Powerful Owl Research Articles

Avian prey intake and breeding success parity of the powerful owl in dry, inland Victoria

AbstractApex predators are vulnerable to environmental changes which can cascade through trophic levels of an ecosystem. Investigating prey‐predator relationships is important for directing conservation efforts and understanding how species may respond to ecosystem changes. This case study examined the diet and breeding success of the threatened powerful owl Ninox strenua in central Victoria where the box‐ironbark forests have undergone widespread clearing, fragmentation, and degradation. The powerful owl preys predominantly on arboreal mammals, however, some birds are also consumed. By analysing the contents of regurgitated owl pellets of two owl pairs, we found that birds comprised 29.3% of all prey items and contributed the largest proportion of prey biomass for one pair (34.4%). All mammalian prey species identified in the pellet remains are dependent on tree hollows, which are now a scarce and competitive resource in box‐ironbark forests. Despite consuming a diet lower in mammalian prey than found in other studies, breeding success over five consecutive years was 1.4 chicks fledged per pair per year, which is notably higher than historical observations in the region and similar to powerful owls in other parts of their distribution. Our observations suggest that flexibility in prey selection enables powerful owls to occupy ranges that have undergone significant ecosystem change.

Where to fly? Landscape influences on the movement and spatial ecology of a threatened apex predator

Effectively managing apex predators in human-modified landscapes poses considerable challenges. Habitat fragmentation disperses resources across wider expanses and undermines the ability of apex predators to reach isolated habitat patches as they traverse multi-tenured landscapes comprising unsuitable habitat. Understanding a species response to landscape configuration is key to informing effective management strategies, particularly for threatened, mobile and ecologically important species like apex predators. Here we use GPS tracking data collected from 37 powerful owls (Ninox strenua), an Australian threatened apex predator that occurs across the urban-agricultural-forest gradient, to investigate how landscape characteristics influence their spatial and movement behaviour. We demonstrate that as habitat fragmentation increases, the spatial requirements of powerful owls expand, their home-range shape becomes more intricate and individuals travel further each night, significantly adjusting their movement behaviours and spatial configurations to connect remaining habitat. Landscapes with unified and connected habitats, on the other hand, have smaller spatial requirements, likely due to greater habitat availability that minimises competition for essential resources. This facilitates the establishment of smaller home-ranges and consequently, the occurrence of more territories. Interestingly, landscape characteristics did not influence sequential nightly visitation behaviour, suggesting that powerful owls across all landscape types visit different portions of their home-range each night to exert an unpredictable hunting strategy regardless of local landscape conditions. Our research highlights the importance of integrating the influence of local landscape features and visitation behaviours into decision-making processes. This integration is crucial for informing effective conservation strategies aimed at supporting apex predator survival in disturbed landscapes.

The missing toxic link: Exposure of non-target native marsupials to second-generation anticoagulant rodenticides (SGARs) suggest a potential route of transfer into apex predators

Anticoagulant rodenticides (ARs) are used globally to control rodent pests. Second-generation anticoagulant rodenticides (SGARs) persist in the liver and pose a significant risk of bioaccumulation and secondary poisoning in predators, including species that do not generally consume rodents. As such, there is a clear need to understand the consumption of ARs, particularly SGARs, by non-target consumers to determine the movement of these anticoagulants through ecosystems. We collected and analysed the livers from deceased common brushtail possums (Trichosurus vulpecula) and common ringtail possums (Pseudocheirus peregrinus), native Australian marsupials that constitute the main diet of the powerful owl (Ninox strenua), an Australian apex predator significantly exposed to SGAR poisoning. ARs were detected in 91 % of brushtail possums and 40 % of ringtail possums. Most of the detections were attributed to SGARs, while first-generation anticoagulant rodenticides (FGARs) were rarely detected. SGAR concentrations were likely lethal or toxic in 42 % of brushtail possums and 4 % of ringtail possums with no effect of age, sex, or weight detected in either species. There was also no effect of the landscape type possums were from, suggesting SGAR exposure is ubiquitous across landscapes. The rate of exposure detected in these possums provides insight into the pathway through which ARs are transferred to one of their key predators, the powerful owl. With SGARs entering food-webs through non-target species, the potential for bioaccumulation and broader secondary poisoning of predators is significantly greater and highlights an urgent need for routine rodenticide testing in non-target consumers that present as ill or found deceased. To limit their impact on ecosystem stability the use of SGARs should be significantly regulated by governing agencies.

Can environmental legislation protect a threatened apex predator across different land tenures?

Ecological impact assessments are undertaken in compliance with legislative mandates to evaluate the effects of proposed habitat modification. This task becomes complex when evaluating the impacts on highly mobile species like apex predators. Despite their importance to ecosystem function, environmental policies may inadequately protect apex predator habitat. Here we provide a case study that examines the efficacy of legislation and impact assessment tools in protecting habitat for a wide-ranging and threatened apex predator. The high resource requirements of apex predators, and their utilisation of large areas of high-quality habitat make them ideal conservation surrogates for other less resource demanding species, and as such good case studies in assessing the effectiveness of policy. The powerful owl (Ninox strenua) occurs across many landscape types throughout its distribution, including large tracts of private property and public landholdings, making this species difficult to assess through impact assessments. To examine the level of legislative protection for powerful owls, and how well their habitat use is captured, we compared GPS tracking data to environmental policy and industry impact assessment tools. We found that legislation has limited potential to protect powerful owl habitat and owls are likely dismissed from impact assessments due to their cryptic and wide-ranging behavioural traits. The existing legislative safeguards seem inadequate, and these shortcomings are likely contributing to species decline. There is a critical need for policy to be applicable to both public and private land tenure, and for legislation and impact assessment tools to incorporate research data for effective conservation and management.

Improved Load Frequency Control in Power Systems Hosting Wind Turbines by an Augmented Fractional Order PID Controller Optimized by the Powerful Owl Search Algorithm

The penetration of intermittent wind turbines in power systems imposes challenges to frequency stability. In this light, a new control method is presented in this paper by proposing a modified fractional order proportional integral derivative (FOPID) controller. This method focuses on the coordinated control of the load-frequency control (LFC) and superconducting magnetic energy storage (SMES) using a cascaded FOPD–FOPID controller. To improve the performance of the FOPD–FOPID controller, the developed owl search algorithm (DOSA) is used to optimize its parameters. The proposed control method is compared with several other methods, including LFC and SMES based on the robust controller, LFC and SMES based on the Moth swarm algorithm (MSA)–PID controller, LFC based on the MSA–PID controller with SMES, and LFC based on the MSA–PID controller without SMES in four scenarios. The results demonstrate the superior performance of the proposed method compared to the other mentioned methods. The proposed method is robust against load disturbances, disturbances caused by wind turbines, and system parameter uncertainties. The method suggested is characterized by its resilience in addressing the challenges posed by load disturbances, disruptions arising from wind turbines, and uncertainties surrounding system parameters.

Silent killers? The widespread exposure of predatory nocturnal birds to anticoagulant rodenticides

Anticoagulant rodenticides (ARs) influence predator populations and threaten the stability of ecosystems. Understanding the prevalence and impact of rodenticides in predators is crucial to inform conservation planning and policy. We collected dead birds of four nocturnal predatory species across differing landscapes: forests, agricultural, urban. Liver samples were analysed for eight ARs: three First Generation ARs (FGARs) and five SGARs (Second Generation ARs). We investigated interspecific differences in liver concentrations and whether landscape composition influenced this. FGARs were rarely detected, except pindone at low concentrations in powerful owls Ninox strenua. SGARs, however, were detected in every species and 92 % of birds analysed. Concentrations of SGARs were at levels where potential toxicological or lethal impacts would have occurred in 33 % of powerful owls, 68 % of tawny frogmouths Podargus strigoides, 42 % of southern boobooks N. bookbook and 80 % of barn owls Tyto javanica. When multiple SGARs were detected, the likelihood of potentially lethal concentrations of rodenticides increased. There was no association between landscape composition and SGAR exposure, or the presence of multiple SGARs, suggesting rodenticide poisoning is ubiquitous across all landscapes sampled. This widespread human-driven contamination in wildlife is a major threat to wildlife health. Given the high prevalence and concentrations of SGARs in these birds across all landscape types, we support the formal consideration of SGARs as a threatening process. Furthermore, given species that do not primarily eat rodents (tawny frogmouths, powerful owls) have comparable liver rodenticide concentrations to rodent predators (southern boobook, eastern barn owl), it appears there is broader contamination of the food-web than anticipated. We provide evidence that SGARs have the potential to pose a threat to the survival of avian predator populations. Given the functional importance of predators in ecosystems, combined with the animal welfare impacts of these chemicals, we propose governments should regulate the use of SGARs.

Using thresholds to determine priorities for apex predator conservation in an urban landscape

As landscapes are increasingly modified due to anthropogenic processes such as urbanisation or development for agriculture, the need to understand wildlife habitat requirements is imperative. This is particularly pertinent for species that are threatened, or apex predators with specific nest, den, or food requirements. Identifying responses to habitat with thresholds can provide an understanding of what resources species are using or avoiding, and their interactions with the surrounding environment. In this research we investigated space use and habitat requirements of the threatened apex predator, the powerful owl (Ninox strenua) in Greater Melbourne, Australia. We deployed GPS devices to 21 urban powerful owls over five years and found owls had an average home range size of 397 ha, and an average core-range of 84 ha. Home range size and positioning was driven by tree cover and urban land cover, while core ranges were restricted to treed environments with a limited area of impervious surfaces and housing. We used thresholds to identify-three priorities for powerful owl conservation in Melbourne. Priority 1: Ensuring river corridors and public open spaces are adequately protected. Priority 2: Limit property densities near rivers and protected areas. Priority 3: Finding opportunities for revegetation to expand and enhance habitat over time. Our research demonstrates how species-specific thresholds can inform land use planning to ensure wildlife species are maintained within highly modified environments.

Toward Interspecies Art and Design: Prosthetic Habitat-Structures in Human-Owl Cultures

Abstract Urbanization severely reduces opportunities for nonhuman habitation and undermines nonhuman subjectivities, aesthetic experiences, behaviors, traditions, and cultures. In response, humans need to reimagine cities as places for interspecies cohabitation. In this article, a team of architects and ecologists demonstrates that such reimagination depends on the cultural behaviors of multiple species. The authors illustrate the implications of this dependence by designing and discussing nesting structures for the powerful owl (Ninox strenua). The project shows that prosthetic habitats can serve as useful provocation for thinking about interspecies cultures. The authors use this work to propose productive avenues for further research.

A framework for computer‐aided design and manufacturing of habitat structures for cavity‐dependent animals

AbstractThe decline of critical habitat structures, such as large old trees, is a global environmental challenge. The cavities that occur in these trees provide shelter and nesting sites for many species but can take centuries to develop. Artificial cavities, including nest boxes and carved logs, offer an increasingly important conservation response. However, current methods of designing, manufacturing and deploying such habitats have constraints that limit innovation, feasibility and effectiveness. In response, this article aims to provide new and broadly useable methods that can improve the design of habitat structures for cavity‐dependent animals.To address the shortcomings of existing methods, we develop an approach that uses computer‐aided design techniques of generative and parametric modelling to produce structures that satisfy stakeholder needs, computer‐aided manufacturing techniques of 3D printing and augmented‐reality assembly to build functional prototypes, and computer‐assisted techniques of laser scanning and data‐driven design to support installation, monitoring and iterative improvement of designs. We demonstrate this approach through a case‐study project that designs and instals habitat structures for the powerful owlNinox strenua, a cavity‐dependent and threatened bird.Through a comparison with existing methods, our pilot study shows that computer‐aided design and manufacturing can provide novel and useful approaches to develop artificial habitat‐structures. Computer‐aided design finds geometries that approximate the complex characteristics of natural tree cavities and automatically produces new versions to suit diverse sites or species. Computer‐aided manufacturing integrates materials that match the performance of naturally occurring habitat structures and facilitates the assembly of complex geometries by non‐experts. Computer‐assisted techniques produce precisely fitting and easy‐to‐instal designs, which support gradual improvement through ongoing prototyping and evaluation.These capabilities highlight how advanced design techniques can improve aspects of artificial habitat‐structures through geometric innovation, novel construction techniques and iterative exploration. Significantly, computational approaches can result in designs that can perform well, are easy to construct and instal and are applicable in many situations. Our reusable workflow can aid in the tasks of practical conservation and support ecological research by effectively negotiating the needs of both humans and target species.

Widespread exposure of powerful owls to second-generation anticoagulant rodenticides in Australia spans an urban to agricultural and forest landscape

The powerful owl (Ninox strenua) is a threatened apex predator that consumes mainly arboreal marsupial prey. Low density populations reside in urban landscapes where their viability is tenuous. The catalyst for this research was the reported death of eight powerful owls around Melbourne, Australia, in less than one year (2020/2021). Eighteen deceased owls were toxicologically screened. We assessed toxic metals (Mercury Hg, Lead Pb, Cadmium Cd and Arsenic As) and anticoagulant rodenticides (ARs) in liver (n = 18 owls) and an extensive range of agricultural chemicals in muscle (n = 14). Almost all agricultural chemicals were below detection limits except for p,p-DDE, which was detected in 71% of birds at relatively low levels. Toxic metals detected in some individuals were generally at low levels. However, ARs were detected in 83.3% of powerful owls. The most common second-generation anticoagulant rodenticide (SGAR) detected was brodifacoum, which was present in every bird in which a rodenticide was detected. Brodifacoum was often present at toxic levels and in some instances at potentially lethal levels. Presence of brodifacoum was detected across the complete urban-forest/agriculture gradient, suggesting widespread exposure. Powerful owls do not scavenge but prey upon arboreal marsupials, and generally not rodents, suggesting that brodifacoum is entering the powerful owl food web via accidental or deliberate poisoning of non-target species (possums). We highlight a critical need to investigate SGARs in food webs globally, and not just in species directly targeted for poisoning or their predators.

Abstracts from the Spectra 2018 Symposium Part 4: Interspecies

Abstracts from the Spectra 2018 Symposium Part 4: <i>Interspecies</i>

Where to sleep in the city? How urbanisation impacts roosting habitat availability for an apex predator

Increased urbanisation is placing respite areas for wildlife under stress, with the impact of anthropogenic disturbances such as noise, artificial light and infrastructure compounding as urban areas expand and become more populated. One essential, and sometimes overlooked behavioural activity is where urban wildlife sleep or rest. This is especially important for urban predators that are wide-ranging and exhibit specific ecological requirements. The powerful owl (Ninox strenua) is one such species. To ensure the future survival of urban powerful owls it is critical that we understand where they choose to roost/sleep and why. To determine these roosting characteristics, we used roosting data collected from GPS tagged powerful owls across Melbourne, Australia and examined these data at different spatial scales to provide a holistic understanding of habitat selection. At the landscape scale, potentially suitable roosting habitat was restricted heavily by urban and agricultural land use. Population-wide, roosts were located within dense tree cover with some flexibility between individuals in distance to river systems and tolerance of road density. At the microhabitat-scale, individual owls displayed flexibility by roosting in a variety of indigenous, non-indigenous native and exotic tree species. These considerations will assist urban planners to conserve suitable roosting habitat, while restoration efforts should be prioritised on private land and along river systems where roosting habitat can be enhanced and expanded, increasing landscape connectivity for other wildlife.

Photography can determine the sex of a predator with limited sexual dimorphism: A case study of the powerful owl

The ability to distinguish (in the field) the sex of wildlife that show limited sexual dimorphism is, at best, challenging but is nonetheless essential to ensure appropriate conservation strategies are implemented. We developed a technique using highly varied images, similar to those taken by amateur photographers, to accurately sex individual powerful owls (Ninox strenua) through the measurement of facial features. Powerful owls show extremely limited sexual dimorphism and have been almost impossible to sex without genetic analysis, however, we report a process that results in the unambiguous assignment of sex. Image selection was extremely important; images where the owl’s head and body faced towards the camera, in an alert posture, were selected. We derived five facial features (inter-nostril distance, inter-eye distance, head width, forehead height and facemask), all measured in pixels to account for variation in the resolution and the size of images. Ratios were then produced from these facial features enabling standardised metrics, which we tested with regard to the assignment of sex. Logistic regression analysis indicated that the ratio of head width to the inter-nostril distance was the key sexually diagnostic relationship, giving 100% accuracy in sex determination (assessed against known-sex birds). We also identified a sex-specific plumage character; where facemask feathers protrude beyond the profile of the contour feathers of the head, the bird was a female, whereas when these feathers did not protrude beyond the profile, the bird was a male. For powerful owls, simple image analysis reliably determines the sex of individuals and has potential as an extremely cost efficient approach, that can provide essential information on species dynamics such as sex ratios, social organization and behaviour. The use of photographic images is especially beneficial for species that are cryptic or are extremely difficult to capture. The quantification and analysis of images captured by amateurs enables a greater contribution of citizen scientists to conservation research.

A comparison of urban and peri-urban/hinterland nocturnal birds at Brisbane, Australia

This study identified and compared the abundance and detectability of owls and other nocturnal birds, over 1 year, in an urban parkland of a Brisbane suburb to a peri-urban/hinterland/rainforest site 27km away. Five owl species were detected, but only at the peri-urban/hinterland/rainforest site, they were powerful owl Ninox strenua, southern boobook Ninox boobook, sooty owl, Tyto tenebricosa, masked owl Tyto novaehollandiae and barn owl Tyto alba. A single southern boobook was detected outside the study, at the urban site. The tawny frogmouth Podargus strigoides was only detected at the urban site whereas the plumed frogmouth Podargus ocellatus plumiferus was only detected at the rainforest site. The bush stone-curlew Burhinus grallarius was the most frequently detected nocturnal species, yet we discuss its recent decline in Brisbane. Incidentally recorded mammals, reptiles, frogs and diurnal birds are given. The rainforest site had more scansorial mammals whereas the urban site had more possums, dogs and cats.

Predation of a Grey Goshawk Accipiter novaehollandiae with a Powerful Owl Ninox strenua as the likely predator

Strong circumstantial evidence is presented for a case of predation of a Grey Goshawk Accipiter novaehollandiae by a Powerful Owl Ninox strenua along Cattai Creek in the Mitchell Park section of Cattai National Park in the Greater Sydney region, New South Wales, in October 2017. Evidence includes the feathery remains of a Grey Goshawk originating from a plucking post on the forest floor, located within an active Powerful Owl roosting site indicated by Powerful Owl feathers, pellets and whitewash. Although the Powerful Owl is known to prey on large birds, our observations constitute the first evidence of predation of a Grey Goshawk by a Powerful Owl.

Joining the dots: How does an apex predator move through an urbanizing landscape?

Examining the movement of apex predators is difficult in urban environments due to private land ownership; however, understanding their movement is critical given the current and rapidly increasing rate of urbanization globally. Of equal importance is the understanding of what landscape factors allow these movements to occur. We used the powerful owl (Ninox strenua), an urban apex predator in Melbourne, Australia, as a case study to understand their movement ecology in urban environments.Owl movement was recorded using automated GPS logging devices deployed on ten powerful owls, resulting in 10870 GPS locations. In combination with these positions, four environmental covariates, and a priori understanding of owl ecology were used to assign movements to three different states (prey handling/eating, foraging and transitory) based on step length and turning angles between sequential locations in a hidden Markov model.We demonstrate that the environmental covariate combination of time of night, Euclidean distance to riparian vegetation, and NDVI best described movement states. Owl movement states changed across the night. Shorter movements with many turns were made towards the beginning of the night in riparian areas with high NDVI. This behavior is most likely linked to prey handling, suggesting powerful owls are more likely to hunt early in the evenings and as such travel short distances while carrying large prey items. Transitory movements with limited changes in turning angles were the dominant movement state towards the end of the night. As owls leave areas of high NDVI, they quickly travel long distances across cleared land and impervious surfaces to connect to the next habitat patch where they then transition back into shorter step lengths where NDVI is higher.This research highlights the critical importance of riparian vegetation and high NDVI areas in driving powerful owl movement and foraging in urban landscapes. Conservation priority should be placed on retaining and restoring riparian corridors as areas not only for powerful owls and their prey, but also for many other species that utilize similar resources.

Avian viral surveillance in Victoria, Australia, and detection of two novel avian herpesviruses.

Viruses in avian hosts can pose threats to avian health and some have zoonotic potential. Hospitals that provide veterinary care for avian patients may serve as a site of exposure of other birds and human staff in the facility to these viruses. They can also provide a useful location to collect samples from avian patients in order to examine the viruses present in wild birds. This study aimed to investigate viruses of biosecurity and/or zoonotic significance in Australian birds by screening samples collected from 409 birds presented to the Australian Wildlife Health Centre at Zoos Victoria’s Healesville Sanctuary for veterinary care between December 2014 and December 2015. Samples were tested for avian influenza viruses, herpesviruses, paramyxoviruses and coronaviruses, using genus- or family-wide polymerase chain reaction methods coupled with sequencing and phylogenetic analyses for detection and identification of both known and novel viruses. A very low prevalence of viruses was detected. Columbid alphaherpesvirus 1 was detected from a powerful owl (Ninox strenua) with inclusion body hepatitis, and an avian paramyxovirus most similar to Avian avulavirus 5 was detected from a musk lorikeet (Glossopsitta concinna). Two distinct novel avian alphaherpesviruses were detected in samples from a sulphur-crested cockatoo (Cacatua galerita) and a tawny frogmouth (Podargus strigoides). Avian influenza viruses and avian coronaviruses were not detected. The clinical significance of the newly detected viruses remains undetermined. Further studies are needed to assess the host specificity, epidemiology, pathogenicity and host-pathogen relationships of these novel viruses. Further genome characterization is also indicated, and would be required before these viruses can be formally classified taxonomically. The detection of these viruses contributes to our knowledge on avian virodiversity. The low level of avian virus detection, and the absence of any viruses with zoonotic potential, suggests low risk to biosecurity and human health.

Another successful breeding season for the Powerful Owls

Another successful breeding season for the Powerful Owls

Remote camera capture of a Powerful Owl Ninox strenua bathing and drinking

Images captured by remote camera of a Powerful Owl Ninox strenua probably bathing and drinking are documented and described. The images add important visual records to the few published written descriptions of these behaviours.

Species distribution models derived from citizen science data predict the fine scale movements of owls in an urbanizing landscape

Apex predators are critical to ecological function, however their life history traits are often not conducive to survival in urban environments. While this can result in the loss of some apex predators, others are able to inhabit and utilize urban environments. Understanding predator resource requirements and the factors driving their distribution is often difficult due to their cryptic nature, however, this understanding is essential, given the current rate of urban expansion. In this research we use a threatened apex predator, the powerful owl (Ninox strenua) as a case study. Specifically, we aim to (1) develop a Species Distribution Model (SDM) to ascertain environmental variables driving habitat suitability across an urban gradient (2) determine fine scale spatial movements of powerful owls using GPS telemetry; (3) validate the SDM against collected GPS movement data; and (4) evaluate habitat predicted by the SDM against current reserve systems to establish whether they are adequate for the future protection of this species. We used MaxEnt and citizen science data to produce SDMs that predicted habitat suitability for powerful owls and identified the environmental variables driving habitat across the landscape. Fine-scale spatial movements for urban powerful owls, gained via GPS telemetry, were used to establish home-range sizes, validate models and assess the fit of telemetry data against SDM predictions. Rivers, vegetation (particularly dense tree cover) and distance to riparian areas were the ecological variables driving predicted habitat for powerful owls across the urban gradient. There was a strong relationship between habitat predicted by the SDM and the fine scale movements of powerful owls in urbanized environments. Home-ranges within this urban study were notably smaller than previous estimates established for forested environments. The powerful owls in our study were also shown to utilize considerable amounts of habitat outside of the reserve system. This has severe conservation implications because it is often the space outside of reserves that are at most risk from urban intensification. Conservation of the powerful owl in urban environments, therefore, needs to focus on both habitat management within existing reserves, and on establishing clear vegetation management strategies in the surrounding urban matrix.