where fire suppression may havecaused shortage of natural food. Recently burned habitat elsewhere support abundant food, but no parrots. Fecundity of captive-bred individuals was significantly worse than wild-bred individuals (0.8 vs. 3 fledglings respectively), mostly due to infertility. Bacterial septicemia due to contaminated food caused mortalities of at least four nestlings. Fostering captive-bred nestlings to the wild showed some potential as a recovery tool, with 2 of 4 nests accepting a foster nestling, and one of these fledging successfully. Captive-bred birds had poorer feather condition than wild birds. Addressing food shortages and the addition of new managementactions to improve population recruitment are critical and urgent recovery priorities. We suggest recovery priorities for the species arising from our results, including emergency intervention to prevent imminent extinction.

Effect of nest cavity morphology on reproductive success of a critically endangered bird

ABSTRACT Population limitation is the outcome of cumulative and synergistic processes that act on species over multiple spatial scales. Tree cavity dependent animals are good case studies for exploring processes that potentially limit populations across multiple scales. Fine-scale cavity characteristics have important consequences for predator exclusion and fecundity, while broad-scale processes (food or habitat availability) can determine population viability. We considered the relative importance of cavity morphology in limiting the breeding success of a critically endangered secondary cavity nesting bird that is severely affected at broad scales by nest predation. Swift Parrots (Lathamus discolor) select nest cavities where the minimum entrance diameter is positively associated with cavity depth, floor diameter and maximum entrance diameter. These cavity characteristics are adaptive because they exclude native predators by physically preventing access to the nest chamber; only one introduced nest predator is able to overcome this passive nest defence. Introduced Sugar Gliders (Petaurus breviceps) could prey on Swift Parrot nests irrespective of nest cavity morphology. We found no effect of cavity morphology on the number of eggs laid or fledglings reared by Swift Parrots. This suggests that fine-scale nest cavity characteristics do not influence the nest success of Swift Parrots beyond their effectiveness in excluding native Tasmanian predators.

Undetected Allee effects in Australia’s threatened birds: implications for conservation

ABSTRACT Allee effects occur when survival or reproductive success declines with decreasing population size or density. Species most severely impacted by Allee effects may be the very species for which these effects will be hardest to detect and overcome. This impedes effective conservation through a lack of evidence to drive management actions. We review the literature to identify (1) component Allee effects (components of fitness) which could lead to a demographic Allee effect (effect of all components on the population growth rate) in bird populations; and (2) traits that make species susceptible to component Allee effects. Concurrently, we assess the potential for undetected Allee effects to negatively influence the population growth rate of 14 critically endangered Australian bird species or subspecies. Whilst some (e.g. Helmeted Honeyeater) are unlikely to suffer from a demographic Allee effect, several (e.g. Great Knot, Orange-bellied Parrot) are susceptible to a number of component Allee effects and, hence, a demographic Allee effect. However, traits of the Regent Honeyeater suggests this species’ decline in particular is accelerated by an undetected demographic Allee effect. For this species and others, an inability to detect Allee effects need not preclude efforts to account for their potential presence through precautionary conservation management.

Immediate action required to prevent another Australian avian extinction: the King Island Scrubtit

Abstract For small and rapidly declining populations acting fast to prevent extinction is crucial. However, many endangered species receive little attention or management action. Action paralysis can prevail for several reasons, particularly for data deficient species when conservation resources are scarce. Here we draw attention to one of the worlds rarest birds, the King Island Scrubtit (Acanthornis magnus greenianus), a subspecies of a monotypic genus. Recognised as critically endangered for more than two decades, conservation action is virtually non-existent despite a rapid population decline. To establish current baseline information using a repeatable cost-effective monitoring methodology we surveyed 154 sites at eight locations as well as additional sites within the agricultural matrix. We detected the King Island Scrubtit at 28 sites in three locations (Nook Swamp, Colliers Swamp and Pegarah State Forest). At these locations, we estimated overall occupancy to be 0.35 (s.e. 0.05) and detectability to be 0.68 (s.e. 0.05) during a single site visit. We estimate the current area of occupancy of the bird to be <1 km2, declining. This study documents previously unrecognised threats (acid sulfate soils, macropod browsing and wind-throw) and provides a path forward to population recovery. Our results highlight the need for urgent action to prevent Australia’ s next avian extinction.

Policy failure and conservation paralysis for the critically endangered swift parrot

The critically endangered swift parrot (Lathamus discolor) is among the best studied Australian threatened species. Despite extensive outreach to the public and policy makers, conservation management has not kept pace with advances in knowledge and scientific evidence. Here we summarise policy and management failings that allow swift parrot breeding habitat in Tasmanian forests to continue to be logged. This practice continues in spite of extensive evidence demonstrating that the cessation of logging of swift parrot breeding habitat in Tasmania is urgently required to secure the species.