Rohan H. Clarke

Precision wildlife monitoring using unmanned aerial vehicles

Unmanned aerial vehicles (UAVs) represent a new frontier in environmental research. Their use has the potential to revolutionise the field if they prove capable of improving data quality or the ease with which data are collected beyond traditional methods. We apply UAV technology to wildlife monitoring in tropical and polar environments and demonstrate that UAV-derived counts of colony nesting birds are an order of magnitude more precise than traditional ground counts. The increased count precision afforded by UAVs, along with their ability to survey hard-to-reach populations and places, will likely drive many wildlife monitoring projects that rely on population counts to transition from traditional methods to UAV technology. Careful consideration will be required to ensure the coherence of historic data sets with new UAV-derived data and we propose a method for determining the number of duplicated (concurrent UAV and ground counts) sampling points needed to achieve data compatibility.

Prevalence and composition of marine debris in Brown Booby (Sula leucogaster) nests at Ashmore Reef.

Anthropogenic debris is ubiquitous in the marine environment and has been reported to negatively impact hundreds of species globally. Seabirds are particularly at risk from entanglement in debris due to their habit of collecting food and, in many cases, nesting material off the oceans surface. We compared the prevalence and composition of debris in nests and along the beach at two Brown Booby (Sula leucogaster) colonies on Ashmore Reef, Timor Sea, a remote area known to contain high densities of debris transported by ocean currents. The proportion of nests with debris varied across islands (range 3-31%), likely in response to the availability of natural nesting materials. Boobies exhibited a preference for debris colour (white and black), but not type. The ephemeral nature of Brown Booby nests on Ashmore Reef may limit their utility as indicators of marine pollution, however monitoring is recommended in light of increasing demand for plastic products.

Predicting the spatial distribution of a seabird community to identify priority conservation areas in the Timor Sea.

Understanding spatial and temporal variability in the distribution of species is fundamental to the conservation of marine and terrestrial ecosystems. To support strategic decision making aimed at sustainable management of the oceans, such as the establishment of protected areas for marine wildlife, we identified areas predicted to support multispecies seabird aggregations in the Timor Sea. We developed species distribution models for 21 seabird species based on at-sea survey observations from 2000-2013 and oceanographic variables (e.g., bathymetry). We applied 4 statistical modeling techniques and combined the results into an ensemble model with robust performance. The ensemble model predicted the probability of seabird occurrence in areas where few or no surveys had been conducted and demonstrated 3 areas of high seabird richness that varied little between seasons. These were located within 150 km of Adele Island, Ashmore Reef, and the Lacepede Islands, 3 of the largest aggregations of breeding seabirds in Australia. Although these breeding islands were foci for high species richness, model performance was greatest for 3 nonbreeding migratory species that would have been overlooked had regional monitoring been restricted to islands. Our results indicate many seabird hotspots in the Timor Sea occur outside existing reserves (e.g., Ashmore Reef Marine Reserve), where shipping, fisheries, and offshore development likely pose a threat to resident and migratory populations. Our results highlight the need to expand marine spatial planning efforts to ensure biodiversity assets are appropriately represented in marine reserves. Correspondingly, our results support the designation of at least 4 new important bird areas, for example, surrounding Adele Island and Ashmore Reef.

Climate drying amplifies the effects of land-use change and interspecific interactions on birds

AbstractContext Climate change may amplify the effects of land-use change, including induced changes in interspecific interactions.ObjectivesTo investigate whether an avifauna changed over a period of severe drought, and if changes in avifaunas were related to changes in vegetation characteristics and the irruption of a despotic native species, the noisy miner Manorina melanocephala.MethodsIn the box–ironbark forests of south-eastern Australia, we resurveyed the avifaunas and remeasured vegetation characteristics in 120 forest transects in 2010–2011 that had previously been measured in 1995–1997.ResultsThe avifauna changed markedly over the prolonged drought, and changes were more marked in smaller fragments of remnant vegetation in which more pronounced vegetation change had occurred. The noisy miner increased differentially in smaller remnants adding to the declines, especially for small-bodied birds.ConclusionsLong droughts interspersed with short wet periods are projected for the region, so the imposition of climate effects on an already much-modified region has profound implications for the avifauna. The noisy miner has (and continues) to benefit from both land-use and climate change, so future sequences of drought interspersed with short wet periods are likely to lead to further changes in the avifauna as the miner extends its occupancy. Differential reductions in small nectarivores and insectivores will affect ecosystem processes, including the control of defoliating insects, seed dispersal and pollination.

Green Tongues into the Arid Zone: River Floodplains Extend the Distribution of Terrestrial Bird Species

Floodplain and riparian ecosystems have cooler, wetter microclimatic conditions, higher water availability and greater vegetation biomass than adjacent terrestrial zones. Given these conditions, we investigated whether floodplain ecosystems allow terrestrial bird species to extend into more arid regions than they otherwise would be expected to occupy. We evaluated associations between aridity and the occurrence of 130 species using bird survey data from 2998 sites along the two major river corridors in the Murray–Darling Basin, Australia. We compared the effects of aridity on species occurrence in non-floodplain and floodplain ecosystems to test whether floodplains moderate the effect of aridity. Aridity had a negative effect on the occurrence of 58 species (45%) in non-floodplain ecosystems, especially species dependent on forest and woodland habitats. Of these 58 species, the negative effects of aridity were moderated in floodplain ecosystems for 22 (38%) species: 12 showed no association with aridity in floodplain ecosystems and the adverse effects of aridity on species occurrence were less pronounced in floodplain ecosystems compared to non-floodplain ecosystems for ten species. Greater vegetation greenness indicated that floodplain vegetation was more productive than vegetation in non-floodplain ecosystems. Floodplain ecosystems allow many terrestrial species to occur in more arid regions than they otherwise would be expected to occupy. This may be due to higher vegetation productivity, cooler microclimates or connectivity of floodplain vegetation. Although floodplain and riparian ecosystems will become increasingly important for terrestrial species persistence as climate change increases drying in many parts of the world, many are also likely to be highly affected by reduced water availability.

The effects of land-use change on the endemic avifauna of Makira, Solomon Islands: endemics avoid monoculture

Abstract Unprecedented rates of deforestation on tropical islands are threatening high numbers of endemic species, and empirical evidence is needed to better understand the implications of changes in land-use on biodiversity and to guide conservation actions. We assessed the effects of changes in land-use on the lowland avifauna of the tropical island of Makira in the Solomon Islands. We examined species richness and community assemblages, with a particular focus on endemism and functional traits, to provide further insight into the conservation value of the dominant types of land-use on Makira (i.e. intact forest, secondary forest, food gardens, mixed Cocoa plantations, and monoculture Cocoa plantations). We found species richness was similar across habitats, but endemic-species richness decreased as intensity of land-use increased. There were significant differences in the occurrence of functional groups between habitats. Fifteen of the 42 species observed showed significant variation in abundance across habitats. Of those species that varied, 12 were endemic to Makira or to Melanesia, with seven of these endemics being absent from the monoculture Cocoa plantations. As tropical islands have less functional redundancy than continental land masses, protecting the remaining forest and improving habitat connectivity will be even more critical for conserving their endemic species and maintaining ecosystem functioning.

What Determines Habitat Quality for a Declining Woodland Bird in a Fragmented Environment: The Grey-Crowned Babbler Pomatostomus temporalis in South-Eastern Australia?

Understanding what constitutes high quality habitat is crucial for the conservation of species, especially those threatened with extinction. Habitat quality frequently is inferred by comparing the attributes of sites where a species is present with those where it is absent. However, species presence may not always indicate high quality habitat. Demographic parameters are likely to provide a more biologically relevant measure of quality, including a species’ ability to successfully reproduce. We examined factors believed to influence territory quality for the grey-crowned babbler (Pomatostomus temporalis), a cooperatively breeding woodland bird that has experienced major range contraction and population decline in south-eastern Australia. Across three broad regions, we identified active territories and determined the presence of fledglings and the size of family groups, as surrogates of territory quality. These measures were modelled in relation to habitat attributes within territories, the extent of surrounding wooded vegetation, isolation from neighbouring groups, and the size of the neighbourhood population. Fledgling presence was strongly positively associated with group size, indicating that helpers enhance breeding success. Surprisingly, no other territory or landscape-scale variables predicted territory quality, as inferred from either breeding success or group size. Relationships between group size and environmental variables may be obscured by longer-term dynamics in group size. Variation in biotic interactions, notably competition from the noisy miner (Manorina melanocephala), also may contribute. Conservation actions that enhance the number and size of family groups will contribute towards reversing declines of this species. Despite associated challenges, demographic studies have potential to identify mechanistic processes that underpin population performance; critical knowledge for effective conservation management.

Methods for ageing and sexing the Black-eared Miner, Manorina melanotis, and the Yellow-throated Miner, M. flavigula

Abstract Morphometric data on 92 Black-eared Miners and 47 Yellow-throated Miners that had been independently sexed using molecular techniques were analysed to investigate size dimorphism between the sexes. We found that both species are sexually dimorphic in size, with males being the larger sex. Discriminant analyses of morphometric data were used to develop a simple method for sexing both species in the hand. Additionally, alula shape was consistent with other methods that we applied for ageing individuals. Sex-specific size differences between Black-eared and Yellow-throated Miners detected here add further support to the contention that they represent different taxa. The application of these sexing and ageing techniques for both species of mallee miner will improve ongoing field management of the endangered Black-eared Miner.

Resource partitioning between species and sexes in Great Frigatebirds and Lesser Frigatebirds

ABSTRACT Seabirds inhabiting large, multispecies colonies face intraspecific and interspecific competition for prey and this often results in foraging strategies that partition resources. Here, we identified mechanisms that facilitate partitioning of resources between 2 congeneric tropical seabirds, Great Frigatebirds (Fregata minor) and Lesser Frigatebirds (F. ariel), for which traditional research methods have documented high levels of resource overlap. Stable isotope analysis (SIA) indicated that throughout the breeding cycle, male and female Great Frigatebirds consumed prey with higher δ15N compared to male Lesser Frigatebirds. This trend was not significant when comparing δ15N values of male and female Great Frigatebirds to female Lesser Frigatebirds. During the breeding period, GPS tracking and SIA indicated considerable spatial overlap among species and sexes. This contrasted with SIA of samples that provide insight into nonbreeding resource acquisition because these indicated that male Great Frigatebirds and male Lesser Frigatebirds had lower δ13C values than females of each species, signifying greater use of offshore foraging grounds by males of both species. Together these results suggest that body size differences influence trophic position of the prey consumed. Furthermore, central-place foraging constraints, and spatially unpredictable resource distribution, limit potential for spatial differences in foraging strategies when breeding. By contrast, spatial distribution of foraging differs during the nonbreeding period as the requirement for central-place foraging is lifted.

Genetic structure and sex-biased dispersal of a declining cooperative-breeder, the Grey-crowned Babbler, Pomatostomus temporalis, at the southern edge of its range

Abstract Loss and fragmentation of habitat can disrupt genetic exchange between populations, which is reflected in changes to the genetic structure of populations. The Grey-crowned Babbler (Pomatostomus temporalis) is a cooperatively breeding woodland bird, once common and widespread in south-eastern Australia. The species has suffered population declines of >90% across its southern distribution as a result of loss and fragmentation of habitat. We investigated patterns of genetic diversity and population structure of Grey-crowned Babblers in fragmented habitats at the southernmost extent of its range. We sampled blood from 135 individual Babblers from 39 groups stratified into six subpopulations in three regions. Genotypic data were used to estimate genetic diversity, population substructure, local relatedness and dispersal patterns. Individuals showed high heterozygosity within regions, and varying numbers of private alleles among regions suggested differences in levels of connectivity between regions. Four genetic clusters revealed population substructure consistent with treeless landscapes acting as strong barriers to gene flow. In contrast to previous studies, we identified a male-biased dispersal pattern and significant isolation-by-distance patterns for females at fine spatial scales. We recommend that conservation plans for this species incorporate opportunities to increase and enhance corridor areas to facilitate genetic exchange among subpopulations.