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Does urbanization have the potential to create an ecological trap for powerful owls (Ninox strenua)?

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... These high densities of potential prey attract birds of prey to hunt and even to breed in urban environments (Chace and Walsh, 2006;Rutz, 2008;Solonen and Ursin, 2008). While it is evident that urbanization is causing the restructuration of faunal assemblages, the effect of urbanization on individual species is more complex than initially perceived (González-Oreja, 2011;Isaac et al., 2014). ...
... Raptors breeding near urban areas largely increase the consumption of certain species included in the range of optimal prey mass, which positively affect breeding success and brood size (Drewitt and Dixon, 2008;zuberogoitia et al., 2013;Martínez-Hesterkamp, 2015). The abundance of feeding resources also attracts floaters, wintering and non-territorial birds, which directly occupy cities (Pirovano et al., 2000;Cade and Burnham, 2003;Isaac et al., 2014). However, urban environments may not contain the full complement of resources required by a species (Chace and Walsh, 2006). ...
... Nest site availability is one of the main limiting factors in urban areas and those that already exist are usually of poor quality (Altwegg et al., 2014). One of the consequences may be the establishment of long-term non-breeding territories, which would act as ecological traps (see Battin, 2004;Isaac et al., 2014;Fasciolo et al., 2016), ultimately reducing fitness components (Schlaepfer et al., 2002;Remes, 2003). ...
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Birds of prey have been, in comparison to other avian groups, an uncommon study model, mainly due to the limitations imposed by their conservative life strategy (low population density and turnover). Nonetheless, they have attracted a strong interest from the point of view of conservation biology because many populations have been close to extinction and because of their recognised role in ecosystems as top predators and scavengers and as flagship species. Today, after more than a century of persecution, and with the exception of some vultures still very much affected by illegal poisoning, many populations of birds of prey have experienced significant recoveries in many regions of Spain and the European Mediterranean. These changes pose new challenges when addressing the conservation of raptors in the coming decades. On this basis, and from a preferentially Mediterranean perspective, we have focused our attention on the need of describing and quantifying the role of these birds as providers of both regulating (rodent pest control and removal of livestock carcasses) and cultural ecosystem services. Moreover, we revisited persisting conflicts with human interests (predation of game species) and call attention to the emergence of new conflicts with a strong social and media component such as the predation on live cattle by vultures. Also, the rampant humanization of the environment determines the need for new solutions to the growing, yet scarcely explored, problem of accidents in new infrastructures such as mortality in wind farms. Finally, we explored in depth the ecological response of birds of prey to large-scale habitat changes such as urbanisation and abandonment of marginal lands that are also expected to increase in the near future. We urgently need more scientific knowledge to provide adequate responses to the challenge of keeping healthy populations of avian predators and scavengers in a rapidly changing world.
... These high densities of potential prey attract birds of prey to hunt and even to breed in urban environments (Chace and Walsh, 2006;Rutz, 2008;Solonen and Ursin, 2008). While it is evident that urbanization is causing the restructuration of faunal assemblages, the effect of urbanization on individual species is more complex than initially perceived (González-Oreja, 2011;Isaac et al., 2014). ...
... Raptors breeding near urban areas largely increase the consumption of certain species included in the range of optimal prey mass, which positively affect breeding success and brood size (Drewitt and Dixon, 2008;zuberogoitia et al., 2013;Martínez-Hesterkamp, 2015). The abundance of feeding resources also attracts floaters, wintering and non-territorial birds, which directly occupy cities (Pirovano et al., 2000;Cade and Burnham, 2003;Isaac et al., 2014). However, urban environments may not contain the full complement of resources required by a species (Chace and Walsh, 2006). ...
... Nest site availability is one of the main limiting factors in urban areas and those that already exist are usually of poor quality (Altwegg et al., 2014). One of the consequences may be the establishment of long-term non-breeding territories, which would act as ecological traps (see Battin, 2004;Isaac et al., 2014;Fasciolo et al., 2016), ultimately reducing fitness components (Schlaepfer et al., 2002;Remes, 2003). ...
... Much recent research, therefore, has concentrated on powerful owls in urban and urban-fringe areas, particularly in Melbourne, where in some instances these urban and suburban birds are successfully breeding. 14 ...
... 37,38,39 Our initial modeling focused on the powerful owl, 28 with later modeling assessing potential prey and tree cavity occurrence to produce layers for MCDA. 14,19,40 We collected presence data for the models from fieldwork and supplemented these where possible with citizen science atlas datasets. We employed measures to restrict spatial and historical biases associated with presence data derived from atlas datasets. ...
... This illustrates the potential for urban environments to form an ecological trap due to the lack of suitable tree cavities for breeding. 14 ...
Chapter
Once thought to live only in large forested areas, the powerful owl (Ninox strenua), Australia’s largest and most iconic of owls (figure 11.1), surprisingly is now turning up frequently in the cities of eastern Australia. Powerful owls require ample prey and large tree cavities for nest sites; how this top-order predator is able to survive in human-dominated landscapes is an important question for conservation and the focus of ongoing research. The powerful owl is endemic to Australia, resident in the three eastern mainland states and the Australian Capital Territory, and classified nationally as “rare.”2,3 First described by Gould in 1838, powerful owls are an unusual raptor in that they do not exhibit reversed sexual size dimorphism, the prevalent trait among raptors in which females are larger than males. For reasons still not understood, male powerful owls grow to a height of 65 cm and weigh up to 1,700 g, compared to females, which grow to a height of 54 cm and weigh up to 1,308 g.1
... Hogan and Cooke, 2010), spatial ecology (e.g. Isaac et al., 2014a) and movements of powerful owls (Bradsworth et al., 2017;Carter et al., 2019), however, few studies have specifically focused on the selection and use of roosting habitat (Cooke et al., 2002;McNabb and McNabb, 2011). Powerful owls persist throughout Melbourne across a gradient of modification; therefore Melbourne provides the ideal location to investigate how modified habitats impact powerful owl roost availability. ...
... Could fragmented roosting habitat be the most important resource explaining restricted distribution (Webster et al., 1999) of powerful owls in modified environments? Food availability would likely be the most important consideration, however distribution is not food-related since powerful owls have an abundant prey source across the entire landscape (Cooke et al., 2006;Isaac et al., 2014a). Although nest sites are a limited resource in modified environments and could limit distribution, owls have been known to occupy and roost in areas without nest hollows (Isaac et al., 2014). ...
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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.
... If resources are unavailable or lack sufficient quality, as is often the case in urban areas, there are significant implications for the demographics of the urban population (Cody 1985). For species with specialised breeding requirements such as hollow-dependant breeders, urbanized environments often lack the resources required for breeding and as such breeding outputs are substantially reduced by urbanisation (Cooke et al. 2006;Hindmarch et al. 2012;Isaac et al. 2014a;Rottenborn 1999). Where species have less demanding breeding habitat requirements, novel habitat types and abundant food resources common to urban systems, may enhance breeding outcomes resulting in population levels higher than those in more natural environments (Stracey and Robinson 2012). ...
... Habitat specialists (termed urban avoiders), may tolerate moderate forms of urbanization but their expansion to areas with increased human habitation may be constrained by a lack of specialist habitat resources (Christina and Marzluff 2005;Degraaf and Wentworth 1986;Lim and Sodhi 2004). One such example is the powerful owl, a nocturnal species that demonstrates a tolerance to moderate forms of urbanization but is limited from colonising more intensively urbanized areas due to a lack of hollow-bearing trees required for breeding (Cooke, Wallis and Webster 2002;Isaac et al. 2014a). ...
Thesis
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The tawny frogmouth is a nocturnal bird species endemic to Australia. While many species of wildlife worldwide experience detrimental outcomes from urbanization, this thesis demonstrates the resilience and adaptability of this unique species to landscape change by human beings.
... The urban success of these species is thought to be because of a combination of factors including reduced persecution, increased availability of nesting sites, and relatively high prey availability (Kettel et al. 2018). However, larger raptors such as eagles are generally absent or relatively rare in urban areas, most likely because of their larger home range sizes, specific habitat requirements, and specialist diets (Newton 1979, Chace and Walsh 2006, Isaac et al. 2014. For some raptor species that do breed in urban areas, an "ecological trap" can emerge if, for example, (1) the availability of suitable nesting sites does not match an abundance of suitable prey (Sumasgutner et al. 2014a), or (2) urban prey items transmit diseases (van Velden et al. 2017), or (3) the available habitat cannot support a species' overall breeding requirements (Isaac et al. 2014). ...
... However, larger raptors such as eagles are generally absent or relatively rare in urban areas, most likely because of their larger home range sizes, specific habitat requirements, and specialist diets (Newton 1979, Chace and Walsh 2006, Isaac et al. 2014. For some raptor species that do breed in urban areas, an "ecological trap" can emerge if, for example, (1) the availability of suitable nesting sites does not match an abundance of suitable prey (Sumasgutner et al. 2014a), or (2) urban prey items transmit diseases (van Velden et al. 2017), or (3) the available habitat cannot support a species' overall breeding requirements (Isaac et al. 2014). ...
Article
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Urban areas can be attractive to certain species because of increased food abundance and nesting availability, which in turn may increase productivity or breeding rates. However, there are also potential costs associated with urban living such as higher nest failure, poorer body condition, or increased prevalence of disease. These costs may result in species trading off the number of young produced against the condition of their young. African Crowned Eagles (Stephanoaetus coronatus) are a rare example of large, powerful apex predators that breed in some urban areas in Africa. In this study, we explored the breeding performance of these eagles across an urbanization gradient in KwaZulu-Natal Province, South Africa, over 7 breeding seasons. We predicted that living in an urban environment would increase productivity through an increase in breeding rate (shifting from typically biennial breeding to annual breeding). We then explored if there were any hidden costs associated with such a change in breeding strategy by examining the body condition of chicks from pairs that had successfully bred in the previous year. We found that pairs in more urban areas were more likely to breed annually, resulting in higher breeding rates, but were also less likely to successfully fledge a chick (i.e. lower breeding success). These 2 contrasting responses counteracted each other and resulted in similar productivity across the urbanization gradient. For those eagles that bred in consecutive years, annual breeding did not appear to have a negative cost on chick condition. The switch to annual breeding is thought to be a response to improved or more constant food sources in urban areas, while higher failure rates might be because of increased nest disturbances from anthro-pogenic sources (e.g., vegetation clearing, development of industrial areas, human and car traffic). However, although urbanization negatively affected the breeding success of African Crowned Eagles, they are able to persist and thrive in this highly transformed environment, likely through an increased breeding rate. La urbanización está asociada con un aumento de la tasa reproductiva, pero con una disminución del éxito reproductivo, en una población urbana casi amenazada de Stephanoaetus coronatus RESUMEN Las áreas urbanas pueden ser atractivas para ciertas especies debido al aumento de la abundancia de alimento y de la disponibilidad para anidar, lo cual a su vez puede elevar las tasas de productividad o reproductivas. Sin embargo, también hay costos potenciales asociados con la vida urbana como mayor fracaso del nido, peor condición corporal o aumento de la prevalencia de enfermedades. Estos costos pueden hacer que las especies intercambien la cantidad de crías producidas LAY SUMMARY • One species that is hardly recognized as an urban adapter is the Crowned Eagle in the metropoles of Durban and Pietermaritzburg, South Africa. • We explored the breeding performance of Crowned Eagles across different levels of urbanization, and specifically teased apart breeding rate (i.e. if an eagle breeds annually or every other year) and breeding success (i.e. if they fledge a young or not in a given year). • We showed that Crowned Eagles change their breeding strategy in urban areas by increasing their breeding rate, but found nest failures occurred more often at more urbanized sites. These contrasting responses counteracted each other and resulted in similar productivity across the urbanization gradient and highlighted the value of long-term data. en contra de la condición de sus crías. Stephanoaetus coronatus es un raro ejemplo de grandes y poderosos depredadores tope que crían en algunas áreas urbanas en África. En este estudio, exploramos el desempeño reproductivo de estas águilas a través de un gradiente de urbanización en la Provincia de KwaZulu-Natal, Sud África, a lo largo siete estaciones reproductivas. Predijimos que vivir en un ambiente urbano aumentaría la productividad a través de un aumento en la tasa reproductiva (cambiando de una reproducción típicamente bienal a una reproducción anual). Luego exploramos si hubo algunos costos ocultos asociados con tal cambio en la estrategia reproductiva, examinando la condición corporal de los polluelos de parejas que habían criado exitosamente el año previo. Encontramos que las parejas en las áreas más urbanas tuvieron mayor probabilidad de reproducirse anualmente, resultando en tasas reproductivas más altas, pero también tuvieron menos probabilidad de emplumar exitosamente un polluelo (i.e., menor éxito reproductivo). Estas dos respuestas contrastantes se contrarrestaron mutuamente y resultaron en una productividad similar a lo largo del gradiente de urbanización. Para aquellas águilas que se reproducen en años consecutivos, la reproducción anual no parece tener un costo negativo en la condición del polluelo. Se piensa que el cambio hacia la reproducción anual es una respuesta frente a fuentes de alimento mejores o más constantes en las áreas urbanas, mientras que las tasas más altas de fracaso podrían deberse al aumento de los disturbios de los nidos a partir de fuentes antropogénicas (e.g., clareo de la vegetación, desarrollo de áreas industriales, tráfico humano y de autos). Sin embargo, aunque la urbanización afectó negativamente el éxito reproductivo de S. coronatus, es capaz de persistir y prosperar en este ambiente altamente transformado probablemente a través de un aumento en la tasa reproductiva.
... Traditionally regarded as an old growth forest specialist, this species is known to occur in urban landscapes (e.g. Cooke et al., 2018), however, their presence is restricted due to land clearance and increased impervious surfaces (Isaac et al. 2013(Isaac et al. , 2014. Most research to date has focussed on ecological aspects such as diet, breeding, home range and habitat use; however, their extremely limited sexual dimorphism has precluded adequate assessments of population demography. ...
... Traditionally regarded as an old growth forest specialist, this species is known to occur in urban landscapes (e.g. Cooke et al., 2018), however, their presence is restricted due to land clearance and increased impervious surfaces (Isaac et al. 2013(Isaac et al. , 2014. Most research to date has focussed on ecological aspects such as diet, breeding, home range and habitat use; however, their extremely limited sexual dimorphism has precluded adequate assessments of population demography. ...
Article
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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.
... Powerful Owls are substantially larger than boobooks, take larger prey, and are 2634 potentially even less likely to be impacted by competition for nest hollows. However, their 2635 requirement for larger nest hollowswhich are often scarcer in fragmented habitatshas 2636 apparently led to failures of established pairs to breed until a suitable nest box was provided 2637(Isaac et al., 2014a).2638 While boobooks and other predatory birds are unlikely to be severely impacted by 2639 nest competition by most introduced bird species, they may be negatively impacted by other2640 potential nest hollow competitors. ...
... Within Australia, only a few studies have addressed landscape-level impacts of urban and agricultural development on predatory birds and most have focused specifically on Powerful owls (Ninox strenua). In Powerful Owls, one model suggested that high prey abundance in urban woodland fragments could create an ecological trap if prey availability serves as cue to preferentially establish territories in areas without adequate nesting hollows 130(Isaac et al., 2014a). This followed on from a previous model that predicted declining habitat suitability with urbanization in Powerful Owls(Isaac et al. 2013). ...
Thesis
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The effects of habitat fragmentation on native wildlife can vary depending on the type of land use occurring in the matrix between remaining habitat fragments. I used Australian boobooks (Ninox boobook) in Western Australia to investigate interactions between matrix type and four different potential threatening processes: secondary poisoning by anticoagulant rodenticides (ARs); limitation of juvenile dispersal and impacts on spatial genetic structure; breeding site availability; and infection by the parasite Toxoplasma gondii. I also conducted a literature review on the use and regulation of ARs in Australia and published accounts of non-target impacts in order to contextualise exposure patterns observed in boobooks. The review revealed records of confirmed or suspected poisoning across 37 vertebrate species in Australia. World literature relating to AR exposure in reptiles suggests that they may be less susceptible to AR poisoning than birds and mammals. This relative resistance may create unevaluated risks for wildlife and humans in Australia where reptiles are more abundant than in cooler regions where AR exposure has been studied in greater depth. I analysed AR residues in boobook livers across multiple habitat types. Second generation anticoagulant rodenticides were detected in 72.6% of individuals sampled. Total AR concentration correlated positively with the proportion of urban land use within an area approximately the size of a boobook’s home range centred on the point where the sample was collected. ARs originating in urban habitat probably pose a substantial threat to boobooks and other predatory wildlife species. No spatial genetic structure was evident in boobooks across habitat types. I observed one individual dispersing at least 26km from its natal home range across urban habitat. The apparent permeability of anthropogenically altered landscapes probably explains the lack of spatial genetic structure and is likely related to the observed ability of boobooks to use resources in both urban and agricultural matrices. Boobooks did not appear to be limited by the availability of suitable nesting sites in urban or agricultural landscapes. Occupancy did not change significantly over the duration of the study in remnants provided with artificial nest boxes in either landscape type. However, in one instance, boobooks successfully used a nest box located in an urban bushland. Nest boxes may be a useful management tool in highly-altered areas where natural hollows are unavailable. Toxoplasma gondii seropositivity in boobooks did not vary significantly by landscape type but was more prevalent in individuals sampled during cooler wetter times of year. Risk of exposure due to greater cat abundance in urban and agricultural landscapes may be offset by creation of environmental conditions less favourable to the survival of T. gondii oocysts in soil. Taken together, this body of research demonstrates variation in relationships between different types of habitat fragmentation and threatening processes related to fragmentation. This research also raises questions about how habitat fragmentation is discussed and studied in the context of species which are capable of making extensive use of matrix habitat. I recommend greater consideration of the concept of “usable space” when studying fragmentation impacts in habitat generalists.
... If resources are unavailable or lack sufficient quality, as is often the case in urban areas, there is significant implications for the demographics of the urban population (Cody, 1985). For species with specialised breeding requirements such as hollow-dependant breeders, urbanized environments often lack the resources required for breeding and as such breeding outputs are substantially reduced by urbanisation (Cooke, Wallis, Hogan, White, & Webster, 2006;Hindmarch, Krebs, Elliott, & Green, 2012;Isaac, Cooke, Ierodiaconou, & White, 2014;Rottenborn, 1999). Where species have less demanding breeding habitat requirements, novel habitat types and abundant food resources common to urban systems, may enhance breeding outcomes resulting in population levels higher than those in more natural environments (Stracey & Robinson, 2012). ...
... However, species occurrence alone is insufficient to ascertain whether novel habitats are supporting self-sustaining populations, since they could represent ecological "sinks" or "traps" where survival and/or reproductive rates are too low to sustain viability over time (Battin, 2004;Johnson, 2007;Pulliam, 1988;Van Horne, 1983). For example, Isaac et al. (2014) found that urban environments may act as an ecological trap for the threatened Powerful Owl (Ninox strenua), which appears to use habitat and food availability (arboreal mammals) as cues for settlement, despite a lack of tree cavities that are essential for breeding and therefore population persistence. Thus, to truly evaluate the potential of novel habitats to support threatened species, studies need to go beyond simple documentation of species occurrence and quantify more informative metrics of individual-and/or populationlevel fitness such as condition, survival, reproduction and demographic features (Johnson, 2007;Van Horne, 1983). ...
... For example, recent clearcuts or open wetlands could be acting as poorer or higher quality breeding habitat for these species. For other species of birds, a reduction in insect prey availability has been a driving factor for lower fitness in ecological traps (Estany-Tigerstrom et al., 2013;Isaac et al., 2014). Furthermore, recent research on Eastern Whip-poor-will suggests that looking at local prey availability is crucial to understanding the habitat selection and decline of these birds (English et al., 2016). ...
... The use of presence-only data sets collected by citizen scientists, however, provides a viable alternative to presence/absence field surveys for apex predators (e.g. Santos et al., 2006;Isaac et al., 2014a;Angelieri et al., 2016). These datasets are also readily available through museums and government agencies and are an important source of public and private investment in biodiversity monitoring (Weston et al., 2006;Elith et al., 2011). ...
Article
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.
... As species loss continues to occur at unprecedented rates globally, it is paramount that we adopt robust methods to monitor changes in species distribution over time (Isaac et al. 2014a). Different methods of species detection are well documented; however, optimising the efficiency of these methods is often less well understood, especially when monitoring predators that occur at low densities, are cryptic in nature and can be notoriously difficult to detect. ...
Article
Context Due to their important ecological roles, predators are increasingly being suggested as targets for biodiversity studies investigating how they respond to landscape change and transformation. But there is limited literature investigating our capacity to accurately monitor changes in their occupancy. Aims To test the efficacy of playback surveys for monitoring owls as a basis for investigating change in owl occupancy over time. We ask whether playback is an effective tool, and whether it can be optimised to improve its utility. Methods Using the urban-forest interface of Melbourne, Australia, as a case study, we used playback techniques to survey for the presence of three owl species: the powerful owl (Ninox strenua); southern boobook (Ninox boobook); and eastern barn owl (Tyto javanica). Sites were repeat surveyed at least 16 times throughout the year and occupancy models were developed to establish how season and temperature influence nightly detection probabilities of owls. Key results All three species of owl were detected through playback survey approaches, but the detection probabilities varied greatly between species and across seasons and temperature conditions. Eastern barn owls are poor candidates for playback surveys due to their low detection probabilities. The southern boobook and powerful owl are responsive to playback, but detection probabilities are influenced by season and/or temperature conditions. To optimise survey approaches, southern boobooks should be surveyed during spring and summer and the powerful owl should be surveyed on nights where the minimum temperature is near 20°C. Conclusions Although there is considerable interest in using predators such as owls to monitor biodiversity impacts associated with landscape change, poor detection rates can limit their utility. However, optimising survey approaches that consider shifting detection probabilities under different conditions such as time of year or temperature may improve the utility of predators as surrogates in biodiversity monitoring. Implications Optimising survey approaches for owls considerably reduces the window of opportunity in which to conduct surveys. To counter this, the intensity of survey effort needs to be increased during key periods. The use of highly trained citizen science teams may be one effective way of delivering such an approach.
... However, fragmentation of forests and the abundance of prey in urban areas compel owls to enter cities [3]. Yet, the lack of nesting hollows means that owls cannot breed in most urban locations [4]. Moreover, even the fast-growing trees take 150-500 years to form hollows large enough to support owl breeding [5]. ...
Chapter
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Anthropogenic degradation of the environment is pervasive and expanding. Human construction activities destroy or damage habitats of nonhuman lifeforms. In many cases, artificial replacement habitats become necessary. However, designing for the needs and preferences of nonhuman lifeforms is challenging. Established workflows for this type of designing do not exist. This paper hypothesises that a multi-scale modelling approach can support inclusive, more-than-human design. The case-study project tests this approach by applying computational modelling to the design of prosthetic habitats for the powerful owl (Ninox strenua). The proposed approach simulates owls’ perception of the city based on scientific evidence. The tools include algorithmic mapping, 3D-scanning, generative modelling, digital fabrication and augmented-reality assembly. Outcomes establish techniques for urban-scale planning, site selection, tree-scale fitting, and nest-scale form-making. The findings demonstrate that computational modelling can (1) inform more-than-human design and (2) guide scientific data collection for more inclusive ecosystem management.
... Care must be taken, however, to avoid creating sink habitat or ecological traps for native species (e.g. encouraging species to areas where breeding success is poor) (Isaac et al. 2014). ...
Article
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Rural landscape change as a consequence of human population growth is a major challenge for nature conservation in the twenty-first century. Rural regions are globally experiencing change driven by diverse factors, including agricultural intensification, new agricultural commodities, residential development, and land abandonment. Understanding how different land-use trajectories affect biodiversity is critical for making informed decisions for the conservation of species in modified environments. We examined the impact of different land-uses on bird communities in the western Strzelecki Ranges, a formerly forested but now rural region in south-east Australia. We selected 25 study landscapes, each 1 km², representing seven land-uses typical of rural regions: townships, lifestyle properties (low-density acreages or hobby farms), dairy farming, beef grazing, horticulture, tree plantation and natural forest. Terrestrial birds were systematically surveyed at 10 sites in each study landscape and the results pooled to represent the whole landscape. We recorded 80 native and 8 exotic species of birds, of which 46 species were classified a priori as forest species typical of the region. Different trajectories of land-use have generated variation in landscape structure, with a primary gradient of change from forest to rural townships. The composition of bird communities and the richness of four species-response groups showed marked differences across land-use types. The mean richness of forest species, for example, was greatest in natural forest land-use (30.0 species) and lowest in dairy farming land-use (14.5 species). Key lessons from this study include: (1) these diverse land-uses, typical of rural regions, are creating novel assemblages of birds that differ from that of the former forested environment; (2) land-use in this region is dynamic and so further re-assortment of bird communities can be expected through time; (3) despite such change, a component of the original forest avifauna persists, even in highly modified landscapes; and (4) each land-use type offers opportunities for nature conservation while also meeting the needs of people and agricultural production.
... Powerful owls are long-lived, top order predators that primarily prey on arboreal native possums and gliders (Cooke et al., 2006). In recent years these owls have been documented more frequently in human-modified environments (e.g., Bradsworth et al., 2017;Carter et al., 2019;Isaac et al., 2014) accompanied by an increase in reported mortalities. We collected the remains of 10 powerful owls between 2004 and 2019. ...
Article
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.
... He emphasizes the mutual adaptability and feedback mechanism between economic and ecological environment. Isaac B emphasized the importance of understanding the relationship between them [2]. Later, researches on the relationship between urbanization and resources and environment mainly focus on the evolutionary trend. ...
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Environmental problems are drawing more and more attention from all sectors. Considering China’s current development background, it is very important to research the coordinated development level of resources and environment. This paper constructs the coupling index system of resource and environment. Then, we analyze the spatio-temporal situation and its influencing factors of the coordinated development in 26 provincial capitals and 4 municipalities in 2005, 2010 and 2015. It is concluded that the spatial distribution of the coupling coordination degree in China is unbalanced. The coupling coordination degree shows the characteristics of decreasing first and then improving. In general, this paper provides theoretical guidance and method support for quantitative analysis of the horizontal coupling coordination degree between resource and environmental development.
... Nesting owls use large hollows, high off the ground, and in proximity to food and flowing water (McNabb 1996). The supply of natural hollows is diminishing, and almost none exist in inner cities (Isaac et al. 2014). Information documenting successful hollows and their surrounds could significantly aid the design of replacements. ...
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Trees belong to humanity’s heritage, but they are more than that. Their loss, through catastrophic fires or under business-as-usual, is devastating to many forms of life. Moved by this fact, we begin with an assertion that heritage can have an active role in the design of future places. Written from within the field of architecture, this article focuses on structures that house life. Habitat features of trees and artificial replacement habitats for arboreal wildlife serve as concrete examples. Designs of such habitats need to reflect behaviours, traditions and cultures of birds, bats, and other animals. Our narrative highlights the nonhuman aspect of heritage, seeking to understand how nonhuman stakeholders can act as users and consumers of heritage and not only as its constituents. Our working definition states that more-than-human heritage encompasses tangible and intangible outcomes of historical processes that are of value to human as well as nonhuman stakeholders. From this basis, the article asks how the established notions of heritage can extend to include nonhuman concerns, artefacts, behaviours and cultures. As a possible answer to this question, the hypothesis tested here is that digital information can (1) contribute to the preservation of more-than-human heritage; and (2) illuminate its characteristics for future study and use. This article assesses the potential of three imaging technologies and considers the resulting data within the conceptual framework of more-than-human heritage, illuminating some of its concrete aspects and challenges.
... To fully understand the implications of parasites and pathogens on avian hosts it is necessary to examine patterns of parasitism across habitat types and potentially interacting threatening processes. For example, Cooper's Hawks (Accipiter cooperii) appeared to preferentially inhabit urban areas of Tucson, Arizona (Battin 2004) where there are higher densities of prey species (Isaac et al. 2014). Urban Cooper's Hawks have higher rates of nest failure as nestlings die from trichomoniasis (Boal and Mannan 1999), a protozoan vectored by feral pigeons. ...
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In Australia, Toxoplasma gondii is an introduced parasite with a wide host range. House cats (Felis catus) are one of its definitive hosts. Little is known about T. gondii infection rates in Australian wildlife. Since cat abundance varies with landscape composition, we hypothesised that T. gondii infection would be more prevalent in urban and agricultural landscapes than intact bushland and sought to use samples from the Southern Boobook (Ninox boobook) as an indicator of ecosystem-wide T. gondii contamination. We used modified agglutination tests to determine T. gondii seropositivity in serum and meat juice samples taken from boobooks. Moderately low levels of seropositivity were detected and non-significant landscape-related patterns of seroprevalence were observed. We also examined correlations and interactions with owl age, season, injury status and exposure to an anticoagulant rodenticide. Only season showed significant correlations with observed seropositivity. To the best of our knowledge, this is the first published detection of T. gondii seropositivity in a wild predatory bird in Australia.
... However, species occurrence alone is insufficient to ascertain whether novel habitats are supporting self-sustaining populations, since they could represent ecological "sinks" or "traps" where survival and/or reproductive rates are too low to sustain viability over time (Battin, 2004;Johnson, 2007;Pulliam, 1988;Van Horne, 1983). For example, Isaac et al. (2014) found that urban environments may act as an ecological trap for the threatened Powerful Owl (Ninox strenua), which appears to use habitat and food availability (arboreal mammals) as cues for settlement, despite a lack of tree cavities that are essential for breeding and therefore population persistence. Thus, to truly evaluate the potential of novel habitats to support threatened species, studies need to go beyond simple documentation of species occurrence and quantify more informative metrics of individual-and/or populationlevel fitness such as condition, survival, reproduction and demographic features (Johnson, 2007;Van Horne, 1983). ...
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Understanding how fundamental aspects of species’ ecology, such as diet, are affected in human‐dominated landscapes is vital for informing management and conserving biodiversity – particularly where species influence important ecosystem functions. Digging, mycophagous (‘fungus‐eating’) mammals play various such roles, including the dispersal of hypogeal (‘truffle‐like’) fungi. The endangered, mycophagous southern brown bandicoot (Isoodon obesulus obesulus: Peramelidae) persists in a peri‐urban landscape south‐east of Melbourne, Australia, where it occupies both ‘novel’ habitats (linear strips of vegetation along roadsides, drains and railway lines) and ‘remnant’ habitats (larger blocks of native vegetation) within dedicated conservation areas. It remains unknown how bandicoot diet, including the diversity of hypogeal fungi, varies between these habitat types, yet this could have important conservation implications. Our study aimed to (i) compare the diet of I. o. obesulus at novel and remnant sites; and (ii) attain knowledge of hypogeal fungal diversity in these different contexts. We collected 133 bandicoot scats over 23 months and examined both broad diet composition and diversity of fungi consumed. Bandicoot diet differed between site types; in particular, ants were more prominent in scats from remnant sites, while millipedes and seeds were more prominent in scats from novel sites. All scats contained fungal spores, with hypogeal taxa comprising at least 35 of the 78 ‘morphotypes’ found at novel sites and 28 of the 59 detected at remnant sites. Fewer samples were collected at remnant sites, but they appeared to contain a greater richness of hypogeal fungi per scat. We did not detect any differences in fungal composition between site types. However, our sampling effort was insufficient to estimate true morphotype richness at either site type. Our study highlights the adaptable generalist diet of the southern brown bandicoot, as well as the likely under‐appreciated diversity of hypogeal fungi that can occur in highly modified, novel ecosystems.
Chapter
Lands modified by humans vary widely in their environmental features, from areas that retain much of their natural character to areas in the urban core that retain little natural character. For example, a city that was built on lands that were once covered by a forest might be dominated at its core by pavement and buildings and support only a few trees, many of which are nonnative species. Areas surrounding the urban core usually are residential neighborhoods composed of private homes and small parks, where trees are more common. On the outskirts of the city are exurban areas dominated by natural forest vegetation with only scattered houses and other human structures. Consequently, urban areas often represent a gradient of development¹ that spans an array of natural and anthropogenic features, many of which influence the probability of an area being inhabited by a species (figure 4.1). Some raptors are capable of inhabiting urban environments at one or more points along this gradient, provided the areas support their specific habitat resources and match their tolerance of human activity.2,3
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The effect of urbanization on birds typically has been evaluated through comparison of species composition between natural and urbanized habitats. However, few studies have examined the changes in species abundance as an urban area grows. During a 5-year period, we monitored two populations of burrowing owls (Athene cunicularia) nesting in separate urban areas with contrasting development and evaluated the tolerance of this species to increasing urbanization. The study was carried out in two small touristic coastal villages: Mar Chiquita and Camet Norte (Buenos Aires Province, Argentina). We digitalized satellite images and evaluated the interannual advance of the urbanized area at each village while simultaneously recording the changes in the number and location of burrowing owl nests. During the study period, the area occupied by buildings showed a slight change in Mar Chiquita (+ 17%) and a great expansion in Camet Norte (+ 269%). However, the number of owl nests increased in similar proportion in Mar Chiquita (+ 25%) and Camet Norte (+ 26%), and the maximum nest density was also similar for both villages (~ 0.14 nests/ha). Our results indicate that, unlike many raptors that are negatively affected by urbanization, burrowing owls may not be adversely impacted by nesting in areas with moderate levels of urban development.
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The three large forest owls of southeastern Australia, the Powerful Owl Ninox strenua, Sooty Owl Tyto tenebricosa and Masked Owl T. novaehollandiae, often occur sympatrically but little is known about how they partition their habitat. The places where owls obtain their food and what they eat may have a crucial bearing on our understanding of their habitat requirements. Totals of 1,672 prey items from 47 Powerful Owl territories, 1,466 items from 28 Sooty Owl territories, and 175 items from six Masked Owl territories (or locations) were analysed. There was virtually no overlap between the diets of the Powerful Owl and Masked Owl. The Powerful Owl preyed almost exclusively on arboreal mammals, most of which weighed 50–100% of adult owl body weight, supplemented by diurnal birds. In contrast, the Masked Owl preyed almost exclusively on small terrestrial and scansorial mammals, most of which weighed 3–20% of adult owl body weight, supplemented by diurnal birds. At any one site, both owls appeared to specialise on just one or two prey species. The diet of the Sooty Owl was strikingly different by its generalist nature, comprising , at any one site, a wide range of arboreal and terrestrial or scansorial mammals, mostly weighing 2–100% of adult owl body weight. The Sooty Owl appeared to take any available small and medium-sized mammals and foraged throughout its more limited habitat (rainforest, tall moist eucalypt forest) from the forest canopy to the ground. Geographical variation in owl diets was related to differences in the availability of potential prey. All three species were found to survive and breed successfully in the coastal and foothill forests of southeastern New South Wales on a diet composed principally of prey species that are not dependent on old-growth forest.
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The distribution of records for the seven species of owls that have been recorded in the Sydney region are presented. Records made during the past decade have been compared, where possible, with records made since the beginning of the twentieth century. Information is also presented on aspects of the ecology (diet, habitat, nest sites, roost sites, breeding success) of these species in the Sydney region. The Powerful Owl is widely distributed, albeit at very low population density, throughout the outer suburbs of the greater metropolitan area, particularly where these suburbs adjoin substantial areas of bushland and reserves. The Sooty Owl and the Masked Owl are restricted to a few such locations near Sydney, but both are more common in the wetter and the drier forests, respectively, of the Central Coast. The Barking Owl appears to be uncommon and of concern because this species is poorly conserved in national parks of the region and its habitat is threatened by continued clearing for agriculture and urban developments. The Grass Owl appears to be a rare vagrant to the Sydney region. The Southern Boobook and the Barn Owl may be common in the region, but their distribution and abundance appears to have been under-represented by official records. The status of all owls is imperfectly known within the most suburban parts of the Sydney metropolitan area and on surrounding semi-rural properties. Efforts are needed to encourage broadscale community participation in voluntary surveys for owls (and several of their main prey species) throughout residential areas. The conservation of owls in the Sydney region depends on the protection of extensive bushland areas from urban and rural development, especially the major forested gully systems which provide essential nesting, roosting and core foraging habitat for most species. The role of fire frequency and weed control in Sydney's urban bushland needs to be examined in terms of its impact on populations of the Common Ringtail Possum, and other important prey species of the owls.
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We collated and analysed records of mammal species (native and introduced) from across 32 Local Government Areas that comprise the Greater Melbourne region. Records of each species were examined for temporal changes in presence or absence. The region has a particularly diverse mammalian fauna with records of 92 species, including 19 marine mammals that have been recorded in Port Phillip. This total represents 65% of Victoria's mammalian fauna. About one-third of the 51 native terrestrial species have undergone a demonstrable decline in the region, to the point where their future presence is in doubt. Five species are no longer found in the region and the status of another three is uncertain. In contrast, up to five native terrestrial species are thought to have increased in abundance in recent decades, including the spectacular colonisation of the city by the Grey-headed Flying-fox as a year-round resident.
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An investigation was done to determine the occurrence and composition of avian fauna community in the urbanizing city of Nairobi, Kenya. We conducted bird counts in sample sites randomly distributed over the Nairobi landscape within a two-year period. The proportion of seven different land cover types derived from within a 500 m radius of classified satellite image described the habitat condition of each sample site. Multivariate analysis of the site and species data indicated that savannah vegetation, forest and agriculture land cover types were the main environmental gradients that differentiated the sample sites. Four clusters of sample sites occurred on the ordination plane according to canonical correspondence analysis (CCA). From 50 families of birds observed, species related to bush and scrub habitats occurred at a rate of about 31 %, followed by grassland species at 20 % and forest species at about 16 % rate. Out of CCA, five functional groups of birds were distinguishable. The proportion of sites occupied by birds per functional group and mean count of individual birds declined significantly, p < 0.0001, as groups of birds changed from being urban-related to savannah and then to forest-related species. One cluster comprised birds marked as having conservation concern status and related mainly to savannah vegetation of scrub and grasslands. In this landscape context, features such as native savannah vegetation and woodland accompanied by a process of controlled land use, could greatly mitigate negative impacts of ecosystem degradation on the sensitive tropical urban bird biodiversity.
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The diet of a pair of Powerful Owls, successfully breeding in regrowth open forest and woodland at Mt. Coot-tha, Brisbane, was assessed over two consecutive years. Diet was examined by analysing pellets and prey remains found below roosts and identifying carcasses the birds were holding. Eight mammal, sixteen bird and two insect species were recorded as prey, ranging in weight from 1 kg to 2 g. Fruit-bats, Common Ringtail Possums and Scalybreasted Lorikeets were taken most frequently. The estimated biomass of the four prey groups consumed each year was fruit-bats (46% both years), Common Ringtail Possum (25% in 1989, 29% in 1990), other arboreal marsupial species (17% and 7%) and diurnal birds (12% and 18%). There was a significant difference in biomass among prey groups each year. The frequency and biomass of prey groups in the diet did not differ significantly between the two years. There was no significant variation in the frequency of prey groups taken during the first four stages of the breeding cycle (incubation to fledgling) each year. Predation on Black and Greyheaded Fruit-bats and Scaly-breasted Lorikeets, species that are normally nomadic blossom and fruit feeders, occurred during all stages of the breeding cycle. Predation on the Common Ringtail Possum (predominantly juveniles) took place in suburbs adjacent to the study site. Hunting was observed within parkland and along forest edges.
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Arboreal marsupials play an essential role in ecosystem function including regulating insect and plant populations, facilitating pollen and seed dispersal and acting as a prey source for higher-order carnivores in Australian environments. Primarily, research has focused on their biology, ecology and response to disturbance in forested and urban environments. We used presence-only species distribution modelling to understand the relationship between occurrences of arboreal marsupials and eco-geographical variables, and to infer habitat suitability across an urban gradient. We used post-proportional analysis to determine whether increasing urbanization affected potential habitat for arboreal marsupials. The key eco-geographical variables that influenced disturbance intolerant species and those with moderate tolerance to disturbance were natural features such as tree cover and proximity to rivers and to riparian vegetation, whereas variables for disturbance tolerant species were anthropogenic-based (e.g., road density) but also included some natural characteristics such as proximity to riparian vegetation, elevation and tree cover. Arboreal marsupial diversity was subject to substantial change along the gradient, with potential habitat for disturbance-tolerant marsupials distributed across the complete gradient and potential habitat for less tolerant species being restricted to the natural portion of the gradient. This resulted in highly-urbanized environments being inhabited by a few generalist arboreal marsupial species. Increasing urbanization therefore leads to functional simplification of arboreal marsupial assemblages, thus impacting on the ecosystem services they provide.
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Most dietary studies of Powerful Owls Ninox strenua have been from forested habitats or partially disturbed habitats on the urban fringe. The diets of single Powerful Owls roosting in two inner city parks in Melbourne, Victoria, in 2008 and 2009 were analysed. Common Brushtail Possum Trichosurus vulpecula and Common Ringtail Possum Pseudocheirus peregrinus were the only prey species recorded in the Fitzroy Gardens (occurring in equal numbers in the Owl's diet), whereas Common Brushtail Possums and Black Rats Rattus rattus were recorded in the diet of the Flagstaff gardens bird. This is a less diverse prey selection than recorded in the only other inner city dietary analysis for this species.
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Human development impacts the landscape by altering the size and shape of natural habitat patches, replacing natural vegetation with other types such as lawns and row crops, or introducing environmental stressors such as increased human activity and pollutants. We investigated the effects of human alterations to the landscape on the distribution of 3 mammalian carnivores (coyote [Canis latrans ], raccoon [Procyon lotor ], and red fox [Vulpes vulpes ]) along an urban-rural gradient in northern Illinois. Distribution of each species was assessed from occurrence at scent stations placed within or along the edges of 47 sites ≥ 4 ha, representing 7 different natural or anthropogenically altered habitats. We averaged presence or absence scores across several seasonal samples over a year, and used an outlying mean index analysis to compare them to environmental variables gathered for each site, including habitat and landscape metrics presumed to reflect varying degrees of anthropogenic influence across the urban-rural gradient. Coyotes used a variety of habitats within the rural part of the gradient. Red foxes were found in forest interiors or shrubland and old fields near forests where coyotes were least detected. Both canids were detected more often in areas of lower human densities but prey abundance was not a strong determinant of their occurrence. Overall occurrence along the gradient was highest for raccoons, which were positively associated with urban areas with relatively high residential land use.
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Although spatial scale is important for understanding ecological processes and guiding conservation planning, studies combining a range of scales are rare. Habitat suitability modelling has been used traditionally to study broad-scale patterns of species distribution but can also be applied to address conservation needs at finer scales. We studied the ability of presence-only species distribution modelling to predict patterns of habitat selection at broad and fine spatial scales for one of the rarest mammals in the UK, the grey long-eared bat (Plecotus austriacus). Models were constructed with Maxent using broad-scale distribution data from across the UK (excluding Northern Ireland) and fine-scale radio-tracking data from bats at one colony. Fine-scale model predictions were evaluated with radio-tracking locations from bats from a distant colony, and compared with results of traditional radio-tracking data analysis methods (compositional analysis of habitat selection). Broad-scale models indicated that winter temperature, summer precipitation and land cover were the most important variables limiting the distribution of the grey long-eared bat in the UK. Fine-scale models predicted that proximity to unimproved grasslands and distance to suburban areas determine foraging habitat suitability around maternity colonies, while compositional analysis also identified unimproved grasslands as the most preferred foraging habitat type. This strong association with unimproved lowland grasslands highlights the potential importance of changes in agricultural practices in the past century for wildlife conservation. Hence, multi-scale models offer an important tool for identifying conservation requirements at the fine landscape level that can guide national-level conservation management practices.
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Background/Question/Methods Maxent, one of the most commonly used methods for inferring species distributions and environmental tolerances from occurrence data, allows users to fit models of arbitrary complexity. Model complexity is typically constrained via a process known as L1 regularization, but at present little guidance is available for setting the appropriate level of regularization, and the effects of inappropriately complex or simple models are largely unknown. In this study, we demonstrate the use of information criterion approaches to setting regularization in Maxent, and compare models selected using information criteria to models selected using other criteria that are common in the literature. We evaluate model performance using occurrence data generated from a known “true” initial Maxent model, using several different metrics for model quality and transferability. Results/Conclusions We demonstrate that models that are inappropriately complex or inappropriately simple show reduced ability to infer habitat quality, reduced ability to infer the relative importance of variables in constraining species’ distributions, and reduced transferability to other time periods. We also measure the relative effectiveness of different model selection criteria, and demonstrate that information criteria may offer significant advantages over the AUC-based methods commonly used in the literature.
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Large carnivores need large areas of relatively wild habitat, which makes their conservation challenging. These species play important ecological roles and in some cases may qualify as keystone species. Although the ability of carnivores to control prey numbers varies according to many factors and often is effective only in the short term, the indirect effects of carnivores on community structure and diversity can be great. Perhaps just as important is the role of carnivores as umbrella species (i.e., species whose habitat area requirements encompass the habitats of many other species). Conservation areas large enough to support populations of large carnivores are likely to include many other species and natural communities, especially in regions such as the Rocky Mountains of Canada and the United States that have relatively low endemism. For example, a plan for recovery of grizzly bears (Ursus arctos) proposed by Shaffer (1992) covers, in part, 34% of the state of Idaho (compared to 8% covered by a U.S. Fish and Wildlife Service proposal) and would capture 10% or more of the statewide ranges of 71% of the mammal species, 67% of the birds, 61% of the amphibians but only 27% of the reptiles native to Idaho. Two-thirds (67%) of the vegetation types in Idaho would have 10% or more of their statewide area included in the Shaffer plan. The U.S. Fish and Wildlife Service recovery zones provide a much poorer umbrella. The umbrella functions of large carnivores are expected to be poorer in regions with high endemism. The application of metapopulation concepts to large carnivore conservation has led to proposals for regional reserve networks composed of wilderness core areas, multiple-use buffer zones, and some form of connectivity. The exceptional vagility of most large carnivores makes such networks feasible in a region with low human population density, such as the Rocky Mountains, but mortality risks still need to be addressed. Roads are a major threat to carnivore recovery because of barrier effects, vehicle collisions, and increased accessibility of wild areas to poachers. Development, especially for tourism, is also becoming a threat in many parts ofthe region. Los carnívoros mayores requieren de extensas áreas de hábitat relativamente natural, lo cual hace de su conservación un reto. Estas especies juegan un papel ecológico importante y pueden, en algunos casos, ser consideradas como especies clave. Aunque la capacidad de los carnívoros para controlar la abundancia de sus presas varia en función de numerosos factores y a menudo solo es a corto plazo, los efectos indirectos de los carnívoros sobre la estructura y diversidad de la comunidad pueden ser grandes. Posiblemente igual importancia tiene el papel de los carníivoros como especies sombrilla (i.e., especies cuyos requerimientos de extensión del hábitat comprenden los hábitats de muchas otras especies). Es probable que áreas de conservación suficientemente grandes para mantener poblaciones de carnívoros mayores incluyan muchas otras especies y comunidades naturales, especialmente en regiones con endemismo relativamente bajo, tal como las Montañas Rocallosas. Por ejemplo, un plan de recuperación de osos pardos (Ursus arctos) propuesto por Schaffer (1992) abarca, en parte, el 34% del estado de Idaho (comparado con el 8% del Servicio de Pesca y Vida Silvestre de los E.U.) abarcaria el 10% o más de los rangos estatales de distribución del 71% de las especies de mamiferos, 67% de aves y 61% de anfibios, pero solo el 21% de reptiles nativos de Idaho. Dos tercios (67%) de los tipos de vegetación de Idaho tendrían 10% o más de su extensión en el estado incluida en la propuesta de Schaffer. Las zonas de recuperación propuestas por el Servicio de Pesca y Vida Silvestre constituyen una sombrilla Más pequeña. Se espera que en regiones de alto endemismo la función cobertora de los carnívoros mayores es más pobre. La aplicación del concepto de metapoblación en la conservación de carnívoros mayores ha llevado a propuestas de redes regionales de reservas interconectadas de alguna manera y compuestas por zonas núcleo y zonas de amortiguamiento de usos múltiples. La vagilidad excepcional de la mayoria de los carnívoros permite dichas redes en una región con baja densidad poblacional humana, tal como las Montañas Rocallosas, aunque los riesgos de mortalidad deberán ser considerados. Los caminos son una amenaza mayor para la recuperación de carnívoros por fungir como barreras, propiciar colisiones con vehículos y facilitar el acceso a cazadores furtivos. El desarrollo especialmente para el turismo también se está convirtiendo en una amenaza en muchas partes de la región.
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The Powerful Owl is an elusive species inhabiting the forests of mainland eastern Australia. Obtaining crucial information on aspects of their breeding behaviour and dispersal has proven extremely difficult, even though other aspects of their ecology are well studied. Here we use molecular methods to investigate the breeding behaviour and dispersal of the Powerful Owl in two different habitats: highly fragmented forest along the urban fringe and continuous forest. DNA profiles of Powerful Owls were obtained predominately from shed feathers collected opportunistically between 1995 and 2006. Seven breeding pairs of Powerful Owls were identified, from which shed feathers were collected during 2003, 2004 and 2005. By comparing DNA profiles, one pair of Owls was found to have occupied the same breeding site for 10 years (1995-2005). The dispersal or movements of five offspring from this pair was also determined to be either of two scenarios: (1) the juvenile moves from the natal territory; however, isn't breeding; and (2) the juvenile is recovered as part of a breeding pair. Two pairs of Owls breeding in the urban fringe habitat were closely related, but no incidences of extra-pair fertilisation were detected among pairs in either habitat. This study provides new information about the breeding behaviour and dispersal of the Powerful Owl, and shows the potential of using genetic data sourced from shed feathers for studying cryptic, rare or elusive species.
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The diet of powerful owls (Ninox strenua) living at Christmas Hills, 35 km north-east of Melboume, was examined by analysis of 686 regurgitated pellets collected over two years. Mammalian prey was found in 89%, insects in 13%, vegetation in 11% and birds in 10% of the pellets. Of the mammals, common ringtail possums occurred most frequently in the pellets over the year. There was no seasonal difference in the frequency of occurrences of common ringtail possums and sugar gliders in pellets. However, common brushtail possums were more likely to be taken in spring than in the other seasons. More adult common ringtail possums were taken as prey than were other age classes over the year, except in summer when high numbers of young were consumed by the owls.
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ABSTRCT.--The Powerful Owl (Ninox strenua) is Australia's largest owl and is considered of least concern nationally. Although a number of studies have reported on the ecology of Powerful Owls inhabiting forests, few have focused on these owls living in urban areas. We report on the characteristics of different roost trees used by Powerful Owls in a continuum of habitats from urban Melbourne to the more forested outskirts. Records of weather conditions and daily temperatures were also analyzed to deter- mine whether the owls were selecting particular roost trees for specific climatic conditions. We found that roost-tree height and perch height was highly correlated, with the owls always roosting in the top one-third of the tree, regardless of the tree height. As ambient temperature increased perch height decreased, and vice-versa, but owls always roosted in the top one-third of the roost tree. Powerful Owls did not simply move up and down the one tree, but moved to more suitable trees according to the weather conditions. Hence, the species requires a structurally heterogeneous habitat to provide roost trees for different temperatures. Furthermore, successful management of this species in the future will require the protection of structurally diverse vegetation.
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This study investigates the diet of six breeding pairs of powerful owls in the Yarra Valley Corridor in Victoria, Australia, and compares prey consumption with prey availability. The six sites represent a continuum of habitats, ranging from urban Melbourne, through the urban fringe interface to a more forested landscape. We found that powerful owls in the Yarra Valley Corridor are reliant almost exclusively on arboreal marsupial prey as their preferred diet, with 99% of their overall diet comprising four arboreal marsupial species. These four species (the common ringtail possum, common brushtail possum, sugar glider and greater glider) were also the most abundant species observed while spotlighting; however, their abundance varied along the continuum. There was a strong positive relationship with the presence of these species in the diet and their site-specific availability, indicating that the powerful owl is a generalist hunter, preying on the most available prey at a given site and in a given season. This study suggests that food resources are high in these disturbed urban fringe sites and it is unlikely that food availability in urban environments will limit the potential survival of urban powerful owls.
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The current diet of the sooty owl (Tyto tenebricosa) was determined by analysing freshly regurgitated pellets collected beneath their roosting sites in East Gippsland, Victoria. Comparisons were then made to: i) prehistoric and historic diet from bone deposits found in cave roosts, and ii) diet of a sympatric owl species the powerful owl (Ninox strenua). Sooty owls consumed a large array of terrestrial mammal species prior to European settlement, however, only three terrestrial species were detected in their current diet, a reduction of at least eight species since European settlement. To compensate, sooty owls have increased their arboreal prey consumption from 55% to 81% of their diet. Arboreal species are also a major component of the powerful owl diet and this prey shift by sooty owls has increased dietary overlap between these two species. Predation by foxes (Vulpes vulpes), and other feral species, is likely to have reduced the amount of terrestrial prey available to sooty owls since European settlement. Investigation of sooty owl diet changes may offer a unique monitoring system for evaluating the ability of fox control strategies to influence increases in critical weight range mammals.
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Human-induced biotic homogenization resulting from landscape change and increased competition from widespread generalists or 'winners', is widely recognized as a global threat to biodiversity. However, it remains unclear what aspects of landscape structure influence homogenization. This paper tests the importance of interspecific competition and landscape structure, for the spatial homogeneity of avian assemblages within a fragmented agricultural landscape of eastern Australia. We used field observations of the density of 128 diurnal bird species to calculate taxonomic and functional similarity among assemblages. We then examined whether taxonomic and functional similarity varied with patch type, the extent of woodland habitat, land-use intensity, habitat subdivision, and the presence of Manorina colonies (a competitive genus of honeyeaters). We found the presence of a Manorina colony was the most significant factor positively influencing both taxonomic and functional similarity of bird assemblages. Competition from members of this widespread genus of native honeyeater, rather than landscape structure, was the main cause of both taxonomic and functional homogenization. These species have not recently expanded their range, but rather have increased in density in response to agricultural landscape change. The negative impacts of Manorina honeyeaters on assemblage similarity were most pronounced in landscapes of moderate land-use intensity. We conclude that in these human-modified landscapes, increased competition from dominant native species, or 'winners', can result in homogeneous avian assemblages and the loss of specialist species. These interacting processes make biotic homogenization resulting from land-use change a global threat to biodiversity in modified agro-ecosystems.
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Chapter
Historically, the Powerful Owl (Ninox strenua) has been seen as a southeastern Australian species restricted to, or most numerous in, dense gullies of tall open forests in hilly or mountainous areas of the coast and Great Divide. However, recent research has revealed that Powerful Owls may breed numerously and successfully in a wider range of habitats than previously believed, including the forests and woodlands within the metropolitan areas of some major cities.Here we report on the breeding of a number of pairs of Powerful Owls in the Yarra Valley, Victoria. Study sites ranged from relatively undisturbed, wet sclerophyll forest 80 km from central Melbourne, through dry sclerophyll, eucalypt-dominated open forest with some disturbance, to a highly disturbed urban parkland only 18 km from central Melbourne. We found that Powerful Owls breed successfully in some urban areas, but are limited in the amount of human disturbance they can tolerate near their nesting hollow. In the most heavily utilized section of the urban parkland, all breeding attempts were unsuccessful and in one year the young were apparently eaten by one of the parents. This followed construction of a timber boardwalk under the nest tree during the breeding season. The Powerful Owls subsequently moved to a more secluded nesting hollow and raised two young. Recommendations for management of Powerful Owls in urban areas are discussed in the contextof these results.
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A pair of Powerful Owls Ninox strenua was studied at each of two sites near Melbourne, Victoria, for three years (1977-1979) and 15 years (1980-1994 inclusive) respectively, by diurnal and nocturnal observation. Home ranges were mapped, nest sites characterised and breeding chronology and success monitored. General observations at these and eight other sites, of roosting, courting, nesting, parental and juvenile behaviour, fledgling mortality, hunting, interspecific conflicts, bathing, and camouflage posing, are presented. The regularly used parts of the home ranges of two pairs were each estimated as c. 300 ha, although for one pair this applied only to the breeding season. One pair used seven nest trees in 15 years, commonly two or three times each (range 1-4 times) over consecutive years before changing trees. Nest-switching may have been encouraged by human inspection of hollows. Nest entrances were 8-40 m (mean 22 m) above ground. The owls clearly preferred the larger and older trees (estimated 350-500+ years old), beside permanent creeks rather than seasonal streams, and in gullies or on sheltered aspects rather than ridges. Laying dates were spread over a month from late May, with a peak in mid June. The breeding cycle occupied three months from laying to fledging, of which the nestling period lasted 8-9 weeks. Breeding success was 1.4 young per pair per year and 94% nest success; early nests in gullies were more successful than late nests on slopes. The post-fledging dependence period lasted 6-7 months from fledging. The diet consisted mostly of possums and gliders, primarily the Common Ringtail Possum Pseudocheirus peregrinus (78-89% by number). A resident breeding pair of owls took at least 95 major prey items in 368 days.
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A subadult Powerful Owl Ninox strenua was radio-tracked on 21 nights, over 4 weeks, in order to assess the possible impacts of habitat restoration involving removal of weed-tree roosts at Mt Evelyn, Victoria, in 2003. The Owl was found to be at least partly dependent on its parents until 7-8 months old (5-6 months post-fledging). This bird ranged and roosted in an area of ∼90 ha over a period of 4 weeks before dispersing from its natal territory. It often roosted alone during the day, but responded at night when its parents called by meeting them and begging for food. The home-range increased suddenly to ∼550 ha over three nights preceding its apparent dispersal away from the adults territory. The radio-tagged Owl was found roosting in Sweet Pittosporum Pittosporum undulatum (18 times), Monterey Pine Pinus radiata (4 times), White Willow Salix alba (4 times) and Hazel Pomaderris Pomaderris aspera (once). Only the last is indigenous to the area, and the other species are considered to be weed trees.
Chapter
Humans are transforming Earth’s landscape to an unprecedented degree in both magnitude and rate (Meyer and Turner 1992). We alter the landscape through the extraction of resources, the development of industry, the practice of agriculture, the pursuit of recreation, and the building of structures. These alterations affect every ecosystem on Earth (Vitousek et al. 1997).
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This study reports the diet of the powerful owl (Ninox strenua) in East Gippsland, from a dataset of 2009 vertebrate prey items collected from 53 sites. Mammals dominated the diet at all sites, but birds were also consumed regularly. The greater glider (Petauroides volans) was the dominant dietary item across the region in terms of both frequency of consumption and biomass contribution. There was geographical dietary variation between coastal and foothill forest sites, with the sugar glider (Petaurus breviceps) and birds consumed more frequently in foothill forests, whereas the common ringtail possum (Pseudocheirus peregrinus) was frequently consumed only in coastal forests. Typically, a higher percentage of powerful owl diet comprised birds closer to cleared land. The dietary reliance upon hollow-dependent mammals in foothill forests (averaging >70%) is of conservation concern, especially when non-hollow-dependent prey are rare. Forest management activities, especially logging, that reduce densities of hollow-bearing trees in the landscape are therefore likely to decrease the long-term carrying capacity of the landscape for the powerful owl.
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The MaxEnt software package is one of the most popular tools for species distribution and environmental niche modeling, with over 1000 published applications since 2006. Its popularity is likely for two reasons: 1) MaxEnt typically outperforms other methods based on predictive accuracy and 2) the software is particularly easy to use. MaxEnt users must make a number of decisions about how they should select their input data and choose from a wide variety of settings in the software package to build models from these data. The underlying basis for making these decisions is unclear in many studies, and default settings are apparently chosen, even though alternative settings are often more appropriate. In this paper, we provide a detailed explanation of how MaxEnt works and a prospectus on modeling options to enable users to make informed decisions when preparing data, choosing settings and interpreting output. We explain how the choice of background samples reflects prior assumptions, how nonlinear functions of environmental variables (features) are created and selected, how to account for environmentally biased sampling, the interpretation of the various types of model output and the challenges for model evaluation. We demonstrate MaxEnt’s calculations using both simplified simulated data and occurrence data from South Africa on species of the flowering plant family Proteaceae. Throughout, we show how MaxEnt’s outputs vary in response to different settings to highlight the need for making biologically motivated modeling decisions.
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Resource availability is a limiting factor influencing the distribution and composition of faunal communities. Globally, hollow bearing trees are a resource required by wildlife at all trophic levels, and are used for a diverse range of ecological functions. In the northern hemisphere avian species act as primary hollow excavators, whereas the southern hemisphere must rely on complex interactions between stochastic events, and eventual decay. Hollow formation is therefore a slow process in the southern hemisphere. In contrast, hollow loss is quite rapid and influenced greatly by anthropogenic impacts. To identify the ecological characteristics driving hollows over an urban to forest gradient as a resource for the powerful owl (Ninox strenua) and its prey we used presence-only modelling. The potential for an area to support tree hollows suitable for powerful owls and their prey was linked to the density of ephemeral rivers, land cover, tree cover and distance from riparian vegetation. The potential for large hollows throughout the landscape, suitable for the powerful owl, was also influenced by density of permanent rivers. Potential habitat for tree hollows, capable of supporting powerful owls and their prey was greatest in forested environments, declining with increased urbanization. However the urban region still supported some smaller tree hollows suitable for arboreal marsupials. Managing for urban dwelling species, is not as simple as retaining old hollow producing trees or providing alternate nesting structures. We also need to mitigate increased mortality associated with built environments (e.g. electrocution, collisions).
Article
Analysis of pellets shows that the most common item of prey is the Ringtailed Possum. The Sugar Glider is taken less commonly and other vertebrates and invertebrates only occasionally. A possible instance of scavenging is reported. The relation between the Owl's dietary needs and its conservation is discussed.
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Between 2004 and 2008 the diet and breeding success of a pair of Powerful Owls Ninox strenua were studied near Lakes Entrance, Victoria. In early November 2006 the adult female Powerful Owl was captured and radio-tracked for a period of 7.5 months. During this time the Owl's location was recorded on 111 occasions, including 65 nocturnal locations over 29 nights. Her home-range was calculated as 1589 ha using the Minimum Convex Polygon (MCP) method, or 871 ha based on the 95% Adaptive Kernel method. The area of forested habitat within the MCP home-range was 896 ha (the remainder representing cleared land). Her activity was centred primarily on the nesting gully where two dependent juveniles roosted, but several long-distance foraging expeditions (including roosting) that occurred more than 2.5 km from the juveniles were recorded. Arboreal mammals and birds dominated the Owls' diet. Low prey availability is suggested as being responsible for the single successful breeding event recorded in four nesting seasons.
Article
We tested the equal preference ecological trap hypothesis for breeding yellow-bellied sapsuckers (Sphyrapicus varius) along a time-since-harvest gradient (1-5 yr, 16-20 yr, 21-25 yr, and >60 yr) in selection system-logged hardwood forests in Algonquin Provincial Park, Ontario. Yellow-bellied sapsuckers preferred 1-5 year and >60-year-old cuts equally and more than 16-20 year and 21-25-year-old cuts. More-abundant arthropod food and/or higher-quality sap resources may have attracted yellow-bellied sapsuckers to 1-5 year and >60-year-old cuts. Only 52% of pairs raised fledglings in 1-to 5-year-old cuts during years when nest predation by American black bears (Ursus americanus) was common, the incidence of which was negatively related to increased availability of American beech (Fagus grandifolia) nuts from the previous autumn. By contrast, 88% of pairs raised fledglings in all years in >60-year-old cuts. One-to 5-year-old cuts were demographic sinks that represent equal-preference ecological traps in years when nest predation by bears was common, whereas >60-year-old cuts were always demographic sources. High-quality habitat cues for nesting yellow-bellied sapsuckers appear to be retained for 1-5 years after selection system logging but fail to deliver safe nest sites. Cavities excavated in heart-rot-infected nest trees are least likely to be depredated because cavity walls are typically harder and deter entry by depredating bears. Retaining more potential nest trees per ha at harvest (especially American beech with heart-rot) may increase the proportion of sapsucker nests that are excavated in bear-resistant trees, thereby reducing nest predation and increasing fecundity.
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With the rise of new powerful statistical techniques and GIS tools, the development of predictive habitat distribution models has rapidly increased in ecology. Such models are static and probabilistic in nature, since they statistically relate the geographical distribution of species or communities to their present environment. A wide array of models has been developed to cover aspects as diverse as biogeography, conservation biology, climate change research, and habitat or species management. In this paper, we present a review of predictive habitat distribution modeling. The variety of statistical techniques used is growing. Ordinary multiple regression and its generalized form (GLM) are very popular and are often used for modeling species distributions. Other methods include neural networks, ordination and classification methods, Bayesian models, locally weighted approaches (e.g. GAM), environmental envelopes or even combinations of these models. The selection of an appropriate method should not depend solely on statistical considerations. Some models are better suited to reflect theoretical findings on the shape and nature of the species’ response (or realized niche). Conceptual considerations include e.g. the trade-off between optimizing accuracy versus optimizing generality. In the field of static distribution modeling, the latter is mostly related to selecting appropriate predictor variables and to designing an appropriate procedure for model selection. New methods, including threshold-independent measures (e.g. receiver operating characteristic (ROC)-plots) and resampling techniques (e.g. bootstrap, cross-validation) have been introduced in ecology for testing the accuracy of predictive models. The choice of an evaluation measure should be driven primarily by the goals of the study. This may possibly lead to the attribution of different weights to the various types of prediction errors (e.g. omission, commission or confusion). Testing the model in a wider range of situations (in space and time) will permit one to define the range of applications for which the model predictions are suitable. In turn, the qualification of the model depends primarily on the goals of the study that define the qualification criteria and on the usability of the model, rather than on statistics alone.
Article
Context. Urbanisation is one of the most damaging landscape-scale disturbance processes leading to significant and potentially irreversible changes in biodiversity. How apex predators respond to urbanisation is poorly understood, largely because of their low density and low detectability. Given the important functional roles of apex predators in ecosystems, it is critical that research investigates how they respond to urbanisation, and how urban systems can be designed to better support apex predators. Aims. The present research aims to examine how an avian apex predator, the powerful owl, responds to a complete urban–forest gradient in southern Victoria, Australia. Specifically, the research aims to understand the environmental attributes that drive habitat suitability for powerful owls across the urban–forest gradient. Methods. Using a total of 683 independent field-and atlas-derived records of powerful owls across the study site, the research takes a presence-only modelling approach. The presence points were modelled against a series of geospatial variables that were determined a priori on the basis of the known ecology of powerful owls. Key results. Potential powerful owl habitat declined in a dramatic fashion in response to increasing levels of urbanisation, ranging from 76% of the forest landscape to 21% of the urban landscape. Powerful owl habitat availability across the urban–forest gradient is positively influenced by tree cover, productivity (normalised difference vegetation index) and proximity to river systems and riparian vegetation. Conclusions. Presence-only modelling has provided a useful way for investigating the response of an apex predator to a gradient of urbanisation. Although powerful owl habitat availability is negatively reduced by urbanisation, there is significant scope to manage urban landscapes to either maintain or improve the availability of habitat across the gradient. Implications. High resource-requiring species, such as apex predators, have the capacity to be detrimentally affected by urbanisation processes. Presence-only modelling, however, provides a useful tool for investigating how these difficult-to-detect species are affected by urbanisation, and ultimately inform how landscapes can be managed to maximise habitat availability for apex predators.
Article
Habitat models are now broadly used in conservation planning on public lands. If implemented correctly, habitat modelling is a transparent and repeatable technique for describing and mapping biodiversity values, and its application in peri-urban and agricultural landscape planning is likely to expand rapidly. Conservation planning in such landscapes must be robust to the scrutiny that arises when biodiversity constraints are placed on developers and private landholders. A standardized modelling and model evaluation method based on widely accepted techniques will improve the robustness of conservation plans. We review current habitat modelling and model evaluation methods and provide a habitat modelling case study in the New South Wales central coast region that we hope will serve as a methodological template for conservation planners. We make recommendations on modelling methods that are appropriate when presence-absence and presence-only survey data are available and provide methodological details and a website with data and training material for modellers. Our aim is to provide practical guidelines that preserve methodological rigour and result in defendable habitat models and maps. The case study was undertaken in a rapidly developing area with substantial biodiversity values under urbanization pressure. Habitat maps for seven priority fauna species were developed using logistic regression models of species-habitat relationships and a bootstrapping methodology was used to evaluate model predictions. The modelled species were the koala, tiger quoll, squirrel glider, yellow-bellied glider, masked owl, powerful owl and sooty owl. Models ranked sites adequately in terms of habitat suitability and provided predictions of sufficient reliability for the purpose of identifying preliminary conservation priority areas. However, they are subject to multiple uncertainties and should not be viewed as a completely accurate representation of the distribution of species habitat. We recommend the use of model prediction in an adaptive framework whereby models are iteratively updated and refined as new data become available.
Article
we studied the nesting ecology of American Kestrels (F&o sparverius) in Berks and Lehigh Counties, Pennsylvania, from 1987-1991. Kestrels used 99 (76%) of 130 nest boxes dispersed throughout a 1000~km2 study area. A total of 259 nesting attempts was noted: 67, 53, 49, 3.5, and 55 in 1987, 1988, 1989, 1990, and 1991, respectively. Of the 259 nesting attempts, 124 (49%) successfully fledged at least one offspring. We measured five macrohabitat and 14 microhabitat variables at the 130 nest boxes. Ten (53%) variables were correlated to levels of nest-box use and nesting success. Kestrels most frequently used nest boxes with high nestling-light intensity (P = 0.02) and low nest-box concealment (P = 0.05). Frequently used boxes were associated with extremely open habitat dominated by herbaceous vegetation (P < 0.005). Nesting kestrels avoided using boxes associated with dense habitats, such as late-successional old fields. Frequently used nest boxes were farther from forested areas than unused boxes (P = 0.05). Nest boxes with southeast orientations were used more frequently than expected (P < 0.025), and all other orientations were used in proportion to availability. Kestrels had the greatest nesting success when using nest boxes with high selection-light intensities (P = 0.05). Received 12 Dec. 1996, accepted 25 Mar. 1997.
Article
The diet of the powerful owl was studied, by analysis of regurgitated pellets, at Coranderrk Reserve, Victoria; regional variation in the diet was assessed at 4 other sites: Ironbark Basin Reserve, Point Addis: Gormandale; Beaufort; Philip I. The ringtail possum, Pseudocheirus peregrinus, was the most common prey species. Secondary prey species also formed a major part of the diet. The sugar glider, Petaurus breviceps, was important at Coranderrk Reserve and Gormandale, and the Australian magpie, Gymnorhina tibicen, at Ironbark Basin Reserve and Philip I. At Beaufort, G. tibicen and P. peregrinus were equally preyed on. A marked seasonal variation was found in the diet at Coranderrk Reserve: P. breviceps was the major prey item in autumn and P. peregrinus in winter; a number of other prey species were taken when abundant or easy prey. At Coranderrk the powerful owls were estimated to take one major prey item every 1.4 days or about 260 major prey items each year.
Article
The endangered Australian subtropical rainforest understorey shrub Triunia robusta, is restricted to the south-east Queensland region of Australia. The potential pre-clearing and current distribution of the species was modelled by relating species presence at recorded locations to correlated abiotic and biotic factors, which in combination, were then used as a surrogate for predicting distribution of the species habitat over its known range. From a defined study area of 330,000 ha, output of geographic areas likely to contain T. robusta habitat at three levels of probability were generated for pre-clearing vegetation, and vegetation classified as remnant in 1999. Potential pre-clearing distribution was compared with potential current distribution to ascertain the likely impact of clearing of native vegetation on the extent, pattern, and contiguity of T. robusta habitat. For pre-clearing vegetation, a total area of 45,480 ha was identified as potential T. robusta habitat. For vegetation classified as 1999 remnant, 13,440 ha were identified, representing an overall reduction of 70% in potential habitat for T. robusta. The model was partially validated, with T. robusta found at six new locations. Allowing for errors from spatial mismatching, five of the sites were located within habitat patches predicted by the model. A number of local areas containing high densities of predicted habitat patches were identified to guide searches for unrecorded populations. Strategically located areas linking known populations containing suitable or potentially suitable habitat that may be available for introduction of new populations were identified. The results indicate that the species former centre of range was in lowland areas adjacent to the north arm of the Maroochy River. Clearing and fragmentation of T. robusta habitat is the most likely cause of the apparent decline in distribution and abundance of the species.
Article
We studied nest site and habitat characteristics associated with 75 Great Horned Owl (Bubo virginianus) nests in Connecticut, northern New Jersey, and southeastern New York. Nest sites were categorized as either urban (30) or rural (45) and were compared to data from available habitat (24 random sites for microhabitat; 70 random sites for macro- habitat). Urban nest trees were significantly larger in diameter and taller than rural nest trees, and accordingly, nests were higher in urban nest trees as well. Urban nest sites were significantly different than random sites for all eight habitat variables, but rural nests were significantly different for only five variables. Urban nests were significantly different than rural nests for five of eight habitat variables. Only urban owl nests had significantly lower site basal area, higher conifer composition, and lower shrub cover. Both urban and rural owl nests showed lower canopy cover and closer proximity to forest edge, paved roads, human habitation, and water than random sites. Although both urban and rural Great Horned Owls demonstrated habitat selection (use different from availability), urban owls showed a stronger degree of selection, probably because of the greater complexity of habitats available in the urban landscape.