Ian Radford

Department of Environment and Conservation (Western Australia) · Science and Conservation Division

Tropical granivorous finches often form large flocks around resources. The composition of these flocks, whether they are random groups of individuals or comprise related birds travelling together, is currently unknown. To bridge this knowledge gap, we combined high-frequency location tracking with comprehensive genetic sequencing to investigate the...

Prescribed burning is frequently used in savanna vegetation in Australia and worldwide. In north‐east Queensland savanna burning has been proposed for the control of woody weeds including Cryptostegia grandiflora (rubbervine), an invasive shrub/vine of riparian savanna. However, burning as a management tool can have non‐target impacts on ecosystems...

In the tropical savannas of northern Australia, many native mammal species are experiencing rapid and ongoing declines due to multiple interacting threats. These mostly arboreal and semi-arboreal mammals are reliant on tree hollows for shelter, which may be contributing to their decline. We monitored 198 nestboxes over three years across a 100-km t...

Context The decline of the greater bilby (Macrotis lagotis), or Ngarlgumirdi (Yawuru), like other critical-weight range Australian mammals, is believed to be primarily due to the synergetic impacts of predation by feral cats and foxes, habitat disturbance caused by large introduced herbivores, and increases in the frequency and intensity of wildfir...

In our present age of extinction, conservation managers must use limited resources efficiently to conserve species and the genetic diversity within them. To conserve intraspecific variation, we must understand the geographic distribution of the variation and plan management actions that will cost-effectively maximise its retention. Here, we use a g...

Background The granivorous finches of Australia’s tropical savannas heavily rely on a sequence of perennial and annual grass seed production to feed throughout the year. An increase in late dry season wildfires has been suggested to detrimentally effect seed production sequence and has been attributed to poor physiological condition and a reduction...

Abstract Mammal declines across northern Australia are one of the major biodiversity loss events occurring globally. There has been no regional assessment of the implications of these species declines for genomic diversity. To address this, we conducted a species‐wide assessment of genomic diversity in the northern quoll (Dasyurus hallucatus), an E...

Estimating trends in population size is critical for understanding population status and assessing the success of management interventions. Visual counts of birds as they congregate around predictable locations, such as waterholes, is a popular technique for estimating population size. Bird counts are used as a proxy for abundance, but how the rela...

Ecological niche theory dictates that sympatric species cannot occupy the same ecological niche at the same time. Sympatric granivorous finch species in tropical savannas appear to contradict this theory by moving in mixed‐species flocks and feeding together upon the same resources. Here, we explored this contradiction by tracking individuals from...

Background Information on site utilisation and movement is essential for managing species' resource requirements. Collecting these data requires frequent location sampling of multiple individuals, which can be challenging for small-bodied animals due to the often-large size of animal-borne satellite-based telemetry devices. We show how coded VHF-ra...

Northern Australia has undergone significant declines among threatened small and medium-sized mammals in recent decades. Conceptual models postulate that predation by feral cats is the primary driver, with changed disturbance regimes from fire and feral livestock in recent decades reducing habitat cover and exacerbating declines. However, there is...

Native mammals are suffering widespread and ongoing population declines across northern Australia. These declines are likely driven by multiple, interacting factors including altered fire regimes, predation by feral cats, and grazing by feral herbivores. In addition, the loss of tree hollows due to frequent, intense fires may also be contributing t...

Tree hollows are a critical resource for many arboreal vertebrates, including many threatened species. In northern Australia’s vast tropical savannas, arboreal mammals are of particular conservation concern, as many have exhibited rapid population declines in recent decades. To understand the extent to which arboreal vertebrates compete for tree ho...

ContextInvasive predators are a key threat to biodiversity worldwide. In Australia, feral cats are likely to be responsible for many extinctions of native mammal species in the south and centre of the continent. AimsHere we examine the effect of feral cats on native rodent populations in the second of two translocation experiments. Methods In a wil...

Context. Tree hollows are a key habitat resource for hollow-nesting species, including the northern Australian Gouldian finch (Erythrura gouldiae). Certain fire and disturbance regimes limit tree hollow availability in the northern Australian savannas. Aims. This study investigated the influence of fire regime and vegetation structure on the densit...

Conservation management is improved by incorporating information about the spatial distribution of population genetic diversity into planning strategies. Northern Australia is the location of some of the world's most severe ongoing declines of endemic mammal species, yet we have little genetic information from this regional mammal assemblage to inf...

Tree cavities are important denning sites for many arboreal mammals. Knowledge of cavity requirements of individual species, as well as potential den overlap among species, is integral to their conservation. In Australia’s tropical savannas, development of tree cavities is enhanced by high termite activity, and, conversely, reduced by frequent fire...

Despite substantial investment in prescribed burning for biodiversity conservation there has been surprisingly little demonstration of its efficacy in achieving intended conservation aims for fauna. In the case of northern Australia’s threatened mammal fauna, most studies have reported negative responses to fire. We used satellite-derived fire scar...

Predators are fundamentally important in regulating many global ecosystems, and perturbations of predator populations through impacts by invasive species are frequently implicated in the degradation of these ecosystems. In considering recent declines of native critical weight range (35–5500 g) mammals in northern Australia, most attention has focus...

Hollows in standing trees are an important ecological resource for many Australian vertebrates, including a range of threatened mammals, reptiles and birds. However, the ecology of tree hollows, and the extent to which they support hollow-dependent fauna, has been severely under-studied in northern Australia. This study evaluated the reliability of...

Hollows in standing trees are an important ecological resource for many Australian vertebrates, including a range of threatened mammals, reptiles and birds. However, the ecology of tree hollows, and the extent to which they support hollow-dependent fauna, has been severely under-studied in northern Australia. This study evaluated the reliability of...

Strategies for mitigating climate change through altered land management practices can provide win–win outcomes for the environment and the economy. Emissions trading for greenhouse gas (GHG) abatement in Australia's remote, fire‐prone, and sparsely populated tropical savannas provides a financial incentive for intensive fire management that aims t...

Apex predators are fundamentally important in regulating many ecosystems, and perturbations of their populations are frequently implicated in ecosystem declines or collapses. In considering small mammal declines in northern Australia, most attention has focused on interactions between a mammalian apex predator—the dingo Canis dingo—and a meso-preda...

The Gouldian finch (Erythrura gouldiae, Gould 1844) is a threatened grass finch (Estrildidae) endemic to the tropical savannas of northern Australia. Current fire regimes, consisting of frequent and extensive fire across these savanna grasslands, affect the type and availability of grass seed for granivores. Gouldian finches are particularly affect...

Seeds of native grasses are an important food source for granivorous finches throughout the tropical savannas of northern Australia. The iconic Gouldian finch (Erythrura gouldiae), a threatened species endemic to these savanna grasslands, relies almost exclusively on the grass seeds of annual Sorghum spp. when breeding, and appears to time breeding...

Tree hollows are a vital wildlife feature, whose abundance and availability has declined in many regions due to broad-scale vegetation clearance, timber-harvesting, and disturbance such as fire. In the temperate forests and woodlands of eastern and southern Australia, the loss of large, old trees and associated tree hollows has severely impacted po...

The savanna biome is one of the least invaded among global biomes, although the mechanisms underpinning its resistance to alien species relative to other biomes is not well understood. Invaders generally are at the resource acquisitive end of functional global plant trait variation and in low-resource savanna environments we might expect that succe...

Fire is a pervasive feature of the tropical savannas of northern Australia. Increasingly extensive and intensive fires have had an adverse effect on grass layer diversity. Reduced grass species diversity and abundance are important correlates of the decline of granivores in these tropical savannas. The Gouldian finch (Erythrura gouldiae), an endang...

Landscape attributes often shape the spatial genetic structure of species. As the maintenance of genetic connectivity is increasingly a conservation priority, the identification of landscape features that influence connectivity can inform targeted management strategies. The northern quoll (Dasyurus hallucatus) is a carnivorous marsupial that has ex...

The domestic cat (Felis catus) is an invasive exotic in many locations around the world and is thought to be a key factor driving recent mammal declines across northern Australia. Many mammal species native to this region now persist only in areas with high topographic complexity, provided by features such as gorges or escarpments. Do mammals persi...

Mammalian species in northern Australia are declining. The resources that many species from this region require to persist in the landscape remain poorly understood. We examined habitat selection and diet of the scaly-tailed possum (Wyulda squamicaudata, hereafter called Wyulda) in the northwest Kimberley, Western Australia, in relation to variatio...

Patch mosaic burning, in which fire is used to produce a mosaic of habitat patches representative of a range of fire histories ('pyrodiversity'), has been widely advocated to promote greater biodiversity. However, the details of desired fire mosaics for prescribed burning programs are often unspecified. Threatened small to medium-sized mammals (35...

Fire regimes are changing throughout the world. Changed fire patterns across northern Australian savannas have been proposed as a factor contributing to recent declines of small- and medium-sized mammals. Despite this, few studies have examined the mechanisms that underpin how species use habitat in fire-affected landscapes. We determined the habit...

Postfire resprouting and recruitment from seed are key plant life-history traits that influence population dynamics, community composition and ecosystem function. Species can have one or both of these mechanisms. They confer resilience, which may determine community composition through differential species persistence after fire. To predict ecosyst...

Introduction: Recent studies at sites in northern Australia have reported severe and rapid decline of several native mammal species, notwithstanding an environmental context (small human population size, limited habitat loss, substantial reservation extent) that should provide relative conservation security. All of the more speciose taxonomic group...

Introduction: Recent studies at sites in northern Australia have reported severe and rapid decline of several native mammal species, notwithstanding an environmental context (small human population size, limited habitat loss, substantial reservation extent) that should provide relative conservation security. All of the more speciose taxonomic group...

Context Changed fire regimes are an important threatening process to savanna biodiversity. Fire-sensitive vegetation such as pindan and its fauna may be particularly susceptible to fire impacts. Invasion by alien species is an additional threatening process. The toxic anuran Rhinella marina is a well publicised invader of savannas. Little is known...

Small mammal species are declining across northern Australia. Predation by feral cats Felis sylvestris catus is one hypothesised cause. Most evidence of cat impacts on native prey comes from islands, where cat densities are often high, but cats typically occur at low densities on mainland Australia. We conducted a field experiment to measure the ef...

We construct a state-and-transition model for mammals in tropical savannas in northern Australia to synthesize ecological knowledge and understand mammalian declines. We aimed to validate the existence of alternative mammal assemblage states similar to those in arid Australian grasslands, and to speculate on transition triggers. Based on the arid g...

The remote and sparsely populated Kimberley region is a major centre of endemism in the Australian monsoonal tropics that is threatened by uncontrolled fire following the disruption of Aboriginal burning practices. A recent study of the ant fauna of the Mitchell Falls area of the northern Kimberley revealed that 44 % of the species are known only f...

This paper examines the hypothesis that non-native plant invasions are related to fluctuating resource availability as proposed by Davis et al. (2000). I measured relative functional responses of both invasive and native plants to changed resource availability due to nutrient enrichment and rainfall, and to increased disturbance. Data are presented...

Patches of fire-sensitive vegetation often occur within fire-prone tropical savannas, and are indicative of localized areas where fire regimes are less severe. These may act as important fire refugia for fire-sensitive biota. The fire-sensitive tree Callitris intratropica occurs in small patches throughout the fire-prone northern Australian savanna...

Understanding mechanisms underlying fire regime effects on savanna fauna is difficult because of a wide range of possible trophic interactions and feedbacks. Yet, understanding mechanisms underlying fauna dynamics is crucial for conservation management of threatened species. Small savanna mammals in northern Australia are currently undergoing wides...

This paper documents the effects of fire on grass‐layer invertebrates in tropical savannas of the Kimberley region of north‐western Australia, in the context of resource availability for consumers. Inappropriate fire regimes have been identified as a factor threatening a number of vertebrate groups, including small mammals, across northern Australi...

This article provides a context to, attempts an explanation for, and proposes a response to the recent demonstration of rapid and severe decline of the native mammal fauna of Kakadu National Park. This decline is consistent with, but might be more accentuated than, declines reported elsewhere in northern Australia; however, such a comparison is con...

Frequent and extensive fires are becoming increasingly common throughout the tropical savannas of northern Australia. This fire regime has been implicated in both habitat alteration and losses of biodiversity. Granivorous birds are particularly affected because of the effect of fire on grass seed availability. The endemic Gouldian finch (Erythrura...

This paper presents the first systematic description of the ant fauna of the dominant savanna landscapes of the remote northern Kimberley region of far northwestern Australia, an area of extremely high conservation value for other taxa. These conservation values are threatened by inappropriate fire regimes and invasion by the introduced cane toad B...

The processes underlying plant invasions have been the subject of much ecological research. Understanding mechanisms of plant invasions are difficult to elucidate from observations, yet are crucial for ecological management of invasions. Hieracium lepidulum, an asteraceous invader in New Zealand, is a species for which several explanatory mechanism...

A key conservation issue in north-western Australia is recent declines in biodiversity, especially among the nationally threatened critical weight range (35g-5kg) mammals. Changed fire regimes are implicated as a cause of these declines, but it is unclear whether declines are related to fire, or to other key threatening processes. In this review, h...

High leaf area has been associated statistically with plant invasiveness, but few studies have quantified metabolic costs of this trait. We have little information on whether high leaf area provides a universal growth advantage or an advantage only under limited conditions. We ask, do invasive Hieracium lepidulum and co-occurring aliens in New Zeal...

Abstract Riparian habitats are highly important ecosystems for tropical biodiversity, and highly threatened ecosystems through changing disturbance regimes and weed invasion. An experimental study was conducted to assess the ecosystem impacts of fire regimes introduced for the removal of the exotic woody vine, Cryptostegia grandiflora, in tropical...

Abstract One of the key environmental factors affecting plant species abundance, including that of invasive exotics, is nutrient resource availability. Plant functional response to nutrient availability, and what this tells us about plant interactions with associated species, may therefore give us clues about underlying processes related to plant a...

Hybridization between native and invasive species can have several outcomes, including enhanced weediness in hybrid progeny, evolution of new hybrid lineages and decline of hybridizing species. Whether there is a decline of hybridizing species largely depends on the relative frequencies of parental taxa and the viability of hybrid progeny. Here, th...

Many studies have highlighted the relationship between nutrient fluctuations and enrichment in the process of plant invasion. However, invasion may be also associated with conditions of plant stress, either nutrient depletion or toxicity, in the environment. In this study, we investigate the possible role of nutrient stress in the invasion of Hiera...

Recent comparative glasshouse experiments have failed to isolate growth or competitive performance that would explain invasiveness in Hieracium lepidulum in New Zealand. It has been noted in a number of studies that root infection by arbuscular mycorrhizal fungi (AMF) can alter growth and competitive performance in invasive species. We therefore te...

The current taxonomy of the Senecio pinnatifolius complex (formerly Australian S. lautus) is inadequate in describing intra-specific variation. We present several putative taxa as alternatives to current subspecies, based on variants observed during both herbarium surveys and field studies. We sought to establish whether these taxa were objectively...

This paper describes a process-based metapopulation dynamics and phenology model of prickly acacia, Acacia nilotica, an invasive alien species in Australia. The model, SPAnDX, describes the interactions between riparian and upland sub-populations of A. nilotica within livestock paddocks, including the effects of extrinsic factors such as temperatur...

Abstract A demographic study was conducted in the northern Australian Astrebla grasslands to determine the importance of habitat type in influencing invasion patterns of Acacia nilotica, an exotic leguminous tree from Africa and Asia. One of the repeated patterns observed for A. nilotica is that denser populations are often associated with riparian...

Acacia nilotica is a tree of international significance both as a beneficial plant and as a species prone to thicket formation and negative impacts on savannas throughout much of its range. While fire has been identified as a useful tool for controlling negative impacts of some Acacia species in Africa, A. nilotica adult trees are apparently fire t...

Paddock-scale Acacia nilotica L. Willd. ex Del. (prickly acacia) spatial distribution, seed production and dispersal patterns were investigated in the Astrebla (Mitchell) grasslands of northern Australia as a step toward predicting future patterns of invasion. A number of hypotheses were tested based on what we know of this species in both Australi...

An impact assessment study was undertaken to determine seed predation rates by two bruchid beetles, Bruchidus sahlbergi Schilsky and Caryedon serratus Olivier, on the invasive shrub Acacia nilotica (L.) Willd. ex Del. The former bruchid was released as a biological control agent for A. nilotica, whereas the latter is naturalized in Australia. We at...

A comparative ecological study of closely related invasive and non-invasive species, Senecio madagascariensis and S. lautus (Asteraceae), investigated what traits might confer invasive ability in very similar species. Life-history attributes of the weed S. madagascariensis were compared to five habitat-specific subspecies of S. lautus: S. l. alpinu...

The shrubby vine Cryptostegia grandiflora and the shrub Ziziphus mauritiana were both introduced to northern Australia over 100 years ago and have become invasive in savanna woodland environments. Data from a land resource survey were used to examine regional- and landscape-scale distribution patterns of these species in the Dalrymple Shire, an are...